Effect of surgical reduction of left ventricular outflow obstruction on hemodynamics, coronary flow, and myocardial metabolism in hypertrophic cardiomyopathy

To assess the impact of operative reduction of left ventricular outflow obstruction in hypertrophic cardiomyopathy, measurements of great cardiac vein flow, oxygen and lactate content, left ventricular pressures, and cardiac index were measured at rest and during pacing stress in 20 consecutive patients (13, myotomy-myectomy; six, mitral valve replacement; one, both myotomy-myectomy and mitral valve replacement) who underwent both preoperative and postoperative studies. All had angiographically normal epicardial coronary arteries. Operation resulted in reduction in outflow gradient (64 ± 38 to 4 ± 7 mm Hg, p < 0.001) and in left ventricular systolic pressure (186 ± 32 to 128 ± 22 mm Hg, p < 0.001) and was associated with reduction in great cardiac vein flow (101 ± 26 to 78 ± 16 ml/min, p < 0.001) and oxygen consumption in the anterior left ventricle and septum (11.9 ± 4.1 to 8.4 ± 1.9 ml O₂/min, p < 0.001) in the basal state. During rapid atrial pacing, 13 of 20 patients experienced chest pain postoperatively, whereas all 20 developed chest pain during preoperative pacing, with an improvement in pacing anginal threshold (or heart rate 150 if no chest pain was experienced) of 16 ± 18 beats/min (p < 0.001). The peak great cardiac vein flow (161 ± 41 to 131 ± 45 ml/min, p < 0.025) and myocardial oxygen consumption (19.4 ± 6.1 to 14.3 ± 5.5 ml O₂/min, p < 0.005) during pacing, which correlated directly with the severity of the basal left ventricular gradient (p = 0.011 and p = 0.002, respectively), were also reduced by surgery. Lactate metabolism during pacing changed from net production before surgery to net consumption after operation (-17 ± 47.6 to 4.4 ± 29.8 μmol/min, p < 0.01), with six of 20 patients producing lactate after surgery compared with 13 of 20 before surgery (p = 0.06). The six patients with the highest peak great cardiac vein flow (> 175 ml/min) during preoperative pacing had greater symptom and metabolic benefit during pacing after surgery compared with the 14 patients with lower peak coronary flow. Postpacing left ventricular end-diastolic pressure (30 ± 7 to 23 ± 7 mm Hg, p < 0.001) and pulmonary artery wedge pressure (24 ± 6 to 20 ± 5, p < 0.001) were reduced after surgery. Thus, operative relief of left ventricular outflow obstruction and reduction in left ventricular systolic pressure favorably affects myocardial oxygen consumption and metabolism, due to more advantageous matching of myocardial oxygen delivery to oxygen demands during stress. The particularly marked benefit in those patients with the highest peak flow capacity before surgery may be due to less intrinsic abnormality in coronary flow delivery, perhaps due to less small vessel coronary disease, thereby favoring restoration of a more normal coronary flow reserve after surgery.