Reduction of myocardial wall tension during cold pressor stress after myocardial revascularization

The effects of myocardial revascularization on cardiac function remain controversial despite clinical improvement. A study was designed to determine the effects of revascularization on the myocardial response to stress. Stress was induced using the cold pressor (CP) test in which th patient places his arm in ice water for one minute. All patients were tested before and one week and six months after surgery. Ejection fraction and cardiac index were determined with a noninvasive nuclear technique. Fifteen patients were studied (five patients received propranolol hydrochloride therapy after surgery, and ten patients did not receive this therapy). Cuff systolic blood pressure (BP) was obtained simultaneously with the nuclear study. The double product (heart rate x systolic BP) was calculated and used as an index of stress induced by the CP test. The results indicate that, during stress, myocardial wall tension is significantly reduced after adequate revascularization (565 dynes/cm from a preoperative value of 458 dynes/cm [P less than .001].) Patients achieved a higher cardiac index (3.58 L/min/sq m as compared with a preoperative value of 2.51 L/min/sq m) and double product (13,600 as compared with a preoperative value of 11,900) while, at the same time, tension was reduced. This suggest that increasing coronary blood flow through bypass surgery reduces myocardial wall tension during stress. This may be the reason myocardial revascularization achieves a lower incidence in late myocardial infarction when compared with medical therapy.