Chapter 27: Disorders of Cardiac Function & Circulatory Shock

Welcome to Last Minute Lecture.

This free chapter overview is designed to help students review and understand key concepts.

These summaries supplement not replaced the original textbook and may not be redistributed or resold.

For complete coverage, always consult the official text.

Welcome back to The Deep Dive.

Today we're diving head first into something pretty huge, really critical.

The whole landscape of cardiac failure.

Think of this as your essential guide to how the heart breaks down, pathologically speaking.

We're going from the outside in sac, plumbing, muscle, the works.

Yeah, it's absolutely essential stuff.

And the sources, they give us a pretty clear map.

It basically splits into two big territories.

First, we're looking at specific problems with the heart structure, you know, where things go wrong, pericardium, coronary arteries, valves, the muscle itself.

Okay.

And second, we connect all that to the big system failures, heart failure and circulatory shock.

The main thread here, the thing we keep coming back to is why, why does this damage cause those symptoms?

Got it.

Okay.

Let's start on the outside then with the pericardium, that protective sac, right?

Double layered holds maybe what, 50 milliliters of fluid usually, just lubrication.

Exactly that.

Just enough to let the heart move smoothly.

But when that sac gets inflamed, well, that's acute pericarditis.

And clinically, it often presents with a classic triad.

It's pretty distinctive.

Okay.

What's the triad?

Sharp chest pain, often sudden.

Then there's this unique sound, a pericardial friction rub, sounds like layers rubbing together, kind of scratchy.

And third, characteristic ECG changes, those widespread ST segment elevations.

And I remember something about posture helping,

like sitting up makes it better.

Yeah.

That seems like a key bedside clue.

It really is.

The pain often eases when you sit up and lean forward, which helps differentiate it from, say, the pain of a heart attack.

That's important.

Definitely.

So inflammation,

that usually means fluid buildup, right?

And effusion.

Right.

Pericardial effusion.

But here's a crucial point.

It's not always about how much fluid builds up.

The real danger often lies in how fast it accumulates.

Okay.

So a lot of fluid slowly building up might be okay, but a little bit really fast is bad news.

Precisely.

If it's slow, the pericardium can stretch, adapt a bit.

But rapid accumulation, that leads to cardiac tamponade.

The heart literally gets squeezed.

Squeezed so it can't fill properly.

Exactly.

It compresses the ventricles, messes up diastolic filling, and your cardiac output just tanks.

And this compression, it leads to a really specific sign called pulses paradoxes.

Pulses paradoxes.

Yeah.

That's dramatic.

What does that look like physiologically?

Well, think about breathing in.

Normally, your systolic blood pressure might dip just a tiny bit.

But with tamponade, the heart's already squished.

So when you inhale, more blood comes back to the right side, pushing the septum, the wall between the ventricles over into the left ventricle.

Oh, so it makes the left side even smaller temporarily.

You got it.

It severely restricts the left ventricles output during inspiration, causing a much bigger and exaggerated drop in systolic blood pressure.

That's pulses paradoxes, a key sign of tamponade.

Okay, clear.

Moving inward then.

The plumbing coronary artery disease, CAD.

The big cause here is atherosclerosis, right?

Plac buildup.

Overwhelmingly, yes.

Atherosclerosis is the main culprit.

And when you think about the immediate crisis, like a heart attack, it boils down to a simple imbalance.

Oxygen supply versus oxygen demand in the heart muscle.

Makes sense.

What drives the demand side most?

Several things, how hard the heart contracts, the pressure it pumps against, which is wall stress.

But, you know, heart rate is arguably the biggest factor.

A faster heart needs more oxygen.

And beats less efficiently, too, probably.

Right.

And crucially, a faster rate means less time in diastole.

And diastole is when the coronary arteries actually get perfused, when they receive their own blood supply.

So high heart rate is a double whammy.

So when that supply demand scale tips way off balance,

that's acute coronary syndrome, ACS.

Exactly.

ACS is a spectrum.

At one end, you have unstable angina.

That's chest pain due to ischemia, lack of oxygen.

But, and this is key, there's no actual muscle death, no infarction yet.

Okay.

Ischemia without infarction.

What's next up the severity scale?

Then you get into actual heart attacks, myocardial infarctions.

