Quantitation of regional myocardial function by cine computed tomography: pharmacologic changes in wall thickness

To determine the capability of high speed computed transmission tomography to quantitate regional wall thickening dynamics over a wide range of physiologic states, left ventricular wall thickening was studied in nine anesthetized mongrel dogs in the control state and during separate infusions of dobutamine (10 micrograms/kg per min) and phenylephrine (25 micrograms/kg per min). After an intravenous bolus of contrast medium the heart was imaged from base to apex with serial transverse images in eight short-axis cine computed tomographic planes. In each dog during each experimental condition, 50 ms scans spanning the cardiac cycle were acquired at each anatomic level. Left ventricular epicardial and endocardial boundaries were identified on end-diastolic and end-systolic images at the equatorial left ventricular planes by an objective threshold contour method validated in a series of experiments performed on ex vivo anatomic specimens. End-diastolic and end-systolic frames were automatically realigned by superposition of epicardial centers of gravity and then rotated using a cross correlation function. The left ventricular wall thickness was measured manually at 16 points around the circumference by two independent observers. For the group of dogs the average percent wall thickening was 40.5 +/- 28.2% and varied among segments from 18 to 70% in the control state. After dobutamine was administered, significant increases in heart rate and cardiac output (p less than or equal to 0.01) were accompanied by an increase in the average wall thickening (73.6 +/- 51.2%; p less than or equal to 0.001) in the left ventricle; the average wall thickening among segments ranged from 46 to 97%. After phenylephrine administration, significant increases in mean blood pressure and cardiac output (p less than or equal to 0.01) were noted along with a significant increase in average left ventricular wall thickening (60.3 +/- 52.5%; p less than or equal to 0.001). Despite an overall increase in the percent wall thickening, no statistically significant changes in segmental contraction pattern between control and drug intervention states were observed. The wall thickness measurements were highly reproducible between the two independent readers (reliability coefficient = 0.99). Cine computed tomography-derived measurements can potentially be used for quantitative assessment of left ventricular wall thickening dynamics of a single heartbeat during acute interventions, such as the administration of drugs.