ECG as a screening tool for detection of significant functional mitral regurgitation in patients with left bundle branch block

Abstract Background Functional mitral regurgitation (FMR) may occur in the left bundle branch block (LBBB) due to mechanical left ventricular (LV) dyssynchrony, by the imbalance between the tethering and the closing forces exerted on the mitral apparatus1-3. Progressive FMR and LV remodeling result in a reciprocal worsening downward spiral and worse clinical outcomes1-3. Therefore, timely screening and follow-up of these patients to prevent the irreversible progression of FMR is required. To date, only LBBB morphology and QRS duration have been proven predictors of FMR4. Purpose This study aimed to assess the relationship between ECG parameters of LV dyssynchrony and the severity of FMR in patients with LBBB. Methods We retrospectively included 154 consecutive patients with LBBB, in sinus rhythm, who had an echocardiogram, with no more than mild organic valvular heart disease. We measured the following intraventricular dyssynchrony markers: LV activation times (LVAT), intrinsicoid deflection (ID) in lateral and aVF leads and a newly defined marker – the difference (Diff) between aVL and aVF ID’s (Diff_IDaVL_aVF). These two leads record the electrical activation of the two opposing myocardial segments adjacent to the posteromedial and anterolateral papillary muscles, respectively5 (Figure 1). Based on the severity of FMR, the patients were divided into two groups: no/mild FMR (grade II or less) (61%), and significant FMR (grade III and IV) (39%). Results In patients with significant FMR, the LVAT measured in lateral leads, the IDaVL and Diff_IDaVL_aVF were significantly longer, but IDaVF was significantly shorter compared to patients with no/mild FMR (p<0.001). Of all studied ECG parameters, the Diff_IDaVL_ aVF was the parameter that had the strongest correlation with significant FMR (r correlation coefficient 0.82, p < 0.001). In multivariable analysis the Diff_IDaVL_aVF (p = 0.010) was the only parameter independently correlated with significant FMR. On ROC analysis the best cut-off for significant FMR prediction was 55 ms (AUC of 0.99, sensitivity 90% and specificity 97%) (Figure 2). Conclusions In LBBB, a simple intraventricular dyssynchrony ECG parameter can provide insights into FMR severity. A 55 msec Diff_IDaVL_aVF identifies significant FMR that may benefit from early medical or CRT treatment to avoid progression and worse prognosis.