Chapter 13: Cardiac Pathology

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Welcome back to the Deep Dive.

Today we're doing something a little bit different.

Usually we take a broad stack of articles from all over the internet, but today we're focusing on a single,

incredibly dense source.

We really are.

We're walking through, you could say, the engine room of the human body.

We're breaking down Chapter 13 of the USMLE Step 1 lecture notes on pathology.

The topic is the heart.

It's a heavy one, and I mean that literally and figuratively.

If you look at the statistics in the notes, ischemic heart disease is still the leading cause of death in the United States.

So while we are technically reviewing a medical text for students, we're actually talking about the mechanism of mortality for a huge portion of the modern world.

That's really the mission today, isn't it?

We want to take these tables, these lists of defects, and these palm lines of necrosis and actually turn them into a story, a narrative.

A narrative, yes.

We want to get to the why behind the failure.

We're going to act as your guides through the anatomy of a breakdown from, say, the plumbing issues of blocked arteries to the structural failures of the gals and the muscle itself.

And that's the only way to tackle this, really.

If you just memorize lists, you'll forget them by tomorrow.

But if you understand the mechanism, the logic behind it, you own it.

So we're going to follow the chapter structure.

Exactly.

We'll follow it logically.

We'll start with ischemic heart disease.

That's the supply and demand problem.

Then we move to heart failure, what happens when the pump itself starts to quit.

We'll look at valvular disease, which is essentially door trouble in the heart.

And we'll finish up with the really complex wiring and structural issues of congenital defects and cardiomyopathy.

It's a full itinerary.

So let's not waste any time.

Let's start with the big one.

Ischemic heart disease or IHD.

The text sets the stage immediately by defining this as a problem secondary to coronary artery disease.

But I like how they frame it fundamentally as almost like an economic crisis inside the body.

That is the best analogy for it.

It's purely a supply and demand issue.

The myocardium, the heart muscle, is a very demanding customer.

I mean, it works 24 -7 and it needs a constant, completely uninterrupted supply of oxygen.

The coronary arteries are the delivery trucks.

They are.

And if those trucks get stuck in traffic, which in this case is sclerosis or plaque buildup, the supply just drops.

And if the supply drops below the demand, you get ischemia.

The text notes this typically happens in middle -aged men and post -menopausal women.

But let's look at the symptoms.

The most common one is angina pectoris.

Which is Latin for strangling of the chest.

It's a vivid image, but the notes make a critical distinction here that I think trips a lot of people up.

Angina is ischemia, but it is not infarction.

This is so crucial.

In angina, the cells are starving.

They are, you know, crying out for help, but they're not dead yet.

It's a reversible injury.

It's a warning shot.

A huge warning shot, yes.

And there are three types of warning shots.

We need to distinguish between stable, unstable,

and Prince metal angina.

Let's start with stable angina.

The text gives a very specific number here.

Seventy five percent stenosis.

Yeah.

Why that number?

What's the magic in seventy five percent?

Well, that's really the tipping point.

You see, if an artery is hardened by atherosclerosis and narrowed by less than seventy five percent, usually enough blood gets through to keep the heart happy at rest.

So sitting on the couch, you're fine.

You're fine.

Your heart rate is 60.

No problem.

But if you have more than seventy five percent narrowing, that reserve capacity is gone.

The moment you run for a bus or get angry at an email, your heart rate spikes.

The demand goes way up.

And the narrow pipe can increase the flow to max.

It can't keep up.

So you get pain.

Crushing chest pain.

Crushing chest pain.

But and this is why it's called stable.

It's predictable.

You know what brings it on.

You stop running.

The demand goes down and the pain stops.

Or you take nitroglycerin.

Or you take nitroglycerin.

Which does what?

Exactly.

How does that work?

It's a vasodilator.

It essentially dilates the veins more than the arteries, which reduces the amount of blood returning to the heart.

So it's not about forcing the blocked artery open.

Not primarily.

It's more about reducing the preload.

Less blood returning means the heart doesn't have to work as hard to pump it out.

It lowers the workload.

It helps balance that supply and demand equation.

But from the demand side, that makes sense.

The notes also mention an ECG finding for this ST segment depression.

Yes.

And this is a key clue.

It indicates subendocardial ischemia.

Subendocardial.

So the inner layer of the heart.

Exactly.

Think of the heart wall like a thick steak.

The blood vessels sit on the outside surface and then dive inward.

So the deepest part of the muscle, the subendocardium, is the furthest from the blood supply.

The last to get fed?

The last to get fed and the first to starve.

If flow is low, that inner layer suffers first.

That electrical struggle shows up on the ECG as ST depression.

OK, so stable is a fixed plumbing problem.

