Long-term outcomes of inducible very fast ventricular tachycardia (cycle length 200-250 ms) in patients with ischemic cardiomyopathy.

BACKGROUND: The long-term outcomes of patients with inducible very fast ventricular tachycardia (VFVT) of cycle length (CL) 200 to 250 ms have not been well studied. METHODS: Consecutive patients with ischemic cardiomyopathy with a left ventricular ejection fraction (LVEF) of 320 ms). The primary endpoint was spontaneous ventricular arrhythmia or sudden death. RESULTS: The mean age was 63 +/- 12 years and mean LVEF was 29 +/- 7%. At mean follow-up of 38 +/- 25 months (median 30 months), the primary endpoint rate was 6.6%, 34%, 44%, and 71% in groups A, B C, and D, respectively (P < 0.001). Neither mode of induction of VT nor LVEF altered the observed pattern in the primary endpoint. There was no significant difference in the primary endpoint among implanted cardioverter defibrillator recipients in groups B and C (38% vs 45%, P = 0.43). Adjusted hazard ratios for the primary endpoint compared to group A were 3.2, 3.5, and 7.0 in groups B, C, and D, respectively (P < 0.05). CONCLUSIONS: Inducible VFVT (200-250 ms) is a clinically significant arrhythmia with adverse long-term outcomes and should not be considered a nonspecific finding of PVS.

Transmural mapping of myocardial refractoriness and endocardial dispersion of repolarization in an ovine model of chronic myocardial infarction.

BACKGROUND: Myocardial refractoriness and repolarization is an important electrophysiological property that, when altered, increases the risk of arrhythmogenesis. These electrophysiological changes associated with chronic myocardial infarction (MI) have not been studied in detail. We assessed the influence of left ventricular (LV) scarring on local refractoriness, repolarization, and electrogram characteristics. METHODS: MI was induced in five sheep by percutaneous left anterior descending artery occlusion for 3 hours. Mapping was performed at 19 +/- 6 weeks post-MI. A total of 20 quadripolar transmural needles were deployed at thoracotomy in the LV within and surrounding scar. Bipolar pacing was performed from each needle to assess the effective refractory period (ERP) of the subendocardium and subepicardium. The activation (AT) and repolarization (RT) times, and modified activation recovery interval (ARI(m)) were determined from endocardial unipolar electrograms recorded in sinus rhythm simultaneously from all needles. Scarring was quantified histologically and compared with electrophysiological characteristics. RESULTS: Increased scarring corresponded with increased ERP (P < 0.01), decreased subendocardial electrogram amplitude (P < 0.001), and slope (P < 0.001). ERP did not differ between endocardium and epicardium (P > 0.05). The ARI(m) and RT were prolonged during early myocardial activation (P < 0.001). After adjusting for AT, the RT and ARI(m) were prolonged in areas of scarring (P < 0.001). After adjusting for electrogram amplitude, the ARI(m) was prolonged in dense scar (P < 0.05). CONCLUSIONS: We confirmed histologically that scarring contributes to prolongation of repolarization, increased refractoriness, and reductions in conduction and voltage post-MI. Prolongation of repolarization may be further augmented when local activation is earliest or electrogram voltage is decreased within scar.

Discriminatory therapy for very fast ventricular tachycardia in patients with implantable cardioverter defibrillators.

