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Abstract
One of the drawbacks of permanent His bundle pacing has been the relatively high pacing thresholds. The present experimental study was proposed to address this issue. In this article the authors present preliminary evidence that His bundle pacing can be achieved with subthreshold stimulation, thereby providing for increased battery life and consequently longer replacement intervals. Possible mechanisms underlying the paradoxical effects of subthreshold stimulation before and after the onset of complete atrioventricular block are also discussed.
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Post-repolarization refractoriness increases vulnerability to block and initiation of reentrant impulses in heterogeneous infarcted myocardium. Comput Biol Med 2015; 65:209-19. [PMID: 25987316 DOI: 10.1016/j.compbiomed.2015.04.037] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2015] [Revised: 04/04/2015] [Accepted: 04/27/2015] [Indexed: 11/23/2022]
Abstract
UNLABELLED Myocardial infarction causes remodeling of the tissue structure and the density and kinetics of several ion channels in the cell membrane. Heterogeneities in refractory period (ERP) have been shown to occur in the infarct border zone and have been proposed to lead to initiation of arrhythmias. The purpose of this study is to quantify the window of vulnerability (WV) to block and initiation of reentrant impulses in myocardium with ERP heterogeneities using computer simulations. We found that ERP transitions at the border between normal ventricular cells (NZ) with different ERPs are smooth, whereas ERP transitions between NZ and infarct border zone cells (IZ) are abrupt. The profile of the ERP transitions is a combination of electrotonic interaction between NZ and IZ cells and the characteristic post-repolarization refractoriness (PRR) of IZ cells. ERP heterogeneities between NZ and IZ cells are more vulnerable to block and initiation of reentrant impulses than ERP heterogeneities between NZ cells. The relationship between coupling intervals of premature impulses (V1V2) and coupling intervals between premature and first reentrant impulses (V2T1) at NZ/NZ and NZ/IZ borders is inverse (i.e. the longer the coupling intervals of premature impulses the shorter the coupling interval between the premature and first reentrant impulses); this is in contrast with the reported V1V2/V2T1 relationship measured during initiation of reentrant impulses in canine infarcted hearts which is direct. IN CONCLUSION (1) ERP transitions at the NZ-IZ border are abrupt as a consequence of PRR; (2) PRR increases the vulnerability to block and initiation of reentrant impulses in heterogeneous myocardium; (3) V1V2/V2T1 relationships measured at ERP heterogeneities in the computer model and in experimental canine infarcts are not consistent. Therefore, it is likely that other mechanisms like micro and/or macro structural heterogeneities also contribute to initiation of reentrant impulses in infarcted hearts.
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Chiale PA, Baranchuk A, González MD, Sánchez RA, Garro HA, Fernández PA, Avalos CQ, Enriquez A, Elizari MV. The mechanisms of spontaneous termination of reentrant supraventricular tachycardias. Int J Cardiol 2015; 191:151-8. [DOI: 10.1016/j.ijcard.2015.04.239] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/28/2015] [Revised: 03/23/2015] [Accepted: 04/30/2015] [Indexed: 10/23/2022]
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Postrepolarization refractoriness in acute ischemia and after antiarrhythmic drug administration: Action potential duration is not always an index of the refractory period. Heart Rhythm 2012; 9:977-82. [DOI: 10.1016/j.hrthm.2012.01.021] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/30/2011] [Indexed: 11/17/2022]
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Bao L, Kefaloyianni E, Lader J, Hong M, Morley G, Fishman GI, Sobie EA, Coetzee WA. Unique properties of the ATP-sensitive K⁺ channel in the mouse ventricular cardiac conduction system. Circ Arrhythm Electrophysiol 2011; 4:926-35. [PMID: 21984445 DOI: 10.1161/circep.111.964643] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Background- The specialized cardiac conduction system (CCS) expresses a unique complement of ion channels that confer a specific electrophysiological profile. ATP-sensitive potassium (K(ATP)) channels in these myocytes have not been systemically investigated. Methods and Results- We recorded K(ATP) channels in isolated CCS myocytes using Cntn2-EGFP reporter mice. The CCS K(ATP) channels were less sensitive to inhibitory cytosolic ATP compared with ventricular channels and more strongly activated by MgADP. They also had a smaller slope conductance. The 2 types of channels had similar intraburst open and closed times, but the CCS K(ATP) channel had a prolonged interburst closed time. CCS K(ATP) channels were strongly activated by diazoxide and less by levcromakalim, whereas the ventricular K(ATP) channel had a reverse pharmacological profile. CCS myocytes express elevated levels of Kir6.1 but reduced Kir6.2 and SUR2A mRNA compared with ventricular myocytes (SUR1 expression was negligible). SUR2B mRNA expression was higher in CCS myocytes relative to SUR2A. Canine Purkinje fibers expressed higher levels of Kir6.1 and SUR2B protein relative to the ventricle. Numeric simulation predicts a high sensitivity of the Purkinje action potential to changes in ATP:ADP ratio. Cardiac conduction time was prolonged by low-flow ischemia in isolated, perfused mouse hearts, which was prevented by glibenclamide. Conclusions- These data imply a differential electrophysiological response (and possible contribution to arrhythmias) of the ventricular CCS to K(ATP) channel opening during periods of ischemia.
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Affiliation(s)
- Li Bao
- Department of Pediatrics, NYU School of Medicine, New York, NY 10016, USA
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Affiliation(s)
- Reid K Nakamura
- Advanced Veterinary Care Center, 15926 Hawthorne Blvd, Lawndale, CA 90260, USA.
