Ventricular Origin of Bidirectional Tachycardia

Electrophysiological, hemodynamic and angiographic studies were performed on an 18 year old woman with asymptomatic recurrent bidirectional tachycardia of eight years' duration and mild hyperkalemic periodic paralysis. Multiple surface electrocardiograms and His bundle and right atrial electrograms revealed that 1) all beats during bidirectional tachycardia originated in the left ventricle; 2) the two forms of ventricular beats in the bidirectional tachycardia had qR patterns in lead V1 (suggesting left ventricular origin) and axes in the frontal plane of −75° and +110°; 3) the interectopic interval of the two forms of QRS in bidirectional tachycardia was relatively fixed at 440-470 msec; 4) the runs of bidirectional tachycardia always terminated with the beat with right axis deviation; 5) fusion between sinus beats and one of the two forms of ventricular beats produced multiform complexes observed on the electrocardiogram; 6) the sinus beats showed T wave abnormalities and their A-H and H-V intervals were normal. Lidocaine and atrial pacing at an interval of 500 msec each separately suppressed the arrhythmia. Administration of potassium chloride to a blood level 5.4 mEq/liter and of procainamide did not affect the arrhythmia. Hemodynamic, left ventricular and coronary angiographic studies were normal. Bidirectional tachycardia in this case originated in the left ventricle and was unassociated with digitalis intoxication or demonstrable nonelectrical cardiac pathology.