Mechanisms and clinical significance of transient atrioventricular block during dobutamine stress echocardiography

OBJECTIVE The purpose of this study was to investigate the possible mechani sm and the clinical significance of transient atrioventricular block (AVB) during dobutamine stress echocardiography (DSE). BACKGROUND Transient AVE occurs rarely during DSE; however, the mechanisms responsible for blocks are unclear. METHODS A retrospective analysis of clinical, echocardiographic, catheteriz ation, revascularization and head-up tilting test data was conducted in pat ients who developed transient AVE during DSE. RESULTS A total of 302 patients with known or suspected coronary artery dis ease (CAD) underwent DSE before coronary angiography between November 1997 and August 1998. Transient AVE developed in 12 patients during the test. Mo bitz I block was noted in six patients and Mobitz II: block in the other si x patients. Nine of these 12 patients were subsequently shown to have CAD a nd three had no significant coronary artery stenosis. Mobitz II block was o bserved only in patients with CAD, while Mobitz I block occurred in three p atients with and three patients without CAD (p < 0.05). Eight of the nine p atients with CAD underwent a successful coronary angioplasty with or withou t stenting and a repeat DSE revealed no recurrence of heart block except in one patient. I-lead-up tilting test in the 12 patients revealed a positive response in three of the nine patients with and all three patients without CAD. A negative head-up tilting test was likely to be observed in patients with, as compared with those without, CAD in this study population (p < 0. 05). CONCLUSION Transient AVB is not an infrequent manifestation during DSE. Bot h myocardial ischemia and neurally mediated vagal reflex may be responsible for this phenomenon. The development of Mobitz II block during DSE is indi cative of the presence of CAD. A successful revascularization in patients w ith CAD who develop transient AVE may abolish this phenomenon. (J Am Coll C ardiol 1999;34:998-1004) (C) 1999 by the American College of Cardiology.