Aims: Patients with repaired tetralogy of Fallot (rTOF) frequently have right bundle branch block. To better understand the contribution of cardiac dyssynchrony to dysfunction, we developed a method to quantify left (LV), right (RV), and inter-ventricular dyssynchrony using standard cine cardiac magnetic resonance (CMR).
Methods and results: Thirty patients with rTOF and 17 healthy controls underwent cine CMR. Patients were imaged twice to assess inter-test reproducibility. Circumferential strain curves were generated with a custom feature-tracking algorithm for 12 LV and 12 RV segments in each of 4-7 short-axis slices encompassing the ventricles. Temporal offsets (TOs, in ms) of the strain curves relative to a patient-specific reference curve were calculated. The intra-ventricular dyssynchrony index (DI) for each ventricle was computed as the standard deviation of the TOs. The inter-ventricular DI was calculated as the difference in median RV and median LV TOs. Compared with controls, patients had a greater LV DI (21 ± 8 vs. 11 ± 5 ms, P < 0.001) and RV DI (60 ± 19 vs. 47 ± 17 ms, P = 0.02). RV contraction was globally delayed in patients, resulting in a greater inter-ventricular DI with the RV contracting 45 ± 25 ms later than the LV vs. 12 ± 29 ms earlier in controls (P < 0.001). Inter-test reproducibility was moderate with all coefficients of variation ≤22%. Both LV and RV DIs were correlated with measures of LV, but not RV, function.
Conclusion: Patients with rTOF have intra- and inter-ventricular dyssynchrony, which can be quantified from standard cine CMR. This new approach can potentially help determine the contribution of dyssynchrony to ventricular dysfunction in future studies.
Keywords: Cardiac magnetic resonance; Dyssynchrony; Magnetic resonance imaging; Tetralogy of Fallot.
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