Then comes Verapamil, which is a calcium channel blocker like
Diltiazem. Perhaps is has something to do with the nature
of how a Class IV anti-arrhythmic affects the cardiovascular system. It decreases or slows conduction through theĀ AV node, and reduces the contractility of the heart, so it could be inappropriate in cases of heart failure. I believe that Diltiazem works on the reentrant type of SVT called AVNRT.