Chapter 27: Disorders of Cardiac Function, and Heart Failure and 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 really getting into the heart of the matter.

We're mapping out cardiac dysfunction, heart failure, and circulatory shock.

We're essentially synthesizing Chapter 27 from Porth's Pathophysiology.

That's the plan.

Our goal.

Give you a clear path through these complex topics, the mechanisms, the signs, the treatments, without getting totally lost in the weeds.

We want you to see how it all connects, pathologically and clinically.

Exactly.

And you really have to think of the heart as, well, a system with multiple parts that can fail.

We'll start with the outside layer, the pericardium, then look at the blood supply, coronary artery disease, then the muscle itself, cardiomyopathies, infections,

and the valves, the internal plumbing.

And all of that leads us directly into understanding heart failure and shock as sort of the end result of these problems.

Okay.

Let's start right there on the outside with the pericardium.

It's a sac, two layers.

Yep.

Visceral and parietal layers.

And normally there's just a little bit of fluid in between maybe 50 mL for lubrication.

But inflammation there, pericarditis, that's known for being really painful.

Why is that?

It's heavily innervated.

So yeah, acute pericarditis often presents with pretty severe pain.

It's frequently viral or sometimes we don't know the cause, idiopathic, and it often resolves on its own.

The treatment's interesting.

NSAIDs are standard.

Right.

Non -steroidal anti -inflammatories.

But we're also using colchicine more.

And that works differently, doesn't it?

Not like a typical NSAID.

Totally different mechanism.

It's still anti -inflammatory, but it works by stopping microtubules from forming properly.

Okay.

Which basically means it stops leukocytes, those white blood cells, from moving to the area and doing their inflammatory thing.

It's a neat, targeted approach.

What if fluid builds up in that space?

Yeah.

An effusion?

Yeah, a pericardial effusion.

If that happens quickly or a lot of fluid builds up, you get cardiac tamponade, the heart gets squeezed.

And how does that show up clinically?

Well, the key thing is that tamponade makes the normal drop in blood pressure during inhalation much, much worse.

Normally, your stroke volume and systolic pressure dip a tiny bit when you breathe in.

Right.

Because the septum bulges slightly leftward.

Tamponade exaggerates that effect hugely.

And if it's severe, you have to drain that fluid fast.

Pericardiocentesis.

Exactly.

Needle through the chest wall, aspirate the fluid, can be life -saving.

Okay.

Moving from the sac to the vessel supplying the heart muscle itself.

Coronary artery disease.

CAD.

So CAD is basically reduced blood flow through the coronary arteries, usually because of atherosclerosis plaque buildup.

And this is what sets the stage for angina, heart attacks, even sudden death.

And the heart's oxygen demand is unique, right?

It really is.

It pulls out about 70 % of the oxygen delivered to it, even when you're just sitting there.

Wow.

70 % at rest.

Yeah.

Most tissues extract way less.

Yeah.

So because there's not much oxygen reserve left in the blood, the only way the heart can get more oxygen during exercise is by drastically increasing blood flow, maybe four or five times higher.

So how does it control that flow?

Several factors.

Aortic pressure matters, how much the vessels get squeezed during contraction.

But the big one is autoregulation based on metabolism.

Meaning the heart muscle itself signals for more blood.

Precisely.

When the heart muscle cells work harder, they release metabolites.

And adenosine is a really critical one.

It's a powerful vasodilator opening up those vessels locally to match blood flow to the demand right where it's needed.

Okay.

That brings us to a really crucial point in understanding ACS, acute coronary syndromes.

The difference between stable and unstable plaque.

This is absolutely key.

A stable plaque is like a fixed narrowing.

It causes predictable problems.

You exert yourself, you get chest pain, stable angina, you rest or take nitro, it goes away.

It's ischemia, but it's predictable.

And there's the unstable kind.

That's the dangerous one.

It typically has a big fatty core and just a thin wheat cap over it.

If that cap ruptures, boom, platelets rush in, a clot forms right there.

And that's what triggers an acute coronary syndrome, unstable angina and STEMI or STEMI.

And when someone comes in with suspected ACS, the ECG and blood tests are vital.

What are the ECG signs?

We're looking closely at the ST segment.