Predictable.

Now contrast that with Prince metal variant angina.

This one seems, well, trickier.

It's erratic.

It's a completely different mechanism.

Prince metal isn't about a fixed plaque blockage.

It's about vasospasm.

So the artery itself is cramping up.

Like a muscle cramp in the vessel wall itself, yes.

And because it's a spasm, it doesn't care if you're exercising.

It can happen at rest.

You could be sound asleep.

That's terrifying.

It is.

But the ECG looks different here.

In Prince metal, because the artery clamps shut completely for a moment, the ischemia is transmural.

Transmural meaning through the whole wall.

The entire thickness of the wall.

So you see ST segment elevation, not depression.

It looks like a full -blown heart attack on the ECG for a few minutes.

But like stable angina, the text says nitroglycerin still works here.

Yes, because the nitro directly relaxes that smooth muscle spasm in the artery wall.

It opens the pipe back up.

OK, so we have stable, which is the fixed pipe with exertional pain,

and Prince metal, the spastic pipe with resting pain.

Then we have the one that signals imminent danger.

Unstable angina.

This is the red flag.

This is the one you do not ignore.

In unstable angina, the game has totally changed.

You have that atherosclerotic plaque we talked about, but now something has shifted.

It's ruptured.

It has disrupted, exactly.

And a thrombus, a blood clot, has formed on top of it.

It's not fully blocking the artery yet.

It's non -occlusive, but it's there and it's precarious.

So the flow is critically and unpredictably reduced.

Precisely.

The text describes the crescendo pattern.

The pain starts coming more often.

It lasts longer.

And crucially, it's now happening at rest.

And the nitroglycerin might not work as well.

It might not.

This is the body just screaming that a full -blown heart attack, an MI, is knocking on the door.

The risk of progression is very high.

Which brings us right to the main event.

Myocardial infarction, or MI.

So now we've crossed the line from ischemia to infarction.

We have.

We aren't just starving cells anymore.

We are killing them.

Correct.

The definition from the text is coagulative necrosis.

That is the specific type of cell death we see in the heart.

And in the vast majority of cases, this is due to an acute thrombosis.

That clot we saw starting an unstable angina.

It's now completely blocked the vessel.

It has.

Zero flow.

Game over for those muscle cells.

I want to spend a minute on the geography of this.

The notes have a figure, 13 to 1, that maps out which arteries get hit most often.

I feel like this is super high yield for understanding the damage.

It's essential.

You really have three main pipes feeding the heart muscle.

The most commonly blocked one, and this accounts for about 45 % of cases, is the left anterior descending artery, the LAD.

The infamous widow maker.

A grim nickname, but it's anatomically accurate.

The LAD feeds the anterior wall of the left ventricle and the anterior part of the septum.

That's the powerhouse of the heart.

So if you knock that out.

You lose a massive amount of your pumping capacity.

It's a devastating injury.

And the runner up.

The right coronary artery, or RCA, that's about 35 % of cases.

It feeds the posterior wall of the ventricle, and very importantly, it often supplies the electrical nodes, the SA and AV nodes.

So blockages there might present with rhythm problems.

Exactly.

Bradycardia, heart block, things like that.

And finally, you have the left circumflex, which is about 15 % of cases, and that hits the lateral wall of the left ventricle.

So the location of the clot determines the location of the death.

But the depth of the death matters too.

The text lists transmural versus subendocardial infarcts.

Right.

And this goes back to what we said about the stake earlier.

If you block one of those main pipes, the LAD or the RCA completely, you will eventually kill the whole thickness of the wall.

That's transmural.

That's transmural.

And that gives you the classic ST elevation on the ECG.

The STEMI.

And subendocardial.

How does that happen?

That's necrosis of just the inner one third to one half of the wall.

Interestingly, the text notes this isn't usually from a single, completely blocked pipe.

It's often from global hypotension.

Like a patient in shock.

Exactly.

Imagine a patient goes into shock from bleeding out.

The overall blood pressure plummets.

The heart is pumping desperately, but there just isn't enough pressure to push blood into those deep inner layers against the constant squeeze of the muscle.

So the whole inner lining of the ventricle suffers at once.

It does.

It's a circumferential injury to that vulnerable subendocardium.

And the ECG reflects that difference.

Yes.

You don't get that big ST elevation.

Instead, you get ST depression.

So clinically, we call this an NSTEMI, a non -ST elevation MI.

OK.

Now let's talk about diagnosis.

A patient comes into the emergency room.

They have the classic symptoms.

Crushing chest pain radiating to the jaw and the left arm.

Diaphoresis, sweating, nausea.

Maybe they say they have a feeling of impending doom.

Which is a real symptom, by the way.

