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A Kadish

Publications and source records attributed to A Kadish.

At least 19 recordsLinked to original sources
PubMed2001

Polymorphic ventricular tachycardia, long Q-T syndrome, and torsades de pointes.

PMVT is an uncommon arrhythmia with multiple causes. Classification and management are based on the Q-T interval. Torsades de pointes denotes PMVT in the setting of a prolonged Q-T interval and usually is iatrogenic in origin, although congenital LQTS is being recognized more frequently. Therapy of PMVT focuses on the establishment of hemodynamic stability, the removal or correction of precipitants, and the acute and long-term inhibition of subsequent episodes. Evaluation of these patients should include a thorough history and physical examination and an assessment for underlying heart disease and known [figure: see text] eliciting factors. Long-term management must be tailored to the individual and the underlying cause and should be conducted by an experienced cardiac electrophysiologist.

Anti-Arrhythmia Agents↗
PubMed2001

Effects of sex and age on electrocardiographic and cardiac electrophysiological properties in adults.

Although differences in patient sex in heart rate and QT interval have been well characterized, sexual differences in other cardiac electrophysiological properties have not been well defined. The study population consisted of 354 consecutive patients without structural heart disease or preexcitation who underwent clinically indicated electrophysiological testing in the drug-free state. Atrial, AV nodal, and ventricular effective refractory periods (AERP, AVNERP, VERP) were determined at a pacing cycle length of 500 ms using an 8-beat drive train and 3-second intertrain pause. There were 124 men and 230 women with a mean age of 45 +/- 19 and 47 +/- 18 years, respectively. The sinus cycle length (SCL) was longer in men than in women (864 +/- 186 and 824 +/- 172 ms, respectively, P < 0.05). The QRS duration was significantly longer in men (90 +/- 12 ms) than women (86 +/- 13 ms) (P < 0.005). The HV interval was 48 +/- 9 ms in men and 45 +/- 8 ms in women (P < 0.05). The sinus node recovery time (SNRT) was significantly longer in men than in women (1215 +/- 297 ms and 1135 +/- 214 ms, respectively, P < 0.05). AERP and VERP were similar in both sexes. Aging did not influence sexual differences in cardiac electrophysiological properties, although, it independently prolonged the SCL, PR, and QT intervals, AH and HV intervals, SNRT, AVNERP, and the AV Wenckebach cycle length. The SCL, QRS duration, HV interval, and SNRT were significantly longer in men than in women. Aging prolonged cardiac conduction and increased the SCL but the effects were similar in both sexes. AERP and VERP were unaffected by aging or sex.

Adult↗
PubMed2001

Excitable gap in canine fibrillating ventricular myocardium: effect of subacute and chronic myocardial infarction.

INTRODUCTION: The existence of an excitable gap during ventricular fibrillation (VF) has been suggested in several prior studies. However, the effects of myocardial infarction on the presence and duration of an excitable gap during VF have not been evaluated. METHODS AND RESULTS: Electrophysiologic study was performed in normal dogs and in dogs with subacute and chronic infarction. Experimental infarction was produced by left anterior descending coronary ligation. The excitable gap was determined indirectly using either evaluation of intrinsic wavefronts during VF or from the shortest activation interval at individual sites using recordings from a 112-electrode plaque sutured to the epicardial surface of the left ventricle. The excitable gap also was correlated to local electrophysiologic and anatomic properties. The excitable gap using the wavefront propagation method and shortest activation method was significantly longer in subacute infarction dogs (48 +/- 17 msec and 37 +/- 18 msec, respectively) and chronic infarction dogs (41 +/- 14 msec and 35 +/- 14 msec, respectively) than normal dogs (32 +/- 13 msec and 30 +/- 11 msec, respectively; P < 0.05 normal vs subacute and chronic infarction dogs in both methods). The excitable gap occupied approximately 30% and 27% of the VF cycle length in all three groups using the wavefront propagation and shortest activation method, respectively. The excitable gap correlated better with local ventricular refractoriness determined using the wavefront propagation method than with the shortest activation method, but not at all with refractoriness determined using extrastimulus testing. Tissue necrosis was noted in subacute infarction dogs and fibrosis in chronic infarction dogs, but the gap was not highly correlated with anatomic changes. CONCLUSION: During VF, an excitable gap exists in both normal and infarcted canine ventricular myocardium. It is significantly longer in the presence of infarction. These finding have implications for understanding the pathophysiology of VF and targeting antiarrhythmic therapies.