OBJECTIVES: We assessed the efficacy of antitachycardia pacing (ATP) and low-energy (5J) shock for very fast ventricular tachycardia (VFVT), cycle length 200-250 ms, in patients with implantable cardioverter defibrillators (ICDs). METHODS AND RESULTS: One hundred and fifty-two consecutive patients with standard indications for ICD therapy were enrolled. Before discharge from the hospital each patient had an electrophysiological study (EPS) performed through the device, to assess the efficacy of ATP and low-joule shock at terminating VFVT. Initial therapy for VFVT consisted of three bursts of ATP followed by low-energy shock, and high-energy shocks as required. The mean age of enrolled patients was 63 +/- 13 years, and the mean left ventricular ejection fraction (LVEF) was 31 +/- 13%. During the predischarge EPS, a total of 125 VT episodes were induced in 64 patients. In patients with VFVT, the success rate of ATP was 30% (14/46), the acceleration rate was 26% (12/46), and the success rate of low-energy shock was 86% (25/29). In patients with fast ventricular tachycardia (FVT), cycle lengths 251-320 ms, the success rate of ATP was 62% (24/39), the acceleration rate was 18% (7/39), and the success rate of low-energy shock was 94% (17/18). CONCLUSIONS: This study has demonstrated for the first time that ATP and low-energy shock are effective, as an alternative to high-energy shock, to revert induced VFVT. Low-energy shock has a very high success rate for VT slower than VFVT. Clinical studies are required prior to consideration for empiric programming.

Comparison of left ventricular ejection fraction and inducible ventricular tachycardia in ST-elevation myocardial infarction treated by primary angioplasty versus thrombolysis.

Electrophysiologic studies predict the risk for sudden death after myocardial infarction (MI). Although primary angioplasty has become the preferred method of treatment for ST-elevation MI, intravenous thrombolysis remains the first-line treatment in 30% to 70% of cases worldwide. Rates of ventricular tachyarrhythmias may vary according to type of reperfusion treatment. This study was undertaken to examine the hypothesis that the left ventricular ejection fraction (LVEF) and rates of inducible ventricular tachycardia may be more favorable in treatment with primary angioplasty rather than thrombolysis. Consecutive patients receiving primary angioplasty (n = 225) or thrombolysis (n = 195) for ST-elevation MI were included. The mean LVEF was 48 +/- 12% for the primary angioplasty group and 46 +/- 13% for the thrombolysis group (p = 0.30). The proportion of patients with LVEFs <40% was 30% in the primary angioplasty group and 30% in the thrombolysis group (p = 0.98). Patients with LVEFs <40% underwent electrophysiologic studies. Ventricular tachycardia was inducible in 23 of 66 primary angioplasty patients (34.8%) compared with 21 of 55 (38.1%) thrombolysis patients (p = 0.69). Implantable cardiac defibrillators were inserted in 30 patients, of whom 8 (27%) had appropriate device activations. The mean time from MI to first spontaneous activation was 387 +/- 458 days. In conclusion, patients treated with thrombolysis or primary angioplasty for ST-elevation MIs had similar resultant LVEFs and rates of inducible ventricular tachycardia. There was a surprisingly high rate of spontaneous defibrillator activations, often occurring late after MI.

Comparison of unipolar versus bipolar ablation and single electrode control versus simultaneous multielectrode temperature control.

BACKGROUND: Creation of linear lesions using multielectrode catheters may be effective at treating cardiac arrhythmias. OBJECTIVE: We compared unipolar versus bipolar ablation, evaluated the effects of varying effective electrode areas, and compared single electrode versus multielectrode temperature control during multielectrode radiofrequency ablation. METHODS: Intramural radiofrequency ablation was performed on five greyhounds at thoracotomy, from an epicardial approach using a 0.8 mm diameter bipolar electrode needle. Fifteen left ventricular ablations were performed per animal. Intramural ablation was performed to maintain a constant electrode-tissue interface. The distal and proximal electrodes measured 1.5 and 1.0 mm in length respectively with an interelectrode distance of 4 mm. Radiofrequency energy was applied to both electrodes simultaneously for 60 s using a target temperature of 80 degrees C. During bipolar ablation, the temperature was regulated from either the distal (BPA1.5) or proximal (BPA1.0) electrode only. During unipolar ablation (UPA), the temperature at both electrodes were simultaneously controlled. Lesions were assessed histologically. RESULTS: During UPA, consistent target temperatures were achieved at both electrodes. In comparison to UPA, the temperature at both electrodes were significantly decreased during BPA1.0. During BPA1.5 a significant (p < 0.001) temperature increase (94.7 +/- 2.1 degrees C) was observed at the 1.0 mm electrode. BPA1.0 resulted in reduced (p = 0.008) lesion width at the 1.5 mm electrode and no change in lesion depth (p = 0.064) at both electrodes compared to UPA. Conversely, lesion dimensions increase significantly at both electrodes during BPA1.5. CONCLUSION: Unipolar multielectrode ablation with simultaneous temperature control at both electrodes is more predictable and hence likely to be safer than bipolar ablation.

