Abstract 2729: Dobutamine Myocardial Strain Rate Response is Transmurally Inhomogeneous
Background Echocardiographic strain rate (SR) measurements during dobutamine (DB) infusion are used to quantify myocardial function and to assess myocardial viability. The transmural SR distributions across the LV wall and the DB effect at each wall depth are not well understood. We tested the hypothesis that SR distribution and SR augmentation with DB are transmurally homogeneous.
Methods Eight sheep had 2 triads of radiopaque beadsets inserted into the anterobasal and lateral equatorial wall with additional markers silhouetting the LV. After 1 week, 4-D marker dynamics were studied using biplane videofluoroscopy to measure radial SR in the subepicardium, midwall, and subendocardium at baseline and during a low-dose DB bolus (0.5–1.0μg/kg).
Results: DB increased heart rate (116±15 to 128±18 min−1), peak LVP (108±10 to 120±17 mmHg), and dP/dtmax (1,903±479 to 2,999±365 mmHg/s, all P < 0.001), but not stroke volume (30±12 to 27±13 ml, P=0.27). At baseline, in both the anterobasal and lateral equatorial wall, peak radial SR was smallest in the subepicardium and greatest in the subendocardium. The subepicardial peak radial SR, however, was unaffected with low-dose DB, but the midwall and subendocardial response increased with increasing depth (See Table⇓).
Conclusions: This study describes that SR distribution and SR response to DB are not transmurally homogeneous. There is a gradient of SR from subendocardium to subepicardium which becomes even more pronounced with DB. This finding has clinical implications where echo measurements of SR within the wall would likely underestimate subendocardial function and overestimate subepicardial function, especially during DB stress echocardiography. More complete fundamental understanding of LV wall thickening mechanics is needed to refine how we assess regional and global LV wall systolic function and myocardial viability clinically.