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Fukuda K, Watanabe J, Yagi T, Wakayama Y, Nakano M, Kondo M, Kumagai K, Miura M, Shirato K, Shimokawa H. A Sodium Channel Blocker, Pilsicainide, Produces Atrial Post-Repolarization Refractoriness through the Reduction of Sodium Channel Availability. TOHOKU J EXP MED 2011; 225:35-42. [DOI: 10.1620/tjem.225.35] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Affiliation(s)
- Koji Fukuda
- Department of Cardiovascular Medicine, Tohoku University Graduate School of Medicine
| | - Jun Watanabe
- Department of Cardiovascular Medicine, Tohoku University Graduate School of Medicine
| | - Takuya Yagi
- Department of Cardiovascular Medicine, Tohoku University Graduate School of Medicine
| | - Yuji Wakayama
- Department of Cardiovascular Medicine, Tohoku University Graduate School of Medicine
| | - Makoto Nakano
- Department of Cardiovascular Medicine, Tohoku University Graduate School of Medicine
| | - Masateru Kondo
- Department of Cardiovascular Medicine, Tohoku University Graduate School of Medicine
| | - Koji Kumagai
- Department of Cardiovascular Medicine, Tohoku University Graduate School of Medicine
| | - Masahito Miura
- Department of Cardiovascular Medicine, Tohoku University Graduate School of Medicine
| | - Kunio Shirato
- Department of Cardiovascular Medicine, Tohoku University Graduate School of Medicine
| | - Hiroaki Shimokawa
- Department of Cardiovascular Medicine, Tohoku University Graduate School of Medicine
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Hirose M, Yano S, Nakada T, Horiuchi-Hirose M, Tsujino N, Yamada M. Nicorandil ameliorates impulse conduction disturbances during ischemia in isolated arterially perfused canine atria. Int J Cardiol 2011; 146:37-43. [DOI: 10.1016/j.ijcard.2009.06.011] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/07/2009] [Revised: 04/30/2009] [Accepted: 06/06/2009] [Indexed: 11/29/2022]
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Saito T, Sato T, Miki T, Seino S, Nakaya H. Role of ATP-sensitive K+ channels in electrophysiological alterations during myocardial ischemia: a study using Kir6.2-null mice. Am J Physiol Heart Circ Physiol 2005; 288:H352-7. [PMID: 15598870 DOI: 10.1152/ajpheart.00695.2004] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The role of cardiac ATP-sensitive K(+) (K(ATP)) channels in ischemia-induced electrophysiological alterations has not been thoroughly established. Using mice with homozygous knockout (KO) of Kir6.2 (a pore-forming subunit of cardiac K(ATP) channel) gene, we investigated the potential contribution of K(ATP) channels to electrophysiological alterations and extracellular K(+) accumulation during myocardial ischemia. Coronary-perfused mouse left ventricular muscles were stimulated at 5 Hz and subjected to no-flow ischemia. Transmembrane potential and extracellular K(+) concentration ([K(+)](o)) were measured by using conventional and K(+)-selective microelectrodes, respectively. In wild-type (WT) hearts, action potential duration (APD) at 90% repolarization (APD(90)) was significantly decreased by 70.1 +/- 5.2% after 10 min of ischemia (n = 6, P < 0.05). Such ischemia-induced shortening of APD(90) did not occur in Kir6.2-deficient (Kir6.2 KO) hearts. Resting membrane potential in WT and Kir6.2 KO hearts similarly decreased by 16.8 +/- 5.6 (n = 7, P < 0.05) and 15.0 +/- 1.7 (n = 6, P < 0.05) mV, respectively. The [K(+)](o) in WT hearts increased within the first 5 min of ischemia by 6.9 +/- 2.5 mM (n = 6, P < 0.05) and then reached a plateau. However, the extracellular K(+) accumulation similarly occurred in Kir6.2 KO hearts and the degree of [K(+)](o) increase was comparable to that in WT hearts (by 7.0 +/- 1.7 mM, n = 6, P < 0.05). In Kir6.2 KO hearts, time-dependent slowing of conduction was more pronounced compared with WT hearts. In conclusion, the present study using Kir6.2 KO hearts provides evidence that the activation of K(ATP) channels contributes to the shortening of APD, whereas it is not the primary cause of extracellular K(+) accumulation during early myocardial ischemia.
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Affiliation(s)
- Tomoaki Saito
- Department of Pharmacology, Chiba University Graduate School of Medicine, 1-8-1 Inohana, Chuo-ku, Chiba 260-8670, Japan
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Amitzur G, Shenkar N, Leor J, Novikov I, Eldar M. Modulation of ventricular fibrillation in isolated perfused heart by dofetilide. J Cardiovasc Pharmacol 2003; 41:838-48. [PMID: 12775960 DOI: 10.1097/00005344-200306000-00003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The authors studied the involvement of IKr potassium current in ventricular fibrillation during perfusion. Electrophysiologic parameters were measured before and after dofetilide administration (2.5, 7.5, and 12.5 x 10-7 M, n = 8) in isolated perfused feline hearts. During pacing, these parameters included epicardial conduction time, refractoriness, and the fastest rate for 1:1 pacing/response capture. During 8 minutes of electrically induced tachyarrhythmias, they included heart rate and normalized entropy reflecting the degree of organization. In all groups, arrhythmia rate was slower in the right ventricle than in the left ventricle. Dofetilide decreased the arrhythmia rate more than it increased organization, reduced its maintenance, or increased difficulty in initiation. Refractoriness was prolonged in a reverse use-dependent way which was less than 1:1 pacing/response capture. Unexpectedly, a moderate prolongation of conduction time was observed. Inverse correlation was found between the arrhythmia rate and changes in refractoriness and conduction time and between the degree of organization and refractoriness (both ventricles) and conduction time (right ventricle). Dofetilide, which intensively blocks IKr current and unexpectedly suppressed conduction, has different quantitative effects on fibrillation features. These changes in fibrillation suggest that these effects are mainly associated with refractoriness prolongation and do not seem to be attenuated by conduction suppression.
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Affiliation(s)
- Giora Amitzur
- Neufeld Cardiac Research Institute, Sheba Medical Center, Tel Hashomer 52621, Israel.
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Scherlag BJ, Patterson E, Jackman WM, Lazzara R. The elusive extracellular AV nodal potential: studies from the canine heart, ex vivo. J Interv Card Electrophysiol 2002; 7:39-52. [PMID: 12391419 DOI: 10.1023/a:1020816016042] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Various forms of extracellular recordings from the AV node (AVN) have been reported. However, lack of consistent validation have precluded the use of such recordings in experimental and clinical studies. In 14 Langendorff perfused dog hearts, the triangle of Koch (TOK) was exposed and an octapolar electrode catheter (2 mm rings, 2 mm spacing) was inserted under the endocardium so that the bipolar pairs recorded electrograms from the apex to the base of the TOK. All recording were filtered between 0.05 and 250 Hz, except for a His bundle (Hb) recording (30-250 Hz) made from another bipolar electrode catheter placed in the aortic root. Transmembrane action potentials (AP) were recorded close to the sites of extracellular electrograms. Pin electrodes at the periphery of the bath were arranged to register two ECG leads from the volume conductor. During recovery of electrical activity 11 of 14 preparations developed a junctional rhythm that initially manifested only an AV nodal extracellular and corresponding intracellular AV nodal potentials followed gradually by conduction to the Hb and ventricles but no retrograde atrial activation; 3 preparations initially produced Hb rhythms based on extracellular and transmembrane AP recordings from the AVN and Hb. The amplitude and duration of the AVN extracellular potentials (average: 97 +/- 26 microV and 92 +/- 25 msec, respectively) during AVN rhythms, significantly differed from those during atrial pacing (262 +/- 185 microV and 78 +/- 26 msec, p < 0.05). Histologic sections of the sites underlying the electrodes recording AVN potentials showed AVN tissue throughout. We conclude that extracellular AV nodal potentials are independent waveforms with specific qualitative and quantitative characteristics that distinguish them from adjacent atrial, transitional, Hb or ventricular potentials.
