Abstract
The impact of left bundle branch block (LBBB) related mechanical dyssynchrony on left ventricular (LV) diastolic function remains unclear. 4D flow cardiovascular magnetic resonance (CMR) has provided reliable markers of LV dysfunction: reduced volume and kinetic energy (KE) of the portion of LV inflow which passes directly to outflow (Direct Flow) has been demonstrated in failing hearts compared to normal hearts. We sought to investigate the impact of mechanical dyssynchrony on diastolic function by comparing 4D flow in myopathic LVs with and without LBBB. CMR data were acquired at 3 T in 22 heart failure patients; 11 with LBBB and 11 without LBBB matched according to several demographic and clinical parameters. An established 4D flow analysis method was used to separate the LV end-diastolic (ED) volume into functional flow components based on the blood’s timing and route through the heart cavities. While the Direct Flow volume was not different between the groups, the KE possessed at ED was lower in LBBB patients (P = 0.018). Direct Flow entering the LV during early diastolic filling possessed less KE at ED in LBBB patients compared to non-LBBB patients, whereas no intergroup difference was observed during late filling. Pre-systolic KE of LV Direct Flow was reduced in patients with LBBB compared to matched patients with normal conduction. These intriguing findings propose that 4D flow specific measures can serve as markers of LV mechanical dyssynchrony in heart failure patients, and could possibly be investigated as predictors of response to cardiac resynchronization therapy.
Highlights
In the normal cardiac conduction system, the electric potential reaches the left ventricular (LV) myocardial walls nearly simultaneously, which enables the LV to contract and relax in a synchronous manner
The left bundle branch block (LBBB)-related mechanical dyssynchrony can contribute to LV diastolic dysfunction which in turn may augment the development of adverse cardiac remodeling [5]
Twenty-two heart failure patients were enrolled; eleven patients with LBBB and eleven patients without LBBB matched according to LV ejection fraction (EF), LV enddiastolic volume (EDV) index, heart rate, age and gender
Summary
In the normal cardiac conduction system, the electric potential reaches the left ventricular (LV) myocardial walls nearly simultaneously, which enables the LV to contract and relax in a synchronous manner. In approximately one-fourth of cases heart failure is associated with left bundle branch block (LBBB) [1]. This electrical block in the main fascicle of the LV conduction system leads to dyssynchronous LV contraction and relaxation. Left ventricular dyssynchrony has been associated with increased morbidity and mortality, and prolongation of QRS duration has been identified as predictor of adverse events [2,3,4]. The LBBB-related mechanical dyssynchrony can contribute to LV diastolic dysfunction which in turn may augment the development of adverse cardiac remodeling [5]
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