It's not just poetic.

That sympathetic nervous system surge is so massive that the brain correctly interprets it as a major survival threat.

But the text has this bold clinical correlate about atypical presentations.

Who do we need to worry about not showing up with that classic picture?

You need to have a very high index of suspicion for diabetics, the elderly and women.

Diabetics specifically often have advanced neuropathy nerve damage.

So they don't feel the pain?

They might not feel the chest pain at all.

They might just present with sudden confusion or fatigue or shortness of breath.

We call these silent MIs.

If you're waiting for that textbook chest pain, you might miss the diagnosis entirely.

So we have to rely on biomarkers.

Blood tests.

The notes present a comparison in table 1311 between CKMB and troponin.

Now today in modern medicine, we hear troponin all the time.

It's the gold standard.

So why does the text even bother with CKMB?

This is a fantastic clinical logic puzzle.

It connects the physiology to practice.

Troponin I and T are amazing.

They are cardiac specific, very sensitive.

They rise within three to four hours, pee around 16 hours.

And this is the key.

They stay elevated for seven to 10 days.

So it's great for proving you had a heart attack any time in the last week.

Yes.

But let's imagine a patient.

They had a heart attack four days ago.

They're in the hospital recovering.

Their troponin level is sky high as expected.

Now suddenly they grab their chest again.

They look awful.

Are they having another heart attack?

Exactly.

Or is it just pain from the first one?

If you check their troponin, it's already high.

It tells you nothing new about what happened in the last hour.

You're flying blind.

You're flying blind with troponin there.

And that's where CKMB saves the day.

CKMB rises fast, but it also clears fast.

It's usually back to normal within two to three days.

So four days post MI,

their CKMB should be low.

It should be back at baseline.

So if you measure it and it's spiking again, you know for sure you have a reinfarction, a new event on top of the old one.

That is a crucial distinction.

It's all about the kinetics of the molecule.

Speaking of kinetics and time, this next section is my absolute favorite part of the chapter.

It's the evolution of myocardial infarction.

The timeline of necrosis.

It reads like a forensic report.

The text breaks down the gross changes, what the heart looks like to the naked eye, and the microscopic changes.

What's happening at the cellular level over time.

I want to walk through this step by step because understanding this timeline explains exactly when and why specific complications happen.

Let's do it.

This is the story of the body trying to clean up a disaster.

Okay, start the clock.

Zero to 12 hours.

I've just had the occlusion.

What do we see?

Grossly.

Almost nothing.

If you looked at the heart on an autopsy table right after the event, it would look pretty normal.

Maybe a little bit mottled after about four hours.

But under the microscope.

Microscopically, early on, you start to see these wavy fibers.

The muscle fibers are dead.

They aren't contracting anymore.

But the healthy muscle around them is still pulling and squeezing.

So the dead fibers get stretched out.

They get stretched and buckled into these wavy lines.

You might also see something called contraction bands.

These dense pink stripes.

This happens if a little bit of blood flow returns for a moment, and calcium leaks back into the dead cells, causing the proteins to seize up in one last titanic contraction.

Okay, let's move to days one to three.

This is the acute phase.

Now the immune system wakes up.

Grossly, the tissue starts to turn a pale yellow color.

It's obviously dying.

And microscopically, the cavalry has arrived.

The neutrophils.

The first responders?

The first responders of acute inflammation.

They just swarm the dead tissue.

Their job is to attack and digest.

But there's no bacteria to attack.

It doesn't matter.

They see necrosis.

They attack.

They release all these powerful enzymes to break down the dead cells.

And then we get to days three to seven.

This seems like the most critical window in the text.

It is.

This is the period of maximum danger.

Grossly, you see a central yellow soft area with a bright red border.

That red border is hyperdemia.

New blood vessels forming at the edge to support the cleanup crew.

And the cleanup crew has changed.

It has.

Microscopically, the neutrophils are dying off and the macrophages move in.

Macrophage.

Literally big eater.

Exactly.

And they are voracious.

They are there to consume the dead muscle cells and the dead neutrophils.

They are effectively dissolving the heart wall to clear out all the debris.

But here's the problem.

They haven't laid down any new structure yet.

No scar tissue yet.

They are just removing material.

They are just digging.

So the wall is essentially turning into mush.

Correct.

The structural integrity of that part of the heart is at its absolute lowest point during this window.

And this directly explains the complication section.

The text flags this three to seven day window as the danger zone for rupture.

Yes.

This is not a coincidence.

If the pressure inside the ventricle is high, and it is, and the wall is being actively eaten by macrophages, it can pop.

If the free wall, the outside wall ruptures, blood shoots out into the pericardial sac.

The sac around the heart.

Right.

