Epicardial Electrodes Research Articles

Biventricular Endocardial Pacing Is Superior to Triventricular Epicardial Pacing in an Ischemic Canine Heart Failure Model

Introduction: Left ventricular (LV) endocardial (Endo) and triventricular (TriV) epicardial (Epi) pacing have been proposed as an alternatives to biventricular (BiV) pacing for cardiac resynchronization therapy (CRT) but it is unknown which is approach is superior. We determined which approach most improved hemodynamics in ischemic canines with heart failure. Methods: The left bundle branch was ablated in 7 canines and epicardial electrodes were placed at 4 sites. Multiple microemoblizations were performed until LV ejection fraction reduced to less than 35%. A right atrial (RA) and right ventricular (RV) were implanted. An atrial transseptal Endo lead was placed at the 4 sites. LV dP/dtmax was measured during BiV Endo, BiV Epi and TriV Epi at 3 AV delays. Percent change from RA pacing was calculated and the greatest improvement with each approach was compared with repeated measures ANOVA. Results: BiV Endo pacing increased dP/dtmax more than BiV Epi and TriV Epi pacing (26.1±11.6% vs. 20.7±10.5% and 22.7±9.2%, p<.05). There was no significant difference between BiV Epi and TriV Epi pacing. Conclusion: BiV Endo pacing was superior to BiV Epi and TriV Epi pacing. BiV Endo pacing is a promising approach to improve CRT and does not require additional leads. Further exploration of Endo pacing in humans is warranted.

Spinal Cord Stimulation Causes Potentiation of Right Vagus Nerve Effects on Atrial Chronotropic Function and Repolarization in Canines

Experimental evidence suggests that spinal cord stimulation (SCS) can cause augmentation of parasympathetic influences on the heart via enhanced vagus nerve (VgN) activity. Herein, we investigated whether this might lead to enhanced inducibility of vagally mediated atrial tachyarrhythmias (AT) and whether such actions depend on intact autonomic neural connections with central neurons. Epidural SCS electrodes were implanted at T1-T4 in anesthetized canines. Sinus cycle length prolongation, atrial repolarization changes (191 epicardial electrode sites), and AT inducibility in response to right VgN stimuli applied at the cervical level were determined before and during SCS. VgN-induced sinus cycle length prolongation was potentiated during SCS among the animals with intact neural connections or bilateral vagotomy proximal to the stimulation site, whereas such prolongation was unaffected by SCS among animals with bilateral decentralization of stellate ganglia. Likewise, the atrial surface area in which VgN-induced repolarization wave form changes were identified was significantly augmented during SCS among the former but not among the latter. AT facilitation occurred during SCS in the majority of animals with intact neural connections, particularly among those displaying relatively greater potentiation of vagally mediated sinus cycle length prolongation. The data indicate that SCS may cause potentiation of parasympathetic influences on the atria in response to cervical VgN stimulation. Such SCS effects appear to be mediated via decreased tonic inhibitory sympathetic influences in the presence of intact stellate ganglion connections to central neurons.

Cardiac resynchronization therapy for management of congestive heart failure after repair of tetralogy of Fallot in an elderly patient

A 65-year-old woman underwent total correction of tetralogy of Fallot with closure of ventricular septal defect, right ventricular outflow patch, pulmonary valve replacement and tricuspid valve repair. Pacemaker implantation using epicardial electrodes was simultaneously needed because she had complete atrioventricular block. The postoperative course was excellent. Eighteen months postoperatively, she was admitted with severe congestive heart failure and frequent ventricular arrhythmia. Echocardiography and cardiac catheterization revealed depressed left ventricular function caused by conduction delay. Cardiac resynchronization therapy with a defibrillation system was effective for improvement of left ventricular function. Ventricular contractility rapidly recovered to normal, and the patient has been asymptomatic for two years since implantation.

