Chapter 24: Heart Failure Drugs

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Welcome back to the Deep Dive.

Today, we're jumping into, well, a really core topic,

managing heart failure with pharmacology.

It's definitely a big one.

You have dense clinical stuff.

So if you're trying to get a handle on the mechanisms, the guidelines, those crucial nursing checks from your textbook chapter, we're here to sort of break it down.

Absolutely.

And just to set the stage, heart failure, you know, it affects millions over 5 .8 million in the US alone.

And it's not really a single disease.

Right.

It's a syndrome.

Exactly.

A clinical syndrome where the heart just can't pump enough blood out.

The cardiac output isn't meeting the body's needs.

And while the outlook can be tough, that Framingham study showed about a 50 % 5 -year survival rate.

Wow.

That really highlights why getting the drug therapy right is so, so critical.

So, okay, before we dive into the specific drugs, we need some basic terms, right?

How these drugs actually work on the heart muscle.

For sure.

There are three key concepts.

First is inotropic.

This refers to the force of the heart's contraction.

So how hard it squeezes.

Precisely.

A positive inotropic drug makes it squeeze harder, increases the force.

Didoxin is a classic example we'll get to.

Okay.

Inotropic is force.

What's next?

Then there's chronotropic.

This one's about the rate, the heart rate.

Fast or slower?

Yep.

A positive chronotropic effect speeds the heart up while a negative chronotropic effect slows it down.

Got it.

Force, rate, and the last one.

Is dramatropic.

This relates to the conduction speed,

specifically how fast the electrical signals travel through the heart's AV node.

Ah, so like the wiring.

Kind of, yeah.

A negative dramatropic effect slows that conduction down.

Understanding these three inotropic, chronotropic, dramatropic effects, it's fundamental to seeing how these HF meds work and what effects you need to monitor.

Okay.

That makes sense.

So we've got this condition, the heart's not pumping enough, and we have these tropic ways drugs can influence it.

But the type of heart failure matters too, doesn't it?

Absolutely.

Pathophysiology -wise, we often think about left -sided versus right -sided failure.

With left -sided HF, the left ventricle isn't pumping blood out effectively to the body.

So where does it go?

It backs up.

Into the lungs.

Into the lungs.

That's why you get those classic respiratory symptoms, pulmonary edema, that wet cough, shortness of breath, or dyspnea.

And right -sided.

If the right side fails, the backup is different.

It backs up into the systemic venous circulation, the body's veins.

That's where you see swelling in the legs.

Exactly.

Pedal edema,

maybe liver congestion, and that really visible neck vein distension, jugular venous distension, or JVD.

Okay.

And how do we measure how bad the failure is, especially on the left side?

The key metric there is ejection fraction, or EF.

It's basically a percentage telling you how much blood the left ventricle pumps out with each beat compared to the total amount that was in it.

And normal's pretty high, right?

Yeah.

A healthy EF is around 65%.

In heart failure, that fraction, that ratio, drops significantly.

Which brings us to two related ideas the drugs target.

Preload and afterload.

Okay.

Explain those.

So think of preload as the volume filling the ventricle right before it contracts.

It's the stretch on the muscle fibers, like how full a water balloon is before you squeeze it.

Afterload is the resistance the heart has to push against to get the blood out.

It's the pressure in the aorta and systemic circulation, like the tightness of the nozzle you're trying to shoot the water through.

Right.

Okay.

So preload is volume coming in, afterload is resistance going out.

And understanding that is key to why the treatment approach has changed so much.

Exactly.

It's been a huge shift.

Historically, the focus was often on just making the heart pump harder, those positive inotropes.

Like whipping a tired horse?

Kinda, yeah.

But we realized that just pushing a failing heart harder can actually cause more damage long term.

So the newer guidelines, like the AHAC ones updated in 2021, they focus differently.

How so?

They prioritize blocking the bad guys, the systems that get over -activated in heart failure and cause damage.

Specifically, the renin -angiotensin -aldosterone system, R -A -A -S, and the sympathetic nervous system, SNS.

So instead of just forcing the pump, we're protecting the heart muscle itself.

That's the core idea.

