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Epicardial adipose tissue is present in normal healthy individuals. It is a unique fat depot that, under physiologic conditions, plays a cardioprotective role. However, excess epicardial adipose tissue has been shown to be associated with prevalence and severity of atrial fibrillation. In arrhythmogenic right ventricular cardiomyopathy and myotonic dystrophy, fibrofatty infiltration of the myocardium is associated with ventricular arrhythmias. In the ovine model of ischemic cardiomyopathy, the presence of intramyocardial adipose or lipomatous metaplasia has been associated with increased propensity to ventricular tachycardia. These observations suggest a role of adipose tissue in the pathogenesis of cardiac arrhythmias. In this article, we review the role of cardiac adipose tissue in various cardiac arrhythmias and discuss the possible pathophysiologic mechanisms. [ABSTRACT FROM AUTHOR]

Purpose: Unipolar (UE) and bipolar electrograms (BE) are utilized to identify arrhythmogenic substrate. We quantified the effect of increasing distance from the source of propagation on local electrogram amplitude; and determined if transmural electrophysiological gradients exist with respect to propagation and stimulation depth. Methods: Mapping was performed on 5 sheep. Deployment of >50 quadripolar transmural needles in the LV were located in Cartesian space using Ensite. Contact electrograms from all needles were recorded during multisite bipolar pacing from epicardial then endocardial electrodes. Analysis was performed to determine stimulus distance to local activation time, peak negative amplitude (V-P), and peak-peak amplitude (VP-P) for (1) unfiltered UE, and (2) unfiltered and 30 Hz high-pass filtered BEs. Each sheep was analysed using repeated ANOVA. Results: Increasing distance from the pacing sites led to significant (p<0.01) attenuation of UEs (V-P = 7.0±0.5%; VP-P = 5.4±0.3% per cm). Attenuation of BE with distance was insignificant (Vp-p unfiltered  = 2.2±0.5%; filtered  = 1.7±1.4% per cm). Independent of pacing depth, significant (p<0.01) transmural electrophysiological gradients were observed, with highest amplitude occurring at epicardial layers for UE and endocardial layers for BE. Furthermore, during pacing, propagation was earlier at the epicardium than endocardial layer by 1.6±2.0 ms (UE) and 1.4±2.8 ms (BE) (all p>0.01) during endocardial stimulation, and 2.3±2.4 ms (UE) and 1.8±3.7 ms (BE) during epicardal stimulation (all p<0.01). Conclusions: Electrogram amplitude is inversely proportional to propagation distance for unipolar modalities only, which affected V-P>VP-P. Conduction propagates preferentially via the epicardium during stimulation and is believed to contribute to a transmural amplitude gradient. [ABSTRACT FROM AUTHOR]

Background: Organized atrial tachycardias (OATs) after pulmonary vein isolation (PVI) procedure are common. Arrhythmia mechanisms include mitral annular, ring gap, or roof-dependent gap-related flutters. In this series, we describe a mechanism of arrhythmia utilizing the ridge between left pulmonary vein (PV) and left atrial appendage (LAA) in the Ligament of Marshall (LOM) region. Methods and Results: Five tachycardias involving the LOM region were identified from a group of 240 patients who underwent a single ring PVI procedure for symptomatic atrial fibrillation. The common characteristics of these tachycardias were the endocardial breakout over a broad area adjacent to the LOM region, presence of presystolic or mid-diastolic potentials, and abolition by ablation of the presystolic or mid-diastolic potentials remote from the endocardial breakout site. In all five cases, tachycardias were present after isolation of the veins and posterior left atria. All demonstrated characteristic areas of very slow conduction in the LOM region highlighted by presence of either low voltage, long duration fractionated potentials, or mid-diastolic potentials with a fixed temporal relationship to the subsequent endocardial activation. The pattern of activation and termination of tachycardia during ablation was consistent with an arrhythmia utilizing an electrically insulated tract within LOM and the PV-LAA ridge region. Conclusions: We identified a pattern of arrhythmias involving a concealed presystolic component and a broad endocardial breakout site related to the LOM region. Successful ablation site involved careful identification of small diastolic potentials in the LAA/ridge region or adjacent to the coronary sinus. [ABSTRACT FROM AUTHOR]