Change in size of lesions over 3 weeks after radiofrequency ablation of left ventricle.

INTRODUCTION: The initial success or failure of radiofrequency ablation (RFA) does not always reflect the long-term outcome that can lead to complications such as late atrioventricular block or recurrence of accessory pathways. We hypothesize that these occurrences may be due to a change in lesion size over time. METHODS AND RESULTS: Intramural RFAs were performed on five greyhounds at thoracotomy using an epicardial approach into the left ventricular (LV) wall. Twenty-one gauge needle electrode ablations were created in the anterior aspect of the left ventricle. Radiofrequency energy was delivered at 600 Hz for 60 seconds and at an electrode temperature of 90 degrees C. Eight ablations were created in each greyhound and the chest was closed. After 3 weeks, a further eight ablations were created under the same conditions in the lateral aspect of the LV, ensuring they were well away from the chronic lesions, and the dogs were sacrificed an hour later. All lesions were removed, stained with Gomori Trichrome and measured. There was no significant difference in lesion size detected in the 1-hour-old lesions compared with 3-week-old lesions. Acute lesions were well demarcated by an area of fibrous scar and a central necrotic region. Chronic lesions showed chronic inflammatory cells and strands of collagen. CONCLUSIONS: This study shows no change in lesion dimension over time and hence a change in size may not contribute to a change in RFA outcome over time.

Comparison of radiofrequency ablation in normal versus scarred myocardium.

INTRODUCTION: Reentrant circuits causing ventricular tachycardia are closely associated with previously scarred myocardium. The presence of scar has been blamed for the poor success rate of radiofrequency ablation (RFA) in that context. This article investigates the in vivo effects of radiofrequency ablation in myocardium scarred from acute myocardial infarction. METHODS AND RESULTS: Anterior myocardial infarction was induced in five dogs by ligating the left anterior descending artery. The mean left ventricular ejection fraction after infarction was 38%. At a mean of 15 weeks following myocardial infarction, 50 RFA lesions were created in random order, 25 in scarred and 25 in normal myocardium using a needle electrode (21 gauge, 5 mm in length) introduced from the epicardium of the left ventricle at thoracotomy. During unipolar temperature-controlled RFA (90 degrees C for 60 seconds), intramural temperatures were measured by thermistors at distances of 1, 2, 3, 4, and 5 mm from the ablating electrode. The margins of the lesions were clearly discernible in scar at histological examination in 64% of ablations where the scarring was patchy. There were no significant differences between lesion sizes, intramural temperatures at different distances, total energy required for ablation, or mean impedance during ablation of normal versus scarred myocardium. CONCLUSIONS: Scar does not affect lesion size or intramural temperature profile during RFA if electrode size, tissue contact, and tip temperature are controlled. More radiofrequency energy is not required to maintain tip temperature at 90 degrees C in scar compared to normal myocardium.

Automated ventricular substrate mapping--evaluation in an ovine chronic myocardial infarction model.