And that sac is tough and fibrous.

It doesn't stretch quickly.

So the blood feels that space and it just crushes the heart from the outside.

That's cardiac tamponade.

And it's rapidly fatal.

Very rapidly fatal.

What if the septum, the wall between the ventricles ruptures instead?

Then you get a ventricular septal defect, a VSD, a brand new hole where there shouldn't be one.

Blood shunts from the high pressure left side over to the right side.

You'll suddenly hear a loud new murmur.

And the third type of rupture,

the papillary muscle.

Right.

The small muscles that hold the mitral valve leaflets in place.

If one of those ruptures, the valve unhinges,

you get acute severe mitral insufficiency.

The valve just flops open and blood shoots backward into the lungs.

All of these mechanical catastrophes happen in that three to seven day window specifically because of the macrophage activity.

It's all because of the cleanup crew.

It's not random luck.

It's cellular biology.

Okay.

So let's finish the timeline.

Days 10 to 14.

What's happening now?

The eating is mostly done.

Now we start to build granulation tissue forms.

This is a loose, very vascular connective tissue.

It's like the scaffolding for the final scar.

Grossly, the yellow center starts to get a red fleshy looking border.

And finally, let's see two months later.

You have a white firm scar.

The granulation tissue has been remodeled into dense type three collagen.

It's strong, but here's the kicker.

It's not muscle.

It doesn't pump.

It doesn't pump.

It's just a patch.

So the heart has lost a permanent piece of its contractility in that area.

Before we move off MI, there's a mention of a late complication called Dressler syndrome.

What's that?

Right.

This is an interesting one.

It typically happens weeks later, say six to eight weeks after the MI.

The patient develops pericarditis inflammation of the sac around the heart.

But it's not an infection.

No, it's autoimmune.

The theory is that during the heart attack, the immune system was exposed to heart muscle proteins that it usually doesn't see because they're hidden inside cells.

It got sensitized to them.

Weeks later, it creates antibodies that croc react and attack the pericardium.

Let's zoom out.

We've talked about the acute disaster of an MI.

But what happens if you survive?

Or what if you just have chronic low -grade ischemia over many years?

The text introduces chronic ischemic heart disease.

This is the slow burn.

This is the insidious onset of progressive congestive heart failure.

Basically, over time, all that accumulated ischemic damage leads to replacement fibrosis.

You lose a little muscle here, gain a little scar there.

And the heart changes shape.

It dilates.

It gets baggy and weak.

The remaining healthy muscle tries to bulk up hypertrophy to compensate, but eventually it just burns out.

And this leads us perfectly to the next major station on our road map.

Heart failure.

Congestive heart failure, or CHF.

The text defines this pretty simply.

The heart can't pump enough blood to meet the metabolic needs of the body.

But then it splits it into left versus right failure.

I'll admit, I always found this confusing until I visualized the plumbing.

You have to follow the flow of blood.

It's all about where the traffic backs up.

Let's start with the left ventricle.

Its job is to receive oxygenated blood from the lungs and pump it out to the whole body.

So if the left ventricle fails, if it stops pumping effectively, where does the blood go?

It can't go forward, so it has to back up.

It backs up.

Right into the left atrium and then backward into the pulmonary veins and finally right into the lung tissue itself.

The pressure inside the lung capillaries rises and fluid is forced out of the blood vessels and into the air sacs.

Pulmonary edema.

The lungs fill with fluid.

Exactly.

And that's why all the symptoms of left heart failure are respiratory.

Dyspnea shortness of breath.

Rails, which are crackles when you listen with a stethoscope.

That's literally the sound of air bubbling through fluid.

And orthopnea.

The text mentions pillows.

Ah, the pillow count.

This is classic.

When you lie flat, gravity allows more blood from your legs and abdomen to return to the heart.

A failing left ventricle can't handle that extra volume, so the fluid floods the lungs even worse.

You feel like you're drowning.

You do.

So you have to prop yourself up on two, three, sometimes four pillows just to be able to breathe and sleep.

And paroxysmal nocturnal dyspnea.

That's waking up in the middle of the night gasping for air.

It's the same mechanism.

It just takes a few hours of lying flat for the fluid to accumulate enough to wake you up.

The notes mention a specific microscopic finding here that's pretty interesting.

Heart failure cells.

Yes.

This is a classic pathology image.

Remember, the pressure in the lungs is so high that red blood cells actually get squeezed out of the tiny capillaries and into the alveoli, the air sacs.

They're not supposed to be there.

No.

So the lungs' resident immune cells, the macrophages, see these red blood cells and they eat them.

The iron from the hemoglobin gets stored inside the macrophage as hemocytarin.

We call them hemocytarin -laden macrophages.