Acute Disease↗
PubMed2001

Age, gender, and autonomic tone effects on surface electrocardiographic indices of ventricular repolarization.

BACKGROUND: Prolonged QT offset dispersion (QToD), an index of heterogeneity of ventricular repolarization, is thought to be an independent predictor of all-cause and cardiovascular mortality. However the influence of gender and autonomic tone in healthy adults on age-related changes in measures of ventricular repolarization are not well characterized. METHODS: QToD and T wave complexity were measured in 56 healthy subjects with no detectable heart disease (by echo and stress test)-38 young subjects with a mean age of 28 +/- 4 years and 18 old subjects with a mean age of 71 +/- 7 years. QToD and T wave complexity were computed from 12-lead ECGs using the GE Marquette QT Guard automated analysis program with manual overreading at rest (baseline), following exercise, and double autonomic blockade with atropine and propranolol. Data was analyzed using factorial ANOVA. RESULTS: Young males had a significantly greater QToD than young and old females at baseline (28 +/- 5 ms, 23 +/- 5 ms, and 22 +/- 5 ms, respectively, P < 0.01), an intrinsic effect independent of changes in autonomic tone. In contrast, females had significantly greater T wave complexity than males following exercise and double autonomic blockade with a definite trend at baseline. There was no correlation between T wave complexity and QToD. CONCLUSIONS: Age and gender demonstrate a complex interaction on indices of myocardial repolarization with different measures behaving differently. These findings have implications for better understanding age and gender effects on myocardial electrophysiology.

Adult↗
PubMed2001

Electrophysiologic effects of a novel selective adenosine A1 agonist (CVT-510) on atrioventricular nodal conduction in humans.

BACKGROUND: CVT-510, N-(3(R)-tetrahydrofuranyl)-6-aminopurine riboside, is a selective A(1)-adenosine receptor agonist with potential potent antiarrhythmic effects in tachycardias involving the atrioventricular (AV) node. This study, the first in humans, was designed to determine the effects of CVT-510 on AV nodal conduction and hemodynamics. METHODS AND RESULTS: Patients in sinus rhythm with normal AV nodal function at electrophysiologic study (n = 32) received a single intravenous bolus of CVT-510. AH and HV intervals were measured during sinus rhythm and during atrial pacing at 1, 5, 10, 15, 20, 30, 45, and 60 minutes after the bolus. Increasing doses of CVT-510 (0.3 to 10 microg/kg) caused a dose-dependent increase in the AH interval. At 1 minute, a dose of 10 microg/kg increased the AH interval during sinus rhythm from 93 +/- 23 msec to 114 +/- 37 msec, p = 0.01 and from 114 +/- 31 msec to 146 +/- 44 msec during atrial pacing at 600 msec, p = 0.003). The AH interval returned to baseline by 20 minutes. CVT-510 at doses of 0.3 to 10 microg/kg had no effect on sinus rate, HV interval, or systemic blood pressure, and was not associated with serious adverse effects. At doses of 15 and 30 microg/kg, CVT-510 produced transient second/third degree AV heart block in all four patients treated. One of these patients also had a prolonged sedative effect that was reversed with aminophylline. CONCLUSIONS: CVT-510 promptly prolongs AV nodal conduction and does not affect sinus rate or blood pressure. Selective stimulation of the A(1)-adenosine receptor by CVT-510 may be useful for immediate control of heart rate in atrial fibrillation/flutter and to convert paroxysmal supraventricular tachycardia to sinus rhythm, while avoiding vasodilatation mediated by the A(2)-adenosine receptor, as well as the vasodepressor and negative inotropic effects associated with beta-adrenergic receptor blockade and/or calcium channel blockers.

Adenosine↗
PubMed2000

Is all ventricular fibrillation the same? Influence of mode of induction on characteristics of ventricular fibrillation.