INTRODUCTION: We hypothesized that automated electrogram analysis might enable rapid localization of ventricular scar. This would allow the delivery of interventions such as radiofrequency ablation or therapeutic agents to critical areas within the scar and scar periphery. METHODS: Substrate mapping was performed on seven sheep 36.5 +/- 32.9 weeks after a left anterior descending artery myocardial infarction had been induced. Contact electrograms and the mapping catheter three-dimensional (3D) location were recorded simultaneously. A computer program was written in-house to automatically identify sinus beats, analyze electrogram characteristics (e.g., electrogram amplitude and minimum slope), and integrate the analysis results into a 3D scar map. RESULTS: The total time required to produce the scar maps was a mean of 8.3 +/- 2.0 minutes. The automated substrate mapping (ASM) system beat detection algorithm had a high sensitivity (i.e., detected 87.4% of the recorded beats) and excellent specificity (only one false activation over 58.2 minutes of total recorded data). The system was able to classify the detected beats ('sinus' or 'ectopic') with high specificity (specificity = 97.3% confidence interval (CI): 96.9-97.7) and moderate sensitivity (sensitivity = 78.3% CI: 77.3%-79.5%). The scar area identified by the ASM system correlated well with the pathologically defined scar area (R2 = 0.87 p < 0.001). CONCLUSIONS: ASM enables accurate scar maps to be produced rapidly. This strategy may play an important role for both clinical and research applications, allowing therapeutic agents and radiofrequency ablation to be delivered to critical locations in and around ventricular scar.

Effect of inter-electrode distance on bipolar intramural radiofrequency ablation.

OBJECTIVES: We aimed at evaluating bipolar radiofrequency ablation by correlating inter-electrode distance (ILD) with lesion dimensions and continuity. BACKGROUND: Previous reports indicated that bipolar radiofrequency (RF) current applied to two adjacent sites in vitro, synergistically increased lesion sizes greater than that observed for unipolar RF current delivery using the same electrodes. METHODS: Ablations were performed intramurally to ensure that each electrode surface (radius = 0.4 mm, area = 3.52 mm(2)) provided consistent contact with the myocardium. Ninety-six ablations were performed in four greyhounds using bipolar ablation needles with ILDs of 1, 2, 3, and 4 mm. An epicardial approach was used to ensure accurate positioning of the needles within the myocardium. Lesions were created using temperature-controlled RF delivery for a duration of 60 seconds to achieve 90 degrees C at the electrode proximal to the needle base. Lesion dimensions were determined histologically. RESULTS: Increasing the ILD, decreased lesion width (P = 0.003) but increased lesion depth (P = 0.001). Lesions remained continuous with ILDs of 1-3 mm but became discontinuous at 4 mm. Energy requirements during ablation increased with increasing ILDs. CONCLUSION: Using the above parameters (electrode radius, RF power delivery, time) during bipolar ablation, lesion continuity was critically dependent on the ILD. The maximum ILD threshold to create contiguous overlapping lesions was 3 mm. Lesions of greater width were created using shorter ILDs. Clinically, greater control over lesion dimensions can be obtained by manipulating the ILD distance.

Cooled needle catheter ablation creates deeper and wider lesions than irrigated tip catheter ablation.

OBJECTIVES: To design and test a catheter that could create deeper ablation lesions. BACKGROUND: Endocardial radiofrequency (RF) ablation is unable to reliably create transmural ventricular lesions. We designed an intramural needle ablation catheter with an internally cooled 1.1-mm diameter straight needle that could be advanced up to 14 mm into the myocardium. The prototype catheter was compared with an irrigated tip ablation catheter. METHODS: Ablation lesions were created under general anesthesia in 14 male sheep (weight 44 +/- 7.3 kg) with fluoroscopic guidance. Each of the catheters was used to create two ablation lesions at randomly allocated positions within the left ventricle. The irrigation rate, target temperature, and maximum power were: 20 mL/min, 85 degrees C, 50 W for the intramural needle catheter and 20 mL/min, 50 degrees C, 50 W for the irrigated tip catheter, respectively. All ablations were performed for 2 minutes. After the last ablation, blue tetrazolium (12.5 mg/kg) was infused intravenously. The heart was removed via a left thoracotomy after monitoring the sheep for one hour. RESULTS: There was no evidence of cardiac tamponade in any sheep. The intramural needle catheter lesions were significantly wider (10.9 +/- 2.8 mm vs 10.1 +/- 2.4 mm, P = 0.01), deeper (9.6 +/- 2.0 mm vs 7.0 +/- 1.3 mm, P = 0.01), and more likely to be transmural (38% vs 0%, P = 0.03). CONCLUSIONS: Cooled intramural needle ablation creates lesions that are significantly deeper and wider than endocardial RF ablation using an irrigated tip catheter in sheep hearts. This technology may be useful in treating ventricular tachycardia resistant to conventional ablation techniques.