The role of cardiovascular magnetic resonance imaging in cardiac resynchronisation therapy

Abstract Cardiac electromechanical resynchronisation therapy (CRT) is an effective non-pharmacological treatment of patients suffering from drug refractory heart failure. However, approximately 20–30% of patients are non-responder. Cardiac magnetic resonance imaging (CMR) may play significant role in clarifying many questions in this patient population. Forty-five patients, suffering from severe drug refractory heart failure, underwent CMR before applying CRT. Left ventricular end-diastolic, end-systolic volumes, ejection fraction, myocardial mass, wall motion disturbances, localisation of non-viable myocardium were determined. Left ventricular dyssynchrony was determined by illustrating wall-time thickening in short-axis slices of left ventricle from basis to apex. CMR-proved underlying heart disease were postinfarction heart failure, dilated cardiomyopathy and non-compaction cardiomyopathy in 62, 27 and in 11%, respectively. Mean left ventricular ejection fraction was 24.5±10%, intraventricular dyssynchrony was 200±78 ms. In four patients, requiring surgical revascularisation after unsuccessful coronary sinus electrode implantation, optimal position for epicardial screw-in electrode was selected. According to the results of CMR, biventricular device was not implanted in 7 patients. During the follow-up of the 38 patients, 5 patients (13.16%) were non-responders, despite the approximately 22% non-responder ratio in our whole patient population treated by CRT but without performing previous CMR examination. In this patient population CMR may have a significant role in the selection of responder patient population.

Abstract 2667: Effects of Ranolazine in a Goat Model of Lone Atrial Fibrillation

BACKGROUND: In MERLIN TIMI-36, ranolazine (RAN) reduced the indicidence of new onset AF ( Scirica et al, Circ 2007 ; 116 : 1647 ). At therapeutic concentrations, RAN inhibits the persistent sodium current. At higher concentrations, RAN also inhibits IKs, IKr and late ICaL. We investigated the effects RAN on cardiac electrophysiology in a goat model of AF. In this model, AF itself leads to a progressive shortening of the effective refractory period (ERP) and a gradual increase in AF stability. METHODS: Arrays of atrial epicardial electrodes were implanted in 7 Dutch milk goats. After recovery, experiments were performed at baseline and after 2 and 14 days of artificially maintained AF. At these time points, RAN was infused intravenously for 1 hour to result in plasma concentrations of 4, 8 and 16 uM. ECG parameters, ERP, conduction velocity (CV), AF cycle length (AFCL) and AF episode duration (AFdur) were determined. RESULTS: The main parameters are summarized in the table . At baseline and after 2 days of AF, 8 and 16 uM RAN significantly prolonged the PQ and RR intervals. After 2 days of AF, 8 and 16 uM RAN also significantly prolonged the QT interval and shortened the AFdur. After 14 days of AF, all goats were in persistent AF. At this time, 8 and 16 uM RAN significantly prolonged the AFCL, from 103±3 during solvent infusion to 109±3, 119±5* and 139±9* at 4, 8 and 16 uM RAN, respectively. However, only one out of 7 goats cardioverted during infusion of 16 uM RAN. CONCLUSION: The lowest concentration of ranolazine tested here, which mainly inhibits the late sodium current, did not significantly affect the atrial electrophysiological parameters assessed in this study. Higher doses of ranolazine significantly reduced CV, prolonged ERP and AFCL, and shortened AF episode duration. In the goat model of AF the antiarrhythmic effect appears to be due to action potential prolongation rather than due to late sodium current blockade.

Frequency Analysis of Atrial Electrograms Identifies Conduction Pathways from the Left to the Right Atrium During Atrial Fibrillation—Studies in Two Canine Models

Studies of atrial fibrillation (AF) have demonstrated that a stable rhythm of very short cycle length in the left atrium (LA) can cause fibrillatory conduction in the rest of the atria. We tested the hypothesis that fast Fourier transform (FFT) analysis of atrial electrograms (AEGs) during this AF will rapidly and reliably identify LA-to-right atrium (RA) conduction pathway(s) generated by the driver. During induced atrial tachyarrhythmias in the canine sterile pericarditis and rapid ventricular pacing-induced congestive heart failure models, 380-404 AEGs were recorded simultaneously from epicardial electrodes on both atria. FFT analysis of AEGs during AF demonstrated a dominant frequency peak in the LA (driver), and multiple frequency peaks in parts of the LA and the most of the RA. Conduction pathways from the LA driver to the RA varied from study-to-study. They were identified by the presence of multiple frequency peaks with one of the frequency peaks at the same frequency as the driver, and traveled (1) inferior to the inferior vena cava (IVC); (2) between the superior vena cava and the right superior pulmonary vein (RSPV); (3) between the RSPV and the right inferior pulmonary vein (RIPV); (4) between the RIPV and the IVC; and (5) via Bachmann's bundle. Conduction pathways identified by FFT analysis corresponded to the conduction pathways found in classical sequence of activation mapping. Computation time for FFT analysis for each AF episode took less than 5 minutes. FFT analysis allowed rapid and reliable detection of the LA-to-RA conduction pathways in AF generated by a stable and rapid LA driver.