INTRODUCTION: Little information is available on the relationship between the mode of induction of ventricular fibrillation (VF) to VF characteristics. METHODS AND RESULTS: VF was induced from the anterior left ventricle by programmed electrical stimulation, burst pacing, alternating current (AC), high current S2 at a site remote from S1, T wave shock, and intersecting wavefronts in seven normal dogs and seven dogs with chronic myocardial infarction. Using two electrode arrays, 112 electrograms were recorded from the anterior and lateral wall. Cycle lengths were analyzed and activation vectors were created by summing orthogonally recorded bipolar electrograms. The magnitude of the vector loops was integrated over time to produce an "ensemble vector" index (EVI) whose magnitude is high when beat-to-beat activation direction is consistent and low when activation direction is variable. T wave shock-induced VF had a significantly longer cycle length 1 to 5 seconds after VF onset than other modes of induction (P < 0.05). The frequency-corrected EVI was significantly larger for AC current and T wave shock-induced VF as opposed to all other modes of VF induction in early VF (P < 0.0001). After 10 seconds of VF, these differences persisted only on the anterior wall. CONCLUSION: VF induced in animals by T wave shock and AC current had different characteristics than VF induced by other methods. These findings may have implications for our understanding of VF pathophysiology.

Animals↗
PubMed2000

Effect of underlying heart disease on the frequency content of ventricular fibrillation in the dog heart.

Although prior studies have examined the frequency content of local electrogram characteristics during fibrillation, little is know about the effects of underlying heart disease on these parameters. This study was designed to compare the frequency content of local electrograms during VF in canine models of acute ischemia, subacute infarction, and chronic myocardial infarction (MI) to those in control animals to test the hypothesis that underlying heart disease can alter the basic characteristics of VF. VF was induced using burst pacing in three groups of mongrel dogs. Five dogs were evaluated 8 weeks after LAD occlusion MI, five were evaluated 5 days after experimental MI, and 5 had VF induced before (control) and immediately after LAD occlusion (ischemia). During VF, unipolar electrograms were recorded from 112 sites on the anterior LV and electrograms were evaluated 15 and 30 seconds after VF initiation in each group. Electrograms were analyzed by fast Fourier transform. No significant time dependent changes in VF characteristics were noted. The peak frequency was highest in control animals and 8-week MI, intermediate in 5-day MI, and lowest in acute ischemia (P < 0.01 for pairwise comparisons). In contrast, the fractional of energy within a bandwidth of 25% peak amplitude was highest in acute ischemia, (P < 0.001) and similar in the other three groups. Infarction decreased total energy by approximately 50%. In conclusion, the pressure of ischemia or infarction alters the frequency content of VF in a complex fashion. In addition to decreasing the peak frequency, the shape of the power spectral curve is altered in models of structural heart disease. These results suggest that the electrophysiological changes produced by infarction or ischemia alter the structural organization of ventricular fibrillation.

Animals↗
PubMed2000

Defibrillators in nonischemic cardiomyopathy treatment evaluation.

The Defibrillators in Nonischemic Cardiomyopathy Treatment Evaluation (DEFINITE) is a multicenter randomized trial. Patients will have nonischemic cardiomyopathy (LVEF < or = 35%), a history of symptomatic heart failure and spontaneous arrhythmia (> 10 PVCs/hour or nonsustained ventricular tachycardia defined as 3-15 beats at a rate of > 120 beats/min) on Holter monitor or telemetry within the past 6 months. Patients will be randomized to an implantable cardioverter defibrillator (ICD) versus no ICD. All patients will receive standard oral medical therapy for heart failure including angiotensin converting enzyme inhibitors and beta-blockers (if tolerated). Patients will be followed for 2-3 years. The primary endpoint will be total mortality. Quality-of-life and pharmacoeconomics analyses will also be performed. A registry will track patients who meet basic inclusion criteria but are not randomized. We estimate an annual total mortality of 15% at 2 years in the treatment arm that does not receive an ICD. The ICD is expected to reduce mortality by 50%. Approximately 204 patients will be required in each treatment group. Twenty-five centers will be included in a trial designed to last an estimated 4 years.

Cardiomyopathy, Dilated↗
PubMed1999

Mapping of atrial activation with a noncontact, multielectrode catheter in dogs.

