Conduction defects will most likely be an adverse associated with the use of:
A. verapamil (Isoptin)
B. nifedipine (Adalat CC)
C. diltiazem (Cardizem)
D. felodipine (Plendil)
Correct Answer: A. verapamil (Isoptin).
Verapamil (Isoptin) has the strongest chronotropic effect and will cause a delay in conduction at the SA and AV nodes. Verapamil also increases myocardial oxygen delivery, which helps patients with vasospastic angina. Verapamil correlates with negative chronotropic effects and a decrease in sympathetic nervous system activity.
Option B: The reduced intracellular calcium, results in a reduction of peripheral arterial vascular resistance and dilatation of coronary arteries, leading to a reduction in systemic blood pressure and increased myocardial oxygen delivery. Nifedipine thus has hypotensive and antianginal properties.
Option C: Diltiazem is a negative inotrope (decreased force) and negative chronotrope (decreased rate). The combination, along with coronary artery vasodilation, leads to decreased myocardial oxygen demand, decreased heart rate, and reduced blood pressure.
Option D: Research shows that felodipine has a higher selectivity than other commonly used dihydropyridine calcium channel blockers like amlodipine and nifedipine for vascular tissue in comparison to cardiac tissue. Also, the clinical trials of felodipine have not shown any negative inotropic effect.