Functional significance of collaterals during ameroid-induced coronary stenosis in conscious dogs. Interrelationships among regional shortening, regional flow and grade of coronary stenosis.

Abstract

SUMMARY We studied the relationships among collateral flow, regional myocardial shortening and the grade of coronary stenosis during ameroid-induced chronic coronary constriction in 22 conscious dogs. A radiolucent ameroid, a Doppler flow probe and a cuff occluder were placed on the left circumflex coronary artery (LCx). Regional myocardial shortening and regional myocardial blood flow were assessed simultaneously using ultrasonic dimension gauges and the tracer microsphere technique, respectively, during temporary occlusion of the LCx. Regional hypokinesia and ischemia were attenuated as a function of time during progressive coronary stenosis. Fifty percent recovery and full recovery of regional shortening during occlusion were observed 19 3 and 25 4 days after instrumentation, respectively, when the endocardial blood flow recovered from 0.42 + 0.07 ml/min/g at 7 days to 0.56 0.07 and 0.80 0.05 ml/min/g, respectively. Greater than 75% coronary stenosis coincided with collateral development, as estimated from regional shortening rate and the appearance of angiographically opacified collaterals. Our study confirms that the development of collateral vessels reduces regional ischemia and hypokinesia induced during abrupt coronary occlusion in a canine model. GRADUAL coronary occlusion over a period of days, especially in a canine model, leads to the development of collateral channels, which can be evaluated by measuring peripheral coronary pressure, ' retrograde flow,2',3 reactive hyperemia 7 and regional contraction abnormalities that appear during temporary coronary occlusion.A-'0 However, the relationship between the grade of coronary stenosis and the functional reserve of collateral vessels and the relationship between collateral blood flow and regional shortening during progression of collateral development are unclear.The functional state of collateral channels has been estimated according to the degree of reactive hyperemia3,6 and by regional myocardial contraction.81-0 Recently, an inverse linear relation between the reduction of reactive hyperemia and recovery of contraction abnormalities during temporary coronary occlusion was noted after the implantation of an ameroid constrictor.'0 However, the grade of coronary stenosis is a major determinant of reactive hyperemia.", 12 Therefore, to define the extent to which reactive hyperemia reflects collateral function per se, it may be important to assess both the grade of coronary stenosis and collateral function. In a previous study, we devised a radio-

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“…A chronic ischemic model has also been established by implanting an ameroid constrictor around proximal left circumflex coronary artery (Cardinal, et al, 2004). Since the material of the constrictor absorbs fluid and swells slowly in 3−4 weeks (Tomoike et al, 1983), the obstruction to blood flow was produced very slowly and created a relatively chronic ischemic condition in the heart. Also different stressors, such as transient bouts of rapid ventricular pacing and angiotensin II administration, are used to activate the intrinsic cardiac nervous system and mimic clinical heart diseases (Cardinal, et al, 2004).…”

Development of collateral function with repetitive coronary occlusion in a canine model reduces myocardial reactive hyperemia in the absence of significant coronary stenosis.

“…The values for segment lengths were normalized to an initial EDL as 10 mm by dividing the measured EDL and ESL by the initial control EDL and multiplying by 10 (Tomoike et al, 1983a).…”

“…Two pairs of 5-MHz ultrasonic crystals (Murata) (diameter 2 mm) were placed subendocardially in the left ventricular wall, as described previously (Tomoike et al, 1983a). Briefly, each pair of ultrasonic crystals was inserted into the subendocardial portion, 1-2 cm apart, to measure the regional myocardial length; one pair was placed in the left anterior descending coronary artery (LAD) area as a nonischemic segment length, and the other was placed in the center of the left circumflex coronary artery (LCX) area to measure the extent of regional ischemia.…”

Combined effects of reduced connexin 43, depressed active generator properties and energetic stress on conduction disturbances in canine failing myocardium

“…Two of the CRP-AM dogs died suddenly before the day on which the final study was scheduled. The relative timing (∼2 weeks) for implanting the pacemaker and AM was chosen to maximize the synergy between the two interventions because marked CRP effects (left ventricle dysfunction) have developed by ∼4 weeks [30], whereas the AM material takes up tissue water and swells until the artery becomes obliterated after 2-3 weeks, while collateral vessels develop over this period and at later times [44,51].…”

“…In this model, an arrhythmia substrate is created regionally in the territory of the left circumflex coronary artery (LCx) with a combination of chronic rapid pacing (CRP) and regional reduction of the coronary blood flow reserve in the LCx. An ameroid constrictor (AM) implanted around the LCx causes progressive occlusion over an interval of 2-3 weeks, as collaterals develop, thus avoiding scar formation [44,51].…”