BACKGROUND: Endocardial mapping of sustained arrhythmias has traditionally been performed with a roving diagnostic catheter. Although this approach is adequate for many tachyarrhythmias, it has limitations. The purpose of this study was to evaluate a novel noncontact mapping system for assessing atrial tachyarrhythmias. METHODS AND RESULTS: The mapping system consists of a 9F multielectrode-array balloon catheter that has 64 active electrodes and ring electrodes for emitting a locator signal. The locator signal was used to construct a 3-dimensional right atrial map; it was independently validated and was highly accurate. Virtual electrograms were calculated at 3360 endocardial sites in the right atrium. We evaluated right atrial activation by positioning the balloon catheter in the mid right atrium via a femoral venous approach. Experiments were performed on 12 normal mongrel dogs. The mean correlation coefficient between contact and virtual electrograms was 0.80+/-0.12 during sinus rhythm. Fifty episodes of atrial flutter induced in 11 animals were evaluated. In the majority of experiments, complete or almost complete reentrant circuits could be identified within the right atrium. Mean correlation coefficient between virtual and contact electrograms was 0.85+/-0.17 in atrial flutter. One hundred fifty-six episodes of pacing-induced atrial fibrillation were evaluated in 11 animals. Several distinct patterns of right atrial activation were seen, including single-activation wave fronts and multiple simultaneous-activation wave fronts. Mean correlation coefficient between virtual and contact electrograms during atrial fibrillation was 0.81+/-0.18. The accuracy of electrogram reconstruction was lower at sites >4.0 cm from the balloon center and at sites with a high spatial complexity of electrical activation. CONCLUSIONS: This novel noncontact mapping system can evaluate conduction patterns during sinus rhythm, demonstrate reentry during atrial flutter, and describe right atrial activation during atrial fibrillation. The accuracy of electrogram reconstruction was good at sites <4.0 cm from the balloon center, and thus the system has the ability to perform high-resolution multisite mapping of atrial tachyarrhythmias in vivo.

Animals↗
PubMed1999

Characteristics of ischemic and peri-ischemic regions during ventricular fibrillation in the canine heart.

INTRODUCTION: Although premature beats originating in areas of ischemia have been shown to be important in initiating ventricular fibrillation (VF), the participation of the ischemic zone in maintenance of VF has not been investigated. METHODS AND RESULTS: Ten normal dogs underwent induction of two separate episodes of VF, before and 10 minutes after left anterior descending coronary artery ligation. Ischemic VF was allowed to occur spontaneously or was induced by burst pacing after 10 minutes of ischemia. Unipolar epicardial electrograms were recorded using an 8 x 14 plaque electrode array (interelectrode distance 2.5 mm) placed over the anterior wall. Activation during VF was characterized by VF cycle length (CL) and wavefront organization based on linking analysis of epicardial activation directions at adjacent sites. Individual plaque sites were separated into regions based on electrogram morphology during ischemia: R1 = no ischemia; R2 = mild-to-moderate ischemia (minor ST elevation and QRS widening); and R3 = severe ischemia (marked ST elevation and QRS widening). Percent conduction block was calculated based on the percent of cycles during which sites were not activated during VF. There were no significant differences noted in mean CL or mean percent conduction block in the peri-ischemic region R1 compared to the same region under nonischemic (control) conditions. During ischemia, the mean CL was noted to increase in R2 from 111+/-14 msec (control) to 128+/-29 msec (ischemia) and in R3 from 113+/-14 msec (control) to 150+/-42 msec (ischemia) (P < 0.05). The percentage conduction block in R2 increased from 6%+/-11% (control) to 14%+/-16% (ischemia) and in R3 from 4%+/-6% (control) to 44%+/-21% (ischemia) (P < 0.05). Linking analysis revealed no significant changes in VF organization at distances of 2.5 mm in regions R1 and R2 under both control and ischemic conditions. Premature beats initiating fibrillation originated at the border between the normal and mildly ischemic zones. CONCLUSIONS: (1) Some VF characteristics are altered in ischemic regions including a longer VFCL and greater percentage of functional block. (2) VF characteristics are unchanged in immediately adjacent nonischemic myocardium. (3) Although the ischemic zone may be involved in the initiation of VF and has unique activation characteristics during VF, it does not affect VF characteristics in the adjacent nonischemic zone, suggesting that it may not play a major role in VF maintenance.

Animals↗
PubMed1999

Effect of isoflurane on defibrillation threshold in biphasic active-can defibrillation systems.

In two patients receiving implantable cardioverter-defibrillators (ICD) for spontaneous and inducible ventricular tachyarrhythmias, the use of isoflurane appeared to significantly lower defibrillation thresholds (DFT) at implantation. In the first, at initial implantation and subsequent revision using isoflurane, adequate DFTs were verified by multiple tests. Post-implantation testing using midazolam and fentanyl revealed significantly higher DFTs, necessitating a third operation without isoflurane to obtain an adequate and subsequently verifiable DFT. During the second case, discontinuation of isoflurane intraoperatively resulted in a DFT rise within 25 minutes. In patients receiving general anesthesia for ICD implantation, this possible DFT effect of isoflurane should be recognized.