There's N -STEMI, non -ST segment elevation MI.

This often means the artery isn't completely blocked, maybe intermittently or partially.

There's muscle damage, but it might not go through the whole heart wall thickness.

That's the STEMI.

ST segment elevation MI.

This usually signals a complete blockage of a coronary artery.

The damage typically goes through the entire thickness of the heart wall, a transmural infarct.

This is a major emergency.

Right.

The classic heart attack scenario.

So how quickly do we need to act?

You mentioned vial markers before.

How do they fit in with like when ECG?

Speed is everything for a STEMI.

The goal is reperfusion restoring blood flow, either with clot busting drugs, fibrinolytic agents, or physically opening the artery with PCI, percutaneous coronary intervention.

Ideally that needs to happen within 60 to 90 minutes of first medical contact.

Wow, that's fast.

So decisions are made before lab tests are back.

Often, yes.

The ECG showing that ST elevation is the main trigger for rapid reperfusion.

The blood tests, the biomarkers like troponin I and T, they confirm the diagnosis and tell you about the extent of the damage.

Why troponin specifically?

They're highly specific to heart muscle.

And critically, they stay elevated for a long time, like seven to 10 days.

So even if someone comes in late, troponins can still tell you they had a heart attack.

CKMB, another marker, goes back to normal much faster within two, three days.

Long detection window for troponin.

Okay, so we've done the THAC, the plumbing.

What if the pump itself, the myocardium, the muscle tissue is the problem?

That takes us to cardiomyopathies.

Exactly.

These are diseases directly affecting the heart muscle, causing problems with how it pumps or its electrical activity.

They're quite varied.

A heterogeneous group.

But we often focus on two main structural types.

First, there's hypertrophic cardiomyopathy or HCM.

Here, the left ventricle muscle gets abnormally thick, hypertrophied, for no clear reason like high blood pressure.

Often, the septum, that wall between the ventricles, is disproportionately thick.

Think of figure 2714B in the source that shows that thickened wall.

Thick muscle.

Does that make it stronger?

Or is it a problem?

It's a huge problem.

The muscle becomes stiff, non -compliant.

It can't relax properly to fill with blood during diastole.

So it's a diastolic filling issue.

And tragically, HCM is the most common reason for sudden cardiac death in young athletes.

Wow.

Okay, so that's thick and stiff.

What's the other main type?

The opposite in a way.

Dilated cardiomyopathy or DCM.

Here, the ventricles enlarge, they get stretched out and floppy, kind of like a balloon.

The walls become thinner and the heart's ability to pump blood out, its systolic function is severely weakened.

So a weak baggy pump.

Pretty much.

And this condition, DCM, it's actually the leading reason people need heart transplants worldwide.

That's significant.

Are there other types besides these two structural ones?

Oh, yes.

There are acquired forms too, like myocarditis, which is inflammation of the heart muscle, often caused by a virus.

And then there's the fascinating stress cardiomyopathy, also called takotsubo or broken heart syndrome.

Yeah, it's characterized by sudden temporary left ventricular dysfunction, often triggered by intense emotional or physical stress.

The good news is it's usually reversible.

Okay, muscle covered.

What about the gates, the valves?

Right, valvular heart disease.

The problems here are fundamentally mechanical, two main types of heart disruptions.

Stenosis, where a valve fails to open fully, it becomes stiff, narrowed, creating resistance to blood flow.

Think turbulence.

Okay, stenosis is narrowed opening.

What's the other?

Regurgitation or insufficiency.

This is when a valve fails to close properly.

So blood leaks backward through the valve when it should be shut.

Let's take an example, mitral valve stenosis.

Classic example.

Most often caused by rheumatic fever, usually from a childhood strep infection.

The mitral valve leaflets get inflamed, scarred, and eventually fused together.

The source material mentions it can look like a fish mouth figure, 2719.

Fish mouth.

Okay.

And the consequence.

Well, the left ventricle can't fill properly because blood flow from a left atrium is obstructed.

So the left atrium dilates, pressure backs up into the lungs, causing pulmonary congestion, shortness of breath.

Makes sense.

What about stenosis on the other side, the aortic valve?

Aortic stenosis is super common, especially as people age.

It's usually due to calcification.

The valve just gets stiff and gritty over time.

