Class IV Antiarrhythmics (Calcium channel blockers) Flashcards
What is the mechanism of action of dihydropyridine calcium channel blockers (CCBs)?
Dihydropyridine CCBs (e.g., amlodipine, nifedipine) are potent arteriolar dilators that block L-type calcium channels in vascular smooth muscle, reducing peripheral vascular resistance and lowering blood pressure.
What are the primary indications for dihydropyridine CCBs?
Hypertension, angina (including Prinzmetal angina), and Raynaud phenomenon.
What distinguishes non-dihydropyridine CCBs from dihydropyridine CCBs?
Non-dihydropyridine CCBs (e.g., verapamil, diltiazem) act on the heart to reduce heart rate and contractility, whereas dihydropyridines primarily act as arteriolar dilators. Their mechanism of action revolves around modulating the nodal action potential, particularly by prolonging phase 4 depolarization, which is calcium-dependent. This modulation results in decreased atrioventricular conduction and a long AV node refractory period, which is beneficial in slowing ventricular response rates.
Which of the calcium channel blockers exhibit characteristics of both non-dihydropyridines and dihydropyridines?
diltiazem
Which category of CCB is second line for HCM?
non-dihydropyridine CCBs (e.g., verapamil, diltiazem).
Which calcium channel blockers given for post subarachnoid hemorrhage?
Nimodipine
What is the most common adverse effect of dihydropyridine CCBs?
Peripheral edema, caused by preferential dilation of precapillary arterioles, leading to increased capillary hydrostatic pressure and fluid extravasation. Peripheral edema is a common side effect of calcium channel blocker (CCB) therapy, with a reported incidence of approximately 25% after 6 months of therapy. The edema is likely related to preferential dilation of precapillary vessels (arteriolar dilation), which leads to increased capillary hydrostatic pressure and fluid extravasation into the interstitium. Dihydropyridine (DHP) CCBs (eg, amlodipine and nifedipine) are potent arteriolar dilators and cause more peripheral edema than non-DHP CCBs (eg, diltiazem, verapamil). Other major side effects associated with DHP CCBs include headache, flushing, and dizziness.
How can the incidence of CCB-associated peripheral edema be reduced?
The combination of a CCB with an ACE inhibitor or ARB reduces peripheral edema by normalizing capillary hydrostatic pressure via postcapillary venodilation. Renin-angiotensin system blockers (angiotensin converting enzyme [ACE] inhibitors or angiotensin receptor blockers) cause post-capillary venodilation and can normalize the increased capillary hydrostatic pressure. In clinical studies, the combination of CCBs with ACE inhibitors was associated with a significantly lower risk of peripheral edema compared to CCB monotherapy.
What cardiac side effects are associated with CCBs?
Reflex tachycardia (especially with short-acting agents like nifedipine). A noteworthy clinical manifestation of nondihydropyridine CCBs is the prolongation of the PR interval on ECG, a potential indicator of heart block.
Which CCB is associated with constipation?
Verapamil.
What endocrine-related adverse effect is associated with calcium channel blockers?
Hyperprolactinemia especially with use of verapamil.
What are other side effects of dihydropyridine CCBs?
Headache, flushing, dizziness.
What is the first line medication to counteract CCB toxicity?
Calcium gluconate.