Anesthetics, Intravenous↗
PubMed1997

Ventricular tachycardia in healing canine myocardial infarction: evidence for multiple reentrant mechanisms.

Prior studies have demonstrated that unimorphic VT, sometimes due to epicardial reentry, can be induced in healing canine MI; however, the characterization of the types of reentry involved has differed among prior studies. The purpose of this study was to further characterize the spectrum of epicardial reentrant circuits during induced VT in experimental canine MI. Experimental MI was created by total occlusion of the LAD in dogs. Five days later, programmed stimulation was used to induce VT, which was mapped on the epicardium using a combination of vector and isochronal techniques. Pathological analysis was used to determine regions of transmural MI. Epicardial reentrant circuits were identified in eight dogs. The mean cycle length of induced VT was 212 +/- 32 ms. In 3 of 8 experiments, a region of transmural MI was present, which formed at least a portion of a central zone of block around which reentrant impulses circulated. In five experiments, reentry was functional in nature, although the characteristics of the region of functional conduction block were variable. Long lines of functional block, short lines of block with slow conduction transverse to fiber orientation, and leading circle reentry were each observed in different experiments. Although a zone of slow conduction was identified in seven of the experiments, slow conduction transverse to fiber orientation appeared crucial in maintaining reentry in only three experiments. Multiple reentrant mechanisms of VT may be present in this single canine infarction model. Although a zone of slow conduction is usually present, the characteristics of the region of block are highly variable. However, epicardial reentry accounted for only a minority of induced arrhythmia episodes.

Animals↗
PubMed1996

Implantable cardioverter defibrillator: use in patients with no symptoms and at high risk.

Twenty-seven patients with asymptomatic, nonsustained ventricular tachycardia whose evaluation suggested they were at high risk for sustained ventricular arrhythmias were treated with implantable cardioverter defibrillators. The option of conventional therapy (including the option of no therapy) was presented to each patient and rejected in favor of defibrillator implantation on an experimental basis. Eighteen patients had coronary artery disease and inducible sustained ventricular tachycardia, 8 had idiopathic dilated cardiomyopathy, and 1 had hypertrophic cardiomyopathy and a strong family history of sudden cardiac death. The mean ejection fraction was 27% +/- 10%. Operative morbidity (3%) and mortality (3%) were low. Mean overall survival was 92% and 88% at 1 and 2 years, respectively. Sixteen (59%) of the 27 patients had appropriate defibrillator discharges during a mean follow-up of 35 +/- 15 months. The mean time to first appropriate discharge was 18 +/- 17 months, and mean follow-up after first discharge was 17 +/- 20 months. In conclusion, implantable cardioverter defibrillator placement in high-risk patients without symptoms is a feasible approach that may have resulted in benefit in selected patients. Large-scale randomized trials currently under way will determine the risk/benefit ratio of this management approach.

Actuarial Analysis↗
PubMed1996

Treatment of ventricular tachycardia-induced cardiomyopathy by transcatheter radiofrequency ablation.

Catheter ablation of ventricular tachycardia was successfully performed in a patient with dilated cardiomyopathy (ejection fraction 38%) and a long history of repetitive palpitations. Holter monitoring showed ventricular tachycardia that had a left bundle branch block QRS configuration with inferior axis deviation and was present for about one third of the daytime hours. At electrophysiological testing, ventricular tachycardia was reproduced by isoprenaline infusion. Radiofrequency energy delivered to the right ventricular outflow tract was successful at preventing the induction of ventricular tachycardia. Left ventricular ejection fraction had improved from 38% to 48% one month after ablation. During the follow up period of one year the patient remained free from arrhythmia on no medication. The ejection fraction was 61% one year after ablation. This report confirms that dilated cardiomyopathy can be induced by ventricular tachycardia and demonstrates that dilated cardiomyopathy can be reversed if the tachycardia is abolished by radiofrequency catheter ablation.

Adult↗
PubMed1995

Cellular electrophysiological changes induced in vitro by radiofrequency current: comparison with electrical ablation.

