Myocardial Electrotonic Response to Submaximal Exercise in Dogs with Healed Myocardial Infarctions: Evidence for β-Adrenoceptor Mediated Enhanced Coupling during Exercise Testing
Introduction: Autonomic neural activation during cardiac stress testing is an established risk-stratification tool in post-myocardial infarction (MI) patients. However, autonomic activation can also modulate myocardial electrotonic coupling, a known factor to contribute to the genesis of arrhythmi...
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| Format: | Article |
| Language: | English |
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Frontiers Media S.A.
2015-02-01
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| Series: | Frontiers in Physiology |
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| Online Access: | http://journal.frontiersin.org/Journal/10.3389/fphys.2015.00025/full |
| _version_ | 1819051568009314304 |
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| author | Carlos L del Rio Carlos L del Rio Carlos L del Rio Bradley D Clymer George E Billman |
| author_facet | Carlos L del Rio Carlos L del Rio Carlos L del Rio Bradley D Clymer George E Billman |
| author_sort | Carlos L del Rio |
| collection | DOAJ |
| description | Introduction: Autonomic neural activation during cardiac stress testing is an established risk-stratification tool in post-myocardial infarction (MI) patients. However, autonomic activation can also modulate myocardial electrotonic coupling, a known factor to contribute to the genesis of arrhythmias. The present study tested the hypothesis that exercise-induced autonomic neural activation modulates electrotonic coupling (as measured by myocardial electrical impedance, MEI) in post-MI animals shown to be susceptible or resistant to ventricular fibrillation (VF).Methods: Dogs (n = 25) with healed MI instrumented for MEI measurements were trained to run on a treadmill and classified based on their susceptibility to VF (12 susceptible, 9 resistant). MEI and ECGs were recorded during 6-stage exercise tests (18 min/test; peak: 6.4 km/h @ 16%) performed under control conditions, and following complete β-adrenoceptor (β-AR) blockade (propranolol); MEI was also measured at rest during escalating β-AR stimulation (isoproterenol) or overdrive-pacing.Results: Exercise progressively increased heart rate (HR) and reduced heart rate variability (HRV). In parallel, MEI decreased gradually (enhanced electrotonic coupling) with exercise; at peak exercise, MEI was reduced by 5.3 ± 0.4% (or -23 ± 1.8Ω, P<0.001). Notably, exercise-mediated electrotonic changes were linearly predicted by the degree of autonomic activation, as indicated by changes in either HR or in HRV (P < 0.001). Indeed, β-AR blockade attenuated the MEI response to exercise while direct β-AR stimulation (at rest) triggered MEI decreases comparable to those observed during exercise; ventricular pacing had no significant effects on MEI. Finally, animals prone to VF had a significantly larger MEI response to exercise Conclusions: These data suggest that β-AR activation during exercise can acutely enhance electrotonic coupling in the myocardium, particularly in dogs susceptible to ischemia-induced VF. |
| first_indexed | 2024-12-21T12:06:00Z |
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| id | doaj.art-9af4fdceecbd4dc4a025cd6c5998bddc |
| institution | Directory Open Access Journal |
| issn | 1664-042X |
| language | English |
| last_indexed | 2024-12-21T12:06:00Z |
| publishDate | 2015-02-01 |
| publisher | Frontiers Media S.A. |
| record_format | Article |
| series | Frontiers in Physiology |