Background: The prognostic significance of a second programmed ventricular stimulation (PVS) at electrophysiology study (EPS), when the first PVS is negative for inducible ventricular tachycardia (VT), in patients following myocardial infarction (MI) is unknown. Methods: Consecutive ST-elevation MI patients with left ventricular ejection fraction ⩽40% following revascularization underwent early EPS. An implantable cardioverter defibrillator (ICD) was implanted for a positive (inducible monomorphic VT) but not a negative (no arrhythmia or inducible ventricular fibrillation [VF]/flutter) EPS. The combined primary end point of death or arrhythmia (sudden death, resuscitated cardiac arrest, and spontaneous VT/VF) was assessed in EPS-positive patients grouped according to if VT was induced on the first PVS application, or the second PVS application, when the first was negative. Results: EPS performed a median 8 days post-MI in 290 patients was negative in 70% (n = 203) and positive in 30% (n = 87). In patients with a positive EPS, VT was induced on the first PVS in 67% (n = 58) and the second PVS, after the first was negative, in 33% (n = 29). Predischarge ICD was implanted in 79 of 87 patients with a positive EPS. Three-year primary end point occurred in 20.9 ± 5.6% and 38.3 ± 9.7% of patients with VT induced by the first and second PVS, respectively (P = 0.042) and in 6.3 ± 1.9% of electrophysiology-negative patients (P < 0.001). Conclusions: In patients with post-MI left ventricular dysfunction, VT can be induced in a significant proportion with a second PVS when negative on the first. These patients have a similar higher risk of death or arrhythmia compared to patients with VT induced on the first PVS. [ABSTRACT FROM AUTHOR]

The article presents a study on the accuracy of electroanatomic contact (CARTO) and noncontact (EnSite) systems at scar mapping in a chronic ovine model with intramural plunge needle electrode recording and histological validation. The results of the study showed that both the CARTO contact and EnSite noncontact systems were moderately accurate in identifying postinfarct scar when compared with intramural electrodes and confirmed with histology.

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. [ABSTRACT FROM AUTHOR]

Evaluation of a Thermochromic Dispersive Electrode . Introduction: Burns at the dispersive electrode are serious complications of diathermy and radiofrequency (RF) ablation procedures. We aimed to create a new methodology to reduce the incidence of dispersive electrode related skin burns. We hypothesized that a dispersive electrode incorporating a thermochromic liquid crystal (TLC) layer could accurately measure underlying skin temperatures and help prevent burns. Methods and Results: The TLC electrode was compared with a standard dispersive electrode in 12 male sheep. RF current was delivered with the dispersive electrode fully applied or partially detached to simulate different clinical scenarios. The temperature of the TLC layer, calculated from the hue (color) every 15 seconds, was compared with fluoroptic skin temperature probes. TLC electrodes with a temperature range of 45–58°C were used in six sheep to assess the correlation of TLC temperature distribution with skin temperature and burns. TLC electrodes with a temperature range of 40–50°C were used in another 6 sheep to simulate clinical conditions in which the ablation was stopped if the TLC temperature was >42°C. The TLC measured temperatures correlated well with fluoroptic probes at the skin surface (r = 0.94 ± 0.05, mean of the absolute difference in temperature difference 0.9 ± 0.58°C). Ablations with partial application of standard dispersive electrodes consistently caused skin burns. There were no burns under the TLC electrode when ablations were ceased for temperatures >42°C. Conclusions: TLC-equipped dispersive electrodes were able to accurately measure skin temperature under the electrode. This technology is likely to prevent dispersive electrode related burns. (J Cardiovasc Electrophysiol, Vol. 16, pp. 781-788, July 2005) [ABSTRACT FROM AUTHOR]

Evaluation of a Cooled Needle Ablation Catheter. 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°C, 50 W for the intramural needle catheter and 20 mL/min, 50°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.(J Cardiovasc Electrophysiol, Vol. 16, pp. 1-8, May 2005) [ABSTRACT FROM AUTHOR]

THIAGALINGAM, A., et al.: 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°C and 50°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. (PACE 2004; 27:965–970) [ABSTRACT FROM AUTHOR]

KOVOOR, P., et al.: 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°C, 80°C, 90°C, and 100°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°C, 80°C, and 90°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°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°C. Increasing the length of the intramural ablating electrode to ≥ 5.5 mm and increasing temperatures to 90°C–100°C creates the largest lesions. (PACE 2004; 27[Pt. I]:719–725) [ABSTRACT FROM AUTHOR]

