Profound spatial heterogeneity of coronary reserve. Discordance between patterns of resting and maximal myocardial blood flow.

Abstract

We examined the ability of individual regions of the canine left ventricle to increase blood flow relative to baseline rates of perfusion. Regional coronary flow was measured by injecting radioactive microspheres over 90 seconds in seven anesthetized mongrel dogs. Preliminary experiments demonstrated a correlation between the regional distributions of blood flow during asphyxia and pharmacological vasodilatation with adenosine (mean r = 0.75; 192 regions in each of two dogs), both of which resulted in increased coronary flow. Subsequent experiments, during which coronary perfusion pressure was held constant at 80 mm Hg, examined the pattern of blood flow in 384 regions (mean weight, 106 mg) of the left ventricular free wall during resting flow and during maximal coronary flow effected by intracoronary adenosine infusion. We found that resting and maximal flow patterns were completely uncorrelated to each other in a given dog (mean r = 0.06, p = NS; n = 3 dogs). Furthermore, regional coronary reserve, defined as the ratio of maximal to resting flow, ranged from 1.75 (i.e., resting flow was 57% of maximum) to 21.9 (resting flow was 4.5% of maximum). Thus, coronary reserve is spatially heterogeneous and determined by two distinct perfusion patterns: the resting (control) pattern and the maximal perfusion pattern. Normal hearts, therefore, contain small regions that may be relatively more vulnerable to ischemia. This may explain the patchy nature of infarction with hypoxia and at reduced perfusion pressures as well as the difficulty of using global parameters to predict regional ischemia. Despite the wide dispersion of coronary reserve, we found, by autocorrelation analysis, that reserve in neighboring regions (even when separated by a distance of several tissue samples) was significantly correlated. This also applied to patterns of resting myocardial flow. Thus, both resting coronary blood flow and reserve appear to be locally continuous and may define functional zones of vascular control and vulnerability, respectively.

Absolute Myocardial Blood Flow and Flow Reserve Assessed by Gated SPECT with Cadmium–Zinc–Telluride Detectors Using 99mTc-Tetrofosmin: Head-to-Head Comparison with 13N-Ammonia PET

“…This may apply even more for SPECT measurements because of technical issues and count statistics including lower spatial resolution, which may affect the apparent perfusion values in a nonhomogeneous manner, leading to different patterns in the polar plots for PET and SPECT as depicted in Figures 3 and 4. Differences are also based on biologic variability, because a profound spatial heterogeneity has been observed in regional MBF at rest and in response to vasodilator stress (34,35). The anatomic variability of the coronary trees is another source that has been shown to affect the persegment performance of quantitative MBF measurements.…”

Association between coronary lesion severity and distal microvascular resistance in patients with coronary artery disease

“…In 1990, a study in dogs found that coronary flow reserve is spatially heterogeneous and determined by two distinct perfusion patterns: the resting (control) pattern and the maximal perfusion pattern (1). Normal hearts, therefore, contain small regions that may be relatively more vulnerable to ischemia.…”

“…Normal hearts, therefore, contain small regions that may be relatively more vulnerable to ischemia. This may explain the patchy nature of infarction with hypoxia and at reduced perfusion pressures as well as the difficulty of using global parameters to predict regional ischemia (1).…”

Fractal regional myocardial blood flows pattern according to metabolism, not vascular anatomy

“…Sestier et al (48) found an increase in dispersion of relative regional myocardial flows in dogs, from 22 to 31%, with an adenosine-induced fourfold flow increase while coronary pressure was held constant. Austin et al (2,3) showed with intracoronary adenosine infusion in dogs, elevating flow by 5 to 10 times, that the RD of LV regional flows increased from 20% during the control state to 30%, using piece size resolution of 1% of LV mass. At the same time, the "tracking" or the maintenance of rank position in relative regional flow was almost abolished by hypoxia and by adenosine administration.…”