If you see those under a microscope from a lung sample, you know the lungs have been wet and congested for a long time.

OK.

So left failure equals lung symptoms.

Now what about right heart failure?

So the right ventricle's job is to pump blood to the lungs.

If it fails, blood backs up behind it.

And where is that blood coming from?

From the rest of the body, the veins.

Correct.

So the backup happens in the systemic circulation in the body.

You see the jugular veins in the neck bulging out.

That's jugular venous distension or JVD.

And the liver gets congested.

The liver and spleen swell up hepatosplenomegaly.

Fluid pools in the lowest parts of the body due to gravity.

So you get pitting edema in the legs and ankles.

Or in the belly, which is called a sites.

The liver morphology is quite vivid here.

The text calls it a nutmeg liver.

It's a very visual description.

If you cut a nutmeg seed in half, it has this modeled dark and light pattern.

In a congested liver, the blood backs up and pools in the central veins of the liver lobules, making those areas dark and red.

The surrounding liver tissue is paler, sometimes fatty.

It creates that exact speckled look.

And the most common cause of right heart failure is?

Ironically, it's left heart failure.

It's a domino effect.

If the left side backs up into the lungs, eventually that pressure backs all the way up through the lungs and puts a massive chronic strain on the right ventricle.

So the right ventricle fails because it's trying to push blood into a high pressure waterlogged lung.

Precisely.

But you can have isolated right heart failure.

That's usually due to a primary lung disease like severe COPD or pulmonary fibrosis.

When the lungs themselves are diseased, the arteries in them clamp down, causing pulmonary hypertension.

And the right ventricle has to fight that.

It has to push against that high pressure system day in and day out, and eventually it gives up.

We have a special name for that.

Core Pulmonel.

Okay, so plumbing the arteries and the pump the muscle.

We've covered those.

Now let's talk about the doors.

Valvular heart disease.

Valves are all about keeping flow unidirectional.

And they can fail in one of two ways.

Stenosis, where they won't open wide enough.

Or regurgitation, also called insufficiency, where they won't close tight enough.

The text starts with calcific aortic stenosis.

This is largely a disease of aging.

The text calls it wear and tear.

And that's exactly what it is.

Imagine a door hinge that just gets rusty and stiff over 70 or 80 years.

Calcium deposits build up on the valve leaflets.

They turn into rock.

They essentially turn into rock.

And the left ventricle has to generate absolutely insane pressure to force blood through that tiny rocky opening.

This leads to what's called concentric hypertrophy.

The muscle wall gets incredibly thick to handle the load.

And the danger here?

The danger is that the heart is working so hard, but the cardiac output is fixed by that narrow valve.

If you exert yourself, you can't get more blood out to your brain.

You get syncope fainting or even sudden death.

On the complete flip side of that, we have mitral valve prolapse.

This is a floppy valve.

It's due to something called mixomatous degeneration.

Basically, the connective tissue inside the valve leaflets gets weak and kind of jelly -like.

So when the ventricle squeezes, instead of staying shut, the valve leaflets balloon backward into the left atrium.

Like a parachute.

Exactly like a parachute catching wind.

The text associates this with Marfan syndrome and other connective tissue disorders.

And the classic clinical sign is a sound.

A mid -systolic click.

That's the sound of those cordae tendiney snapping taut as the valve balloons back.

Usually it's benign, but that floppy valve surface can be a place for bacteria to stick.

Which brings us to a topic that feels very old school medicine, but the notes devote a lot of space to it.

Rheumatic fever.

It is old school in the West thanks to antibiotics, but globally it's still a massive cause of valve disease.

And the story here is just tragic.

It starts with a simple strep throat.

Group of beta hemolytic strep.

Right.

And most kids get strep throat and they're fine.

But in some, a few weeks later, something goes terribly wrong.

And it's not the bacteria attacking the heart.

It's our own immune system.

It's molecular mimicry.

It's a tragic case of mistaken identity.

The bacteria has a protein on its surface, the M protein, that looks suspiciously similar to proteins on human heart valves and other tissues.

So the antibodies we make to kill the strep.

They get confused.

Those same antibodies lock onto our own heart valves and trigger a massive inflammatory reaction.

It's friendly fire.

This is a classic type two hypersensitivity reaction.

The diagnosis for this requires the Jones criteria.

The table and the notes list them out very clearly.

Right.

You need evidence of that preceding strep infection plus some major symptoms.

The mnemonic we all learn is usually Jones.

J is for joints, a migratory polyarthritis where the pain moves from knee to elbow, for instance.

O is for the heart.

The O looks like a heart, right.

Carditis.

Inflammation of the whole heart.

N is for nodules, these subcutaneous lumps.