THIAGALINGAM, A., et al.: Catheter Intramural Needle Radiofrequency Ablation Creates Deeper Lesions than Irrigated Tip Catheter Ablation. Radiofrequency ablation of the left ventricle using an endocardially placed electrode is unable to reliably create transmural lesions even with active electrode cooling. To produce deeper radiofrequency lesions, the authors developed and tested a prototype intramural needle ablation catheter that had a distal 1.1-mm diameter straight needle that could be advanced 12 mm into the myocardium. Freshly excised hearts from eight male sheep were perfused and superfused with oxygenated ovine blood. Ablations were performed for 60 seconds with the prototype catheter and a conventional 5-mm irrigated tip ablation catheter at target temperatures of 90°C and 50°C, respectively. The ablation lesions were bisected and stained with blue tetrazolium to assess lesion geometry. The irrigated tip ablation catheter required significantly more power than the intramural needle ablation catheter (37.7 ± 7.3 vs 6.4 ± 2.1 W, P < 0.01). Intramural needle lesions were significantly deeper (12.5 ± 3.0 mm vs 8.3 ± 2.1 mm, P < 0.01) but less wide (3.9 ± 1.1 mm vs 11.5 ± 2.0 mm, P < 0.01) than irrigated tip lesions. There was a high incidence of crater formation (74%), popping (45%), and myocardial charring (29%) during irrigated tip ablation; these phenomena were not observed during intramural needle ablation. The intramural needle ablation catheter creates significantly deeper but narrower lesions without evidence of tissue boiling. This technology may be particularly useful for ablation of ventricular tachycardia originating from regions where tissue depth is increased, like the ventricular septum. (PACE 2003; 26:2146–2150) [ABSTRACT FROM AUTHOR]

Background: Women experience less appropriate implantable cardioverter-defibrillator (ICD) interventions and are underrepresented in randomised ICD trials. Sex-differences in inducible and spontaneous ventricular tachycardia/fibrillation (VT/VF), cardiac arrest and sudden cardiac death (SCD) early post-myocardial infarction (MI) require further study.Methods: Consecutive ST-elevation MI patients with left ventricular ejection fraction (LVEF)≤40% underwent electrophysiology study (EPS) to target early prevention of SCD. An ICD was implanted for a positive (inducible monomorphic VT) but not a negative (no arrhythmia or inducible VF) EPS. The combined primary endpoint of VT/VF (spontaneous or ICD-treated), cardiac arrest or SCD was assessed using competing risk survival analysis in women versus men with adjustment for confounders. Logistic regression was used to determine independent predictors of inducible VT at EPS.Results: A total of 403 patients (16.9% female) underwent EPS. Women were significantly older than men but with similar LVEF (31.5 ± 6.3 versus 31.6 ± 6.4%, p = 0.91). Electrophysiology study was positive for inducible VT in 22.1% and 33.4% (p = 0.066) and an ICD implanted in 25.0% and 33.4% (p = 0.356) of women versus men. Appropriate ICD activations (VT/VF) occurred in 5.9% of women and 36.6% of men (p = 0.012). The adjusted cumulative primary endpoint incidence was significantly lower in women than men (1.6% versus 26.5%, p = 0.03). Female sex was not an independent predictor of inducible VT at EPS (HR 0.63, 95% CI 0.33-1.23, p = 0.178).Conclusions: Women with early post-MI cardiomyopathy had lower VT/VF, cardiac arrest and SCD, compared to men. In ICD recipients the rate of appropriate activations was six-fold less in women compared to men. [ABSTRACT FROM AUTHOR]

Background: Obesity is associated with increased risk of cardiovascular disease. There is little known, however, about the influence of body mass index (BMI) on spontaneously occurring ventricular arrhythmias in patients with ischaemic heart disease. We sought to examine the effect of BMI on the ventricular arrhythmia (VA) recurrence and mortality in defibrillator recipients with ischaemic cardiomyopathy.Methods: Consecutive patients (n = 123) with ischaemic cardiomyopathy (left ventricular ejection fraction (LVEF) ≤ 40%) and a primary or secondary prevention defibrillator were included. Patients were classified according to their BMI as being normal (18.5-24.99, n = 54/ 43.9%), overweight (2 -29.99, n = 43/ 35%) or obese (>30, n = 26/20.3%).Results: The primary combined endpoint of VA recurrence and mortality occurred in 36%, 5.4% and 11.5% of patients with normal, overweight and obese BMI (p = 0.001). When adjusting for risk factors such as ejection fraction, age and triple vessel disease, on multivariable analysis, normal BMI remained a significant predictor for the primary outcome (Hazard Ratio, Normal vs Overweight = 7.1, 95% CI 1.8-25, p = 0.002: Hazard Ratio, Normal vs Obese = 5.5, 95% CI 1.11-25, p = 0.033). There was a non-significant trend towards reduced survival in patients with normal weight in comparison to overweight and obese patients (p = 0.08).Conclusion: In defibrillator recipients with ischaemic cardiomyopathy, BMI appears to be a significant predictor for the combined primary outcome of spontaneously occurring ventricular arrhythmias and mortality. Normal BMI, compared to overweight and obese patients had worse outcomes, suggesting the presence of the obesity paradox in ventricular arrhythmogenesis late post infarction. [ABSTRACT FROM AUTHOR]