The first line drugs now are usually ACE inhibitors,

ARBs, or the newer ARNs, plus specific beta blockers, digoxin.

It's usually only added after those if needed.

Okay, let's dig into those first line R -A -A -S drugs then, starting with the classics, ACE inhibitors,

like lisinopril.

Yep, lisinopril is a very common one.

ACE inhibitors work by blocking the angiotensin -converting enzyme.

Pretty straightforward name, right?

Oh, yeah.

So if you block ACE, you stop angiotensin from being converted to angiotensin the second.

Angiotensin the second does two main things you don't want in heart failure.

Which are?

One, it's a powerful vasoconstrictor.

It squeezes blood vessels.

Two, it triggers aldosterone release, which makes the body hold onto sodium and water.

So blocking it stops the squeezing and stops the fluid retention.

Exactly.

Less vasoconstriction and the kidneys let go of sodium and water diuresis.

This reduces the blood volume, which directly lowers the preload.

Less stretch on the heart makes its job easier.

That's why they're foundational.

But ACE inhibitors have that one really annoying side effect.

Yes, the cough.

That persistent, dry, hacking cough.

It's not dangerous usually, but it drives patients nuts.

Why does it happen?

Well, ACE doesn't just convert angiotensin.

It also breaks down something called bradykinin.

Block ACE, bradykinin builds up, especially in the lungs, and causes irritation.

So if the cough is too much, what's the alternative?

Then you'd likely switch to an angiotensin receptor blocker, or ARB.

Valsartin is a good example.

How are ARBs different?

They work a step later.

Instead of blocking the enzyme that makes angiotensin II, they block the receptors that angiotensin II binds to.

Ah, so they stop angiotensin II from doing its dirty work, but without messing with bradykinsin.

Exactly.

So you still get the vasodilation preventing that squeeze, but you generally avoid the cough.

And ARBs are particularly good at reducing systemic vascular resistance, which is the afterload.

They lower the pressure the heart

Okay, so ACEs may be more preload -focused, ARBs more afterload -focused, generally speaking.

Yeah, a bit of an oversimplification, but yeah, that's a reasonable way to think about their primary benefits.

But both classes share a really serious safety concern.

Pregnancy.

Yes.

Critical point.

Both ACE inhibitors and ARBs are category D in the second and third trimesters.

They can cause major fetal harm or

Absolutely contraindicated.

And nurses really need to hammer that home with patients.

Absolutely.

Plus, you need to watch kidney function, BUN, and creatinine and potassium levels.

They can both cause hyperkalemia, high potassium.

Right.

Okay, now let's talk about the newer kid on the block in this RAAS category.

Yeah.

The ARNI.

That's Valsartensicubitrol or Entresto.

This one seems like a big deal.

It really is.

It's a combination pill.

You've got the ARB Valsartensicubitrol, which we just talked about, but it's combined with Sacubitrol.

And Sacubitrol does what?

Sacubitrol blocks an enzyme called Neprolicin.

Now, Neprolicin normally breaks down some good guys' natural peptides in our body that cause vasodilation and help us excrete sodium.

So blocking the blocker lets the good guys hang around longer.

Precisely.

You get the ARB blocking the negative effects of angiotensin the second, and you get Sacubitrol boosting the body's own helpful mechanisms.

It's a dual approach.

And the results.

Pretty impressive.

Studies showed around a 20 % reduction in cardiovascular death or heart failure hospitalizations compared to just an ACE inhibitor.

Wow.

But there's a catch when switching, right?

Something about timing.

A huge catch.

This is a critical safety point for nurses.

Because of a risk of serious angioedema swelling, potentially life -threatening, you absolutely cannot give an ARNI within 36 hours of the last ACE inhibitor dose.

36 hours.

Got it.

A mandatory washout period.

Non -negotiable.

You have to wait.

Also, like ACEs and ARBs, it has that black box warning for pregnancy, category D, and you still watch for hypotension, hyperkalemia, and changes in creatinine.

Okay.

So that's the RAAS modulation pillar.

Now, the second pillar you mentioned, beta blockers, like metoprolol or carbodylol.

How do they fit in?

They seem counterintuitive, slowing the heart.

Yeah.

It does seem odd at first glance, but they are incredibly important.