E is for erythema marginatum, a specific type of rash with red borders.

And S is for sydenham caria.

Which is?

Involuntary, jerky, purposeless movements.

It's quite striking.

The text also highlights a specific microscopic finding in the acute phase,

the ashoff body.

These are little granulomas collections of immune cells in the heart muscle.

And inside them you find these very weird looking cells called Anichkow cells.

The catechol cells.

Yep.

Because the chromatin in their nucleus forms this wavy dark line that looks just like a caterpillar.

You see those, it's pathognomonic.

It's rheumatic fever.

But the real damage, the lasting damage, is chronic.

Yeah.

Years later.

Oh yes.

The acute inflammation eventually heals, but it leaves behind scars.

The valve leaflets get thick and they fuse together.

The chordae tendine, those little strings holding the valves, they thicken and shorten.

And you get fish mouth stenosis.

Exactly.

The valve opening becomes this rigid buttonhole -like slit.

The mitral valve is almost always the main victim here.

The aortic valve is often second.

So from sterile inflammation to active infection.

Infective endocarditis.

This is bacteria actually growing on the valves.

These things called the vegetations.

The text splits this into acute versus subacute.

Why is this distinction so important?

It saves lives.

It tells you what bug you're likely dealing with and how sick your patient is.

Acute endocarditis is a blitzkrieg.

It's usually caused by staphylococcus aureus.

Very aggressive, virulent bug.

And it can attack a healthy valve.

It can land on a completely normal healthy valve and just chew through it in a matter of days.

You get these large destructive vegetations, high fevers, high mortality.

It's a true emergency.

Subacute is different.

Subacute is a much slower, more indolent process.

It's usually caused by something like streptococcus viridens.

This is a bug with low virulence.

It's weak.

It can't hurt a healthy valve.

So it needs a pre -existing problem.

It needs a damaged surface to stick to.

Maybe a valve with a small congenital defect or one with old rheumatic scarring or that floppy valve from MVP.

It grows slowly.

The patient might just have low -grade fevers and feel run down for weeks.

The clinical signs of endocarditis are fascinating because they're caused by bits of that vegetation breaking off.

Septic emboli, yeah.

They shower out into the bloodstream and you get signs all over the body.

The text lists the classics.

Roth spots or hemorrhages in the retina of the eye.

Osler nodes and Janeway lesions.

Osler nodes are painful bumps on the fingers and toes.

I remember it as oh for ouch.

Janeway lesions are painless red spots on the palms and soles.

And then you can get splinter hemorrhages, which are little streaks of blood under the fingernails.

There are two clinical correlates here that are absolute gold.

First,

5E drug use.

This is a classic board question.

If you inject drugs, you're potentially introducing bacteria directly into your veins.

The very first valve that the venous blood hits on its way back to the heart is the tricuspid valve.

The valve on the right side.

On the right side.

So if you see a patient with endocarditis on their tricuspid valve, you have to suspect IV drug use.

The bug is almost always staph aureus from the skin.

And the second one, streptococcus bovis.

This is a weird one, but so important.

S.

bovis is a bacteria that lives in the gut.

If you find it growing on a heart valve, you have to ask yourself how did it get into the blood?

There must be a breach in the gut wall.

There is.

And it's very strongly associated with one specific breach.

Colorectal cancer.

So finding S.

bovis endocarditis means you must refer that patient for a colonoscopy.

You might find a hidden treatable cancer.

That's an incredible connection.

One last type of endocarditis mentioned.

Morantic or NBTE.

Nonbacterial thrombotic endocarditis.

These are sterile vegetations.

So no bacteria.

They're just little clumps of fibrin and platelets.

They tend to happen in debilitated patients often with advanced cancer or other chronic wasting diseases.

And they can break off too.

Yes.

They're very friable and can embolize easily, causing strokes.

Briefly, let's touch on myocarditis.

This is inflammation of the heart muscle itself, the myocardium.

The most common cause in the US is viral, especially coxsacky A or B viruses.

Globally, you think of parasites like Chagas disease.

It can present as a huge spectrum from being totally asymptomatic causing acute heart failure or leading to a dilated cardiomyopathy down the line.

OK, let's take a breath.

We've done the plumbing, the pump, and the doors.

And now we enter the maze.

Congenital heart defects.

The developmental errors.

The wiring and structural mistakes.

The text says this is the most common type of birth defect and it groups them by color, which I think is helpful.

Blue babies versus blue kids.

Cyanotic versus asianotic.

This confused me at first, so I want to walk through the logic.

Let's start with shunts.

A shunt is just a hole.

An abnormal connection that lets blood mix where it shouldn't.

And blood always follows the path of yeast resistance, which means it flows from high pressure to low pressure.

