Mid-diastolic mitral flow vectors in complete atrioventricular block.

Abstract

An 81-year-old man who was treated for prostate cancer was referred to our department because of bradycardia. He had a 1-month history of shortness of breath. A 12-lead electrocardiogram (ECG) showed complete atrioventricular (AV) block. His blood pressure was 165/78 mmHg and pulse rate was 38 beats/ min. Results of blood sampling were normal. A transthoracic echocardiogram revealed normal left ventricular (LV) wall thickness (interventricular septal thickness, 8 mm; LV posterior wall thickness, 8 mm) and normal LV systolic function (LV end-diastolic dimension, 39 mm; LV end-systolic dimension, 22 mm; LV ejection fraction, 76 %). A color-coded 2-dimensional echocardiogram showed no significant valvular disease. During mid-diastole, mitral forward and regurgitant flows were intermittently observed (Fig. 1). Color-coded M-mode echocardiography also showed intermittent mitral forward and regurgitant flows (Fig. 2). Simultaneous ECG recording indicated a relationship between the timing of the P wave and the T wave and the direction of mid-diastolic flow. Middiastolic mitral inflow was observed when the P wave was on the T wave, while diastolic mitral regurgitation (MR) was observed when the P wave emerged after the T wave (Figs. 1, 2). After treatment of complete AV block by pacemaker implantation, neither type of mitral flow was observed. Mid-diastolic mitral forward flow can be observed in some patients with advanced LV diastolic dysfunction. In these cases, mid-diastolic flow may be a result of interruption of early diastolic mitral inflow (E wave) by transient elevation of LV pressure [1, 2]. In the present case of complete AV block, mid-diastolic forward flow was observed when the P wave overlapped with the T wave. It is probable that mid-diastolic flow in this case might be a result of E wave interruption by transient fall of left atrial (LA) pressure by atrial relaxation. Diastolic MR is observed when the AV pressure gradient is reversed because the mitral valve does not close firmly during diastole. In complete AV block, diastolic MR can be observed when atrial relaxation occurs during ventricular diastole [3]. Moreover, decreased LV compliance [4] and early diastolic LV hyperinflation [5] may also play a part. In this patient with complete AV block, the timing of atrial relaxation might have played a decisive role in the mid-diastolic mitral inflow velocity and diastolic MR.