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Left ventricular function under stress before and after myocardial revascularization
1Department of Surgery, Duke University Medical Center, Durham, NC 27710.
Insights
Patients with coronary artery disease adapt their cardiac function to stress by utilizing increased heart rate and preload. This adaptation is evident both before and after myocardial revascularization surgery.
Area of Science:
- Cardiology
- Cardiovascular Physiology
Background:
- Coronary artery disease (CAD) significantly impacts cardiac function under stress.
- Understanding left ventricular (LV) response to stress is crucial for managing CAD patients.
Purpose of the Study:
- To compare LV responses to stress in patients with CAD before and after myocardial revascularization.
- To evaluate the adaptive mechanisms of cardiac function in response to exercise-induced ischemia and surgical intervention.
Main Methods:
- 35 patients with three-vessel CAD underwent rest and exercise radionuclide angiocardiography before and after aortocoronary bypass grafting (CABG).
- Serial resting studies were performed in the immediate postoperative period (Group A), and repeat stress tests were conducted 3 months post-CABG (Group B).
- Left ventricular ejection fraction, cardiac output, heart rate, and end-diastolic volume were assessed.
Main Results:
- Before CABG, LV ejection fraction decreased during exercise, but cardiac output increased due to elevated heart rate and end-diastolic volume.
- Postoperatively, resting LV function remained stable, but exercise ejection fraction and peak systolic pressure/end-systolic volume ratio improved, with a decrease in end-diastolic volume compared to pre-CABG.
- Immediate postoperative studies showed stable LV ejection fraction despite preload variations.
Conclusions:
- Patients with CAD exhibit chronically adapted cardiac function that leverages heart rate and preload variability to enhance performance under stress.
- Myocardial revascularization improves exercise capacity and LV performance in CAD patients.
- The study highlights the dynamic nature of cardiac adaptation in response to disease and intervention.
Abstract:
To compare left ventricular responses to stress during exercise-induced myocardial ischemia and after myocardial revascularization, 35 patients (mean age 55 +/- 7 years, class III angina) with three-vessel coronary artery disease underwent a rest and exercise initial-transit radionuclide angiocardiography before aortocoronary bypass grafting. Left ventricular ejection fraction decreased during exercise (p less than 0.01), but cardiac output was augmented with an increased heart rate (p less than 0.0001) and left ventricular end-diastolic volume (p less than 0.001). Group A (n = 15) underwent six serial resting studies at different volume loads during the first 24 hours after operation while heart rate and blood pressure were held constant. These data revealed no significant change in left ventricular ejection fraction, but preload varied in all patients because of bleeding and fluid administration, with a mean end-diastolic volume change of 115 to 176 ml. This range of end-diastolic volume was similar to that defined with rest and exercise testing before operation. Group B (n = 20) underwent a repeat rest and exercise test 3 months after operation that demonstrated no change in resting function. However, exercise ejection fraction and peak systolic pressure/end-systolic volume ratio increased (p less than 0.001 and p less than 0.05, respectively) while end-diastolic volume decreased (p less than 0.05) compared with the values before operation. These data indicate that patients with coronary artery disease have chronically adapted cardiac function that makes use of both rapid heart rate and a wide range in preload to augment cardiac function under stress.(ABSTRACT TRUNCATED AT 250 WORDS)