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Affiliation(s)
- Benjamin J Scherlag
- University of Oklahoma Health Sciences Center, Cardiac Arrhythmia Research Institute and Department of Veterans Affairs Medical Center, Oklahoma City, OK 73104, USA.
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Scherlag BJ, Lazzara R. Is there longitudinal dissociation in the undamaged his bundle? In vitro studies in the normal canine heart. J Electrocardiol 2001; 33 Suppl:83-6. [PMID: 11265741 DOI: 10.1054/jelc.2000.20331] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
We investigated the concept of longitudinal dissociation in the His-Purkinje system in vitro. Hearts were excised from the eleven anesthetized dogs and a septal preparation containing the exposed His bundle and the entire right bundle branch and left bundle branch were displayed in a two-dimensional arrangement pinned to the bottom of a superfusion chamber. Tyrodes solution, gassed with 95% O2 and 5% CO2, at 37 degrees C was continuously passed over the preparation. Pacing was performed over a wide range of heart rates (30 to 180/min) from the proximal His bundle and by moving bipolar electrodes we monitored activation at various sites along the right and left bundle branch. The earliest site of muscle activation (27+/-2 msec) on the left septum was a relatively large area in the midposterior septal region; whereas, on the right septum the earliest site of activation (27+/-3 msec) was a relatively small zone at the base of the anterior papillary muscle, (p, N.S). The larger area of early activation on the left compared to the right is consonant with a left to right septal vector accounting for the Q wave in the standard bipolar leads in the normal heart and the loss of Q waves in left bundle branch block. We conclude that His-Purkinje and ventricular muscle activation is remarkably synchronous on both sides of the heart and accounts for optimal contractile function during His bundle or biventricular pacing compared to standard site ventricular pacing, particularly in patients with left ventricular dysfunction.
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Affiliation(s)
- B J Scherlag
- Cardiac Arrhythmia Research Institute at the University of Oklahoma Health Sciences Center, Oklahoma City 73104, USA.
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Amitzur G, Schoels W, Visokovsky A, Lev-Ran V, Novikov I, Mueller M, Kraft P, Kaplinsky E, Eldar M. Role of sodium channels in ventricular fibrillation: a study in nonischemic isolated hearts. J Cardiovasc Pharmacol 2000; 36:785-93. [PMID: 11117380 DOI: 10.1097/00005344-200012000-00015] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Because the role of sodium channels in the initiation and maintenance of VF is not fully elucidated, we studied the significance of sodium channel activity in VF using sodium channel blockers. In nonischemic isolated feline hearts, the following electrophysiologic parameters were measured before and after application of tetrodotoxin (5 x 10(-7) M, n = 6) or lidocaine (1 x 10(-5) M, n = 8): (a) during pacing, epicardial conduction time; refractoriness; the fastest rate for 1:1 pacing/response capture, and all tissue resistivity, indirectly reflecting intercellular electrical resistance; (b) during 8 min of electrically induced tachyarrhythmias, all tissue resistivity; peak frequency (to measure average frequency based on fast-Fourier transformation analysis); and normalized entropy (to measure the degree of arrhythmia organization). In nonischemic isolated rabbit hearts (n = 4), three-dimensional mapping was performed before and after application of lidocaine (1 x 10(-5) M). In feline hearts, lidocaine and tetrodotoxin application resulted in: (a) more spontaneous arrhythmia termination (63-67%) than in nontreated hearts (7%); (b) transformation from mainly VF into ventricular tachycardia with increased organization; and (c) prolongation of conduction time (155-248%) (p < 0.01 for all parameters). The ventricular refractory period was slightly prolonged by tetrodotoxin in the right ventricle and exhibited rate-dependent shortening in control and with lidocaine. Tetrodotoxin and lidocaine reduced the pacing rate for 1:1 pacing/response capture, and all tissue resistivity was not significantly affected. Peak frequency was decreased by tetrodotoxin and lidocaine mainly in the left ventricle (p < 0.01). In nontreated left ventricles, peak frequency was increased over time but was attenuated by lidocaine. In isolated rabbit hearts, several simultaneous wave fronts were detected during VF in nontreated hearts and were reduced to only one or two major wavefronts after application of lidocaine. Suppression of sodium channel activity that primarily slowed conduction time and had little or no effect on ventricular refractory period and all tissue resistivity resulted in less stable and more organized arrhythmias and reduced tachyarrhythmia rate compared with nontreated hearts. These results suggest an active role for sodium channels in the maintenance of ventricular fibrillation.
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Affiliation(s)
- G Amitzur
- Neufeld Cardiac Research Institute, Tel-Aviv University, Tel-Hashomer, Israel.
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Leerssen HM, Vos MA, den Dulk K, van der Zande J, Wellens HJ. Rate dependent effects of procainamide on the threshold current for pacing in the setting of postrepolarization refractoriness in dogs. Pacing Clin Electrophysiol 1999; 22:291-301. [PMID: 10087543 DOI: 10.1111/j.1540-8159.1999.tb00441.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Normally, ventricular APD exceeds the VERP. However, under specific circumstances this relation may change and can become inverse. This phenomenon of postrepolarization refractoriness may be caused by a decrease in excitability. The threshold current (TC) for pacing has never been quantified as a possible explanation for these observations. Using a MAP pacing catheter in the right ventricular apex, the rate dependent behavior of TC, VERP, and APD before and after procainamide (dose 20 mg/kg in 10 min + 5 mg/min infusion) was determined in 17 dogs with chronic complete AV block. Initially, TC was determined with 0.1 mA accuracy. Using a pacing current of at least twice TC, VERP and APD showed a similar, rate dependent shortening for PCLs 800, 575, and 350 ms. Procainamide treatment led to an equal, rate independent VERP and APD increase: no post repolarization refractoriness. Subsequently, accuracy for TC determination was increased to 0.01 mA. Comparing PCLs 800 and 250 ms, TC doubled from 0.05 +/- 0.01 to 0.10 +/- 0.09 mA during control and almost tripled from 0.06 +/- 0.02 to 0.17 +/- 0.10 mA (P < 0.05) after procainamide. Using a fixed pacing current of exactly twice TC found at 800 ms PCL during control, VERP exceeded APD after procainamide treatment at 300 and 250 ms PCL: postrepolarization refractoriness. Increasing the pacing current to twice the rate dependent TC, the relation between VERP and APD normalized: no postrepolarization refractoriness. We conclude that after procainamide, rate dependent TC increase is of major importance for the phenomenon of postrepolarization refractoriness.
