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Association of reduced PR-AC interval with ventricular early potentials in dilated cardiomyopathy
S Fujimoto1, K H Parker, H B Xiao
1Royal Brompton Hospital, London, UK.
Insights
A B point on mitral echograms in dilated cardiomyopathy patients indicates early systolic mitral regurgitation. This regurgitation, linked to abnormal left ventricular activation, delays complete mitral valve closure.
Area of Science:
- Cardiology
- Echocardiography
- Electrophysiology
Background:
- Dilated cardiomyopathy (DCM) can affect mitral valve function.
- Mitral valve echograms may show specific patterns in cardiac disease.
- Signal-averaged electrocardiography (ECG) assesses ventricular electrical activity.
Purpose of the Study:
- To investigate the relationship between mitral valve B points and mitral regurgitation (MR) in DCM.
- To correlate echocardiographic findings with signal-averaged ECG parameters.
- To elucidate the mechanism behind the mitral B point in left ventricular disease.
Main Methods:
- Studied 31 patients with DCM and 15 healthy controls.
- Correlated mitral echogram B points with continuous wave Doppler for MR.
- Analyzed signal-averaged ECG for ventricular early potentials and PR intervals.
Main Results:
- Sixteen DCM patients had a mitral B point; 15 did not.
- B points correlated with early systolic, low-velocity MR.
- Patients with B points showed increased PR intervals and prolonged ventricular early potentials on ECG.
Conclusions:
- The mitral B point in DCM is caused by early systolic MR.
- This MR results from abnormal left ventricular activation, likely bilateral bundle branch block.
- The low-velocity MR jet delays complete mitral valve closure.
Abstract:
We studied 31 patients with dilated cardiomyopathy, correlating mitral valve cusp motion with the continuous wave Doppler signal of mitral regurgitation and the signal averaged electrocardiogram (ECG). Sixteen patients had a B point (early partial closure) on the mitral echogram and 15 did not. Fifteen normal cases were used as controls. The duration of ventricular early potentials (< 40 microV) was measured on the signal averaged ECG of the QRS complex. The PR interval was increased in patients with a B point (190 (33) ms vs. 145 (16) ms in normal, P < 0.01) and PR-AC interval was reduced (25 (71) ms vs. 65 (11) ms in normal, P < 0.05). The B point itself was effectively synchronous with the onset of low velocity early systolic mitral regurgitation, and followed the Q wave of the succeeding beat by 20 ms or less. Early low velocity on mitral regurgitation was not present in patients without a B point. The duration of early potentials was greatly increased in patients with a B point (43 (26) ms) compared both to those without (17 (20) ms, P < 0.01) and to normals (12 (7) ms, P < 0.01) and their duration correlated with B-C interval (r = 0.6, P < 0.02). We conclude that a B point on the mitral echogram in patients with left ventricular disease is due to early systolic low velocity mitral regurgitation which itself results from an abnormal pattern of left ventricular activation, probably bilateral bundle branch block. Once established, this low velocity jet delays complete mitral valve closure.