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Fan L, Sun Y, Choy JS, Kassab GS, Lee LC. Mechanism of exercise intolerance in heart diseases predicted by a computer model of myocardial demand-supply feedback system. COMPUTER METHODS AND PROGRAMS IN BIOMEDICINE 2022; 227:107188. [PMID: 36334525 DOI: 10.1016/j.cmpb.2022.107188] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2022] [Revised: 09/28/2022] [Accepted: 10/16/2022] [Indexed: 06/16/2023]
Abstract
BACKGROUND AND OBJECTIVE The myocardial demand-supply feedback system plays an important role in augmenting blood supply in response to exercise-induced increased myocardial demand. During this feedback process, the myocardium and coronary blood flow interact bidirectionally at many different levels. METHODS To investigate these interactions, a novel computational framework that considers the closed myocardial demand-supply feedback system was developed. In the framework coupling the systemic circulation of the left ventricle and coronary perfusion with regulation, myocardial work affects coronary perfusion via flow regulation mechanisms (e.g., metabolic regulation) and myocardial-vessel interactions, whereas coronary perfusion affects myocardial contractility in a closed feedback system. The framework was calibrated based on the measurements from healthy subjects under graded exercise conditions, and then was applied to simulate the effects of graded exercise on myocardial demand-supply under different physiological and pathological conditions. RESULTS We found that the framework can recapitulate key features found during exercise in clinical and animal studies. We showed that myocardial blood flow is increased but maximum hyperemia is reduced during exercise, which led to a reduction in coronary flow reserve. For coronary stenosis and myocardial inefficiency, the model predicts that an increase in heart rate is necessary to maintain the baseline cardiac output. Correspondingly, the resting coronary flow reserve is exhausted and the range of heart rate before exhaustion of coronary flow reserve is reduced. In the presence of metabolic regulation dysfunction, the model predicts that the metabolic vasodilator signal is higher at rest, saturates faster during exercise, and as a result, causes quicker exhaustion of coronary flow reserve. CONCLUSIONS Model predictions showed that the coronary flow reserve deteriorates faster during graded exercise, which in turn, suggests a decrease in exercise tolerance for patients with stenosis, myocardial inefficiency and metabolic flow regulation dysfunction. The findings in this study may have clinical implications in diagnosing cardiovascular diseases.
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Affiliation(s)
- Lei Fan
- Department of Mechanical Engineering, Michigan State University, East Lansing, MI, USA.
| | - Yuexing Sun
- Department of Mechanical Engineering, Michigan State University, East Lansing, MI, USA
| | - Jenny S Choy
- California Medical Innovations Institute, San Diego, CA, USA
| | | | - Lik Chuan Lee
- Department of Mechanical Engineering, Michigan State University, East Lansing, MI, USA
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Fan L, Choy JS, Raissi F, Kassab GS, Lee LC. Optimization of cardiac resynchronization therapy based on a cardiac electromechanics-perfusion computational model. Comput Biol Med 2022; 141:105050. [PMID: 34823858 PMCID: PMC8810745 DOI: 10.1016/j.compbiomed.2021.105050] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2021] [Revised: 11/10/2021] [Accepted: 11/15/2021] [Indexed: 02/03/2023]
Abstract
Cardiac resynchronization therapy (CRT) is an established treatment for left bundle branch block (LBBB) resulting in mechanical dyssynchrony. Approximately 1/3 of patients with CRT, however, are non-responders. To understand factors affecting CRT response, an electromechanics-perfusion computational model based on animal-specific left ventricular (LV) geometry and coronary vascular networks located in the septum and LV free wall is developed. The model considers contractility-flow and preload-activation time relationships, and is calibrated to simultaneously match the experimental measurements in terms of the LV pressure, volume waveforms and total coronary flow in the left anterior descending and left circumflex territories from 2 swine models under right atrium and right ventricular pacing. The model is then applied to investigate the responses of CRT indexed by peak LV pressure and (dP/dt)max at multiple pacing sites with different degrees of perfusion in the LV free wall. Without the presence of ischemia, the model predicts that basal-lateral endocardial region is the optimal pacing site that can best improve (dP/dt)max by 20%, and is associated with the shortest activation time. In the presence of ischemia, a non-ischemic region becomes the optimal pacing site when coronary flow in the ischemic region fell below 30% of its original value. Pacing at the ischemic region produces little response at that perfusion level. The optimal pacing site is associated with one that optimizes the LV activation time. These findings suggest that CRT response is affected by both pacing site and coronary perfusion, which may have clinical implication in improving CRT responder rates.