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Affiliation(s)
- H M Leerssen
- Department of Cardiology, Cardiovascular Research Institute Maastricht, University Hospital Maastricht, The Netherlands
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Prakash VS, Tai CT, Chen SA. Spontaneous termination of ventricular tachycardia with variable patterns and variable mechanisms? Pacing Clin Electrophysiol 1999; 22:111-3. [PMID: 9990607 DOI: 10.1111/j.1540-8159.1999.tb00306.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A 43-year-old man, with repeated episodes of postmyocardial infarction monomorphic VT, had three forms of induced sustained VT in the electrophysiology lab. The three forms of VT had variable termination patterns with no change, decrease, or increase of cycle length.
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Affiliation(s)
- V S Prakash
- Department of Medicine, National Yang-Ming University, School of Medicine, Taiwan, R.O.C
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Guo H, Euler D, Wang Z, Olshansky B. Autonomic influences in atrial ischemia: vagally mediated atrial conduction improvement. Int J Cardiol 1997; 61:157-63. [PMID: 9314209 DOI: 10.1016/s0167-5273(97)00159-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
To investigate the effects of autonomic nerve activation on electrophysiological properties of ischemic atrial myocardium, experiments were performed in 10 open chest adult dogs anesthetized with xylazine and alpha-chloralose. Ischemia was created in the right atrial free wall by ligation of one or more branches of the right coronary artery. Bipolar electrograms were recorded from multiple sites in the ischemic and non-ischemic zones. The atria were paced at 400 ms and 180 ms to assess conduction properties. One hour after ligation, delayed activation, electrogram fractionation, and electrogram alternans were observed in the ischemic zone. All local conduction abnormalities were heart rate dependent in that they were only observed at a pacing cycle length of 180 ms. The average duration of ischemic zone electrograms was significantly prolonged from 17.7+/-1.6 ms to 26.4+/-1.6 ms (P<0.001). Right and left vagal stimulation significantly shortened the electrogram duration in the ischemic zone from 26.4+/-1.6 ms to 19.7+/-1.1 ms (P<0.01) and 20.0+/-1.1 ms (P<0.01), respectively. Ischemia-induced electrogram alternans was eliminated completely. During right and left stellate stimulation, electrogram duration was not altered and alternans was still present. In conclusion, vagal stimulation in this canine model improves local conduction in ischemic myocardium in the right atrium. This effect may be mediated by a reversal of the ischemia-induced membrane depolarization and a shortening of refractoriness in the atrium during vagal activation.
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Affiliation(s)
- H Guo
- Loyola University Medical Center, Maywood, IL 60153, USA
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Tanaka K, Suzuki F, Hiejima K, Fujimura O. Quantitative analysis of concealed conduction into accessory atrioventricular pathways in Wolff-Parkinson-White syndrome. Pacing Clin Electrophysiol 1997; 20:1342-53. [PMID: 9170136 DOI: 10.1111/j.1540-8159.1997.tb06789.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Concealed conduction is demonstrated to occur in an accessory AV pathway (AP). To test the hypothesis that anterograde and retrograde concealed conduction in the AP would have different characteristics, 35 consecutive patients with single APs were studied. The anterograde or retrograde ERP of the AP could be determined in 23 of those patients. Anterograde concealed conduction in the AP was assessed in the first 13 patients with retrograde AP conduction (6 APs with retrograde conduction only and 5 with both directions) (group A). Retrograde concealed conduction in the AP was evaluated in the remaining 10 patients with anterograde AP conduction (6 APs with anterograde conduction only and 4 with both directions) (group B). The concealed conduction in the AP was quantified by determining the ERP of the AP using a "probe" extrastimulus (Sp) introduced in the opposite chamber. The ERP was determined both during conventional extrastimulus (S1S2 method; ERPc) and during that with an Sp (S1SpS2 method; ERPp). The Sp was delivered before or after the last S1 with various S1Sp intervals. The ERPp was determined at each S1Sp interval. Three distinct patterns in concealed conduction in the AP were noted. In the first pattern, the ERPp was always shorter than the ERPc, whereas the reverse relation was noted in the second pattern. The third pattern showed a combination of the two. In group A, only the first pattern was noted. In group B, the first, second, and third patterns were noted in 4, 2, and 4 patients, respectively. The first pattern was noted only in septal APs and the second and third were seen only in left free-wall APs. The second pattern was seen in patients with retrograde AP conduction, whereas the third one was mainly noted in patients without retrograde AP conduction. These observations indicate that anterograde and retrograde concealed conduction in the AP have different characteristics. Shortening of the ERPp might be due to the "peeling back" phenomenon, and its lengthening might be caused by the presence of the inhomogeneous refractory periods of the AP.
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Affiliation(s)
- K Tanaka
- First Department of Internal Medicine, Tokyo Medical and Dental University, Japan
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Chiale PA, Sanchez RA, Franco DA, Elizari MV, Rosenbaum MB. Overdrive prolongation of refractoriness and fatigue in the early stages of human bundle branch disease. J Am Coll Cardiol 1994; 23:724-32. [PMID: 8113558 DOI: 10.1016/0735-1097(94)90760-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
OBJECTIVES The aim of this study was to assess the response of refractoriness in normal and diseased human bundle branches to changes in cycle length, as well as during a long period of continuous overdrive pacing. BACKGROUND The anterograde refractory period of the bundle branches in patients with functional bundle branch block shortens as the rate is increased. The rate-dependent response of refractoriness in diseased bundle branches is quite different. However, this difference has not been precisely delineated, and its physiologic meaning is uncertain. METHODS Refractoriness of the bundle branches was measured by the extrastimulus technique in 16 patients with tachycardia-dependent bundle branch block and 10 patients with functional bundle branch block, both after basic trains of 8 atrial-paced impulses at different cycle lengths and during a 10-min period of continuous overdrive pacing. RESULTS The baseline refractory period in the bundle branches of patients with functional bundle branch block measured 430 +/- 32 ms (mean +/- SD) and shortened to 368 +/- 30 ms at the shortest cycle length. The maximal effect was reached within the 1st min of overdrive pacing. The baseline refractory period of the bundle branches was significantly longer in patients with tachycardia-dependent bundle branch block (611 +/- 184 ms) and demonstrated a cumulative overdrive prolongation in 15 (83%) of 18 studies with typical manifestations of fatigue. In two other studies, this occurred only after ajmaline administration. CONCLUSIONS A rate- and time-dependent prolongation of refractoriness frequently occurs in diseased human bundle branches. When absent, this response may be induced under the effects of sodium channel blockers. This would suggest that an abnormality in the recovery from inactivation of the sodium channel might underlie the early stages of bundle branch disease.
