Abstract
The reduced reserve of cardiac sympathetic nerve activity is one of the important factors determining the exercise capacity in patients with chronic heart failure (CHF). Recently, 123I-metaiodobenzylguanidine (MIBG). a norepinephrine analogue, has been used to evaluate the integrity of sympathetic efferent innervation. However, little is known whether MIBG imaging reflects exercise capacity and cardiac sympathetic nerve reserve in patients with CHF. The purpose ofthis study was to examine the correlation between quantitative markers of MIBG cardiac imaging and exercise performance in patients with CHF. Twenty-one patients with CHF (NYHA I-III) underwent MIBG cardiac scintigraphy and a symptom-limited exercise using a multistage sitting ergometer. Planar images were obtained in anterior view of the chest 15 minutes and 4 hours after injection of MIBG. The heart to mediastinum uptake ratio (HIM) on the image 4 hours after MIBG injection and the washout rate of cardiac MIBG from 15 minutes to 4 hours (WR) were assessed as markers of sympathetic nerve activity. H/M significantly correlated with % fractional shortening (r = 0.71, p < 0.001) obtained by echocardiography and the plasma level of noradrenaline (r = 0.59, p < 0.01) at rest, but not with the maximal work load, peak heart rates and the increase in heart rates during exercise. On the other hand, WR significantly correlated with the maximal work load (r = 0.70, p < 0.001). peak heart rates (r = 0.51, p < 0.05) and the increase in heart rates during exercise (r = 0.57, p < 0.01). Thus, H/M reflects cardiac dysfunction and sympathetic activity at resting state, whereas WR reflects cardiac chronotropic reserve and exercise capacity. It is, therefore, indicated that we need to take into consideration not only the myocardial uptake but also the washout rate of MIBG for monitoring sympathetic nerve activity in patients with CHF.
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