The left side of the heart is high pressure.

Very high pressure.

It needs to pump blood to the entire body.

The right side is low pressure.

It only has to pump blood next door to the lungs.

So if you have a hole between the two sides.

Blood flows left to right.

From the high pressure left side to the low pressure right side.

Does that make the baby blue?

No.

And think about why.

The blood that's going out to the body is still coming from the left ventricle.

It's fully oxygenated bright red blood.

The leak is just some of that oxygenated blood going back to the lungs for a second.

Unnecessary trip.

It's inefficient.

It's inefficient.

It overworks the right heart in the lungs.

But the baby is pink.

That's why VSD, ASD, and PDA are all asianotic at birth.

But the text mentions Eisenmenger syndrome.

This is the blue kid scenario late cyanosis.

How does a left to right shunt reverse itself?

It's pure physics.

If you spend years dumping extra blood volume into the lungs from that left to right shunt.

The pulmonary arteries eventually react to that chronic high flow.

They thicken.

They clamp down.

You develop severe pulmonary hypertension.

So the pressure in the lungs gets really high.

Eventually the pressure in the lungs and on the right side of the heart gets higher than the pressure on the left side.

On the flow flips.

The shunt reverses.

Now deoxygenated blood from the right side pushes through the hole into the left side and goes out to the body.

Now the kid turns blue.

That's Eisenmenger syndrome.

And it's irreversible damage.

Let's hit the specifics.

Coarctation of the aorta.

This is a narrowing.

It's a pinch in the aorta.

But where that pinch is located is everything.

There are two main types.

Infantile or productile and adult or post -ductile.

Productile means the narrowing is before the ductus arteriosus.

Right.

This is the more severe form.

It's associated with Turner syndrome.

Because the narrowing is before the ductus, the lower body is dependent on the ductus arteriosus for its blood supply.

You get right ventricular hypertrophy.

It presents early in life with cyanosis in the legs.

And post -ductal.

The narrowing is after the ductus arteriosus has closed.

This is the adult form.

Here you see a pressure difference.

You get very high blood pressure before the pinch.

So in the arms.

And low blood pressure after the pinch.

So weak pulses and low pressure in the legs.

And the x -ray finding for this is classic.

Rib notching.

It's so cool.

Because the aorta is pinched, the body creates a detour.

Blood flows through the intercostal arteries that run along the bottom of the ribs.

Over time, these engorged high pressure arteries actually erode the bone of the ribs, creating little notches you can see on an x -ray.

Wow.

OK, now the shunts.

VSD.

Ventricular septal defect.

A hole between the ventricles.

The text says it's the most common congenital heart defect overall.

If you don't count a bicuspid aortic valve, small ones might close on their own.

Large ones are the ones that lead to Eisenmenger.

ASD.

Atrial septal defect.

A hole between the atria.

The osteum secundum type is the most common.

The specific danger here that the text highlights is a paradoxical embolus.

Meaning?

Normally, a blood clot from a leg vein, a DVT, goes to the right heart and then gets stuck in the lung, causing a pulmonary embolism.

But with an ASD, that clot can cross through the hole from the right atrium to the left atrium, enter the left heart, and then get shot up to the brain.

A stroke from a leg clot.

A stroke from a venous clot.

That's a paradox.

PDA.

Patent ductus arteriosus.

This is the connection between the aorta and the pulmonary artery that's supposed to close after birth but fails to.

It's often seen in premature babies or is associated with congenital rubella infection.

The sound is a continuous machinery murmur.

And the pharmacology here is key.

Very key.

Prostaglandin E2 or PGE2 is what keeps the ductus open.

So you can give that to a newborn who needs it.

To close it, you give endomethacin, which is an NAI that blocks prostaglandin synthesis.

The mnemonic is endomethacin ends the patency.

OK, now for the blee babies.

The right to left shunts.

These are kids born blue because deoxygenated blood is getting into the systemic circulation right away.

The text focuses on the T's.

Right.

The big one is tetralogy of phallate.

It's four problems that all stem from one single developmental error.

The septum between the ventricles is displaced.

And the four parts are?

One, you get stenosis of the pulmonary outflow tract.

It's hard for blood to get to the lungs.

Two, because the right ventricle is pushing against that stenosis, you get massive right ventricular hypertrophy, which gives the heart a boot shape on x -ray.

Three, you have a VSD, the hole.

And four, you have an overriding aorta, where the aorta is sitting right on top of the hole, getting blood from both ventricles.

And it's cyanotic because of the stenosis.

Exactly.

It's easier for the deoxygenated blood in the right ventricle to go through the hole, the VSD, and out the aorta than it is to fight its way through that narrow path to the lungs.