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Affiliation(s)
- P A Chiale
- Division of Cardiology, Ramos Mejia Hospital, Buenos Aires, Argentina
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Gonzalez MD, Scherlag BJ, Mabo P, Lazzara R. Conversion of Mobitz type II AV block to 1:1 AV conduction by premature ventricular beats. J Electrocardiol 1992; 25 Suppl:165-72. [PMID: 1284301 DOI: 10.1016/0022-0736(92)90095-h] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Preliminary experiments in a canine model of Mobitz type II atrioventricular (AV) block showed improvement of conduction after premature ventricular beats. In this investigation, the authors studied the mechanism(s) responsible for this response. In vivo studies were performed in 16 anesthetized dogs. Block was induced by ischemia after septal artery occlusion or by mechanical trauma. Two pairs of plunge electrodes were inserted in the proximal and distal His bundle. An electrode catheter was positioned at the level of the aortic root to provide an overall view of His bundle activation. Bipolar pacing was performed from the high right atrium, right ventricular outflow tract, and proximal and distal His bundle. Infra-nodal 2:1 AV block was consistently induced at an atrial rate of 238 +/- 21 beats/min. In 15 dogs a narrow time window (10-60 ms; mean, 32 +/- 6 ms) was found during which premature beats resulted in transient (2-11 beats; n = 9) or persistent (n = 8) restoration of 1:1 AV conduction. Retrograde penetration of the site of block, that is, Hb, was found even when the anterograde impulse was blocked, demonstrating the asymmetric nature of anterograde versus retrograde conduction. In vitro studies were performed in the same hearts. Intracellular recordings were obtained in the damaged His bundle and proximal right bundle. The site of block showed frequent displacements along the bundle. The introduction of a retrograde stimulus during 2:1 block restored 1:1 anterograde conduction.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- M D Gonzalez
- Department of Medicine, University of Oklahoma Health Science Center, Oklahoma City
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Rozanski GJ. Active components of excitability in K+-depolarized ventricular muscle. J Electrocardiol 1989; 22:307-15. [PMID: 2551987 DOI: 10.1016/0022-0736(89)90006-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The steady-state and dynamic characteristics of excitability were assessed in isolated guinea pig papillary muscles depolarized with elevated [K+]o to resting potentials near -60 mV. Transmembrane potentials were recorded from fibers during application of low-amplitude current pulses used to analyze net changes in active membrane components of excitability in terms of elicited local responses and measure threshold current (Ith). Generated local responses were blocked entirely by tetrodotoxin and lidocaine, which increased steady-state Ith by more than 200%. In the absence of Na+ channel-blocking agents, local responses showed marked but characteristic attenuation in a time- and voltage-dependent manner by preceding subthreshold depolarizations, which concomitantly reduced excitability. However, local responses and excitability were also modulated by small changes in [Ca2+]o (+/- 0.7 mmol) and reduced by exposure to slow channel blockers and to Cs+. Thus these data suggest that while the Na+ channel is the primary active component of excitability in partially depolarized ventricular muscle, Ca2+ -mediated and Cs+ -sensitive conductances may also participate, although to a lesser extent. These findings may help explain the frequency-dependence of excitability and conduction under conditions of ischemia in the intact heart.
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Affiliation(s)
- G J Rozanski
- Department of Internal Medicine, University of Nebraska Medical Center, Omaha
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Markel ML, Miles WM, Zipes DP, Prystowsky EN. Parasympathetic and sympathetic alterations of Mobitz type II heart block. J Am Coll Cardiol 1988; 11:271-5. [PMID: 3339166 DOI: 10.1016/0735-1097(88)90091-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
This study examined the effects of changes in parasympathetic and sympathetic tone on the cycle length at which Mobitz type II second degree atrioventricular (AV) block occurred. Four patients who had electrocardiographic evidence of type II AV block and confirmation of block in the His-Purkinje system during electrophysiologic study were evaluated. These patients received intravenous atropine (1.0 to 2.4 mg), propranolol (0.15 mg/kg body weight) or isoproterenol (1 and 2 micrograms/min) alone or in combination. In two of three patients receiving propranolol, the atrial pacing cycle length at which 1:1 His-Purkinje conduction occurred was prolonged relative to control (from 360 to 470 ms and 440 to 590 ms, respectively). In contrast, atropine in the presence of beta-adrenergic blockade shortened the cycle length at which 1:1 His-Purkinje conduction occurred in three of four patients receiving the drug (470 to 390, 630 to 570 and 590 to 560 ms, respectively). Isoproterenol also improved His-Purkinje conduction in the one patient receiving this drug. No agent affected the duration of the HV interval during spontaneous sinus rhythm or right atrial pacing. Thus, drugs that alter autonomic tone influence abnormal His-Purkinje conduction minimally during sinus rhythm but, importantly, may modulate the atrial pacing cycle length at which type II AV block occurs.
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Affiliation(s)
- M L Markel
- Krannert Institute of Cardiology, Indianapolis, Indiana
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Abstract
In recent years an enhanced interest among researchers combined with the availability of new technologies has increased our knowledge of the mechanisms that generate arrhythmias in patients with ischemic heart disease. Convincing evidence has been obtained to support the occurrence of reentry in ischemic myocardium. This has been especially apparent in canine studies in the surviving layers overlying infarctions several days after coronary occlusion. In this planar model, the reentry circuit forms a figure-8 configuration around an arc of functional block due to refractoriness; the center of the arc is the site of unidirectional block and reentry. The reentry circuit is sustained by wavefronts of activation encircling segments in which the tissue on either side is alternately receptive and refractory, a variant of the leading circle model of reentry. The relatively prolonged refractoriness in ischemic tissue is due to time-dependent refractoriness, i.e., postrepolarization refractoriness, which is most prominent in more severely depolarized cells. Slow conduction is related in part to primary depression of the fast channels. There is a great variation in refractory periods in ischemic tissue because of variation in action potential duration and in the duration of time-dependent refractoriness. The depolarized resting potentials of cells in acute ischemia are due in part to extracellular accumulation of potassium and intracellular accumulation of calcium. In the latter stages of ischemia it is likely that abnormalities of ion distribution across the sarcolemma play a role. It has also been demonstrated that ischemic Purkinje fibers show abnormal automaticity, i.e., enhanced phase 4 depolarization at depolarized diastolic potentials, and afterdepolarizations with triggered firing.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- R Lazzara
- Department of Medicine, University of Oklahoma Health Sciences Center, Oklahoma City 73190
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Urushibara S, Kawato M, Nakazawa K, Suzuki R. Simulation analysis of conduction of excitation in the atrioventricular node. J Theor Biol 1987; 126:275-88. [PMID: 3657234 DOI: 10.1016/s0022-5193(87)80235-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The excitation conduction in the atrioventricular node was simulated based on the spatially discrete model of the heart proposed in an earlier paper (Kawato et al., 1986). We constructed a model system composed of the atrium, the atrioventricular node and the Purkinje fiber. Coupling coefficients between these tissues were quantitatively estimated from experimental data on size and membrane capacitance of the three kinds of cardiac cells. We found the following three important features in the simulated excitation conduction along the atrioventricular node. First, shape of action potential was found to be different at different locations of the atrioventricular node although the membrane properties were assumed uniform through the atrioventricular node. Our analysis suggests that the difference in the action potential waveforms observed by Paes de Carvalho & De Almedia (1960) can be ascribed to the electrical influences of the atrium and the His bundle on the atrioventricular node. Second, when the excitation wavefront invaded the atrioventricular node from the atrium, a step was observed in the depolarization phase of the action potential at the atrioventricular node neighboring with the atrium. Janse found a similar step in the real experiment (1969). It is revealed that this step is caused by termination of the junctional current which flows from the atrium to the atrioventricular node. Finally, we found that the conduction velocity measured near the boundary between the atrium and the atrioventricular node was lower than that in the middle part of the atrioventricular node, which is in accordance with the experimental observation by Scher et al. (1959).