If it's elevated STEMI, that usually points to transmural infarct, meaning the damage goes through the full thickness of the heart wall.

And if it's depressed?

ST depression usually suggests unstable angina or an N STEMI, a non -ST elevation MI.

That often means the injury is more limited, maybe just to the inner layer, the sebendocardium.

Do you confirm with biomarkers?

Troponins are the gold standard now.

Definitely.

Troponin I and troponin T, they're very specific to heart muscle damage.

And what's really useful is how they behave over time.

They start to rise within about three hours of injury and stay high for a good week, sometimes 10 days, much better than the old CKMB marker.

For a STEMI, time is muscle.

Reperfusion within 60, 90 minutes is the goal.

What's the immediate drug cocktail?

Right.

You want to act fast.

First, aspirin.

It knocks out cyclooxygenase permanently in platelets, so they can't make thromboxane A2, which makes them sticky.

So less clotting.

Second, beta blockers.

They slow the heart rate, reduce how hard it contracts, basically decreasing the heart's oxygen demand and VO2, protects the stressed muscle.

And ACE inhibitors.

Often started early too, or in the recovery phase.

They help lower blood pressure, reduce resistance the heart pumps against, and importantly, they help prevent harmful changes in the ventricle shape remodeling, which improves long -term survival.

And the actual reperfusion options, getting the artery open.

Three main ways you can use clot busting drugs, fibrinolytic therapy, or more commonly now for STEMI, percutaneous coronary intervention, PCI.

Angioplasty and stenting, the door to balloon time.

Exactly.

Ideally less than 90 minutes from arrival.

And then for more complex or widespread disease, there's bypass surgery, CAG, using a vein from the leg or an artery from the chest wall to detour around the blockages.

All right.

Let's shift focus from the plumbing, the arteries to the heart muscle itself, the cardiomyopathies.

These are diseases of the muscle structure or function.

Right.

And they come in different flavors.

Probably the most talked about in certain contexts is hypertrophic cardiomyopathy or HCM.

The one associated with young athletes and sudden death.

Sadly, yes.

It's often genetic.

The key feature is the left ventricle wall becoming unusually thick, especially the septum between the ventricles for no clear reason like high blood pressure.

This thickening can obstruct blood flow out of the ventricle and also makes it hard for the ventricle to relax and fill properly.

And the opposite problem is dilated cardiomyopathy, DCM.

Correct.

In DCM, the ventricles get enlarged, stretched out, and the walls become thin.

The main problem here is weak contraction, poor systolic function.

The ejection fraction, the percentage of blood pumped out with each beat, can get really low, sometimes under 25 % in advanced stages.

And that leads to complications.

A big one is blood clots forming inside those big sluggish chambers because the blood just isn't moving well, risk of stroke or other emboli.

And then there's the one linked to emotional events, stress cardiomyopathy.

Pocketsubo cardiomyopathy, yeah.

Often called broken heart syndrome.

It's this weird temporary stunning of the heart muscle, usually triggered by intense emotional or physical stress.

It looks just like a heart attack on the ECG and symptoms.

But the arteries are clear.

Usually, yeah.

On an angiogram, you see the bottom part of the left ventricle, the apex, ballooning out strangely, but typically no major blockages,

and it usually recovers.

Okay.

How about infections affecting the heart?

Infective endocarditis, i .e.

This is when microbes, usually bacteria, actually invade the heart valves or the lining of the heart.

And they form vegetations.

Right.

These clumps of dietary, platelets, fibrin, they tend to form on the valve leaflets, especially the aortic and mitral valves.

And they're friable, meaning bits can easily break off.

Causing emboli.

Exactly.

Those pieces travel through the bloodstream and can cause strokes, block arteries in the lungs or limbs.

Plus, the patient usually has persistent bacteria in the blood.

We diagnose it using specific criteria, the modified Duke criteria, which combine clinical signs, blood cultures, and heart imaging.

Now, contrast that direct infection with rheumatic heart disease, RHD.

That's an immune reaction, isn't it?

Yes, a delayed consequence of group A strep throat infection.

It's fascinating, actually.

It's a case of molecular mimicry.

The immune system gets confused.

Pretty much.

Antibodies the body makes against the strep bacteria mistakenly recognize similar -looking proteins on the heart valves and other tissues.

