Source
r/medicalschoolanki•
predepression

Can someone explain the effect of nitrates, beta-blockers, and the combo on ejection time?

Preclinical Question

card ID of one of the cards: 1472782371220 (AnKing v9)

Why exactly do nitrates by themselves decrease ejection time, beta-blockers by themselves cause increased ejection time, and the combination cause little/no effect?

As I understand it, nitrates increase venous dilation -> less preload -> less EDV -> less SV. How does this affect ejection time at all?

Same with beta-blockers -> block Beta-1 -> decrease heart rate/contractility -> how does this increase ejection time exactly?

And I don't even have a semblance of an idea for why the effect of the combination is what it is.

I've found one similar thread on the step 1 sub, which made no sense either.

Posted Jun 29, 2021, 7:48 PM UTC

74
IPayNoGays25k deep•

I like u/munyee23’s comment but here’s the simple way I always thought of it.

Nitrates, like you said, lead to decreased SV = less volume to eject so it ejects it faster, so shorter ejection time

Beta-blockers way easier to understand imo bc they literally slow down HR/decrease contractility = takes more time to eject

More time to eject (b-blockers) + less to to eject (nitrates) = close to zero sum

8
munyee23•

This might be incorrect but when I learned this I always thought about these anki cards in terms of heart rate, and ejection time being reciprocal to heart rate.

Nitrates lead to increased heart rate because of the baroreceptor response, which decreases ejection time.

Beta blockers directly decrease heart rate, which increases ejection time.

If you use both together, the beta blocker blocks the baroreceptor response, so you can't have that increased heart rate, and we just happen to know empirically that the net effect on heart rate is very small when you use both drugs together.

That's how it was explained to me, but happy to be corrected by someone on here!

5
s8037•

B blocker does block beta receptors on heart making them ineffective to autonomous stimulation so when nitrates does vasodilation and there is an autonomic reflex tachycardia it's has no effect on the heart (since beta receptors are blocked) plus there's a negative conduction (domotropic) effect so the impulses are also carried slowly causing heart to slow down hence the net effect is decreased O2 and SV with normal ejection or very insignificant change in ejection

1
[deleted]•

[deleted]

2
DrBigDaddyy•

the real question is, has anyone ever seen a question on this lol

1