CMR Feature Tracking Dyssynchrony Index (CMR-FT DI) Calculator

Inputs for Systolic Dyssynchrony Index (SDI; time-to-peak based) CMR Feature Tracking Dyssynchrony Index: Explanation and Clinical Context Cardiovascular magnetic resonance feature tracking (CMR-FT) enables derivation of strain-time curves from standard SSFP cine images without additional tagging sequences. Mechanical dyssynchrony can be quantified in two complementary ways. First, a systolic dyssynchrony index (SDI) is calculated as the standard deviation of segmental time-to-peak (TTP) strain across the left ventricular model (commonly 16 segments).

Reporting SDI in milliseconds and normalized to the RR interval (% of cardiac cycle) captures absolute and relative temporal dispersion of contraction; lower SDI indicates more synchronous activation. A second, publication-derived approach focuses on the anteroseptal–posterior wall radial delay at the mid-ventricular level. This FT-CMR measure mirrors a validated speckle-tracking echocardiography paradigm and has shown good correlation with echo in diverse QRS durations; a delay ≥130 ms has been used as a dyssynchrony threshold in CRT studies.

Beyond TTP dispersion, frequency-domain metrics like the circumferential uniformity ratio estimate (CURE) summarize synchrony on a 0–1 scale (1 = perfectly synchronous) and demonstrate good inter-study reproducibility; however, CURE requires access to the full strain waveform and specialized processing, so it is not implemented in this simplified calculator. Clinical significance. CMR-FT dyssynchrony assessment can supplement QRS width and scar characterization in CRT work-ups and in research on myocardial discoordination.

While FT-CMR agrees with echocardiographic measures for more marked dyssynchrony and offers high image quality, variability for subtle dyssynchrony and intervendor differences mean values should be interpreted within clinical context and, when feasible, together with scar burden and electrical patterns.