They are cardioprotective.

See, in heart failure, the sympathetic nervous system goes into overdrive.

It's constantly pumping out stress hormones like norepinephrine.

Trying to compensate, but actually causing damage.

Exactly.

It stresses the heart muscle.

Beta blockers block the receptors for these stress hormones.

This dials down the sympathetic overdrive.

So what does that do functionally?

It slows the heart rate, negative perinotropic, reduces the force of contractions slightly, negative inotropic, and decreases how easily abnormal rhythms start, negative dramatropic effects too, reducing automaticity.

Basically, it lets the overworked heart muscle rest and prevents harmful remodeling over time.

Metoprolol is pretty standard.

What's special about carvetolol?

Carvetolol is interesting because it's non -selective.

It blocks beta 1, beta 2, and alpha 1 receptors.

That alpha blockade adds some vasodilation, and there's specific data showing carvetolol slows HF progression in patients with moderate class 2 or 3 heart failure.

But you have to be careful starting them, right?

Start low, go slow.

Absolutely.

You titrate up very carefully because initially, they can worsen symptoms if you start too high or increase the dose too quickly.

Okay, so beta blockers protect the heart by blocking the SNS.

Now sometimes you want to slow the heart rate down without necessarily reducing the contractility as much, right?

Yes, and that led to a newer class, SA node modulators.

The main one is Ivoberdine, brand name Corlenor.

How does Ivoberdine work?

It sounds very targeted.

It is.

It's pretty neat pharmacologically.

It works only on the SA node, the heart's natural pacemaker.

It selectively inhibits specific channels there called FEF channels or funny channels.

Funny channels.

Yeah, they help control the pacing rate.

By inhibiting them, Ivoberdine slows down the firing of the SA node.

So it reduces the heart rate, a strong negative chronotropic effect.

Without significantly affecting the force of contraction, the inotropic effect, which is great for certain patients.

It's indicated for patients with stable symptomatic chronic heart failure, who have an ejection fraction of 35 % or less, who are already on their max tolerated beta blocker dose and still have a resting heart rate of 70 beats per minute or higher.

Very specific niche.

Any big safety flags?

Well, it can increase the risk of atrial fibrillation, bradycardia, obviously, and other conduction issues.

But the really big one is drug interactions.

It's heavily metabolized by the CYP3A4 enzyme.

Ah, the usual suspect.

Yep.

So you have to avoid strong inhibitors or inducers of CYP3A4, and that includes...

Let me guess.

Grapefruit juice.

Bingo.

Grapefruit juice is a strong inhibitor, can dramatically raise Ivoberdine levels, and increase the risk of severe bradycardia, a key patient teaching point.

Good to know.

Okay, let's shift gears to a class usually seen in more acute situations in the hospital.

Phosphatestase inhibitors, or PDIs, like milrinone.

Milrinone primacore is given IV, typically in ICUs, for acute decompensated heart failure.

It's known as an inodulator.

Inodulator, meaning?

Meaning it does two things.

It increases contractility, positive inotropic, and it strongly dilates blood vessels, vasodilator.

How does it do both?

It inhibits the enzyme phosphodiesterase.

Blocking this enzyme leads to more cyclic AMP, or CAMP -P, inside the heart and smooth muscle cells.

More CAMP -P means stronger heart muscle squeeze and relaxation of blood vessels.

So better pump force and less resistance to pump against because the vessels are dilated less after load.

Exactly.

Makes it easier for a struggling heart to get blood out.

But there's a significant downside.

Always a trade -off, isn't there?

Often, yes.

With milrinone, the big risk is ventricular dysrhythmias.

Serious, potentially life -threatening abnormal heart rhythms.

Happens in maybe 12 % of patients.

Requires continuous cardiac monitoring.

And there's that critical drug incompatibility warning, too.

Oh, absolutely critical.

Cannot stress this enough.

Never, ever inject furosemide lasix into an IV line containing milrinone.

They react immediately and form a precipitate.

Basically, they turn into solid chunks in the IV line.

Both drugs become inactive, and you've clogged the line.

It's a major medication error risk.

Wow, okay.

That's one to etch in stone.

So milrinone for acute situations, potent but risky.