Association of electrostimulation with cell transplantation in ischemic heart disease

Until now, cell therapy has constituted a passive therapeutic approach; the only effects seem to be related to the reduction of the myocardial fibrosis and the limitation of the adverse ventricular remodeling. Cardiac resynchronization therapy is indicated in patients with heart failure to correct conduction disorders associated with chronic systolic and diastolic dysfunction. The association of electrostimulation with cellular cardiomyoplasty could be a way to transform passive cell therapy into "dynamic cellular support." Electrostimulation of ventricles following skeletal myoblast implantation should induce the contraction of the transplanted cells and a higher expression of slow myosin, which is better adapted for chronic ventricular assistance. The purpose of this study is to evaluate myogenic cell transplantation in an ischemic heart model associated with cardiac resynchronization therapy. Twenty two sheep were included. All animals underwent myocardial infarction by ligation of 2 coronary artery branches (distal left anterior descending artery and D2). After 4 weeks, autologous cultured myoblasts were injected in the infarcted areas with or without pacemaker implantation. Atrial synchronized biventricular pacing was performed using epicardial electrodes. Echocardiography was performed at 4 weeks (baseline) and 12 weeks after infarction. Echocardiography showed a significant improvement in ejection fraction and limitation of left ventricular dilatation in cell therapy with cardiac resynchronization therapy as compared with the other groups. Viable cells were identified in the infarcted areas. Differentiation of myoblasts into myotubes and enhanced expression of slow myosin heavy chain was observed in the electrostimulated group. Transplantation of cells with cardiac resynchronization therapy caused an increase in diastolic wall thickening in the infarcted zone relative to cells-only group and cardiac resynchronization therapy-only group. Biventricular pacing seems to induce synchronous contraction of transplanted myoblasts and the host myocardium, thus improving ventricular function. Electrostimulation was related with enhanced expression of slow myosin and the organization of myoblasts in myotubes, which are better adapted at performing cardiac work. Patients with heart failure presenting myocardial infarct scars and indication for cardiac resynchronization therapy might benefit from simultaneous cardiac pacing and cell therapy.

Novel catheter guidance technique to the site of origin of the arrhythmia

The purpose of this study was to evaluate the accuracy of our catheter guidance system using Single Equivalent Moving Dipole (SEMD) method to guide the tip of the cardiac ablation catheter to the site of origin of the arrhythmia. 3 different patterns of 8 bipolar electrodes were sutured on the right ventricular myocardium of 3 swine through a standard thoracotomy. Electrode cables passed subcutaneously to a ventral interscapular position were exteriorized, fixed by stay sutures, and the chest closed in layers. The animals' heart rate, pulse oximetry, femoral artery blood pressure, and body temperature were continuously monitored. As the epicardial electrodes connected to a stimulator delivered pacing spikes simulating focal ventricular tachycardia at a rate of 120 bpm, the BioSemi ActiveTwo system at a frequency of 1Khz with a symmetrically patterned array of 64 electrodes placed on the chest measured body surface potentials. A paralytic drug was used to reduce error in cardiac mapping by minimizing muscular activity and allowing for full respirator control of breathing. Both simulation and real catheter's movements were well detected (R=0.95) and the final localization error of a simulation catheter to a pre‐defined target was less than 1 cm in imaginary space, which is equal to 0.4 cm in real space. These data support the validity of SEMD method for localizing the origin of arrhythmia in swine model.