Sotalol is a non-selective beta-adrenergic blocking agent without intrinsic sympathomimetic activity. It has the additional unique property of producing pronounced prolongation of the cardiac action potential duration. Sotalol therapy has been indicated for the management of supraventricular arrhythmias, refractory life threatening ventricular arrhythmias and atrial fibrillation/flutter. Until recently, sotalol was only available in the oral form, however, it was approved for intravenous administration by the US Food & Drug Administration (FDA). The current recommendations are for sotalol 75-150mg to be administered intravenously over 5hours. This rate of administration does not reflect the majority of the research that has been performed with regards to intravenous sotalol. Also, the safety of intravenous bolus dosing of 100mg over 1 and 5minutes has previously been demonstrated. The antiarrhythmic action of sotalol depends on its ability to prolong refractoriness in the nodal and extra nodal tissue. Hence, by giving a lower dose over a long duration, patients may not necessarily benefit from its anti-arrhythmic potential. The purpose of this article is to review the research that has been conducted with regards to dosage and safety of intravenous sotalol, its electrophysiological effects and finally the spectrum of arrhythmias in which it has been used to date. [ABSTRACT FROM AUTHOR]

Background Patients with left ventricular diastolic impairment (LVDI) have higher rates of arrhythmia recurrence following atrial fibrillation (AF) ablation. Past studies have implicated the posterior left atrium (LA) in atrial arrhythmia maintenance in conditions that cause LVDI. We prospectively compared posterior LA isolation (PLAI) with wide antral isolation (WAI) in patients with LVDI having AF ablation. Methods We conducted a sub-study of a previously published large randomized control study that compared PLAI with WAI. Two hundred and twenty consecutive consenting patients referred for catheter ablation of AF (paroxysmal 135, persistent 48, long standing persistent 37) were recruited (female 43, mean age 59 ± 10 years). Transthoracic echocardiography identified 50 (23%) patients with LVDI and preserved left ventricular systolic function (ejection fraction ≥ 50%). Cox regression analysis was utilized to identify independent predictors of atrial arrhythmia after ablation. Results Patients were followed for median 4.6 (inter quartile range 4.0-5.5) years. Patients with LVDI having PLAI had better arrhythmia free survival than patients randomized to conventional ablation (Log rank P = 0.028). The only independent predictor of recurrence utilizing Cox regression analysis was ablation strategy (2.3 [1.15-4.74], P = 0.026). Conclusion Posterior isolation of the LA results in superior atrial arrhythmia free survival in patients with LVDI. Further investigation is required to determine potential mechanisms. [ABSTRACT FROM AUTHOR]

Background--A negative electrophysiology study (EPS) may delineate a subgroup of patients with severely impaired left ventricular ejection fraction (LVEF) whose care can be safely managed long-term without an implantable cardioverter-defibrillator. Methods and Results--Consecutive patients treated with primary percutaneous coronary intervention for ST-segment--elevation myocardial infarction underwent early (median 4 days) LVEF assessment. Patients with LVEF ≤40% underwent EPS. A prophylactic implantable cardioverter-defibrillator was implanted for a positive (inducible monomorphic ventricular tachycardia) but not a negative (no inducible ventricular tachycardia or inducible ventricular fibrillation/flutter) EPS result. Patients who would have become eligible for a late primary prevention implantable cardioverter-defibrillator with LVEF ≤30% or ≤35% with New York Heart Association class II/III heart failure were included and analyzed according to EPS result. Patients with LVEF >40%, ineligible for EPS, were followed up as control subjects (n=1286). The primary end point was survival free of death or arrhythmia (resuscitated cardiac arrest or sustained ventricular tachycardia/ventricular fibrillation). EPS performed in 128 patients with LVEF ≤30% or with LVEF ≤35% and heart failure was negative in 63% (n=80) and positive in 37% (n=48). Implantable-cardioverter defibrillators were implanted in <0.1%, 4%, and 90% of control, EPS-negative, and EPS-positive patients, respectively. The distribution of time to death or arrhythmia was comparable in control patients and EPS-negative patients with LVEF ≤30% or with LVEF ≤35% and heart failure (P=0.738), who both differed significantly from EPS-positive patients (P<0.001). At 3 years, 91.8±3.2%, 93.4±1.0%, and 62.7±7.5% of control, EPS-negative, and EPS-positive patients were tree of death or arrhythmia, respectively. Conclusions--Revascularized patients with ST-segment-elevation myocardial infarction with severely impaired left ventricular function but no inducible ventricular tachycardia have a favorable long-term prognosis without the protection of an implantable cardioverter-defibrillator. [ABSTRACT FROM AUTHOR]