Regional myocardial blood flow and coronary vascular reserve in unanesthetized ponies during pacing-induced ventricular tachycardia.
Abstract: To examine the effects of tachycardia on coronary circulation, transmural distribution of myocardial blood flow (MBF, 15-micron diameter radionuclide-labeled microspheres) was studied in six healthy adult ponies at rest (heart rate = 60 +/- 7 beats . min-1), during ventricular pacing at 150 and 200 beats . min-1, as well as with ventricular pacing at 250 beats . min-1 before and during maximal coronary vasodilatation (iv adenosine infusion; 4 mumole . kg-1 . min-1). Mean aortic pressure and cardiac output were unchanged from control values with ventricular pacing. Whereas ventricular pacing at 150 and 200 beats . min-1 resulted in a progressive uniform increase in transmural MBF and well-maintained endo:epi perfusion ratio, pacing at 250 beats . min-1 did not result in a further increase in MBF compared to pacing at 200 beats . min-1 and the left ventricular (LV) subendocardial:subepicardial (endo:epi) perfusion ratio was significantly less than 1.00 (0.87 +/- 0.05). Blood flow to the LV papillary muscles and subendocardium was significantly less than that recorded at 200 beats . min-1. The LV endo:epi perfusion ratio with ventricular pacing at 250 beats . min-1 during adenosine infusion resulted in a decrease in mean aortic pressure (63% of control value) and a marked further reduction in blood flow to the LV papillary muscles as well as the LV subendocardium, while MBF increased dramatically in the LV subepicardium compared to values observed during ventricular pacing at 250 beats . min-1 alone. This resulted in a LV endo:epi perfusion ratio of 0.39 +/- 0.09. By contrast, transmural right ventricular (RV) MBF increased significantly and the RV endo:epi perfusion ratio was well maintained. These data demonstrate that coronary vasomotion functions to maintain LV subendocardial blood flow in the pony myocardium at a heart rate of 200 beats . min-1, while at 250 beats . min-1 exhaustion of coronary vasodilator reserve in the deeper layers limits further increase in MBF.
Publication Date: 1983-08-01 PubMed ID: 6887834DOI: 10.1016/0022-4804(83)90134-8Google Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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The study investigates the impact of rapid heart rates on blood flow in the hearts of six healthy adult ponies. The results suggest that the coronary arteries maintain the flow of blood in the heart at a rate of 200 beats per minute, but are unable to increase blood flow further at a rate of 250 beats per minute due to exhaustion in deeper layers.
Objective of the Research
- The study was designed to examine the effects of tachycardia (abnormally rapid heart rate) on the coronary circulation, which refers to the movement of blood through the vessels in the heart.
- The researchers particularly focused on understanding the transmural distribution of myocardial blood flow (MBF) – that is, how blood flow changes across the wall of the heart.
Methodology
- The subjects of the study were six healthy adult ponies. They were studied at rest, during ventricular pacing at different rates (150, 200, and 250 beats per minute), and also during maximum dilation of the coronary vessels stimulated by the infusion of adenosine.
- The researchers used radionuclide-labeled microspheres of 15-micron diameter to study the MBF. These are tiny particles that emit radiation, allowing the blood flow to be mapped accurately.
Results
- The study found that when the heart rate was increased to 150 and 200 beats per minute, there was a proportional uniform increase in MBF, with the ratio of blood flow between the inner (endocardial) and outer (epicardial) layers of the heart wall well maintained.
- However, when the heart rate was further increased to 250 beats per minute, there was no corresponding increase in MBF. Furthermore, the ratio of blood flow between the endocardial and epicardial layers decreased significantly, indicating lesser blood flow to the inner layers of the heart.
- Further, when vasodilation was induced using adenosine at this heart rate, there was a substantial decrease in aortic pressure and further reduction in blood flow to the inner layers, while MBF increased dramatically in the outer layers.
- By contrast, for the right ventricle, MBF increased significantly and the perfusion ratio was well maintained.
Conclusion
- These findings illustrate that the coronary arteries are able to maintain blood flow in the hearts of ponies at a rate of 200 beats per minute.
- However, at a rate of 250 beats per minute, the coronary arteries exhaust their reserve in the inner layers, thus restricting any further increase in MBF.
Cite This Article
APA
Parks C, Manohar M, Lundeen G.
(1983).
Regional myocardial blood flow and coronary vascular reserve in unanesthetized ponies during pacing-induced ventricular tachycardia.
J Surg Res, 35(2), 119-131.
https://doi.org/10.1016/0022-4804(83)90134-8 Publication
Researcher Affiliations
MeSH Terms
- Adenosine / pharmacology
- Animals
- Blood Pressure
- Cardiac Output
- Cardiac Pacing, Artificial
- Coronary Circulation
- Coronary Vessels / drug effects
- Coronary Vessels / physiology
- Female
- Heart Rate
- Horses / physiology
- Male
- Microspheres
- Radioisotopes
- Tachycardia / physiopathology
- Vasomotor System / drug effects
- Vasomotor System / physiology
Citations
This article has been cited 2 times.- Hoffman JI, Buckberg GD. The myocardial oxygen supply:demand index revisited. J Am Heart Assoc 2014 Jan 21;3(1):e000285.
- Singh S, Young SS, McDonell WN, O'Grady M. Modification of cardiopulmonary and intestinal motility effects of xylazine with glycopyrrolate in horses. Can J Vet Res 1997 Apr;61(2):99-107.
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