Postoperative junctional ectopic tachycardia

MOT CLE Tachycardie jonctionnelle ectopique A 3-month-old boy underwent surgery for correction of a ventricular septal defect. Three hours after the intervention the patient developed a regular narrow QRS complex tachycardia (Fig. 1) with a ventricular rate (V) of 195 bpm and slower, regular atrial activity (A) at 150 bpm. The QRS configuration was similar to previous sinus beats. An atrial electrocardiogram recorded by a postoperative temporary atrial epicardial electrode (lead I) clearly demonstrated dissociation between atrial activity (arrows) and ventricular activity (asterisks), leading to the diagnosis of postoperative junctional ectopic tachycardia (JET). The patient was treated with moderate hypothermia and atrial overdrive pacing. The QRS morphology of the paced beats was similar to that observed during the tachycardia. As expected, atrial pacing did not terminate the arrhythmia; however, the haemodynamic status of the patient improved and he recovered sinus rhythm 89 hours after the onset of tachycardia. The patient’s subsequent postoperative course was uneventful, and he has remained free of new arrhythmic events after five years of follow-up. Rapid (> 170 bpm) postoperative JET has been reported after 1% of congenital heart repairs. Its aetiology is thought to be related to mechanical irritation of the proximal conduction system during surgery. Despite being a transient phenomenon, postoperative JET may lead to serious haemodynamic compromise due to elevated heart rate and loss of atrioventricular synchrony. Electrocardiographic features include QRS configuration similar to conducted sinus or atrial paced beats, along with either atrioventricular dissociation with ventricular rate faster than the atrial rate or retrograde conduction. This arrhythmia does not respond to electrical cardioversion, atrial overdrive pacing or intravenous adenosine, and the efficacy of antiarrhythmic drugs is usually

Is there a significant transmural gradient in repolarization time in the intact heart?

Is there a significant transmural gradient in repolarization time in the intact heart?

Stenotrophomonas maltophilia pacemaker endocarditis in a patient with d-transposition of the great arteries after atrial switch procedure

We report a case of pacemaker endocarditis due to Stenotrophomonas maltophilia in a 22-year-old Caucasian man with d-transposition of the great arteries after atrial switch procedure. S.maltophilia isolated from blood cultures was susceptible to trimethoprim-sulfamethoxazole and amikacin, and resistant to ciprofloxacin and all tested β-lactam antibiotics. The infected pacemaker system was completely removed by thoracotomy. Simultaneously, a new DDD pacemaker and epicardial electrodes were successfully implanted and selective antibiotic therapy consisting of trimethoprim-sulfamethoxazole (480mg i.v. q 6h) and amikacin (250mg i.v. twice daily) was continued. However, the post-operative course was complicated by septic shock and the patient died on 9th day after surgery. Importantly, S.maltophilia isolated from extracted pacemaker leads was multidrug-resistant including to trimethoprim-sulfamethoxazole, ciprofloxacin, all tested aminoglycosides, and β-lactams, with the exception of ticarcillin-clavulanate. In conclusion, pacemaker endocarditis due to Stenotrophomonas maltophilia is an extremely rare but serious complication of permanent pacing therapy. The susceptibility of S.maltophilia isolates to antimicrobial agents can change during the course of infection. Despite the inherent resistance of S.maltophilia to most β-lactam antibiotics, multidrug-resistant strains may be susceptible in vitro to ticarcillin-clavulanate. Further studies are needed to determine the optimal management of patients with pacemaker endocarditis caused by Stenotrophomonas maltophilia.

Permanent biventricular ICD-implantation in a heart failure second re-do-CABG patient: a case report

Biventricular pacing has been suggested in end-stage heart failure. We present a 59-year-old patient undergoing second re-do CABG (coronary artery bypass graft) and carotid artery endarterectomy. Ejection fraction was 15%, QRS-width 175 ms. Following the carotid and CABG procedure, an implanted single-chamber ICD (implantable cardioverter defibrillator) was upgraded to permanent biventricular DDD pacing by implantation of one epicardial left ventricular and one epicardial atrial electrode. At follow-up two months postoperatively ejection fraction had significantly improved to 45%, the patient underwent stress test with adequate load and reported a good quality of life.

Abstract 4098: Epicardial Amiodarone-Releasing Hydrogel Reduces Inducibility of Atrial Fibrillation in Goats

Amiodarone (AM) is one of the most effective anti-arrhythmic drugs to prevent postoperative atrial fibrillation (AF). However, due to systemic side effects, prophylactic AM therapy is only appropriate for patients at high risk for postoperative AF. This study addressed the hypothesis that local epicardial delivery of AM produces therapeutic myocardial drug concentrations, while systemic levels remain low. Goats (n=14) were instrumented with right atrial epicardial patch electrodes, and a PEG-based hydrogel with AM (1 mg/kg bw) (n=9) or without drug (n=5) was applied to the right atrial epicardium. AF inducibility was assessed up to 28 days in awake goats by applying burst stimuli. Myocardial and plasma AM concentrations were analysed by HPLC. AM-hydrogel produced higher subepicardial than subendocardial drug concentrations, which both remained therapeutic up to 21 days after hydrogel application (fig. 1a ). In this period, AF inducibility was significantly lower in the AM-hydrogel group compared to hydrogel alone (fig. 1b ; p&lt;0.05). Plasma AM and metabolite levels were below detection limits (&lt;30 ng/L) during the 28-day follow-up. Epicardial AM-releasing hydrogel produces sufficient myocardial drug concentrations to reduce AF inducibility up to 3 weeks, whereas plasma drug levels remain undetectably low. This study demonstrates that local delivery of anti-arrhythmic drugs is a feasible approach to obtain therapeutically effective myocardial drug concentrations, while minimizing risk for systemic side effects. Locally applied AM-releasing hydrogel may be a novel strategy to prevent postoperative AF. Figure 1a. Amiodarone Distribution in Right Atrium (n=5) Figure 1b. AF Inducibility After Hydrogel Application (mean + SD)