| spelling | doaj.art-9af4fdceecbd4dc4a025cd6c5998bddc2022-12-21T19:04:42ZengFrontiers Media S.A.Frontiers in Physiology1664-042X2015-02-01610.3389/fphys.2015.00025122828Myocardial Electrotonic Response to Submaximal Exercise in Dogs with Healed Myocardial Infarctions: Evidence for β-Adrenoceptor Mediated Enhanced Coupling during Exercise TestingCarlos L del Rio0Carlos L del Rio1Carlos L del Rio2Bradley D Clymer3George E Billman4The Ohio State UniversityThe Ohio State UniversityQTest LabsThe Ohio State UniversityThe Ohio State UniversityIntroduction: Autonomic neural activation during cardiac stress testing is an established risk-stratification tool in post-myocardial infarction (MI) patients. However, autonomic activation can also modulate myocardial electrotonic coupling, a known factor to contribute to the genesis of arrhythmias. The present study tested the hypothesis that exercise-induced autonomic neural activation modulates electrotonic coupling (as measured by myocardial electrical impedance, MEI) in post-MI animals shown to be susceptible or resistant to ventricular fibrillation (VF).Methods: Dogs (n = 25) with healed MI instrumented for MEI measurements were trained to run on a treadmill and classified based on their susceptibility to VF (12 susceptible, 9 resistant). MEI and ECGs were recorded during 6-stage exercise tests (18 min/test; peak: 6.4 km/h @ 16%) performed under control conditions, and following complete β-adrenoceptor (β-AR) blockade (propranolol); MEI was also measured at rest during escalating β-AR stimulation (isoproterenol) or overdrive-pacing.Results: Exercise progressively increased heart rate (HR) and reduced heart rate variability (HRV). In parallel, MEI decreased gradually (enhanced electrotonic coupling) with exercise; at peak exercise, MEI was reduced by 5.3 ± 0.4% (or -23 ± 1.8Ω, P<0.001). Notably, exercise-mediated electrotonic changes were linearly predicted by the degree of autonomic activation, as indicated by changes in either HR or in HRV (P < 0.001). Indeed, β-AR blockade attenuated the MEI response to exercise while direct β-AR stimulation (at rest) triggered MEI decreases comparable to those observed during exercise; ventricular pacing had no significant effects on MEI. Finally, animals prone to VF had a significantly larger MEI response to exercise Conclusions: These data suggest that β-AR activation during exercise can acutely enhance electrotonic coupling in the myocardium, particularly in dogs susceptible to ischemia-induced VF.http://journal.frontiersin.org/Journal/10.3389/fphys.2015.00025/fullExerciseMyocardial Infarctionelectrotonic couplingβ-Adrenoceptor stimulationArrhythmic risk |
| spellingShingle | Carlos L del Rio Carlos L del Rio Carlos L del Rio Bradley D Clymer George E Billman Myocardial Electrotonic Response to Submaximal Exercise in Dogs with Healed Myocardial Infarctions: Evidence for β-Adrenoceptor Mediated Enhanced Coupling during Exercise Testing Frontiers in Physiology Exercise Myocardial Infarction electrotonic coupling β-Adrenoceptor stimulation Arrhythmic risk |
| title | Myocardial Electrotonic Response to Submaximal Exercise in Dogs with Healed Myocardial Infarctions: Evidence for β-Adrenoceptor Mediated Enhanced Coupling during Exercise Testing |
| title_full | Myocardial Electrotonic Response to Submaximal Exercise in Dogs with Healed Myocardial Infarctions: Evidence for β-Adrenoceptor Mediated Enhanced Coupling during Exercise Testing |
| title_fullStr | Myocardial Electrotonic Response to Submaximal Exercise in Dogs with Healed Myocardial Infarctions: Evidence for β-Adrenoceptor Mediated Enhanced Coupling during Exercise Testing |
| title_full_unstemmed | Myocardial Electrotonic Response to Submaximal Exercise in Dogs with Healed Myocardial Infarctions: Evidence for β-Adrenoceptor Mediated Enhanced Coupling during Exercise Testing |
| title_short | Myocardial Electrotonic Response to Submaximal Exercise in Dogs with Healed Myocardial Infarctions: Evidence for β-Adrenoceptor Mediated Enhanced Coupling during Exercise Testing |
| title_sort | myocardial electrotonic response to submaximal exercise in dogs with healed myocardial infarctions evidence for β adrenoceptor mediated enhanced coupling during exercise testing |
| topic | Exercise Myocardial Infarction electrotonic coupling β-Adrenoceptor stimulation Arrhythmic risk |
| url | http://journal.frontiersin.org/Journal/10.3389/fphys.2015.00025/full |
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