Value of noncontact mapping for identifying left ventricular scar in an ovine model.

BACKGROUND: We assessed the hypothesis that "virtual electrograms" from a noncontact mapping system (EnSite 3000) could be used to localize myocardial scar. METHODS AND RESULTS: Myocardial infarctions were induced in sheep by inflating an angioplasty balloon in the left anterior descending coronary artery for 3 hours. Scar mapping was performed on 8 sheep without inducible ventricular tachycardia by use of the noncontact mapping system and a 256-channel contact mapping system. Transmural mapping needles were inserted into myocardial regions that were (1) scarred, (2) peripheral to the scar, and (3) distant from the scar. Unipolar electrograms were exported from both systems and analyzed on a personal computer workstation. The percentage of myocardial scarring at each needle site was assessed histologically. Pearson's correlation was used to assess the degree of association between various electrogram characteristics and the presence of myocardial scarring. The only noncontact electrogram characteristic that showed any association with the presence of myocardial scarring was the negative slope duration (contact, r=0.62, P<0.001; noncontact, r=0.23, P=0.004). The other electrogram characteristics studied were electrogram maximal deflection (contact, r=0.38, P<0.001; noncontact, r=0.03, P=0.75) and minimal slope (contact, r=0.42, P<0.001; noncontact, r=0.05, P=0.54). CONCLUSIONS: Noncontact electrograms do not reliably identify ventricular scar. Alternative strategies such as importing computed tomography images into the geometry should be used when scar localization is important.

Cooled intramural needle catheter ablation creates deeper lesions than irrigated tip catheter ablation.

Endocardial radiofrequency ablation of the left ventricle does not create transmural lesions reliably even with active electrode cooling. The authors developed a prototype catheter with an internally cooled needle electrode that could be advanced an adjustable distance into the myocardium. Freshly excised hearts from eight male sheep were perfused and superfused using oxygenated ovine blood. Ablations were performed for 2 minutes using the prototype catheter and a conventional endocardial 5-mm irrigated tip ablation catheter at target temperatures of 80 degrees C and 50 degrees C, respectively. The prototype catheter needle was inserted 12 mm deep for all ablations. The maximal power and irrigation rate was 50 W, 20 mL/min for the irrigated tip catheter and 20 W, 10 mL/min for the intramural needle catheter. Intramural needle lesions were significantly deeper (13.5 +/- 2.3 vs 9.1 +/- 1.3 mm, P < 0.01) but less wide (8.7 +/- 1.5 vs 12.7 +/- 1.9 mm, P < 0.01) than irrigated tip lesions. Popping occurred during 12 (37%) of the 32 irrigated tip ablations. Popping did not occur during intramural needle ablation. The cooled intramural needle ablation catheter creates lesions that are significantly deeper than irrigated tip catheters with less tissue boiling. In contrast to irrigated tip ablation, electrode temperature monitoring can be used to determine if a lesion has been created during intramural needle ablation. The cooled intramural needle ablation lesions were of a clinically useful width, addressing one of the main recognized deficiencies of intramural needle ablation.

Intramural radiofrequency ablation: effects of electrode temperature and length.