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Affiliation(s)
- Lei Fan
- Department of Mechanical Engineering, Michigan State University, East Lansing, MI, USA.
| | - Jenny S Choy
- California Medical Innovations Institute, San Diego, CA, USA
| | - Farshad Raissi
- Department of Medicine, University of California, San Diego, La Jolla, CA, USA
| | | | - Lik Chuan Lee
- Department of Mechanical Engineering, Michigan State University, East Lansing, MI, USA
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Fan L, Namani R, Choy JS, Awakeem Y, Kassab GS, Lee LC. Role of coronary flow regulation and cardiac-coronary coupling in mechanical dyssynchrony associated with right ventricular pacing. Am J Physiol Heart Circ Physiol 2020; 320:H1037-H1054. [PMID: 33356963 DOI: 10.1152/ajpheart.00549.2020] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mechanical dyssynchrony (MD) affects left ventricular (LV) mechanics and coronary perfusion. To understand the multifactorial effects of MD, we developed a computational model that bidirectionally couples the systemic circulation with the LV and coronary perfusion with flow regulation. In the model, coronary flow in the left anterior descending (LAD) and left circumflex (LCX) arteries affects the corresponding regional contractility based on a prescribed linear LV contractility-coronary flow relationship. The model is calibrated with experimental measurements of LV pressure and volume, as well as LAD and LCX flow rate waveforms acquired under regulated and fully dilated conditions from a swine under right atrial (RA) pacing. The calibrated model is applied to simulate MD. The model can simultaneously reproduce the reduction in mean LV pressure (39.3%), regulated flow (LAD: 7.9%; LCX: 1.9%), LAD passive flow (21.6%), and increase in LCX passive flow (15.9%). These changes are associated with right ventricular pacing compared with RA pacing measured in the same swine only when LV contractility is affected by flow alterations with a slope of 1.4 mmHg/mL2 in a contractility-flow relationship. In sensitivity analyses, the model predicts that coronary flow reserve (CFR) decreases and increases in the LAD and LCX with increasing delay in LV free wall contraction. These findings suggest that asynchronous activation associated with MD impacts 1) the loading conditions that further affect the coronary flow, which may explain some of the changes in CFR, and 2) the coronary flow that reduces global contractility, which contributes to the reduction in LV pressure.NEW & NOTEWORTHY A computational model that couples the systemic circulation of the left ventricular (LV) and coronary perfusion with flow regulation is developed to study the effects of mechanical dyssynchrony. The delayed contraction in the LV free wall with respect to the septum has a significant effect on LV function and coronary flow reserve.