Now this puts huge pressure on the left ventricle.

How does the LV cope?

It has to work much harder to push blood out through that narrowed opening.

So it adapts by getting thicker LV hypertrophy.

It bulks up its muscle mass to overcome that increased resistance, that afterload.

So muscle thickening is a compensation here.

Now what about the opposite problem on that valve aortic regurgitation, leaky aortic valve?

Right.

AR blood flows back into the left ventricle from the aorta during diastole when the LV should be filling from the atrium.

This means the LV has to handle way more volume than normal incoming blood, plus the leaked back blood.

That sounds like a lot of work for the LV.

It is.

Chronic volume overload.

The LV dilates and hypertrophies to manage this extra volume and maintain overall cardiac output.

And severe chronic AR leads to some really striking physical signs.

Oh, like what?

You get a really wide pulse pressure.

The difference between systolic and diastolic pressure increases.

You might even see the carotid arteries pounding in the neck.

That's Corrigan's pulse.

And the pulse itself feels very forceful and bounding, then collapses quickly called a water hammer pulse.

It's the heart ejecting a huge stroke volume very forcefully.

Wow.

Visible signs of the heart struggling.

Okay, let's pull back from specific parts now and look at the big picture failure.

Heart failure.

The heart just can't keep up, right?

That's the essence of it.

It's a complex syndrome where the heart fails to pump enough blood to meet the body's metabolic needs.

This can manifest as low output or congestion or both.

And I hear about systolic versus diastolic failure.

What's the difference?

Good distinction.

Systolic dysfunction means the heart muscle itself is wick.

It can't contract forcefully enough.

The key measure here is ejection fraction, the percentage of blood pumped out with each beat.

In systolic failure, EF is low, usually under 40%.

Okay, weak pump.

What's diastolic?

Diastolic dysfunction is a problem with filling.

The ventricle, often the left one, becomes stiff and can't relax properly during diastole, so it can't fill adequately.

The ejection fraction might actually be normal or preserved, but because the ventricle doesn't fill well, the overall cardiac output can still be low.

So stiff pump can't fill.

Does this relate to age?

Yes.

Diastolic failure becomes much more common with age and is strongly linked to conditions like hypertension that make the ventricle stiff.

And then there's left versus right -sided failure.

That's about where the symptoms show up.

Exactly.

It's about where the blood backs up.

Left -sided failure primarily affects the lungs.

The left ventricle can't pump blood forward effectively, so pressure backs up into the left atrium and then the pulmonary circulation.

That leads to pulmonary congestion, shortness of breath, dyspnea, trouble breathing when lying flat, orthopnea, crackles heard in the lungs.

Okay, left is lungs.

What about right?

Right -sided failure means the right ventricle isn't pumping effectively to the lungs, so blood backs up in the systemic venous system.

That leads to systemic congestion.

You see swelling in the legs and ankles, peripheral edema, sometimes fluid in the abdomen, ascites, and liver enlargement, hepatomegaly, because blood is backing up there too.

It's almost scary how the body tries to compensate, isn't it?

These mechanisms kick in, but they seem to make things worse long term.

That is the absolute core tragedy of heart failure progression.

The compensatory mechanisms are initially adaptive.

They help maintain output for a while, but eventually they become maladaptive and drive the disease forward.

What are the main ones?

Well, first there's the Frank Starling mechanism.

Basically,

increased filling stretches the heart muscle fibers, causing them to contract more forcefully.

A quick boost to stroke volume, useful initially.

Okay, stretch equals stronger contraction.

What else?

Then the sympathetic nervous system, SNS, gets activated.

Think adrenaline.

It increases heart rate and constricts blood vessels.

This helps maintain blood pressure and perfusion in the short term, but it dramatically increases the heart's workload and its oxygen demand.

Tachycardia also reduces filling time, as we've discussed.

It puts huge strain on an already failing heart.

And there's another system involved too, right?

Something with the kidneys?

Ah yes, the RAAS, the renin angiotensin aldosterone system.

This gets triggered by low blood pressure or reduced blood flow to the kidneys.

It leads to sodium and water retention, trying to increase blood volume, and also causes potent vasoconstriction.

Wait, more volume in tighter vessels.

That sounds like the last thing a failing heart needs.

Exactly.