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Affiliation(s)
- S Urushibara
- Department of Biophysical Engineering, Faculty of Engineering Science, Osaka University, Japan
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Lavergne T, Le Heuzey JY, Bruneval P, Guize L, Boutjdir M, Von Euw D, Peronneau P. Effects of physical parameters of fulguration on electrophysiological and anatomical properties of canine myocardium. Pacing Clin Electrophysiol 1986; 9:1367-75. [PMID: 2432564 DOI: 10.1111/j.1540-8159.1986.tb06725.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
In order to determine the respective roles of catheter (Ct) physical properties and of energy levels in myocardial effects of fulguration, we delivered an electrical shock between the tip electrode of a Ct placed at the apex of the right ventricle and a large cutaneous cathodal electrode in 12 dogs. Two energy levels were used: Group A = 25 J (n = 6) and group B = 100 J (n = 6), and three Cts were studied. These Cts had different resistances (R) and active surface electrodes (S): Ct 1 (R = 0.3 omega, S = 12 mm2), Ct 2 (R = 0.3 omega, S = 2 mm2), Ct 3 (R = 2 omega, S = 13 mm2). Complex ventricular arrhythmias were observed in 5/6 cases at 100 J but only in 1/6 cases at 25 J and were independent of the Ct type. Following the shock, the effective ventricular refractory period (S1 S1 = 300 msec) increased significantly only at 100 J (11%, p = 0.03). Anatomical lesions were wider (10.6 vs. 5.2 mm, p less than 0.05) and deeper (100 vs. 55%, p less than 0.05) in the 100 J group. In contrast, there was no significant difference in the electrophysiological and anatomical changes between the three Cts. In conclusion, arrhythmogenic adverse effects of ventricular Ct fulguration are related to the delivered energy; on the contrary, they seem only slightly dependent on Ct physical properties at these energy levels; a 2 J/kg shock is not only effective but also seems to be safe.
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Abstract
Two patients, one with and one without preexisting conduction system abnormalities, were treated with amiodarone for refractory ventricular arrhythmias. Electrophysiologic testing before and during amiodarone therapy revealed amiodarone-induced HV interval prolongation and second degree intra-His Wenckebach block with no change in QRS configuration during atrial pacing at relatively long cycle lengths. The mechanism responsible for this phenomenon is unclear. These cases illustrate that amiodarone can induce distal conduction system block even in the absence of clinical conduction system disease in a pattern that mimics atrioventricular nodal block.
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Abstract
Substantial gains have been made toward clarifying the mechanisms of arrhythmia in ischemia in animal models. After coronary occlusion in the dog, ischemic myocardial cells have reduced resting potential and slowed and diminished upstrokes of action potentials due to depression of fast channels. As a result, conduction is slow and irregular, especially at shorter cycle lengths, because refractoriness is altered by a delay in recovery of the fast channels beyond the completion of repolarization. These abnormalities occur during the acute phase of arrhythmia in the first half hour after occlusion and persist in surviving the subepicardial layers of myocardial cells for days to weeks. Reentry has been mapped in these surviving layers. Reentrant circuits form around regions of functional block formed by interfaces between responding and refractory myocardium. Standard antiarrhythmic agents generally are fast-channel blockers that further depress conduction and prolong refractoriness in ischemic tissue, causing block in slow conducting segments of the reentry circuits. However, antiarrhythmic agents may cause or accentuate reentrant arrhythmias by virtue of the same depressant actions. The greater likelihood of antiarrhythmic agents suppressing rather than producing reentrant arrhythmias may be due to enhanced depressant effects of antiarrhythmic agents on very slowly conducting tissues that are involved in reentry circuits. After the acute phase, arrhythmias occurring 1 to 4 days after coronary occlusion are probably largely automatic, although the potential for reentry remains if the cycle length is shortened. Abnormally enhanced automaticity and triggered activity are demonstrable in the surviving Purkinje network in regions of infarction, but the role of these phenomena in vivo has not been clarified.(ABSTRACT TRUNCATED AT 250 WORDS)
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Jalife J. The sucrose gap preparation as a model of AV nodal transmission: are dual pathways necessary for reciprocation and AV nodal "echoes"? Pacing Clin Electrophysiol 1983; 6:1106-22. [PMID: 6195631 DOI: 10.1111/j.1540-8159.1983.tb04449.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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Burgess MJ, Coyle J. Effects of premature depolarization on refractoriness of ischemic canine myocardium. J Electrocardiol 1982; 15:335-44. [PMID: 6183387 DOI: 10.1016/s0022-0736(82)81006-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
In 25 pentobarbital anesthetized dogs we measured refractory periods (RPs) of regularly driven complexes and premature ventricular depolarizations (PVDs) with a range of coupling intervals or of regularly driven complexes and the complex following the PVD, i.e. the postextrasystolic depolarization (PED). Measurements were made during control periods and during occlusion of a branch of the left anterior descending coronary artery. The difference in control and occlusion RPs was less following some PVDs with short coupling intervals than following other PVDs with longer coupling intervals. Variations in the coupling interval of PVDs had less effect on RPs of the PVDs in ischemic than in nonischemic tissue. RPs of PEDs were prolonged with respect to RPs of regularly driven complexes in both ischemic and nonischemic tissue, but the prolongation in ischemic tissue was significantly greater than that in nonischemic tissue, 8 +/- 4 msec and 2 +/- 2 msec respectively, p less than .001. The difference in effect of PVDs on RPs of ischemic and nonischemic tissue results in greater disparity of refractoriness between ischemic and nonischemic tissue following some long coupling interval PVDs than following some PVDs with shorter coupling intervals. In addition the greater prolongation of RPs of PEDs in ischemic than in nonischemic tissue can result in increased disparity in RPs than the disparity between ischemic and nonischemic tissue present during regular drive.
