Postextrasystolic pulsus alternans and heart rate

Postextrasystolic (PES) pulsus alternans, an alternation in systolic blood pressure above and then below base line for several beats after a premature ventricular depolarization was noted many years ago in patients with heart failure. We noted in acute animals studies that the occurrence of PES alternans was related to heart rate. We studied five open-chest dogs suppressing intrinsic heart rate by vagal stimulation and pacing the right ventricle over a range of 100-200 beats/min introducing an extrastimulus at 50% of the paced rate. We found that the pressure of the second PES beat was augmented up to 120 beats/min and then began to decrease approximately 10 Torr for each 10-beats/min increase in rate. The physiological variables most closely related to the occurrence of PES alternans were the duration of systole of the first PES (strong) beat and the rate of rapid diastolic filling of the second PES (weak) beat. Postextrasystolic and possibly sustained pulsus alternans is an inevitable consequence of heart rate and of the relationship between ejection and diastolic filling. The details of that relationship and the effects of various diseases determine whether alternans is observed or not.