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Affiliation(s)
- Lei Fan
- Department of Mechanical Engineering, Michigan State University, East Lansing, Michigan
| | - Ravi Namani
- Department of Mechanical Engineering, Michigan State University, East Lansing, Michigan
| | - Jenny S Choy
- California Medical Innovation Institute, San Diego, California
| | - Yousif Awakeem
- California Medical Innovation Institute, San Diego, California
| | | | - Lik Chuan Lee
- Department of Mechanical Engineering, Michigan State University, East Lansing, Michigan
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Fan L, Namani R, Choy JS, Kassab GS, Lee LC. Effects of Mechanical Dyssynchrony on Coronary Flow: Insights From a Computational Model of Coupled Coronary Perfusion With Systemic Circulation. Front Physiol 2020; 11:915. [PMID: 32922304 PMCID: PMC7457036 DOI: 10.3389/fphys.2020.00915] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2020] [Accepted: 07/08/2020] [Indexed: 01/01/2023] Open
Abstract
Mechanical dyssynchrony affects left ventricular (LV) mechanics and coronary perfusion. Due to the confounding effects of their bi-directional interactions, the mechanisms behind these changes are difficult to isolate from experimental and clinical studies alone. Here, we develop and calibrate a closed-loop computational model that couples the systemic circulation, LV mechanics, and coronary perfusion. The model is applied to simulate the impact of mechanical dyssynchrony on coronary flow in the left anterior descending artery (LAD) and left circumflex artery (LCX) territories caused by regional alterations in perfusion pressure and intramyocardial pressure (IMP). We also investigate the effects of regional coronary flow alterations on regional LV contractility in mechanical dyssynchrony based on prescribed contractility-flow relationships without considering autoregulation. The model predicts that LCX and LAD flows are reduced by 7.2%, and increased by 17.1%, respectively, in mechanical dyssynchrony with a systolic dyssynchrony index of 10% when the LAD's IMP is synchronous with the arterial pressure. The LAD flow is reduced by 11.6% only when its IMP is delayed with respect to the arterial pressure by 0.07 s. When contractility is sensitive to coronary flow, mechanical dyssynchrony can affect global LV mechanics, IMPs and contractility that in turn, further affect the coronary flow in a feedback loop that results in a substantial reduction of dPLV/dt, indicative of ischemia. Taken together, these findings imply that regional IMPs play a significant role in affecting regional coronary flows in mechanical dyssynchrony and the changes in regional coronary flow may produce ischemia when contractility is sensitive to the changes in coronary flow.
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Affiliation(s)
- Lei Fan
- Department of Mechanical Engineering, Michigan State University, East Lansing, MI, United States
| | - Ravi Namani
- Department of Mechanical Engineering, Michigan State University, East Lansing, MI, United States
| | - Jenny S Choy
- California Medical Innovation Institute, San Diego, CA, United States
| | - Ghassan S Kassab
- California Medical Innovation Institute, San Diego, CA, United States
| | - Lik Chuan Lee
- Department of Mechanical Engineering, Michigan State University, East Lansing, MI, United States
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Stem cells and injectable hydrogels: Synergistic therapeutics in myocardial repair. Biotechnol Adv 2016; 34:362-379. [PMID: 26976812 DOI: 10.1016/j.biotechadv.2016.03.003] [Citation(s) in RCA: 83] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2015] [Revised: 02/27/2016] [Accepted: 03/07/2016] [Indexed: 02/08/2023]
Abstract
One of the major problems in the treatment of cardiovascular diseases is the inability of myocardium to self-regenerate. Current therapies are unable to restore the heart's function after myocardial infarction. Myocardial tissue engineering is potentially a key approach to regenerate damaged heart muscle. Myocardial patches are applied surgically, whereas injectable hydrogels provide effective minimally invasive approaches to recover functional myocardium. These hydrogels are easily administered and can be either cell free or loaded with bioactive agents and/or cardiac stem cells, which may apply paracrine effects. The aim of this review is to investigate the advantages and disadvantages of injectable stem cell-laden hydrogels and highlight their potential applications for myocardium repair.