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Burgess MJ, Haws CW. Effects of sympathetic stimulation on refractory periods of ischemic canine ventricular myocardium. J Electrocardiol 1982; 15:1-8. [PMID: 7069315 DOI: 10.1016/s0022-0736(82)80038-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
We studied the difference in effect of sympathetic stimulation on refractory periods of ischemic and non ischemic myocardium in eight dogs, and the effect of sympathetic stimulation on dispersion of refractory periods in ischemic myocardium in seven additional dogs. In the first group of dogs, refractory periods of ischemic sites averaged 164 +/- 2.2 msec (M +/- SEM) and those at non ischemic sites averaged 193 +/- 1.8 msec. Sympathetic stimulation shortened refractory periods at non ischemic sites to an average of 183 +/- 2.0 msec and prolonged refractory periods at ischemic sites to an average of 171 +/- 2.2 msec. As a result of the different effects of sympathetic stimulation on refractory periods of ischemic and non ischemic myocardium, refractory periods between ischemic and non ischemic areas were more uniform during sympathetic stimulation than during coronary occlusion alone. In the second group of dogs in which the effects of sympathetic stimulation on dispersion of refractory periods were studied, pooled variances in refractory periods were calculated. There was no statistically significant difference in the pooled variance of refractory periods during control periods and during sympathetic stimulation alone. Coronary occlusion alone significantly increased the variance in refractory periods, but there was no statistically significant difference in the variance of refractory periods during coronary occlusion alone and during coronary occlusion and sympathetic stimulation. Our findings suggest that at some times during the course of myocardial infarction the effects of high sympathetic tone may be partially protective with respect to arrhythmias by reducing inequalities of recovery between ischemic and non ischemic tissue.
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Janse MJ, Kléber AG. Electrophysiological changes and ventricular arrhythmias in the early phase of regional myocardial ischemia. Circ Res 1981; 49:1069-81. [PMID: 7028311 DOI: 10.1161/01.res.49.5.1069] [Citation(s) in RCA: 177] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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Tavazzi L, Salerno JA, Chimienti M, Cobelli F, Ray M, Bobba P. Tachycardia-dependent and bradycardia-dependent intraventricular conduction defects in acute myocardial infarction: electrocardiographic, electrophysiologic, and clinical correlates. Am Heart J 1981; 102:675-85. [PMID: 7282512 DOI: 10.1016/0002-8703(81)90092-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Presence of rate-dependent (RD) intraventricular conduction defects (IVCD) was documented by inducing variations in heart rate in 30 acute myocardial infarction (AMI) patients (10 right bundle branch block, six left bundle branch block, 13 left anterior hemiblocks, and two left posterior hemiblocks). Five IVCDs were tachycardia-dependent (TD), 20 were bradycardia-dependent (BD), and six were both TD and BD. In TD blocks shortest cycles showing normal intraventricular conduction ranged from 410 to 1330 msec (697 +/- 84 SE); in BD blocks longest cycles with normal intraventricular conduction ranged from 450 to 1450 msec (962 +/- 52). In 60% of cases intermittent incomplete RD blocks were also present. In one patients RD-IVCD intermittency remained until discharge; in the others it lasted from 4 minutes to 10 days. Afterwards 19 RD-IVCDs disappeared and four became stable; six patients died during RD-IVCD intermittency period. Disappearance of RD block was preceded by gradual reduction in cycle length showing TD block and lengthening of cycles stopped beats with BD block. Serial observation of RD-IVCDs provides information about sequence of electrophysiologic effects on the intraventricular conduction system in clinical AMI.
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35
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Singer DH, Baumgarten CM, Ten Eick RE. Cellular electrophysiology of ventricular and other dysrhythmias: studies on diseased and ischemic heart. Prog Cardiovasc Dis 1981; 24:97-156. [PMID: 6270731 DOI: 10.1016/0033-0620(81)90002-5] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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36
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Scherlag BJ. Editorial note. Int J Cardiol 1981. [DOI: 10.1016/0167-5273(81)90049-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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38
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Abstract
We have used numerical methods for solving cable equations, combined with previously published mathematical models for the membrane properties of ventricular and Purkinje cells, to simulate the propagation of cardiac action potentials along a unidimensional strand. Two types of inhomogeneities have been simulated and the results compared with experimentally observed disturbances in cardiac action potential propagation. Changes in the membrane model for regions of the strand were introduced to simulate regions of decreased excitability. Regional changes in the intercellular coupling were also studied. The results illustrate and help to explain the disturbances in propagation which have been reported to occur at regions of decreased excitability, regions with changing action potential duration, or regions with changing intercellular coupling. The propagational disturbances seen at all of these regions are discussed in terms of the changing electrical load imposed upon the propagating impulse.
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Pop T, Fleischmann D, Effert S. The vulnerability of the right atrium. III. Electrophysiologic correlates of atrial vulnerability. KLINISCHE WOCHENSCHRIFT 1979; 57:31-6. [PMID: 759715 DOI: 10.1007/bf01476979] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
70 patients were investigated by means of the atrial extrastimulus method at three different driving rates: 80, 100 and 120/min. At each rate the effective, the relative, the total and the functional refractory periods were measured. 30 patients who showed signs of atrial vulnerability at least one of the tested rates were included in the so called vulnerability group. The remaining 40 patients, who did not fulfill the criteria for atrial vulnerability, were included in the nonvulnerability group. When the two groups were compared to each other there were significant larger P waves (p less than 0.005), shorter effective refractory periods (p less than 0.001) and longer relative refractory periods (p less than 0.001) in the vulnerability group. With increasing driving rate there was an increased tendency to repletitive firing in the vulnerability group. The phenomenon of vulnerability correlated well with the rate-induced shortening of the effective and the lengthening of the relative refractory period. The above described phenomena are compatible with the concept of re-entry as the electrophysiologic mechanism of atrial vulnerability in man.