The aim of this study was to evaluate intramural temperature-controlled radiofrequency ablation by determining the intramural temperature profile during ablation and by correlating lesion geometry with intramural electrode size and temperature. Intramural ablation might be useful to create deeper lesions for ventricular tachycardia secondary to underlying heart disease. Intramural radiofrequency ablation was performed in 17 greyhounds at thoracotomy, from an epicardial approach, using a 21-gauge needle electrode. Sixty-eight lesions were created in 11 dogs at electrode temperatures of 70 degrees C, 80 degrees C, 90 degrees C, and 100 degrees C for 60 seconds. Intramural thermocouples at 1-, 2-, 3-, 4-, and 5-mm distances were used to identify simultaneous intramural temperature profile. An epicardial approach was used to ensure accurate positioning of the ablating and temperature monitoring needles within the myocardium with fixed interneedle distances. Ninety-nine radiofrequency ablations were performed in six greyhounds using three different intramural electrode lengths (1 mm, 2.5 mm, and 5.5 mm). Lesions were created at 70 degrees C, 80 degrees C, and 90 degrees C for 60 seconds. All lesions were measured after staining with Gomori Trichrome. Lesion dimensions increased in a highly predictable manner with increasing electrode temperature or length. There was no popping or charring, even with target electrode temperature of 100 degrees C. There was significant correlation between intramural temperature 4 mm from the ablating electrode and lesion width (P < 0.001, R2= 0.45) and depth (P = 0.02, R2= 0.08). Feedback control of electrode temperature enables reliable intramural radiofrequency ablation without impedance rise even with target electrode temperature of 100 degrees C. Increasing the length of the intramural ablating electrode to > or = 5.5 mm and increasing temperatures to 90 degrees C-100 degrees C creates the largest lesions.

Noncontact mapping of the left ventricle: insights from validation with transmural contact mapping.

It is not clear whether the noncontact electrograms obtained using the EnSite system in the left ventricle resemble most closely endocardial, intramural, or epicardial contact electrograms or a summation of transmural electrograms. This study compared unipolar virtual electrograms from the EnSite system with unipolar contact electrograms from transmural plunge needle electrodes using a 256-channel mapping system. The study also evaluated the effects of differing activation sites (endocardial, intramural, or epicardial). A grid of 50-60 plunge needles was positioned in the left ventricles of eight male sheep. Each needle had four electrodes to record from the endocardium, two intramural sites, and the epicardium. Correlations between contact and noncontact electrograms were calculated on 32,242 electrograms. Noncontact electrograms correlated equally well in morphology and accuracy of timing with endocardial (0.88 +/- 0.15), intramural (0.87 +/- 0.15), epicardial (0.88 +/- 0.15), and transmural summation contact electrograms (0.89 +/- 0.14) during sinus rhythm, endocardial pacing, and epicardial pacing. There was a nonlinear relationship between noncontact electrogram accuracy as measured by correlation with the contact electrogram and distance from the multielectrode array (MEA): beyond 40 mm accuracy decreased rapidly. The accuracy of noncontact electrograms also decreased with increasing distance from the equator of the MEA. Virtual electrograms from noncontact mapping of normal left ventricles probably represent a summation of transmural activation. Noncontact mapping has similar accuracy with either endocardial or epicardial sites of origin of electrical activity provided the MEA is within 40 mm of the recording site.

Rapid loading of sotalol or amiodarone for management of recent onset symptomatic atrial fibrillation: a randomized, digoxin-controlled trial.

BACKGROUND: Amiodarone and sotalol are commonly used for the maintenance of sinus rhythm, but the efficacy of these agents administered as high-dose infusions for rapid conversion of atrial fibrillation is unknown. Use in this context would facilitate drug initiation in patients in whom ongoing prophylactic therapy is indicated. METHODS: We assessed the efficacy and safety of rapid high-dose intravenous infusions of amiodarone and sotalol for heart rate control and rapid reversion to sinus rhythm in patients who came to the emergency department with recent-onset symptomatic atrial fibrillation. Patients (n = 140) were randomized to receive 1.5mg/kg of sotalol infused in 10 minutes, 10mg/kg of amiodarone in 30 minutes, or 500 microg of digoxin in 20 minutes. Electrical cardioversion was attempted for patients not converting to sinus rhythm within 12 hours. RESULTS: The rapid infusion of sotalol or amiodarone resulted in more rapid rate control than digoxin. Each of the 3 trial strategies resulted in similar rates of pharmacological conversion to sinus rhythm (amiodarone, 51%; sotalol, 44%; digoxin, 50%; P = not significant). The overall rates of cardioversion after trial drug infusion and defibrillation were high for all groups (amiodarone, 94%; sotalol, 95%,; digoxin, 98%; P = not significant), but there was a trend toward a higher incidence of serious adverse reactions in the amiodarone group. CONCLUSION: The rapid infusion of sotalol or amiodarone in patients with symptomatic recent-onset atrial fibrillation results in rapid control of ventricular rate. Even with high-dose rapid infusions, all 3 agents are associated with a poor overall reversion rate within 12 hours. Almost all patients were returned to sinus rhythm with a combination of pharmacological therapy and electrical cardioversion.