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van den Brom CE, Boly CA, Bulte CSE, van den Akker RFP, Kwekkeboom RFJ, Loer SA, Boer C, Bouwman RA. Myocardial Perfusion and Function Are Distinctly Altered by Sevoflurane Anesthesia in Diet-Induced Prediabetic Rats. J Diabetes Res 2016; 2016:5205631. [PMID: 26824042 PMCID: PMC4707365 DOI: 10.1155/2016/5205631] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/21/2015] [Accepted: 10/05/2015] [Indexed: 12/13/2022] Open
Abstract
Preservation of myocardial perfusion during surgery is particularly important in patients with increased risk for perioperative complications, such as diabetes. Volatile anesthetics, like sevoflurane, have cardiodepressive effects and may aggravate cardiovascular complications. We investigated the effect of sevoflurane on myocardial perfusion and function in prediabetic rats. Rats were fed a western diet (WD; n = 18) or control diet (CD; n = 18) for 8 weeks and underwent (contrast) echocardiography to determine perfusion and function during baseline and sevoflurane exposure. Myocardial perfusion was estimated based on the product of microvascular filling velocity and blood volume. WD-feeding resulted in a prediabetic phenotype characterized by obesity, hyperinsulinemia, hyperlipidemia, glucose intolerance, and hyperglycemia. At baseline, WD-feeding impaired myocardial perfusion and systolic function compared to CD-feeding. Exposure of healthy rats to sevoflurane increased the microvascular filling velocity without altering myocardial perfusion but impaired systolic function. In prediabetic rats, sevoflurane did also not affect myocardial perfusion; however, it further impaired systolic function. Diet-induced prediabetes is associated with impaired myocardial perfusion and function in rats. While sevoflurane further impaired systolic function, it did not affect myocardial perfusion in prediabetic rats. Our findings suggest that sevoflurane anesthesia leads to uncoupling of myocardial perfusion and function, irrespective of the metabolic state.
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Affiliation(s)
- Charissa E. van den Brom
- Department of Anesthesiology, VU University Medical Center, Boelelaan 1117, 1081 HV Amsterdam, Netherlands
- Laboratory for Physiology, VU University Medical Center, Van der Boechorststraat 7, 1081 BT Amsterdam, Netherlands
- *Charissa E. van den Brom:
| | - Chantal A. Boly
- Department of Anesthesiology, VU University Medical Center, Boelelaan 1117, 1081 HV Amsterdam, Netherlands
- Laboratory for Physiology, VU University Medical Center, Van der Boechorststraat 7, 1081 BT Amsterdam, Netherlands
| | - Carolien S. E. Bulte
- Department of Anesthesiology, VU University Medical Center, Boelelaan 1117, 1081 HV Amsterdam, Netherlands
| | - Rob F. P. van den Akker
- Department of Anesthesiology, VU University Medical Center, Boelelaan 1117, 1081 HV Amsterdam, Netherlands
- Laboratory for Physiology, VU University Medical Center, Van der Boechorststraat 7, 1081 BT Amsterdam, Netherlands
| | - Rick F. J. Kwekkeboom
- Laboratory for Physiology, VU University Medical Center, Van der Boechorststraat 7, 1081 BT Amsterdam, Netherlands
| | - Stephan A. Loer
- Department of Anesthesiology, VU University Medical Center, Boelelaan 1117, 1081 HV Amsterdam, Netherlands
| | - Christa Boer
- Department of Anesthesiology, VU University Medical Center, Boelelaan 1117, 1081 HV Amsterdam, Netherlands
| | - R. Arthur Bouwman
- Department of Anesthesiology, VU University Medical Center, Boelelaan 1117, 1081 HV Amsterdam, Netherlands
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van den Brom CE, Bulte CSE, Kloeze BM, Loer SA, Boer C, Bouwman RA. High fat diet-induced glucose intolerance impairs myocardial function, but not myocardial perfusion during hyperaemia: a pilot study. Cardiovasc Diabetol 2012; 11:74. [PMID: 22716959 PMCID: PMC3458910 DOI: 10.1186/1475-2840-11-74] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/24/2012] [Accepted: 06/09/2012] [Indexed: 12/18/2022] Open
Abstract
Background Glucose intolerance is a major health problem and is associated with increased risk of progression to type 2 diabetes mellitus and cardiovascular disease. However, whether glucose intolerance is related to impaired myocardial perfusion is not known. The purpose of the present study was to study the effect of diet-induced glucose intolerance on myocardial function and perfusion during baseline and pharmacological induced hyperaemia. Methods Male Wistar rats were randomly exposed to a high fat diet (HFD) or control diet (CD) (n = 8 per group). After 4 weeks, rats underwent an oral glucose tolerance test. Subsequently, rats underwent (contrast) echocardiography to determine myocardial function and perfusion during baseline and dipyridamole-induced hyperaemia (20 mg/kg for 10 min). Results Four weeks of