Twenty-seven patients with complete right bundle-branch block as the only abnormal finding were studied using high speed M-mode echocardiography to determine the effect of the electrical delay on the mechanical events of right ventricular systole. Pulmonary valve opening (PVOm) was delayed in all cases. In some the delay was mainly between mitral valve closure (MVC) and tricuspid valve closure (TVC), and this was designated proximal block. In the others the main delay was between tricuspid valve closure and pulmonary valve opening and this was designated distal block. The patients were divided into those with proximal and those with distal block by calculating the ratio TVC-PVOm/MVC-TVC. Twelve out of 13 of those with distal delay but only one out of 14 of those with proximal delay had episodes of syncope or near syncope. These results are consistent with previous theories about the pathophysiology of right bundle-branch block. Echocardiography may offer a non-invasive method to estimate the prognosis in isolated right bundle-branch block.
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