The perioperative fate of residual gradients after repair of discrete subaortic stenosis and time-related blood levels of catecholamines

The fate of the residual peak systolic left ventricular-aortic gradient was studied perioperatively in 14 patients with membranous discrete subaortic stenosis. In nine (group A) the initial postrepair left ventricular-aortic gradient was >35 mm Hg (mean 56.8 ± 13.4), and in five (group B) there was no significant postoperative gradient (mean 15.3 ± 3.2 mm Hg). The operation included membranectomy and myectomy. Peak left ventricular-aortic pressure gradient, endogenous levels of norepinephrine, peak rate of risk of left ventricular pressure, cardiac index, systemic vascular resistance, heart rate, and central venous pressure were recorded at the end of cardiopulmonary bypass and in 3-hour intervals for the next 9 hours. In group A during that period there was 67% reduction in peak systolic left ventricular-aortic gradient (from 56.8 ± 13.4 to 18 ± 14 mm Hg, p < 0.001). Concomitant reduction in the initial endogenous norepinephrine level was observed (from 982.1 ± 181 to 422.6 ± 109 pg/ml, p < 0.001). A consistent linear relationship between norepinephrine levels and peak systolic left ventricular-aortic gradient was found (r = 0.78). Systolic left ventricular pressure decreased from 174.2 ± 24.8 to 113.8 ± 14.7 mm Hg (p < 0.001). Marked reduction in peak rate of rise of left ventricular pressure (from 3455 ± 636 to 2161 ± 680 mm Hg/sec, p < 0.001) was observed. Cardiac index increased and systemic vascular resistance decreased during the study period (from 2.11 ± 0.2 to 3.07 ± 0.26 L/min, p < 0.001, and from 2172 ± 331 to 1233 ± 202 dynes/sec/cm^-5, p < 0.001, respectively). There were no significant changes in heart rate (p = not significant) and central venous pressure (p = not significant). Conclusion: Some of the residual perioperative left ventricular-aortic gradients in patients with discrete subaortic stenosis undergoing repairs are dynamic and transient, and are probably related to increased postoperative sympathetic activity.