Cardiac strangulation: a rare, but devastating complication of epicardial pacing causing progressive myocardial ischaemia

A female infant with a history of prematurity (gestational age: 29 weeks) and congenital complete heart block caused by maternal lupus erythematodes underwent implantation of epicardial VVI pacemaker at the age of 3 months followed by surgical closure of an atrial septal defect, implantation of an atrial epicardial electrode, …

A hybrid form of cardiac resynchronisation therapy in patients with failing systemic right ventricles

Late systemic right ventricular (RV) dysfunction after atrial redirection surgery is common. Patients may require cardiac transplantation in early adulthood. We undertook cardiac resynchronisation (CRT)/defibrillator therapy in two patients as a bridge to transplantation. Two males (aged 24, 110 kg and 26 years, 106 kg); having undergone a Mustard procedure for dextro-transposition of the great arteries at 7 and 6 months of age respectively, presented with impaired systemic RV function and New York Heart Association III symptoms. Both patients had dual chamber pacemakers in-situ for sinus bradycardia. Upgrade to CRT was performed by conserving the existing endocardial leads and placement of epicardial electrodes. One demonstrated sustained improvement over a 24 month follow-up period. A hybrid CRT strategy is feasible in patients with failing systemic RVs and pre-existent endocardial dual chamber pacemakers. Appropriate patient selection criteria and optimum lead placement, however, still needs further evaluation in this population.

Rescue peri-operative management of the patient with giant electrical storm and severe left ventricular dysfunction: support by levosimendan and intraaortic balloon counterpulsation☆

We present a case of a 62-year-old male patient (coronary heart disease, and stenosis of aortic valve) with severe left ventricular dysfunction (left ventricular ejection fraction 20%, left ventricular end-diastolic diameter 80 mm, end-diastolic volume 329 ml) who developed giant electrical storm (on the whole 115 episodes of pulseless ventricular tachycardia treated by antiarrhythmics and electrical discharges) with low-elevation of cardiac biomarkers. The patient was referred to emergent cardiac surgery (double coronary bypass grafting, aortic valve replacement, and implantation of left ventricular epicardial electrode). Levosimendan and intraaortic balloon counterpulsation were used for successful weaning from the cardiopulmonary bypass; no other arrhythmia appeared in the post-bypass period. Postoperatively no arrhythmic events were detected, and repeated echocardiographic examinations of the patient in good general condition showed gradual improvement of left ventricular ejection fraction (30-35%), likewise in other parameters (left ventricular end-diastolic diameter 72 mm, end-diastolic volume 285 ml).

Padronização da técnica para cirurgia cardíaca videoassistida: experiência inicial

Minimally invasive cardiac surgery has been performed in major worldwide centers, including procedure such as valves, coronary and congenital surgery. To demonstrate our first works with noninvasive cardiac surgery by mean of the experience gained with general and thoracic surgery. Whenever possible to carry out a minimally invasive cardiac surgery, this was the approach of choice. The left thoracoscopy was used in four cases: (1) symptomatic coronary-pulmonary fistula ligation; (2) implant of an epicardial electrode into the left ventricle for resynchronization; (3) excision of pericardial giant lipoma in the left atrium, and (4) resection of hemangiolipoma in the mediastinum. Right thoracoscopy with extracorporeal circulation through cardiopulmonary bypass via femoral vein and artery and cardiac arrest in ventricular fibrillation with moderate hypothermia were carried out in the following cases: (5) patient with mitral stenosis after surgical repair with Carpentier ring 12 years before. An anterior and posterior commissurotomy without thoracotomy was successfully made; (6) patient with idiopathic dilated cardiomyopathy, high-response atrial fibrillation, and severe mitral insufficiency, underwent mitral repair surgery with Gregori's ring and ablation of the pulmonary veins with radio-frequency catheter. (MAZZE modified). No death occurred in this series and the surgical result in all cases was highly satisfactory. All patients were discharged from hospital with a mean time of 5.5 +/- 5 days after intervention. Our initial experience in this field proves the effectiveness and the viability in introducing this type of technique.

