Click on the image for an enlarged view
The tracing shows mild ST segment depression in inferior leads (II, III and aVf) and T wave inversion in leads I, aVl and V3 to V6. There is a pathological Q wave in aVl (width more than 40 msec). R waves are tall in V5 and V6 suggesting left ventricular hypertrophy. QT interval is 520 msec, which at the heart rate of 60 / min has to be taken as the corrected QT interval (QTc) and is therefore prolonged. Myocardial ischemia is an important and common cause of QT prolongation. Electrolyte abnormalities like hypokalemia are also common cause for QT prolongation. QT interval can be prolonged after a cardiac arrest and associated with giant T wave inversions. Drug induced QT prolongation is also an important aspect which mandates QT testing for all new drugs. Class Ia, Ic and Class III antiarrhythmic drugs can cause prolongation of QT interval and so can a wide array of drugs including macrolide antibiotics and antipsychotic drugs. QT prolongation can predispose to life threatening ventricular tachyarrhythmias.