Then there's transposition of the great vessels.

The wiring is completely prost.

The aorta comes off the right ventricle and the pulmonary artery comes off the left ventricle.

You have two closed loops that don't mix.

The body's blood just circulates to the body, never getting oxygen.

The lungs' blood just loops back and forth to the lungs.

That's not compatible with life.

It is 100 % fatal unless there is a shunt, like a PDA or a VSD, to allow some mixing of blood.

This one is associated with mothers who have diabetes.

And truncus arteriosus.

That's a failure of the main trunk, leaving the heart to divide.

So you just have one giant vessel coming out that serves as both the aorta and the pulmonary artery.

And finally, tricuspid atresia.

The tricuspid valve never forms at all, so no blood can get from the right atrium to the right ventricle.

The right ventricle is tiny, it's hypoplastic, you have to have both an ASD and a VSD to survive.

It's just amazing how mechanical these failures are.

It's not some vague disease.

It's plumbing and wiring gone wrong.

Finally, let's touch on the cardiomyopathies.

The muscle itself is sick.

Right, this is a primary disease of the myocardium.

We have three main flavors.

First is dilated.

The balloon heart.

The balloon heart.

All four chambers are dilated.

The walls are thin and flabby.

It's a big, weak, baggy heart that can't squeeze properly.

This is a systolic failure.

And the causes.

The text lists a bunch.

It can be genetic, but also alcohol abuse.

The holiday heart syndrome chemo drugs like doxorubicin, cocaine use, or the end result of a viral myocarditis from Coxsackie B, and Chagas disease also can be seen in pregnancy.

Next is hypertrophic cardiomyopathy or HOCM.

This is the opposite problem.

The muscle is too thick.

Specifically, the septum gets asymmetrically hypertrophied.

This is the one that's genetic.

Usually an autosomal dominant mutation in the beta myosin heavy chain protein.

And this is the one that affects young athletes.

Yes.

This is the tragic story of the young athlete who just drops dead on the basketball court.

The heart muscle is so thick that the chamber is small and can't fill properly.

That's diastolic failure.

And worse, that thick septum can lock the outflow tract when the heart beats.

And under the microscope.

You see myofibrid disarray.

The muscle cells, instead of being in nice parallel lines, are just a chaotic jumbled mess.

And the last one, restrictive.

This is a stiff heart.

It's not necessarily thick, but it's rigid like leather.

It can't stretch to fill with blood.

So this is also a diastolic failure.

And the causes are usually infiltration.

Right.

Things are being deposited in the heart muscle that shouldn't be there.

The classic causes are amyloidosis, which is a misfolded protein.

Sarcoidosis, which deposits granulomas.

Or Luffler endomyocarditis, which is an infiltration of eosinophils.

Okay, very quickly, cardiac tumors.

Primary tumors of the heart are very rare.

The text highlights two you have to know.

The first is amyxoma.

Benign.

Benign.

It's the most common primary tumor in adults.

It's usually in the left atrium.

And it's this gelatinous mass on a stalk.

It can flop into the mitral valve opening and act like a ball valve, causing intermittent fainting or obstruction.

And the second one.

A rhabdomyoma.

This is a benign tumor of heart muscle.

It's the most common one in children.

And it's very strongly associated with the genetic condition tuberous sclerosis.

And finally, a word on carcinoid heart disease.

This one is chemically fascinating.

It's rare, but it's a great physiology lesson.

A carcinoid tumor, which is usually in the gut and has spread to the liver, releases massive amounts of serotonin into the blood.

That serotonin causes fibrosis of the heart valves.

But, and this is the key, it only affects the right side of the heart, the tricuspid and pulmonary valve.

Exactly, why?

The lungs protect the left side.

Yes.

As the blood passes through the lungs, the lung tissue contains an enzyme,

monoamine oxidase or MAO, which metabolizes and destroys the serotonin.

So the blood that gets to the left heart is clean.

If you see right -sided valve fibrosis, you have to think about a carcinoid tumor.

We have covered a massive amount of ground.

From the blocked artery of a 50 -year -old smoker to the genetic twist of a newborn's aorta, it's really quite a journey.

It's a complex organ, but as you said, understanding the pathology is really about connecting the structure to the symptom.

If you know the anatomy and the flow, you can predict the disease.

That's the takeaway, isn't it?

The heart is a machine.

A brilliant machine, but a machine nonetheless.

It's a pump, some pipes, some valves and some wires.

And like any machine, it can break in very predictable ways.

Thank you for joining us on this deep dive into cardiac pathology.

My pleasure.

Digest this material.

Try to visualize the flow and the backup.

It makes all the difference.

We'll see you on the next dive.