Left Ventricular Function and Chronotropic Responses After Normothermic Cardiopulmonary Bypass With Intermittent Antegrade Warm Blood Cardioplegia in Patients Undergoing Coronary Artery Bypass Grafting

Objective: Recent studies indicate that normothermic cardiopulmonary bypass (CPB) with intermittent antegrade warm blood cardioplegia (IAWBC) may have metabolic and clinical advantages, but limited data exist on its effects on myocardial function. Therefore, we investigated the acute effects of this approach on systolic and diastolic left ventricular function and on chronotropic responses.

Methods: In 10 patients undergoing isolated CABG we obtained on-line left ventricular pressure-volume loops using the conductance catheter before and after normothermic CPB with IAWBC. Steady state and load-independent indices of left ventricular function derived from pressure-volume relations were obtained during right atrial pacing (80-100-120beats/min) to determine baseline systolic and diastolic function and chronotropic responses.

Results: The mean time of CPB was 105+/-36min (median 103, range 60-167min) with a mean aortic cross-clamp time of 75+/-27min (median 69, range 43-129min). Baseline (80beats/min) end-systolic elastance (E(ES)) did not change after CPB (1.22+/-0.53 to 1.12+/-0.28mmHg/ml, P>0.2), while the diastolic chamber stiffness constant (k(ED)) significantly increased (0.014+/-0.005 to 0.040+/-0.007ml(-1), P=0.018) and relaxation time constant (tau) significantly decreased (61+/-3 to 49+/-2ms, P=0.004). Before CPB, incremental atrial pacing had no significant effects on E(ES) and tau but significant negative effects on k(ED) (0.014+/-0.005 to 0.045+/-0.012ml(-1), P=0.013). After CPB, atrial pacing had significant positive effects on E(ES), tau and k(ED) (E(ES): 1.12+/-0.28 to 2.60+/-1.54mmHg/ml, P=0.021; tau: 49+/-2 to 45+/-2ms, P=0.009; k(ED): 0.040+/-0.007 to 0.026+/-0.005mmHg, P=0.010), indicating improved systolic and diastolic chronotropic responses.

Conclusion: On-pump normothermic CABG with IAWBC preserved systolic function, increased diastolic stiffness, and improved systolic and diastolic chronotropic responses. Normalization of the chronotropic responses post-CPB is likely due to effects of successful revascularization and subsequent relief of ischemia.