Cardiac mechanical synchrony couples with myocardial sympathetic innervation. A retrospective study with novel echocardiographic assessment in patients with 123I-mIBG imaging

Purpose: Left ventricular (LV) mechanical synchrony is essential for efficient cardiac function, and its disruption (dyssynchrony) negatively impacts outcomes, particularly in heart failure. Although sympathetic innervation modulates electrical activation and contraction timing, its relationship with mechanical synchrony is underexplored. This study aimed to assess their association using echocardiographic synchrony indices and 123I-mIBG scintigraphy, introducing a novel index (AMP-sync). Methods: We retrospectively analyzed 208 patients who underwent both 123I-mIBG imaging and echocardiography suitable for synchrony assessment within two weeks. Standard deviation of time-to-peak longitudinal strain across 18 LV segments defined the standard synchrony index (SD-sync). AMP-sync was calculated using the sum of the first two harmonics of a two-dimensional Fourier transform of the strain polar map. Sympathetic innervation was assessed by early and late heart-to-mediastinum ratios (H/Mr) and washout rate. Multivariable regression adjusted for age, sex, BMI, and ejection fraction (EF). Patients with QRS > 120 ms were excluded. Results: Both synchrony indices significantly associated with late H/Mr, with AMP-sync showing superior model performance. The relationship followed a robust inverse-square pattern, independent of age, EF, and BMI. AMP-sync explained approximately 30% of the variance in late H/Mr, comparable to EF. Bootstrap validation confirmed the stability of the findings. No significant associations were found with early H/Mr or washout rate. Conclusion: LV mechanical dyssynchrony is independently associated with reduced myocardial sympathetic innervation. The novel AMP-sync index outperformed SD-sync in predicting late H/Mr and may offer added value for patient stratification. External validation of AMP-sync in independent cohorts is warranted before routine clinical adoption.