It's counterproductive long -term.

The volume overload worsens congestion, and the vasoconstriction increases the pressure the heart has to pump against afterload.

Plus, angiotensin II and aldosterone directly contribute to harmful changes in the heart muscle itself.

Remodeling, fibrosis, stiffness.

It's a vicious cycle.

So Starling, SNS, RAAS,

they all start as helpful, but end up driving the failure.

Precisely.

They create this downward spiral.

And clinically, we can actually measure a substance called BNP, B -type natriuretic peptide.

Levels of BNP tend to rise as the ventricles get stretched and overloaded, so it correlates pretty well with the severity of heart failure.

Okay, so when all these compensations fail, when the system is completely overwhelmed,

we get to circulatory shock.

Yes.

Shock is basically profound circulatory failure leading to inadequate oxygen delivery to tissues.

We're talking failure at the cellular level now.

Cells are starved of oxygen.

And what happens in the cells without oxygen?

They can't perform normal aerobic metabolism efficiently.

They're forced to switch to anaerobic metabolism.

This process generates very little ATP, the cell's energy currency, and produces lactic acid as a byproduct.

Lactic acid buildup is toxic and signals widespread tissue hypoxia.

So energy failure and acid buildup.

And shock isn't just one thing, right?

There are different types.

Correct.

It's usually classified based on the underlying cause.

Four main categories.

Cardiogenic shock is pump failure.

The heart itself is the primary problem, like after a massive heart attack.

Okay, pump failure.

What else?

Hypovolemic shock is due to loss of volume, blood volume, plasma volume, whatever.

Think major hemorrhage, severe dehydration, typically when you lose more than, say, 15 -20 % of your circulating volume.

Makes sense.

Volume loss.

Third type.

Obstructive shock.

Here there's a physical blockage to blood flow.

Examples include a large pulmonary embolism blocking outflow from the right ventricle, or cardiac tamponades severely restricting filling.

So a physical block.

And the last one.

Distributive shock.

This is different.

The problem isn't the pump or the volume.

It's the pipes, the blood vessels.

There's massive vasodilation, loss of vascular tone, so the blood pressure even if the volume is normal.

This category includes septic shock, anaphylactic shock, and neurogenic shock.

Okay, let's maybe look at one type in a bit more detail.

Hypovolemic maybe?

How does the body try to fight that volume loss?

Sure.

With hypovolemic shock, as the volume drops, the body goes into overdrive trying to maintain blood pressure.

The sympathetic nervous system cranks up heart rate and causes intense vasoconstriction, clamping down the peripheral vessels.

Ah, so that's why someone in shock might have a fast pulse but feel cold and clammy.

Exactly.

Trying to shunt blood to the vital organs.

This compensation might keep the blood pressure up initially even though the actual stroke volume is falling.

You often see a narrow pulse pressure, systolic, and diastolic pressures getting closer together.

And the RAAS system kicks in too, I bet.

Oh, absolutely.

RAAS and ADH, antidiuretic hormone, work feliously to conserve sodium and water, trying to hold onto every drop of fluid.

The body also tries to pull fluid from the interstitial spaces back into the bloodstream to boost volume.

It's a desperate attempt to maintain circulation.

It really paints a picture from a tiny valve problem or a plaque buildup all the way to total systemic collapse and cellular failure.

It's all interconnected.

It really is.

The journey we took today from specific issues like pericarditis or unstable plaques right through to heart failure and shock, it highlights that balance.

The balance between structure and function, supply and demand, and importantly the balance between the body's adaptive mechanisms like Frank Starling and how those very mechanisms become detrimental as the disease gets worse, like the RAAS system.

So for you listening, a key takeaway really is about location.

Where's the failure?

Sac, plumbing, muscle, valves, and then understanding how the body's attempts to compensate, often quite desperately, end up driving the problem deeper.

That's the core of cardiac pathophysiology, really.

Understanding that progression.

Right.

Okay, go forth and study.

But maybe one last thought to leave you with.

Thinking about that urgency we discussed with ACS and shock.

How critical is that initial rapid assessment, the history, the ECG, compared to waiting for the definitive labs like troponins that confirm the damage is already done?

That initial window seems incredibly vital.

Something to think about.

Absolutely.

Keep asking why until the next deep dive.