Effects of simultaneous insertion of 66 plunge needle electrodes on myocardial activation, function, and structure.

Transmural recordings using plunge needle electrodes are useful in mapping ventricular tachyarrhythmia, but they interfere with activation sequences or damage the myocardium. This study evaluated the effects of insertion of 66 transmural needles on myocardial activation, structure, and function. Epicardial maps were performed at thoracotomy using a 40-electrode plaque in five mongrel dogs. Sixty-six transmural plunge needles were introduced into the anterior aspect of the septum and left ventricle. Transmural maps of unipolar electrograms were recorded every 15 minutes via 124 electrodes over a 2-hour period. Epicardial maps were repeated after the needles were removed. All recordings were performed during sinus rhythm and ventricular pacing at 300- and 200-ms cycle lengths. Gated heart pool studies were performed preoperatively and 2 weeks after thoracotomy. Programmed ventricular stimulation was performed 2 weeks after thoracotomy. In total, 15,996 electrograms were analyzed. Maximum negative dV/dt of each electrogram and the activation time at each electrode did not change significantly over the 2 hours of needle insertion. After removal of the needles, epicardial maps were unchanged compared to before needle insertion. Mean left ventricular ejection fraction 2 weeks after needle insertion was 59% versus 58% before needle insertion (P=0.9). No dogs had inducible ventricular tachycardia. Histology showed contraction bands of 0.8-mm diameter adjacent to the needle tracks but no scarring. Insertion of 66 closely spaced plunge needles did not distort epicardial or transmural maps. Multiple needles did not result in myocardial scarring, left ventricular dysfunction, or predispose to ventricular tachycardia.

Comparison of epicardial and endocardial linear ablation using handheld probes.

BACKGROUND: The optimal technique for producing linear radiofrequency thermal lesions in myocardial tissue is unclear. We compared epicardial ablation on the beating heart with endocardial ablation after cardioplegia. METHODS: Radiofrequency lesions were produced using a multielectrode malleable handheld probe in ovine myocardium with three wall thicknesses. Detailed analysis of lesion dimensions was used to assess the effects of site of ablation, muscle thickness, and duration of ablation. RESULTS: After epicardial atrial ablation, myocardial lesions were detected in all sections without macroscopically visible epicardial fat (n = 10), but only 43% (6/14) of sections with epicardial fat. Three of 24 atrial epicardial sections (13%) and 92% (23/25) of endocardial atrial lesion sections were clearly transmural. In thicker tissues lesion depth was independent of endocardial (right ventricle: 3.9 +/- 1.1 mm, left ventricle: 3.8 +/- 0.7 mm) or epicardial (right ventricle: 3.4 +/- 0.6 mm, left ventricle: 4.3 +/- 0.9 mm) ablation site. Epicardial lesions are less deep in thinner areas of myocardium (p = 0.003). Lesions were all wider than they were deep. There was no significant increase in lesion depth with the increase in ablation duration from 1 to 2 minutes. CONCLUSIONS: Lesions were unlikely to be transmural with either technique when the wall thickness was greater than about 4 mm. Epicardial fat has an important negative effect on epicardial lesion formation. Where epicardial fat is absent epicardially produced lesions penetrate less deeply when the wall thickness is small, possibly due to endocardial cooling by circulating blood. Prolongation of the duration of ablation from 1 to 2 minutes does not significantly increase lesion depth.