The purpose of this study was to examine the cellular electrophysiological effects of radiofrequency energy delivery in an in vitro canine epicardial preparation and compare the effects of those of high energy electrical ablation in a similar preparation. Ten joules of direct current energy or 40 volts of radiofrequency energy were delivered by a 6 French 2-mm tip catheter to the epicardial surface of 2 x 3 cm epicardial strips superfused with Tyrode's solution. Direct current energy delivery produced a crater and central zone of necrosis surrounded by a border zone of viable but damaged tissue that extended up to 10-12 mm from the site of energy delivery. Cellular electrophysiological abnormalities that included a less negative resting membrane potential, decreased peak dV/dT, decreased action potential amplitude, and decreased action potential duration (APD) were approximately linearly related to the distance from the crater edge. In addition, viable and inexcitable cells were frequently interspersed. Between 2 and 5 mm from the crater edge, 36.4% of the cells were inexcitable whereas others displayed normal action potential characteristics. In contrast, radiofrequency current produced a central zone of necrosis surrounded by a smaller border zone. Cellular damage that was qualitatively similar to that produced by direct current energy extended only up to 6-8 mm from the edge of the crater. In addition, severe abnormalities were noted in intracellular potentials recorded within 2 mm of the ablation site, and only minor abnormalities further away. Lesions were relatively homogeneous. Between 2 and 5 mm from the ablation site only 2.6% of the cells were inexcitable (P < 0.05 vs direct current). In conclusion, radiofrequency current produces lesions that are smaller and more homogeneous than those produced by direct current ablation. Although the border zone is small, a region of partially depolarized but viable myocardium is present after radiofrequency current energy delivery. These findings provide a cellular basis for several clinical observations that have been made following radiofrequency current energy delivery.

Action Potentials↗
PubMed1994

Atypical AV junctional reentrant tachycardia following AV nodal modification.

The authors present a patient who initially underwent anterior approach atrioventricular (AV) nodal modification for treatment of typical AV junctional reentrant tachycardia (AVJRT) and subsequently developed clinical episodes of a previously undocumented type of supraventricular tachycardia. Findings during electrophysiologic studies suggest that this tachycardia is due to both anterograde and retrograde conduction in a slow AV nodal pathway. A "slow pathway" potential was identified and dissociated from the local atrial and ventricular depolarizations. Posterior approach AV nodal modification was successfully used to ablate this tachycardia. These findings suggest that atypical AVJRT occurring after AV nodal modification may be "slow-slow" AVJRT.

Atrioventricular Node↗
PubMed1994

Identification of conduction block in cardiac muscle: in vitro observations in canine epicardium.

OBJECTIVE: The aim was to examine the ability of several previously proposed criteria and of "vector mapping" to distinguish slow conduction from conduction block in canine myocardium. METHODS: Two different in vitro preparations of canine epicardium were used. In 10 tissues, an anatomical barrier was simulated by a cut (five longitudinal and five transverse to fibre orientation). Eleven tissues removed two weeks after occlusion-reperfusion infarction were also studied. Isochronal activation maps were constructed from extracellular and intracellular recordings and vector loops formed by summing two orthogonally recorded bipolar electrograms were used to indicate the direction of cardiac activation. RESULTS: In the cut model, electrograms recorded from over the anatomical barrier were usually normal or showed double potentials but could occasionally be fractionated. Isochronal activation maps obtained from extracellular recordings were able to identify five of five anatomical barriers transverse to, but only one of five barriers longitudinal to, fibre orientation. The direction of cardiac activation indicated by vector loops identified conduction block in all 10 preparations. In 11 tissues removed from canine ventricles with experimental myocardial infarction, microelectrode recordings were used to characterise regions as either slow conduction or conduction block. Isochronal activation patterns obtained from extracellular recordings generally showed impulses proceeding through zones of conduction and around zones of conduction block but disagreed with the results of microelectrode impalements in two of 11 cases. Electrogram morphology was also not always able to distinguish slow conduction from block. The direction of cardiac activation determined by vector mapping accurately characterised all regions of tissue as showing either slow conduction or conduction block. CONCLUSIONS: Limited regions of conduction block or slow conduction are frequently present in epicardial tissues removed from experimental myocardial infarction. The morphology of extracellular electrograms and isochronal activation mapping performed from extracellular recordings is often but not always able to distinguish slow conduction from conduction block. Vector mapping is useful in distinguishing slow conduction from conduction block in these situations and may help evaluate myocardial conduction patterns.

Animals↗