Wall thickness of coronary vessels varies transmurally in the LV but not the RV: implications for local stress distribution

Abstract

Since the right and left ventricles (RV and LV) function under different loading conditions, it is not surprising that they differ in their mechanics (intramyocardial pressure), structure, and metabolism; such differences may also contribute to differences in the coronary vessel wall. Our hypothesis is that intima-media thickness (IMT), IMT-to-radius (IMT-to-R) ratio, and vessel wall stress vary transmurally in the LV, much more than in the RV. Five normal Yorkshire swine were used in this study. The major coronary arteries were cannulated through the aorta and perfusion fixed with 6.25% glutaraldehyde and casted with a catalyzed silicone-elastomer solution. Arterial and venous vessels were obtained from different transmural locations of the RV and LV, processed for histological analysis, and measured with an imaging software. A larger transmural gradient was found for IMT, IMT-to-R ratio, and diastolic circumferential stress in vessels from the LV than the nearly zero transmural slope in the RV. The IMT of arterial vessels in the LV showed a slope of 0.7 +/- 0.5 compared with 0.3 +/- 0.3 of arterial vessels in the RV (P <or= 0.05). The slope for venous vessels in the LV was 0.14 +/- 0.14 vs. 0.06 +/- 0.05 in the RV. The present data reflect the local structure-function relation, where the significant gradient in intramyocardial pressure in the LV is associated with a significant gradient of IMT and IMT-to-R ratio, unlike the RV. This has important implications for local adaptation of transmural loading on the vessel wall and vascular remodeling when the loading is perturbed in cardiac hypertrophy or heart failure.

Fig. 1.

A: toluidine blue-stained cross section of an artery of bin order 10 from the epicardial surface of the heart. Magnification ×40. B: toluidine blue-stained cross section of a vein of order 11 from the epicardial surface of the heart. Magnification ×40. C: photomicrograph of a toluidine blue-stained transmural (midmyocardium) arteriole of order 4. Magnification ×1,000. D: photomicrograph of a toluidine blue-stained transmural (midmyocardium) venule of order 3. Magnification ×1,000.

Fig. 2.

A: relation between mean diameter and fractional longitudinal position (FLP) of vessel segments of right coronary artery (RCA), left anterior descending coronary (LAD) artery, and left circumflex (LCX) artery. B: relation between intima-media thickness (IMT) and FLP of vessel segments of RCA, LAD artery, and LCX artery. Total lengths: RCA = 108 ± 11.1 mm, LAD = 79.2 ± 4.1 mm, and LCX = 57.0 ± 9.8 mm. C: relation between mean major diameters and FLP of sinusal veins. CS, coronary sinus; GCV, great cardiac vein; LADV, left anterior descending vein. D: relation between IMT and FLP of sinusal veins. Total length of sinusal veins = 137 ± 11.2 mm.

Fig. 3.

A: relation between IMT and diameter of venous vessels at different transmural locations in the left ventricle (LV). Epi, epicardium; Subepi, subepicardium; mid, midmyocardium; Endo, endocardium. B: relation between IMT and diameter of venous vessels at different transmural locations in the right ventricle (RV). C: relation between IMT and diameter of arterial vessels at different transmural locations in the LV. D: relation between IMT and diameter of arterial vessels at different transmural locations in the RV.

Fig. 4.

A: relation between IMT-to-R ratio and diameter of venous vessels at different transmural locations in the LV. B: relation between IMT-to-R ratio and diameter of venous vessels at different transmural locations in the RV. C: relation between IMT-to-R ratio and diameter of arterial vessels at different transmural locations in the LV. D: relation between IMT-to-R ratio and diameter of arterial vessels at different transmural locations in the RV.

Fig. 5.

A: relation between diastolic circumferential stress and diameter of arterial vessels at different transmural locations in the LV. B: relation between diastolic circumferential stress and diameter of arterial vessels at different transmural locations in the RV.