Now,

let's talk about the old giant digoxin from the Fodskillet plant, right?

That's the one.

Digitalis.

It was the absolute cornerstone of HF therapy for, like, 200 years.

But as we said, it's now second line.

Why is it still used, then?

What's its main benefit?

Its primary beneficial effect is that strong, positive, inner -tropic action.

It makes the heart contract more forcefully.

It does this by inhibiting an enzyme called the sodium -potassium ATPase pump in heart cells.

Okay, stronger squeeze.

But it has other effects, too, right?

Electrical ones.

It does.

Digoxin increases vagal tone that's parasympathetic stimulation.

This leads to a significant negative chronotropic effect, slowing the heart rate.

And it also has a negative dramatropic effect, slowing conduction through the AV node.

So, slows the rate and slows conduction.

That sounds useful if someone has HF and atrial fibrillation.

Exactly.

That's one of its main niches now controlling the heart rate in patients with concurrent AFib and HF.

But the huge issue with digoxin is safety.

Oh, absolutely.

It has what we call a very low therapeutic index.

That means the difference between a dose that helps and a dose that harms is tiny.

Very narrow margin of safety.

What is the therapeutic range?

It's incredibly small, usually 0 .5 to 2 nanograms per milliliter and GML.

Get much above 2 and you're in toxic territory.

And what does digoxin toxicity look like?

It can be subtle at first or quite dramatic.

Common early signs are GI issues, loss of appetite, anorexia, nausea, vomiting.

Also confusion, headache, and definitely bradycardia, slow pulse.

And the really weird one, the visual thing.

Oh, yes.

The classic sign clinicians are taught to look for visual disturbances.

Patients might complain of seeing yellow or green tints to objects or seeing halos around lights.

If you hear that, think digoxin toxicity immediately.

What makes someone more likely to become toxic besides just taking too much?

Electrolytes are key here, specifically hypokalemia, low potassium, and hypomagnesemia, low magnesium.

Low levels of either potassium or magnesium make the heart much more sensitive to digoxin's effects, increasing the toxicity risk even if the blood level isn't technically high.

So monitoring potassium and magnesium is crucial when someone's on digoxin.

Absolutely essential.

Also, kidney function is critical because digoxin is cleared almost by the kidneys.

If renal function declines, the drug can build up quickly.

What if someone does have severe toxicity?

Life -threatening rhythms?

Maybe a sky -high potassium?

Is there an antidote?

Yes, thankfully there is.

It's called digoxin immune fab, brand name Digifab.

How does it work?

It's basically antibody fragments that bind directly to the digoxin molecules circulating in the blood, inactivating them so the body can excrete the complex.

But there's a quirk with monitoring after giving Digifab, isn't there?

A very important one.

After you give Digifab, if you draw a serum digoxin level, it will come back falsely high.

The lab test measures both free digoxin and the digoxin bound to the Digifab.

So the number is useless then?

Pretty much.

You can't rely on the levels anymore.

You have to switch entirely to monitoring the patient's clinical signs and symptoms.

Heart rhythm, pulse rate, are the nausea and visual disturbances resolving.

That becomes your guide.

Got it.

And quickly, any major drug interactions to know with digoxin?

Yes, several common heart drugs can increase digoxin levels significantly sometimes by 50 % or more.

Amiodarone, quinidine, and verapamil are big ones.

If a patient starts one of these, the digoxin dose often needs to be cut in half preventively.

Wow, okay.

Lots to track with digoxin.

Which brings us perfectly to the nursing process.

Given all these complexities, assessment sounds paramount.

It's the foundation of safety.

Before giving any of these heart failure drugs, you need a solid baseline.

What are the absolute must checks?

Current vital signs, obviously.

Blood pressure is huge for the vasodilators.

And for digoxin specifically, you must take the apical pulse for one full minute.

Not radial, apical.

Listen directly to the heart.

One full minute.

Why so long?

To accurately assess both the rate and the rhythm, check for irregularities, then look at your patient, assess peripheral pulses, check for edema, listen to heart and lung sounds or their crap pulse,

monitor intake and output closely,

and daily weights.

Ah, the daily weight.

Same scale, same close, right?