HFD feeding resulted in glucose intolerance compared to CD-feeding. Contractile function as represented by fractional shortening was not altered in HFD-fed rats compared to CD-fed rats under baseline conditions. However, dipyridamole increased fractional shortening in CD-fed rats, but not in HFD-fed rats. Basal myocardial perfusion, as measured by estimate of perfusion, was similar in CD- and HFD-fed rats, whereas dipyridamole increased estimate of perfusion in CD-fed rats, but not in HFD-fed rats. However, flow reserve was not different between CD- and HFD-fed rats. Conclusions Diet-induced glucose intolerance is associated with impaired myocardial function during conditions of hyperaemia, but myocardial perfusion is maintained. These findings may result in new insights into the effect of glucose intolerance on myocardial function and perfusion during hyperaemia.
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Affiliation(s)
- Charissa E van den Brom
- Department of Anesthesiology, VU University Medical Center, Boelelaan 1117, 1081 HV, Amsterdam, The Netherlands.
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Abstract
A considerable body of evidence indicates that elevated resting heart rate is an independent, modifiable risk factor for cardiovascular events and mortality in patients with coronary artery disease. Elevated heart rate can produce adverse effects in several ways. Firstly, myocardial oxygen consumption is increased at high heart rates, but the time available for myocardial perfusion is reduced, increasing the likelihood of myocardial ischemia. Secondly, exposure of the large elastic arteries to cyclical stretch is increased at high heart rates. This effect can increase the rate at which components of the arterial wall deteriorate. Elastin fibers, which have an extremely slow rate of turnover in adult life, might be particularly vulnerable. Thirdly, elevated heart rate can predispose the myocardium to arrhythmias, and favor the development and progression of coronary atherosclerosis, by adversely affecting the balance between systolic and diastolic flow. Comparisons of the effects of the specific heart-rate-lowering drug ivabradine with those of β-blockers could help clarify the pathophysiological effects of elevated heart rate. Effective heart rate control among patients with coronary artery disease is uncommon in clinical practice, representing a missed therapeutic opportunity.
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Affiliation(s)
- Kim M Fox
- Royal Brompton Hospital, Sydney Street, London SW3 6NP, UK.
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Poelzing S, Rosenbaum DS. Nature, significance, and mechanisms of electrical heterogeneities in ventricle. ACTA ACUST UNITED AC 2005; 280:1010-7. [PMID: 15368342 DOI: 10.1002/ar.a.20103] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Previously, dispersion of repolarization (DOR) has been extensively linked to the development of arrhythmias and sudden cardiac death. The electrical heterogeneities that cause DOR between transmural myocyte layers have been reported in a wide variety of animals and humans. The underlying causes of transmural electrical heterogeneities are in part due to heterogeneous functional expression of proteins responsible for ion handling. Recently, we found that electrophysiologic heterogeneities between subepicardial and midmyocardial cells can form a substrate for reentrant ventricular arrhythmias. However, cell-to-cell coupling through gap junctions is expected to attenuate transmural heterogeneities between cell types spanning the ventricular wall. In this article we review a hypothesis that regional uncoupling resulting from expression patterns of gap junctions across the ventricular wall underlies DOR, and DOR can be amplified under disease conditions which remodel gap junctions. We find the principle gap junction protein, connexin43 (Cx43), is selectively reduced in the subepicardium (by 24%) compared to deeper layers of normal canine left ventricle. Additionally, the greatest DOR occurs within the subepicardial-midmyocardial interface, precisely where Cx43 expression is reduced. The present data suggests that ion channel and gap junction heterogeneities act in conjunction to form and maintain transmural DOR. Importantly, both ion channel and gap junction remodeling occurs during many disease states such as heart failure. Importantly, in the absence of ion channel remodeling, pharmacological uncoupling increases transmural DOR, particularly within the epicardial-midmyocardial interface, to values observed in heart failure. Therefore, these data suggest that heterogeneous Cx43 expression produces functionally significant electrophysiologic heterogeneities across the ventricular wall and may be a mechanism for promoting DOR which underlie arrhythmias in heart failure.
