The coronary microcirculation in cyanotic congenital heart disease

Area of Science:

• Cardiovascular Research
• Pediatric Cardiology
• Vascular Biology

Background:

• Cyanotic congenital heart disease (CCHD) presents with increased basal coronary blood flow but normal flow reserve.
• The mechanism preserving flow reserve despite altered hemodynamics in CCHD is not fully understood.
• Coronary microcirculation remodeling is hypothesized to be key to maintaining flow reserve.

Purpose of the Study:

• To investigate the morphometric characteristics of the coronary microcirculation in CCHD.
• To determine if microcirculatory remodeling explains preserved coronary flow reserve in CCHD.
• To compare microcirculatory adaptations in CCHD with those in ventricular hypertrophy.

Main Methods:

• Morphometric analysis of necropsy heart specimens from four groups: Eisenmenger's syndrome (CCHD), hypertrophied abnormal hearts, hypertrophied normal hearts, and normal hearts.
• Immunolabeling of coronary arterioles for smooth muscle alpha-actin.
• Measurement of arteriolar dimensions (axes, area, perimeter) and calculation of length, volume, and surface densities.

Main Results:

• Significant intergroup differences were observed in arteriolar length density (P=0.03) and diameter (P=0.03).
• Hearts with Eisenmenger's syndrome exhibited markedly lower arteriolar length density but a significantly greater mean arteriolar diameter (34%) compared to hypertrophied hearts (P=0.03).
• Arteriolar volume density remained similar across all groups.

Conclusions:

• Remodeling of the coronary microcirculation is the primary mechanism for preserving flow reserve in CCHD.
• An increase in arteriolar diameter compensates for reduced arteriolar length density.
• This compensatory arteriolar enlargement is the principal anatomic basis for maintaining normal coronary flow reserve in CCHD.