This triggers inflammation, and over time, repeated attacks can lead to chronic damage and scarring of the valve.

And it often affects the mitral valve.

It's the classic cause of acquired mitral stenosis, especially in parts of the world where strep throat is common and not always treated promptly.

Diagnosis involves the Jones criteria.

You need proof of a past strep infection, plus specific major signs like heart inflammation, carditis, or arthritis that moves between joints.

Okay, let's talk specifically about valve problems, valvular heart disease.

Two main ways valves fail, right?

Stenosis and regurgitation.

That's the core concept.

Stenosis means the valve is narrowed, stiff, doesn't open fully.

This blocks forward blood flow.

So the chamber before the valve has to work harder.

Exactly.

It has to generate higher pressure to push blood through that narrow opening.

So I think mitral stenosis, the left atrium has to work harder.

Pressure builds up there, and that backs up into the lungs, causing congestion.

And the other type is regurgitation.

Or incompetence or insufficiency.

This means the valve doesn't close properly, so blood leaks backward when it shouldn't.

Like a leaky seal.

Right.

So for example, in aortic regurgitation, blood flows back from the aorta into the left ventricle during diastole when the ventricle should be relaxing and filling from the atrium.

There's a specific type called mitral valve prolapse.

What's that?

That's often described as a floppy valve.

The leaflets are thickened, sort of degenerate, and they bulge or prolapse back into the left atrium when the ventricle contracts.

Does it cause major problems?

Often it doesn't or causes mild symptoms.

Some people get vague chest pain, palpitations, anxiety.

Interestingly,

sometimes symptoms improve if people cut back on caffeine or alcohol.

Let's hit the big ones.

Aortic stenosis, A .S.

Narrowing of the aortic valve.

Right.

So the left ventricle has a harder time ejecting blood into the aorta, its response.

It gets thicker, concentric hypertrophy to generate more force.

And the classic symptoms.

As it gets severe, the textbook triad is

Chest pain, often with exertion.

Syncope, fainting, especially with exertion.

And eventually the symptoms of heart failure.

And aortic regurgitation, AR, the leaky aortic valve.

So blood leaks back into the LV during diastole.

This increases the volume the LV has to handle.

Over time, the LV dilates to accommodate the extra volume.

Clinically, you see signs related to a large stroke volume and rapid runoff of blood from the aorta, leading to a wide pulse pressure, the difference between systolic and diastolic pressure.

A water hammer pulse.

That's the classic description, yeah.

A very forceful pulse that collapses quickly.

Okay, we've looked at the parts, now let's put it together.

Heart failure, HF.

The heart just can't keep up.

Essentially, yeah.

Failure to pump enough blood to meet the body's needs, or doing so only at elevated filling pressures.

A really key concept is cardiac reserve.

Healthy hearts have a lot of reserve capacity.

But in heart failure.

People with HF might be using almost all their cardiac reserve just to function at rest.

There's very little left for any kind of activity.

And cardiac performance depends on that triangle.

Preload, afterload, contractility.

Absolutely.

Preload is the stretch on the muscle fibers at the end of shilling.

Afterload is the resistance the heart has to pump against.

And contractility is the inherent strength of the muscle contraction, often linked to the Frank Starling mechanism, more stretch, stronger contraction, up to a point.

We classify HF into systolic and diastolic dysfunction.

Right.

Systolic dysfunction is basically a pumping problem, weak contractility.

The ejection fraction is low.

Diastolic dysfunction is a filling problem.

The ventricle is stiff, doesn't relax properly.

The EF might look normal, but the pressures inside the ventricle are high during filling.

And the body tries to compensate, but it backfires.

Tragically, yes.

This is the maladaptive compensation.

The body senses low output and activates alarm systems.

The sympathetic nervous system and the RAAS, the randon angiotensin aldosterone system.

Which makes things worse.

In the long run, yes.

Sympathetic activation makes the heart beat faster and harder and constricts blood vessels, all of which increases the heart's oxygen demand and the afterload it's struggling against.

RAAS causes salt and water retention, increasing volume overload, and also directly contributes to harmful remodeling of the heart muscle.

It becomes a vicious cycle.

Is that where BNP comes in?

Brain natriuretic peptide?

Yes.

