Periodic changes in cycle length of ventricular tachycardia: a Wenckebach type exit block?

A 55-year-old female developed ventricular tachycardia (VT) which showed a Wenckebach periodicity in cycle length. She had had a myocardial infarction about ten years previous and, at age 51, felt fatigability and palpitations. The ECG showed VT. Thereafter, she had had palpitations of short duration two to three times a year. On the last admission she developed fatigability; the ECG showed VT. Lidocaine (100 mg i.v.) did not terminate VT. Procainamide (600 mg) could not terminate the VT, but the rate became slower. Programmed stimulation was given at bedside which effectively terminated VT. Electrophysiologic study induced VT in a reproducible manner. Ventricular tachycardia showed initial fluctuation in cycle length which stabilized at 270 msec. Disopyramide therapy (400 mg/day p.o.) was begun and electrophysiologic study was repeated one week later. VT was again induced but the cycle length was a little longer. A periodic change in cycle length from 328 to 442 msec was repeated. The change in cycle length was uniformly found in surface leads (I, II, V1) and intracardiac electrograms from the right ventricular apex and the His bundle region. No change in QRS complex was found and the periodicity was unrelated to atrial activity. A Wenckebach type exit block was therefore suggested; disopyramide might be responsible for the development of the block. We could not find another such case in the literature.