Hemodynamic evaluation of rate augmentation produced by atrial pacing and isoproterenol in the early postoperative phase of cardiac valve surgery.

SUMMARY The hemodynamic effects of atrial pacing were evaluated in a group of 19 patients soon after cardiac valve surgery. Atrial pacing at 30 beats/min above the control rate of 88 beats/min produced an increase in cardiac index of 600 ml/min/m2. Isoproterenol was infused into eight of these patients to produce an increment in heart rate identical to that during atrial pacing. In these patients atrial pacing produced an increment in cardiac index of 400 ml/min/m2 as compared to an increment of 1400 ml/ min/ m2 produced by isoproterenol. It is concluded (1) that atrial pacing is a useful technique for augmenting cardiac index soon after cardiac valve surgery and (2) that isoproterenol provides a greater increment in cardiac index at identical heart rates and the major portion of its effect is directly inotropic. Additional Indexing Words: Rate treppe Chronotropism Inotropism I NOTROPIC support of the heart is often required to treat the myocardial depression commonly found in the early postoperative phase of cardiac surgery. A variety of pharmacologic, electrical, and mechanical methods are available to provide improvement of cardiac performance in this setting. In particular, atrial pacing has been suggested as a useful technique to augment cardiac output in patients with sinus bradyeardia or slow junctional rhythm.' Although the use of this technique has been extended to patients without bradyeardia, limited hemodynamic data exist as to its efficacy.2 A common alternative method of therapy in such circumstances is the administration of isoproterenol.3 While it is well known that this agent substantially increases cardiac output in man, it remains unclear what proportion of this increment can be attributed to heart rate alone. Accordingly we undertook a prospective hemodynamic evaluation of atrial pacing and isoproterenol in 19 patients during the early postoperative phase of cardiac surgery (1) to determine the potential hemodynamic benefits of atrial pacing and (2) to assess the relative 649