Subendocardial ischemia provoked by tachycardia in conscious dogs with coronary stenosis

We assessed limit to cardiac compensation during isovolemic hemodilution (HD) in 14 anesthetized dogs. Radioactive microspheres were used to evaluate myocardial blood flow (MBF) and its transmural distribution (endo/epi). Myocardial O2 consumption (MVO2) and percent lactate extraction were determined. Coronary vasodilator reserve was assessed from reactive hyperemic responses. Dogs were divided into group 1, with intact left anterior descending coronary artery (LAD), and group 2, with critical stenosis of LAD. Measurements were obtained at baseline and during graded HD (Hespan) until cardiac failure (CF). CF occurred at lower hematocrit in group 1 compared with group 2 (9 +/- 1 vs. 17 +/- 1%). In group 1, MBF increased during HD to maintain MVO2 constant; increases in MBF were transmurally uniform until CF, when decreased endo/epi and lactate production suggested subendocardial ischemia. Coronary vasodilator reserve decreased progressively during HD and was absent at CF. In group 2, stenotic LAD demonstrated constant MBF (resulting in decreased MVO2) during HD. At CF, these responses along with reduced endo/epi and lactate production indicated local myocardial ischemia. We conclude that 1) with normal coronary circulation, cardiac function was well maintained over a wide range of hematocrits because increases in MBF were transmurally uniform and sufficient to maintain myocardial oxygenation: CF occurred during extreme HD when MBF became maldistributed, resulting in subendocardial ischemia; 2) critical coronary stenosis impaired coronary vascular adjustment to HD and reduced significantly tolerance of left ventricle to HD; and 3) present findings underscore the importance of recruitment of coronary vasodilator reserve in preserving total and regional myocardial oxygenation during HD.

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Transmural variation in microvascular remodeling following percutaneous revascularization of a chronic coronary stenosis in swine

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00502.2019 ◽

2020 ◽

Vol 318 (3) ◽

pp. H696-H705

Author(s):

Brian R. Weil ◽

Gen Suzuki ◽

John M. Canty

Keyword(s):

Wall Thickness ◽

Coronary Stenosis ◽

Oxygen Demand ◽

Hibernating Myocardium ◽

Myocardial Oxygen Demand ◽

Lumen Area ◽

Subendocardial Ischemia ◽

Microvascular Remodeling ◽

Compensatory Increase ◽

Arteriolar Wall

Remodeling of the coronary microcirculation is known to occur distal to a chronic coronary stenosis, but the reversibility of these changes and their functional significance on maximum myocardial perfusion before and after revascularization is unknown. Accordingly, swine instrumented with a chronic silastic stenosis on the left anterior descending coronary artery to produce hibernating myocardium underwent percutaneous coronary intervention (PCI; n = 8) and were compared with animals with a persistent stenosis ( n = 8), as well as sham controls ( n = 6). Stenotic animals demonstrated an increased subendocardial arteriolar wall thickness-to-lumen ratio (37.8 ± 3.3 vs. 28.3 ± 1.3% in sham, P = 0.04), reduced lumen area per arteriole (597 ± 88 vs. 927 ± 113 μm2, P = 0.04), and a compensatory increase in arteriolar density (9.4 ± 1.0 vs. 5.3 ± 0.4 arterioles/mm2, P < 0.01). As a result, vasodilated flow immediately after PCI was similar to normally perfused remote regions (5.1 ± 1.0 vs. 4.8 ± 0.9 ml·min−1·g−1, P = 0.87). When assessed 1-mo after PCI, increases in wall thickness-to-lumen diameter (42.2 ± 3.3%) and reductions in lumen area per arteriole (638 ± 59 μm2) remained unchanged, but arteriolar density returned to normal (5.2 ± 0.5 arterioles/mm2). As a result, maximum subendocardial flow during adenosine declined and was lower than remote regions (2.6 ± 0.3 vs. 5.9 ± 1.1 ml·min−1·g−1, P = 0.01). There was no microvascular remodeling in subepicardial arterioles, and maximum perfusion remained unchanged. These data demonstrate that subendocardial microvascular remodeling occurs distal to a chronic epicardial stenosis. The regression of arteriolar density without increases in luminal area may precipitate stress-induced subendocardial ischemia in the absence of a physiologically significant stenosis. NEW & NOTEWORTHY Swine with a chronic coronary stenosis exhibit subendocardial microvascular remodeling distal to a critical stenosis characterized by an increase in arteriolar wall thickness and reduction in lumen area with a compensatory increase in arteriolar density. The present study is the first to demonstrate that subendocardial arteriolar density normalizes 1-mo after revascularization, but the lumen area of individual arterioles remains reduced. This leads to a reduction in maximal subendocardial perfusion at this time point despite initial normalization of vasodilator reserve after revascularization. This pattern of chronic microvascular structural remodeling could contribute to recurrent subendocardial ischemia in the absence of coronary restenosis during tachycardia and increases in myocardial oxygen demand.

