Effect of transthoracic shocks on left ventricular function

Although defibrillating shocks are thought to depress ventricular function transiently, the independent effects of high strength shocks (without the metabolic sequelae of pre-shock fibrillation) have not been assessed systematically in humans. Therefore, we delivered three consecutive synchronized monophasic transthoracic shocks (200, 200 and 360 J) at 60s intervals during sinus rhythm and evaluated the effect on left ventricular chamber size and function as determined by transesophageal echocardiography in 11 patients (mean age 67+/-8 years, 9M/2F) with depressed left ventricular function (left ventricular ejection fraction: 14-37%). The shocks did not alter hemodynamics consistently. On average, the shocks did not alter stroke volume, cardiac output, left ventricular ejection fraction or regional wall thickening (all p>0.05 versus baseline). This effect was highly variable and 36% of patients experienced a >25% reduction in cardiac output by the final shock. There was a tendency for regional wall thickening to worsen in the best baseline sextant with an offsetting significant increase in thickening in the worst baseline sextant (p=0.05). Thus, repetitive defibrillation strength transthoracic shocks do not impair left ventricular function consistently in patients with cardiomyopathy. However, the effect is widely variable and potentially important depression of left ventricular function does occur in some patients.