Pharmacologically induced changes in wall thickening dynamics and mid-ventricular volumes in dogs assessed by prospectively gated computed tomography

Assessment of regional wall thickening dynamics is important for monitoring the response of normal and ischemic myocardium to pharmacologic interventions. Because regional wall thickness can be measured on computed tomographic (CT) scans of the heart, the ability of electrocardiogram-gated computed tomography to determine the effects of pharmacologic agents on global and segmental left ventricular (LV) function was assessed. Eight conditioned dogs were studied at a control state and during drug-induced changes in contractility and loading conditions brought about by the use of isoproterenol (0.15 μg/kg/min), phenylephrine (0.3 μg/kg/min), and verapamil (0.2 mg/kg infused over 10 minutes). Ten contrast-enhanced CT slices (1 cm thick) at the same mid-LV level were reconstructed for each 10% of the R-R interval throughout an average cardiac cycle using prospectively gated CT scans. End-diastolic and end-systolic frames were selected and analyzed for the following: septal, apical, and lateral wall thickness, percent wall thickening, end-diastolic and end-systolic mid-LV volume, and percent change in mid-LV volume. During control, end-diastolic and end-systolic LV wall thicknesses (in millimeters) were 12 ± 2 and 15 ± 2 for the septal wall, 8 ± 1 and 11 ± 2 for the apical wall, and 10 ± 1 and 12 ± 1 for the lateral wall, respectively. The percent thickening in these respective segments was 24 ± 8, 36 ± 10, and 28 ± 13. The control end-diastolic and end-systolic mid-LV volumes were 16 ± 3 and 12 ± 3 ml, resulting in a percent change of 27 ± 7%. Phenylephrine induced significant thinning of the walls and impairment of systolic thickening, whereas isoproterenol induced opposite effects. Verapamil produced a significant decrease in mean blood pressure (123 ± 9 versus 99 ± 23 mm Hg, p < 0.025), but end-diastolic wall thicknesses were mildly thicker or showed no change and end-systolic wall thicknesses showed no change compared with those in the control state. Similarly, mid-LV volumes and percent change in mid-LV volumes were not different from those during control. Thus, electrocardiogram-gated computed tomography can be used to assess the effects of pharmacologic interventions on global and segmental LV function.