ECG: QT Interval

Another obscure pie reference unrelated to this post = the "pie in the sky" visual field defect

I know that this post is not directly related to pathology, but it's still medically-oriented so here we go!

Here's a poorly drawn electrocardiogram. From a 12 lead ECG, your reading from lead II should look somewhat like this, but not as bad. 

In layman's terms: each peak and valley represents different points of electrical activity of the heart. 

The QT interval covers the mechanical contraction of the heart's ventricles. It encompasses the period where the ventricles depolarize and then repolarize. 

The QT interval is of importance because anything that makes the QT any longer than it normally is can predispose the heart to Torsades de pointes --> ventricular arrhythmias. Also, arrhythmia is hard to spell. 

Class IA and Class III antiarrhythmics prolong the QT interval by blocking the potassium (K+) channels (makes phase 3 of the pacemaker action potential longer). 

Class IA: Na+ blockers: Quinidine, Procainamide, Disopyramide

Class III: K+ blockers: Sotalol, Dofetilide, Ibutilide, Amiodarone, Dronedarone