Increased left ventricular mass after thoracotomy and pericardiotomy. A role for relief of pericardial constraint?

BACKGROUND: Myocardial stretch and increased ventricular filling can lead to increased rates of myocardial protein synthesis. In animal studies, left ventricular mass increases after pericardiectomy, suggesting relief of a biologically meaningful restraining role and a resultant stimulus for growth. The present study was designed to test the hypothesis that combined thoracotomy and pericardiotomy leads to left ventricular hypertrophy in patients with normal left ventricular ejection fraction undergoing elective bypass surgery. METHODS AND RESULTS: Twenty-five patients with normal left ventricular ejection fraction without active myocardial ischemia underwent Doppler and quantitative two-dimensional echocardiography 1 day before and 6 weeks and 7 months after elective coronary artery bypass surgery. The pericardium was left widely incised in all patients. Left ventricular end-systolic volume, end-diastolic volume, stroke volume, ejection fraction, end-systolic circumferential wall stress, and mass were measured. Left ventricular end-diastolic volume index increased from 51 +/- 11 mL/m2 to 62 +/- 14 mL/m2 (p < 0.05) at 6 weeks and to 66 +/- 14 mL/m2 (p < 0.05 versus baseline, p = NS versus 6 weeks) at 7 months. Left ventricular mass index increased from 109 +/- 23 g/m2 to 127 +/- 24 g/m2 (p < 0.05) at 6 weeks and to 131 +/- 23 g/m2 (p < 0.05 versus baseline, p = NS versus 6 weeks) at 7 months. There were no changes in systolic or diastolic blood pressures, end-systolic circumferential wall stress, or end-systolic volume. CONCLUSIONS: Patients with normal left ventricular ejection fraction develop increases in left ventricular end-diastolic volume and mass after coronary artery bypass surgery. These findings support the hypothesis that the increase in left ventricular end-diastolic volume associated with thoracotomy and pericardiotomy leads to myocardial growth and an increase in left ventricular mass.