The heart releases BNP when the ventricles are stretched and under stress.

Measuring BNP levels in the blood gives us a good idea of how severe the heart failure, particularly the ventricular dysfunction, is.

How does HF look different in kids?

The most common cause in children is congenital heart defects.

Things like holes between the chambers, VSDs.

Because their systems are different, signs can be subtle.

Difficulty feeding, poor growth, fast breathing.

And in right -sided failure, you often see an enlarged liver, hepatomegaly, due to the venous backup.

And in older adults, it can be tricky to spot.

Very much so.

Diastolic dysfunction is more common in older adults, and symptoms can be really nonspecific or blamed on other things.

Instead of classic shortness of breath with activity, they might just have fatigue, confusion,

restlessness, or needing to pee frequently at night nocturia.

You have to have high index of suspicion.

Okay, final topic.

The ultimate circulatory collapse shock.

Let's focus on cardiogenic shock.

This is pump failure, plain and simple.

Usually caused by massive damage from a heart attack.

The heart just can't generate enough pressure to perfuse the organs.

What are the signs?

Severe low blood pressure, hypertension, often cool, clammy, bluish skin, cyanosis, because blood flow is so poor.

A weak, thready pulse, often a narrow pulse pressure.

And confusion or altered mental state due to lack of brain perfusion.

Is there anything we can do mechanically to help the failing pump in cardiogenic shock?

One key device is the intraaortic balloon pump, the IABP.

It's a clever temporary support.

Does it work?

It's basically a balloon inserted into the descending aorta, just below the arteries branching off to the arms and head.

It's timed with the heartbeat.

It inflates during diastole when the heart is resting.

Pushing blood back towards the coronary.

Exactly.

Improving coronary artery perfusion when the heart muscle needs it most.

Then just before the heart contracts, systole, the balloon rapidly deflates.

Creating suction.

Sort of, yeah.

It momentarily lowers the pressure in the aorta, reducing the resistance, the afterload that the weakened left ventricle has to pump against.

So it makes each beat more effective and reduces the heart's workload.

It's neat.

Now let's briefly contrast that pump failure with a completely different type of shock,

that's distributive, right?

Right.

Anaphylaxis isn't a pump problem, it's a container problem, essentially.

It's a massive immune reaction.

Things like histamine get released system -wide.

Causing vasodilation.

Widespread, profound vasodilation.

All the blood vessels relax and expand so the blood pressure plummets.

Plus capillaries become leaky, so fluid shifts out of the vessels into the tissues.

And critically, you often get life -threatening airway swelling, laryngeal edema, and bronchospasm, making it impossible to breathe.

It's an immediate emergency.

So we've covered a lot of ground there.

From issues with the pericardial sac, like tamponade, through blocked arteries and CAD, the different ways the muscle itself can fail in cardiomyopathies, faulty valves causing stenosis or regurgitation.

Right up to the system.

Failures of heart failure and the different kinds of shock.

Yeah, it really shows how interconnected everything is within the cardiovascular system.

I think the big takeaway for anyone listening, especially students, is seeing that direct line from the underlying pathology, like that unstable plaque rupturing, or the immune system attacking the valves and RHD, to the symptoms the patient actually experiences.

Absolutely.

Understanding the why behind the symptoms is crucial.

Why does mitral stenosis cause shortness of breath?

Because of that pressure back up into the lungs.

Why does heart failure cause fatigue?

Because the cardiac output isn't meeting the body's demands.

It makes it all click.

And maybe final thought to leave people with, we talked about aortic stenosis often being caused by calcification.

Similar inflammatory processes as in CAD.

Right.

So it makes you wonder, doesn't it?

We know things like statins, which lower cholesterol and also reduce inflammation, are crucial for CAD.

Could aggressive risk factor management, really targeting that inflammation and those lipids, potentially do more than just prevent heart attacks?

Could it maybe slow down or even prevent the progression of some types of valve disease, like calcific aortic stenosis?

It suggests these processes might be more modifiable than we used to think.

That's a really interesting point.

The potential to modify structural disease through systemic treatments.

Definitely something to think about.

Well, thank you for walking us through all that.

My pleasure.

And thank you for joining us for this deep drive into cardiac pathophysiology.

We hope it was helpful.