Epicardial and intramural excitation during ventricular pacing: effect of myocardial structure

Published studies show that ventricular pacing in canine hearts produces three distinct patterns of epicardial excitation: elliptical isochrones near an epicardial pacing site, with asymmetric bulges; areas with high propagation velocity, up to 2 or 3 m/s and numerous breakthrough sites; and lower velocity areas (<1 m/s), where excitation moves across the epicardial projection of the septum. With increasing pacing depth, the magnitude of epicardial potential maxima becomes asymmetric. The electrophysiological mechanisms that generate the distinct patterns have not been fully elucidated. In this study, we investigated those mechanisms experimentally. Under pentobarbital anesthesia, epicardial and intramural excitation isochrone and potential maps have been recorded from 22 exposed or isolated dog hearts, by means of epicardial electrode arrays and transmural plunge electrodes. In five experiments, a ventricular cavity was perfused with diluted Lugol solution. The epicardial bulges result from electrotonic attraction from the helically shaped subepicardial portions of the wave front. The high-velocity patterns and the associated multiple breakthroughs are due to involvement of the Purkinje network. The low velocity at the septum crossing is due to the missing Purkinje involvement in that area. The asymmetric magnitude of the epicardial potential maxima and the shift of the breakthrough sites provoked by deep stimulation are a consequence of the epi-endocardial obliqueness of the intramural fibers. These results improve our understanding of intramural and epicardial propagation during premature ventricular contractions and paced beats. This can be useful for interpreting epicardial maps recorded at surgery or inversely computed from body surface ECGs.

8 October 1958, D Day for the implantable pacemaker

After the introduction of temporary transcutaneous cardiac pacing by Paul Zoll in 1952, and of the temporary endocardial approach by Seymour Furman in the USA in 1958, the first definitive electronic pacemaker was implanted by Senning and Elmqvist in Sweden on 8 October 1958 using a thoracotomy to suture two epicardial electrodes. Actually, the ‘definitive’ unit placed in the abdominal wall of the pacemaker recipient, Arne Larsson, fired for only three hours. The first replacement, done the following morning, was followed by more than 22 units and numerous surgical interventions until Mr Larsson died in 2001.

Changes in the Spectral Characteristics of Ventricular Fibrillation in Lesions Produced by Radiofrequency Ablation. An Experimental Study

Although electro- physiological databases contain information about changes in the time domain in lesions produced by radiofrequency ablation, very few data on changes in the frequency domain are available. The aim of this study was to investigate changes in the spectral characteristics of ventricular fibrillation in zones with radiofrequency lesions. Recordings of ventricular fibrillation were obtained in 11 isolated perfused rabbit heart preparations using a multiple epicardial electrode located on the left ventricular free wall. Spectral parameters derived by Fourier analysis before and after the creation of transmural radiofrequency lesions were compared. In the ablated zones, significant reductions were observed in the spectral density of the dominant (0.168+/-0.113 mV(2)/Hz vs 0.025+/-0.018 mV(2)/Hz; P< .001) and mean frequencies (0.053+/-0.057 mV(2)/Hz vs 0.012+/-0.016 mV(2)/Hz; P< .001), the normalized energy around the dominant frequency (0.860+/-0.570 vs 0.128+/-0.091; P< .001), and the standard deviation of the power spectrum (0.031+/-0.020 mV(2)/Hz vs 0.004+/-0.001 mV(2)/Hz; P< .001). There was no significant change in the dominant (16.2+/-5.6 vs 14.8+/-1.8 Hz) or mean frequency (17.7+/-3.4 vs 16.6+/-1.3 Hz). The spectral parameters that could be used in a multivariate model to identify the lesion were the standard deviation of the power spectrum and the spectral density of the mean frequency. During ventricular fibrillation, the spectral parameters associated with spectral power and spectral energy were significantly altered in zones with radiofrequency lesions and could be used to identify those zones. There was no significant change in either the dominant or mean frequency in these zones.