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Scherlag BJ, El-Sherif N, Hope RR, Lazzara R. The significance of dissociation of conduction in the canine His bundle. Electrophysiological studies in vivo and in vitro. J Electrocardiol 1978; 11:343-54. [PMID: 712285 DOI: 10.1016/s0022-0736(78)80140-x] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Fractionated His bundle potentials were induced by ischemia or trauma in 30 anesthetized dogs, in vivo. Functional dissociation, i.e., alteration of the activation sequence of portions of these His bundle potentials was demonstrated in vivo as well as in 10 in vitro preparations of the His-Purkinje system. In vivo, plunge wire and electrode catheters were utilized to record from portions of the His bundle. During vagal-induced slowing of the heart rate, atrial pacing or His bundle pacing, His-Purkinje conduction as measured by the H-V interval was constant over a wide range of heart rates, 50-300/min. One or two hours after anterior septal artery ligation, His bundle damage manifested as split His bundle potentials (H, H'). Atrial pacing or proximal His bundle pacing induced H-H' delays with concomitant right or left bundle branch block patterns in ECG leads. However, distal His bundle pacing at comparable or even higher rates produced normal QRS complexes. In other cases, during atrial pacing or with progressive ischemia at a constant rate, H' progressively delayed during the H-V interval or even disappeared into the QRS complex with a concomitant occurrence of right or left bundle branch block. In vitro, a dissected septal preparation was studied containing the His bundle, proximal and distal right bundle and left bundle branches. Normal conduction throughout the His-Purkinje system was observed at pacing rates of 30-220/min. Punctate lesions, anatomically placed above the branching His bundle caused tachycardia-dependent, complete bundle branch blocked with concurrent temporal reversal of proximal and distal His bundle action potentials. These data suggest that ischemic or traumatic lesions in the His bundle may manifest on the electrocardiogram as bundle branch block patterns. From a clinical point of view, a critical site of lesion would markedly increase the liability for A-V blocked although the electrocardiogram alone would not indicate the actual site of lesion. Predestination of fiber tracts and alternative proposals to the pedestination theory are considered to explain QRS aberration due to exclusive His bundle lesions.
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Abstract
The effect of hypoxia on the relationship between refractoriness and transmembrane action potential was studied in isolated canine papillary muscle preparations. Test stimuli were applied at variable intervals after every 10 to 15 driving stimuli, and action potentials were recorded through an intracellular microelectrode located near the stimulus site. During hypoxia of 30 to 90 min duration, induced by nitrogenization of the perfusate, action potential duration (APD) was tremendously decreased in association with decline in the amplitude and rising velocity. The resting potential was also reduced. Concurrently the effective refractory period (ERP) was decreased, but its decrement was smaller than that of the APD. The total refractory period (TRP) was, on the other hand, prolonged. In consequence, not only the TRP but the ERP as well fairly outlasted full repolarization as a result of the hypoxia. The duration of the relative refractory period (RRP) was increased during hypoxia as the result of the changes in ERP and TRP, and graded local responses were registered frequently in the early phase of RRP. These facts were thought to be related to the genesis of arrhythmias in the ischemic heart.
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Sostman HD, Kelley MJ, Langou RA. Perfusion of the canine interventricular septum: significance of right coronary artery supply. Am Heart J 1977; 94:611-7. [PMID: 333890 DOI: 10.1016/s0002-8703(77)80131-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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45
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Yamaguchi I, McCullen A, Mandel WJ. Electrophysiologic effects of anterior septal arterial occlusion. Am J Cardiol 1977; 40:727-32. [PMID: 920609 DOI: 10.1016/0002-9149(77)90188-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The effect of reduction in anterior septal arterial flow on the conduction system was studied in seven anesthetized dogs. After 2 hours of occlusion P-Q, A-H, and H-V intervals as well as atrioventricular nodal effective and functional refractory periods were significantly prolonged, sinoatrial conduction time was prolonged and the heart rate was decreased. The duration of the His bundle electrogram was significantly prolonged and the configuration altered. However, QRS duration did not prolong significantly. Fifteen minutes after reperfusion, A-H interval, duration of the His bundle electrogram, effective refractory period and functional refractory period returned toward control values. However, the H-V and QRS intervals as well as sinoatrial conduction time were unchanged after reperfusion. Thus, reduction of anterior septal arterial flow influences not only the distal but also the proximal portion of the conduction system; the most vulnerable part is probably the His bundle. The distal portion of the conduction system is directly influenced by ischemia itself, whereas the proximal portion is influenced through other mechanisms induced by reduction of anterior septal arterial flow.
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Abstract
The effects of therapeutic concentrations of lidocaine, quinidine and phenytoin on the electrograms and excitability of ischemic canine myocardium were investigated. The threshold stimulation current was determined as the minimum current necessary to drive the ventricles at 300 msec intervals. Administration of the drugs did not change the threshold stimulation current of the control myocardium, but lidocaine (P less than 0.002), quinidine (P less than 0.01) and phenytoin (P less than 0.05) all markedly increased the threshold stimulation current of the ischemic tissue. The effects on the electrograms were small but consistent with current electrophysiological knowledge. This selective depression of the electrical activity of the ischemic tissue may form an important mechanism of action of these antiarrhythmic agents. However, this same effect may under certain conditions precipitate serious arrhythmias.
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48
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Kohlhardt M. [Transmembrane inward currents during excitation of the heart (author's transl)]. KLINISCHE WOCHENSCHRIFT 1975; 53:1089-99. [PMID: 1206966 DOI: 10.1007/bf01614276] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
During excitation of the myocardial cell 2 transmembrane inward currents occur. The initial fast Na current is responsible for the upstroke of the normal action potential. The slow inward current is triggered at a threshold potential of about -40 mV and causes the plateau phase of action potential. Under physiological conditions Ca ions are the main charge carriers of the slow inward current. Both inward currents are mediated by 2 membrane channels which are independent from each other. The normal excitability of the myocardial cell depends upon the availability of the fast Na channel but the transmembrane Ca supply will be determined by the Ca conductance of the slow channel. After inactivation of the fast Na channel the excitability of the myocardial cell does not disappear completely. In this situation the slow inward current can mediate action potentials (so called Ca action potentials). The slow inward current can be considered as the predominant mediator of the excitation process in the pacemaker cells of the sinoatrial node and the av node. Specific inhibitors of the slow membrane channel (verapamil, D 600, Ni, Co, and Mn ions) block the transmembrane Ca current leading to excitation contraction uncoupling. The excitation process will be impaired only if it is carried by the slow inward current alone. Specific inhibitors of the fast Na channel reduce the Na-dependent excitability of the myocardial cell without significant changes of the Ca current. The existence of 2 separate channels in the ventricular myocardium allows selective alteration of contractility without concomitant changes of the Na-dependent excitation process or, conversely, the reduction of excitability whereas the Ca current remains unchanged.
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