Coronary compliance in patients following orthotopic heart transplantation. An intravascular ultrasound study

The detection of coronary stiffness in cardiac allografts using MR imaging

OBJECTIVE

To test the hypothesis that biomechanical changes are quantitatively related to morphological features of coronary arteries in heart transplant (HTx) recipients.

MATERIALS AND METHODS

With IRB approval, three-dimensional (3D) magnetic resonance (MR) angiography and two-dimensional (2D) black-blood stead-state free precession (SSFP) MR imaging were performed to image coronary arteries of 36 HTx patients. Contours of coronary wall were manually drawn. For each coronary segment, coronary wall thickness, wall area, lumen area (in systole and diastole) were acquired. Coronary distensibility index (CDI) and the percent of the coronary wall occupying the vessel area (PWOV) were calculated.

RESULTS

There are totally 98 coronary segments eligible for quantitative analysis from 27 HTx patients. The CDI is 4.90 ± 2.44 mmHg(-1). The mean wall thickness is 1.49 ± 0.24 mm and the PWOV is 74.6% ± 7.5%. CDI has moderate correlations with wall thickness (r=-0.531, P<0.001) and with PWOV (R=-0.435, P<0.001).

CONCLUSIONS

Detected with coronary MR imaging, CDI is quantitatively correlated with the morphological features of the coronary artery in HTx patients. Coronary stiffness has the potential to become an alternative imaging biomarker for the quantitative assessment of the status of cardiac allografts.

A study on the compliance of a right coronary artery and its impact on wall shear stress

A computational model incorporating physiological motion and uniform transient wall deformation of a branchless right coronary artery (RCA) was developed to assess the influence of artery compliance on wall shear stress (WSS). Arterial geometry and deformation were derived from modern medical imaging techniques, whereas the blood flow was solved numerically employing a moving-grid approach using a well-validated in-house finite element code. The simulation results indicate that artery compliance affects the WSS in the RCA heterogeneously, with the distal region mostly experiencing these effects. Under physiological inflow conditions, coronary compliance contributed to phase changes in the WSS time history, without affecting the temporal gradient of the local WSS nor the bounds of the WSS magnitude. Compliance does not cause considerable changes to the topology of WSS vector patterns nor to the localization of WSS minima along the RCA. We conclude that compliance is not an important factor affecting local hemodynamics in the proximal region of the RCA while the influence of compliance in the distal region needs to be evaluated in conjunction with the outflow to the myocardium through the major branches of the RCA.

Determinants of coronary artery compliance in subjects with and without angiographic coronary artery disease

OBJECTIVES

The goal of this study was to determine factors contributing to the biomechanical properties of coronary arteries in people with and without angiographic coronary artery disease (CAD).

BACKGROUND

The stiffness of the aorta is known to increase with increasing age and in the presence of CAD. However, little is known about the mechanics of coronary arteries, which may have important clinical consequences.

METHODS

Intravascular ultrasound was used to determine the mechanical properties of coronary arteries and plaque behavior in subjects with CAD (n = 38), those with chest pain but angiographically normal coronary arteries (N) (n = 9) and those early (<2 weeks) after cardiac transplant (T) (n = 14).

RESULTS

Coronary arteries dilated during systole in all groups, but cross-sectional compliance and distensibility were lowest in the proximal left anterior descending artery (LAD) in the subjects with CAD compared with the N and T groups (compliance: 1.2 +/- 0.2 vs. 1.7 +/- 0.5 and 2.7 +/- 0.6 x 10(-2) mm(2) mm Hg(-1) [mean +/- SEM] respectively, p < 0.02 CAD vs. T; distensibility: 0.8 +/- 0.2 vs. 1.7 +/- 0.5 and 1.7 +/- 0.3 x 10(-3) mm Hg(-1), p < 0.05 CAD vs. T). There was extensive plaque in the CAD group, and plaque was also present in the N group, but minimal atheroma was present in the T group. Plaque cross-sectional area diminished significantly during systole in both the LAD and circumflex arteries. Absolute changes were: 0.50 +/- 0.30, 0.33 +/- 0.11 and 0.68 +/- 0.13 mm(2) in the proximal LAD, distal LAD and proximal circumflex arteries, respectively. In subjects with atheroma, there was a significant correlation between cross-sectional compliance and plaque compression at all sites, and plaque compression was a significant determinant of cross-sectional compliance at both proximal sites in multiple regression analyses with age, mean arterial pressure and extent of plaque as the other independent variables.

CONCLUSIONS

A major determinant of the systolic increase in coronary luminal area in patients with atheroma is a reduction in plaque cross-sectional area during systole.

Transplant vasculopathy

Transplant vasculopathy constitutes the major impediment to long-term survival in heart transplant recipients. Within the "response to immune injury" paradigm, it can best be understood as the resultant of an orchestrated recipient immune response to the initial allogenic stimulus by graft vascular endothelium. This response incorporates the elaboration of complex coordinated cytokine patterns and corresponding cell types including B-lymphocytes, T-helper1- and T-helper2-cells, cytotoxic T-cells, macrophages, and polymorphonuclear cells. These attack the alloantigenic vascular endothelium and lead, by complex cytokine signaling, to migration of donor smooth muscle cells from the media into the intima, associated with a switch from the contractile to a synthetic phenotype. In conjunction with recipient T-cells, macrophages, and lipids, the intimal fibroproliferative growth of the donor vessel is hereby initiated.