Calcium channel blockers (Lecture 11) Flashcards
What are the Ca+ L channels responsible for in the heart?
Responsible for the plateau phase of action potential in the cardiac muscle which may trigger the release of internal Ca2+.
How do calcium channel blockers work (cardiac, SA node, AV node and vascular).
They decrease heart rate (decreased impulse generation), decrease conductance (decrease impulse conduction), and decrease contractility (electro-mechanical coupling).
What calcium channel blocker would you use for hypertension, arrhythmias and angina? And why?
Hypertension: Dihydropiridine such as amlodipine. (Needs a vasodilator)
Arrhythmias: diltiazem (very potent rate controller)
Angina: verapamil/diltiazem (decrease in cardiac contractility therefore supply-demand and rate controller allowing blood to flow through the coronaries during diastole).
What is the dihydropyridine which we need to know? What is its mechanism of action?
Amylodipine: works on the arterioles which decreases afterload.
How is amlodipine vaso-selective?
Why do you need to be cautious of amlodipine in angina?
The heart is rarely in the inactive state, therefore, is cardiac selective. Arterial smooth muscle is much more likely to be in the inactive state.
Be aware because it can cause reflex tachycardia if blood pressure drops too quickly, this will dramatically increase the myocardial oxygen demand.
Explain the mechanism of action of verapamil?
What effect does verapamil have on high vs low heart rates?
Becuase it acts on the open channels (and blocks them), it will have more of an effect on higher heart rates. This means that it promotes inactive channel conformation as it interferes with the refractory period of the drug bound channel.
What is verapamil good for?
Angina and hypertension.
What is verapamil not good for?
Not good in heart failure.
Why is diltiazem useful for arrythmias?
What is its mechanism of action?
It can also be used in angina as it reduces the amount of work that the heart needs to do.
Which drugs should not be used in combination with calcium channel blockers?
BETA BLOCKERS.