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Detection of latent coronary stenosis in conscious dogs: regional functional and electrocardiographic responses to isoprenaline

Cardiovascular Research ◽

10.1093/cvr/14.8.476 ◽

1980 ◽

Vol 14 (8) ◽

pp. 476-481 ◽

Cited By ~ 5

Author(s):

A. BATTLER ◽

K. P GALLAGHER ◽

V. F FROELICHER ◽

T. KUMADA ◽

W S. KEMPER ◽

...

Keyword(s):

Coronary Stenosis ◽

Conscious Dogs

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Improvement of pacing induced regional myocardial ischemia by solcoseryl in conscious dogs with coronary stenosis.

Japanese Circulation Journal ◽

10.1253/jcj.48.150 ◽

1984 ◽

Vol 48 (2) ◽

pp. 150-156

Author(s):

TOSHIO SHIMADA ◽

SHIGETAKE SASAYAMA ◽

MASAAKI TAKAHASHI ◽

GENTA OSAKADA ◽

CHUICHI KAWAI

Keyword(s):

Myocardial Ischemia ◽

Coronary Stenosis ◽

Conscious Dogs ◽

Regional Myocardial Ischemia

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Response to brief coronary stenosis in conscious dogs after ventricular sympathectomy

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1987.252.5.h923 ◽

1987 ◽

Vol 252 (5) ◽

pp. H923-H932

Author(s):

C. E. Jones ◽

I. Y. Liang ◽

H. J. Mass ◽

P. A. Gwirtz

Keyword(s):

Heart Rate ◽

Blood Flow ◽

Coronary Stenosis ◽

Mechanical Performance ◽

Diastolic Pressure ◽

Left Ventricular ◽

Conscious Dogs ◽

Maximal Rate ◽

Coronary Pressure ◽

Peripheral Coronary Pressure

Left ventricular responses to 2-min circumflex occlusion were studied in conscious dogs. In nonsympathectomized controls at 2, 4, and 8 wk after surgery for cardiac instrumentation, segmental shortening in the posterior ventricle significantly decreased by 111, 87, and 81% of the preocclusion values, respectively (P less than 0.05). The decrease in shortening was associated with increases in end-diastolic pressure of 9, 9, and 8 mmHg (P less than 0.05), decreases in the maximal rate of pressure generation of 305, 272, and 340 mmHg/s (P less than 0.05), and increases in heart rate of 28, 21, and 20 beats/min, respectively (P less than 0.05). After 2 and 4 wk of ventricular sympathectomy, posterior segmental shortening declined by 38 and 31%, respectively (P less than 0.05), but these decreases were less than in controls (P less than 0.05). Shortening did not change during occlusion after 8 wk of sympathectomy. Diastolic pressure increased by 6 mmHg (P less than 0.05), and the rate of pressure generation decreased by 232 mmHg/s (P less than 0.05) in the 2-wk sympathectomized ventricle. These variables did not change significantly after 4 and 8 wk of sympathectomy. After 2, 4, and 8 wk of sympathectomy, the increases in heart rate during circumflex occlusion were not different from controls (P greater than 0.05). Thus chronic sympathectomy preserved ventricular function during occlusion. This effect was attributable to a reduced preocclusion mechanical performance with a reduction in blood flow requirement and to an increased collateral perfusion, as indicated by a higher peripheral coronary pressure during occlusion in sympathectomized ventricles.

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