Every single time.

It's one of the best indicators of fluid retention or loss.

And of course, keep a close eye on those crucial labs.

Remind us which ones?

Potassium, sodium, magnesium, calcium,

kidney function tests, BUN and creatinine, and often cardiac biomarkers like BNP or NT -pro -BNP, which help gauge the severity of HF in response to therapy.

Okay, now that apical pulse rule for digoxin.

You check for a full minute.

What's the action threshold?

The standard rule is if the apical pulse is less than or equal to 60 beats per minute, or if it's suddenly high, like greater than or equal to 100 beats per minute, you hold the dose and notify the prescriber immediately.

Don't give it until you get clarification.

Hold to 60 or 100, got it.

Now let's talk about a really basic but potentially lethal error source.

Writing the dose down, decimal points.

Oh, this is so, so important, especially with potent drugs like digoxin, where the dose is often less than a milligram.

The rule from ISMP, the Institute for Safe Medication Practices, is clear.

Always use a leading zero before decimal point for doses less than one.

So write 0 .25 milligrams, not just 0 .25 milligrams.

Correct.

Because if that tiny decimal point gets missed or isn't seen clearly, 0 .25 could easily be misread as 25, a hundredfold overdose, potentially fatal with digoxin.

And the flip side.

Never use a trailing zero after a whole number.

Write 1 milligram, not 1 .0 milligram.

Why not?

Because if the decimal point in 1 .0 gets missed, it could be misread as 10, a tenfold overdose.

Again, potentially lethal.

It sounds simple, but these zero errors cause catastrophic mistakes.

It really drives home how careful you have to be.

Okay, finally, patient education.

What do people need to know for managing these meds safely at home?

Several key things.

Encourage wearing a medical alert bracelet stating they have heart failure and listing key meds.

Because many of these drugs cause vasodilation, teach them about slow position changes, sitting up slowly, dangling feet before standing to avoid dizziness or fainting from orthostatic hypotension.

Make sense.

Emphasize they should never abruptly stop taking their heart failure medications even if they feel better.

Rebound effects can be dangerous.

And specifically for oral digoxin, there's a dietary point.

Advise them to avoid taking digoxin within about two hours of eating high fiber foods like bran muffins or cereals or lots of dairy products.

These can interfere with the drug's absorption from the gut.

Interesting detail.

Okay, so we've assessed, implemented safely, now evaluation.

How do we know if the therapy is actually working?

What does success look like?

You look for improvement in the signs and symptoms.

You want to see increased urine output, meaning less fluid retention.

You want decreased edema, less shortness of breath, fewer crackles in the lungs on auscultation.

Patients should report less fatigue.

Their peripheral pulses might feel stronger, skin warmer and drier.

Objective improvements.

Great.

Okay, let's try to wrap this up.

Key takeaways from this deep dive.

Well, we saw the big shift, right?

From just boosting the pump to protecting the heart muscle.

RAS modulators, your ACEs, ARBs, and especially the ARNAS are now front and center, first line therapy.

Beta blockers are essential for their cardioprotective effects, blocking that harmful sympathetic overdrive.

Milrinone is that potent IV inodilator for acute decompensation, but watch for dysrhythmias and that furosemide incompatibility.

And digoxin.

Digoxin, the old workhorse, is now second line, useful for its inotropic boost and rate control AFib, but always demanding super careful monitoring because of that razor thin therapeutic window, .5 .2 NGML, and the critical importance of potassium and magnesium levels.

Perfect summary.

So as we close out, maybe a final thought for our listeners to chew on.

Yeah, I think, you know, looking at how rapidly things are changing, the strong data behind ARNAS, like on Tresto, the development of targeted drugs, like Avobradine, it really makes you think.

The provocative question is, how do we as nurses and clinicians continually adapt our practice?

How do we refine our protocols to safely manage these increasingly complex combination therapies, anticipate new interactions, and keep our patients safe in this high stakes field?

That constant adaptation, that vigilance, that's really the cutting edge of nursing care and heart failure today.

A challenging but vital thought.

Constant learning and adaptation are key.

Thank you so much for walking us through that complex landscape, and thank you for joining us on The Deep Dive.

We'll catch you next time.