VENTRICULAR-TACHYCARDIA AS DEFAULT DIAGNOSIS IN BROAD COMPLEX TACHYCARDIA

In the differential diagnosis of broad complex tachycardia, the most i mportant decision is whether or not the tachycardia is ventricular, si nce this type carries the worst prognosis. However, the rules for a di agnosis of ventricular tachycardia are so complex that they are not sa tisfied in many cases, and the default diagnosis, supraventricular tac hycardia, is erroneously accepted. We sought to reverse this strategy; unless simple rules for a positive diagnosis of supraventricular tach ycardia were satisfied, ventricular tachycardia was diagnosed by defau lt. The criterion for a diagnosis of supraventricular tachycardia was electrocardiographic (ECG) findings typical of bundle branch block (le ft = rS or QS wave in leads V1 and V2, delay to S wave nadir < 70 ms, and R wave and no Q wave in lead V6; right = rSR' wave in lead V1 and an RS wave in lead V6, with R wave height greater than S wave depth). Twelve-lead ECGs were done for 102 consecutive patients with broad-com plex tachycardia (QRS width > 110 ms). Two observers, who were unaware of definitive diagnoses validated by electrophysiology, by our diagno stic rules made correct diagnosis of ventricular tachycardia in 63 and 62 of 69 patients, respectively, and correct diagnoses of supraventri cular tachycardia in 28 and 22 of 33 patients (sensitivity for ventric ular tachycardia 90% and 91%, specificity 67% and 85%). One observer t hen sought independent P waves in cases diagnosed as supraventricular tachycardia; sensitivity for the diagnosis of ventricular tachycardia rose to 96%, with a specificity of 64%. These criteria, which require only knowledge of typical bundle branch block patterns, were highly se nsitive for the important diagnosis of ventricular tachycardia.