Assessment of distribution and evolution of Mechanical dyssynchrony in a porcine model of myocardial infarction by cardiovascular magnetic resonance

Background: We sought to investigate the relationship between infarct and dyssynchrony post-myocardial infarct (MI), in a porcine model. Mechanical dyssynchrony post-MI is associated with left ventricular (LV) remodeling and increased mortality. Methods: Cine, gadolinium-contrast, and tagged cardiovascular magnetic resonance (CMR) were performed pre-MI, 9 +/- 2 days (early post-MI), and 33 +/- 10 days (late post-MI) post-MI in 6 pigs to characterize cardiac morphology, location and extent of MI, and regional mechanics. LV mechanics were assessed by circumferential strain (eC). Electro-anatomic mapping (EAM) was performed within 24 hrs of CMR and prior to sacrifice. Results: Mean infarct size was 21 +/- 4% of LV volume with evidence of post-MI remodeling. Global eC significantly decreased post MI (-27 +/- 1.6% vs. -18 +/- 2.5% (early) and -17 +/- 2.7% (late), p < 0.0001) with no significant change in peri-MI and MI segments between early and late time-points. Time to peak strain (TTP) was significantly longer in MI, compared to normal and peri-MI segments, both early (440 +/- 40 ms vs. 329 +/- 40 ms and 332 +/- 36 ms, respectively; p = 0.0002) and late post-MI (442 +/- 63 ms vs. 321 +/- 40 ms and 355 +/- 61 ms, respectively; p = 0.012). The standard deviation of TTP in 16 segments (SD16) significantly increased post-MI: 28 +/- 7 ms to 50 +/- 10 ms (early, p = 0.012) to 54 +/- 19 ms (late, p = 0.004), with no change between early and late post-MI time-points (p = 0.56). TTP was not related to reduction of segmental contractility. EAM revealed late electrical activation and greatly diminished conduction velocity in the infarct (5.7 +/- 2.4 cm/s), when compared to peri-infarct (18.7 +/- 10.3 cm/s) and remote myocardium (39 +/- 20.5 cm/s). Conclusions: Mechanical dyssynchrony occurs early after MI and is the result of delayed electrical and mechanical activation in the infarct.