A system and method for controlling cardiac ventricular tachyarrhythmias by acquiring a pressure signal representative of coronary venous pressure (CVP) from a pressure sensor implanted within a coronary vein of the patient. A CVP index is derived based on the pressure signal. The onset of a ventricular tachyarrhythmia episode is detected based on a cardiac rates signal. The CVP index and the rate signal are monitored and, responsive to the rate signal indicating a sustained tachycardia episode during the episode monitoring period, anti-tachycardia therapy selectively withheld and the episode monitoring period is extended based on the CVP index.