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Affiliation(s)
- Steven Poelzing
- Heart and Vascular Research Center, Case Western Reserve University, Cleveland, OH 44109, USA
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Poelzing S, Akar FG, Baron E, Rosenbaum DS. Heterogeneous connexin43 expression produces electrophysiological heterogeneities across ventricular wall. Am J Physiol Heart Circ Physiol 2004; 286:H2001-9. [PMID: 14704225 DOI: 10.1152/ajpheart.00987.2003] [Citation(s) in RCA: 128] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Recently we found that electrophysiological (EP) heterogeneities between subepicardial and midmyocardial cells can form a substrate for reentrant ventricular arrhythmias. However, cell-to-cell coupling through gap junctions is expected to attenuate transmural heterogeneities between cell types spanning the ventricular wall. Because connexin43 (Cx43) is the principal ventricular gap junction protein, we hypothesized that transmural EP heterogeneities are in part produced by heterogeneous Cx43 expression across the ventricular wall. The left ventricles of eight dogs were sectioned to expose the transmural surface. To determine whether heterogeneous Cx43 expression influenced EP function, high-resolution transmural optical mapping of the arterially perfused canine wedge preparation was used to measure transmural conduction velocity (thetaTM), dV/dt(max), transmural space constant (lambdaTM), and transmural gradients of action potential duration (APD). Relative Cx43 expression, quantified by confocal immunofluorescence, was significantly lower (by 24 +/- 17%; P < 0.05) in subepicardial compared with deeper layers. Importantly, reduced subepicardial Cx43 was associated with transmural heterogeneities of EP function evidenced by selectively reduced subepicardial thetaTM (by 18 +/- 9%; P < 0.05) compared with deeper layers. In subepicardial regions, dV/dt(max) was fastest (by 19 +/- 15%) and lambdaTM was smallest (by 18.1 +/- 2%), which suggests that conduction slowing was attributable to localized uncoupling rather than reduced excitability. The maximum transmural APD gradients occurred in the same regions where Cx43 expression was lowest; this suggests that Cx43 expression patterns served to maintain APD gradients across the transmural wall. These data demonstrate that heterogeneous Cx43 expression is closely associated with functionally significant EP heterogeneities across the transmural wall. Therefore, Cx43 expression patterns can potentially contribute to arrhythmic substrates that are dependent on transmural electrophysiological heterogeneities.
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Affiliation(s)
- Steven Poelzing
- Heart and Vascular Research Center and Department of Biomedical Engineering, MetroHealth Campus, Case Western Reserve University, Cleveland, Ohio 44109-1998, USA
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Affiliation(s)
- R Erbel
- Department of Cardiology, University Essen, Hufelandstrasser 55, D-45122 Essen, Germany.
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Kuecherer H. The Added Clinical Value of Second Generation Ultrasound Contrast Agents. Echocardiography 2003; 20 Suppl 1:S3-9. [DOI: 10.1046/j.1540-8175.20.s1.2.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
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Erbel R, Heusch G. Spontaneous and iatrogenic microembolization. A new concept for the pathogenesis of coronary artery disease. Herz 1999; 24:493-5. [PMID: 10609154 DOI: 10.1007/bf03044219] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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