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The hemodynamic and metabolic response to pacing after aortocoronary bypass
Insights
Early after aortocoronary bypass surgery, ventricular function is preserved at rest. However, atrial pacing improved cardiac output, while ventricular pacing impaired function, highlighting pacing
Area of Science:
- Cardiovascular Surgery
- Cardiac Anesthesia
- Critical Care Medicine
Background:
- Long-term outcomes of aortocoronary bypass (ACB) show preserved ventricular function.
- Myocardial reserve in the early postoperative period after ACB may be suboptimal.
- Cold potassium cardioplegia is a common method for myocardial protection during ACB.
Purpose of the Study:
- To assess early postoperative myocardial reserve after ACB.
- To evaluate the impact of atrial and ventricular pacing on myocardial performance.
- To determine the adequacy of myocardial reserve under stress in the immediate postoperative period.
Main Methods:
- Nineteen patients undergoing elective ACB with cold potassium cardioplegia were studied.
- Hemodynamic, metabolic, and nuclear angiographic measurements were used to assess performance.
- Patients were evaluated at rest and during atrial and ventricular pacing (119 bpm).
Main Results:
- Myocardial performance was preserved at rest 2-6 hours post-reperfusion, with no ischemic metabolism.
- Atrial pacing significantly increased cardiac index without compromising hemodynamics or ejection fraction.
- Ventricular pacing did not alter cardiac index but decreased hemodynamic function and ejection fraction, with altered substrate metabolism.
Conclusions:
- Ventricular performance is preserved at rest immediately after ACB using cold potassium cardioplegia.
- Myocardial reserve is adequate for atrial pacing stress but not for ventricular pacing stress.
- The choice of pacing mode in the immediate postoperative period after ACB has significant therapeutic implications.
Abstract:
Long-term follow-up of aortocoronary bypass has shown good preservation of ventricular function. However, myocardial reserve in the immediate postoperative period may not be optimal. Nineteen patients who underwent elective aortocoronary bypass protected with cold potassium cardioplegia were studied in the early postoperative period at rest and during the stress of atrial and ventricular pacing. Performance was assessed by hemodynamic, metabolic and nuclear angiographic measurements. In the first 2--6 hours after aortic cross clamping, myocardial performance was preserved at rest and there was no evidence of ischemic metabolism. Atrial pacing at a rate of 119 beats/min caused a significant increase in cardiac index (p less than 0.01) without deterioration in hemodynamics, ejection fraction or metabolic status. At the same rate, ventricular pacing did not change the cardiac index and there was a decrease in hemodynamic function. Ejection fraction decreased from 56% to 44% (p less than 0.05) without a change in end-diastolic volume. Lactate, pyruvate and beta hydroxybutyrate extractions were changed to net production. Ventricular performance was preserved at rest immediately after aortocoronary bypass done with multidose cold potassium cardioplegia, with adequate reserve to meet the stress of atrial but not ventricular pacing. We conclude that the therapeutic implications of the type of pacing selected in the immediate postoperative period may be important.