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INTRODUCTION We sought to explore the relationship between ventricular tachycardia (VT) and premature ventricular complex (PVC) burden (from implantable cardioverter-defibrillator diagnostics), before and during corticosteroid use in patients with newly diagnosed clinically manifest cardiac sarcoidosis (CS). METHODS A single-centre, prospective cohort study was performed in consecutive patients who met all of the following criteria: (1) presentation with clinically manifest CS, (2) abnormal myocardial fluoro-deoxyglucose (FDG) uptake on positron emission tomography scan, (3) plan for implantation with implantable cardioverter-defibrillator device that reports accurate PVC count, (4) plan to initiate corticosteroids after the device healing period. Data were collected during each device interrogation visit for all patients in the study. For each inter-visit period the total number of episodes of VT-sustained and nonsustained, and the number of PVCs was obtained. Each inter-visit period was classified into one of the following three periods: (1) New diagnosis of treatment-naive active disease without corticosteroids during the period. (2) Known treatment-naive active disease with corticosteroids initiated during the inter-visit period. (3) On corticosteroid therapy during the entire period. RESULTS A total of 20 patients with a mean age of 59.7 ± 7.7 years were recruited and 82 inter-visit periods were analyzed. All patients were corticosteroid responders based on FDG uptake. The maximum left ventricular standardized uptake value was 11.14 ± 5.19 before corticosteroid initiation and 4.07 ± 0.88 after (p

Introduction In patients with ischemic heart disease and ventricular tachycardia (VT) refractory to high dose amiodarone, the two most common therapeutic options are adjunctive mexiletine therapy or catheter ablation. There are little existing data on the efficacy of these strategies. We examined the relative efficacy of adjunctive mexiletine and catheter ablation among patients enrolled in the VANISH trial. Methods All subjects enrolled in the VANISH trial who had VT refractory to high dose (≥ 300 mg daily) amiodarone at baseline were included. Per protocol, subjects randomized to escalated drug therapy received adjunctive mexiletine. Results Nineteen of the 259 patients were receiving high-dose amiodarone at baseline and 11 were randomized to escalated therapy with mexiletine and 8 to ablation. The adjunctive mexiletine group had a higher rate of the primary composite outcome (death, VT storm, or appropriate shock) in comparison to catheter ablation (HR 6.87 [2.08-22.8]). Over 90% of the patients in the adjunctive mexiletine/group experienced a primary endpoint during a median 9.2 months' follow-up. There was no difference in the rate of adverse events between the two groups. Conclusions Mexiletine has limited efficacy in the treatment of recurrent VT despite high-dose amiodarone therapy, in patients with ischemic heart disease. Catheter ablation is a superior strategy in this population.

Introduction The standard 4-minute application time for transcatheter cryoablation was determined in the 1990s when the system employed less potent chlorofluorocarbon refrigerants. The current refrigerant, nitrous oxide, generates substantially colder temperatures, with a faster cooling rate. Methods and results We conducted a preclinical study on 32 mongrel dogs with stratified randomization of right atrial, right ventricular, and left ventricular chambers to 2-minute versus 4-minute application times using 8-mm electrode tip cryocatheters (Freezor Max, Medtronic CryoCath LP, Montreal, Canada). Animals were sacrificed one month after the procedure. Three-dimensional morphometric analyses were conducted in a blinded fashion. A total of 193 identified ablation lesions were processed for histological analyses, 102 with 2-minute applications and 91 with 4-minute applications. Ablation lesion surface area (167.8 ± 21.6 mm2 vs. 194.3 ± 22.6 mm2 , P = 0.40), maximum depth (4.4 ± 0.2 mm vs. 4.5 ± 0.2 mm, P = 0.71), and volume (125.7 ± 69.5 mm3 vs. 141.0 ± 83.5 mm3 , P = 0.25) were similar between groups. Overall, 90.2% of ablation lesions in the right atrium were transmural, 45.6% in the right ventricle, and 2.4% in the left ventricle, with no differences between 2-minute and 4-minute application times (P = 0.55). Thrombus was detected on the endocardial surface of 0.0% and 3.3% of ablation lesions created with 2-minute and 4-minute application times, respectively (P = 0.10). Conclusion Single 2-minute and 4-minute application times result in catheter ablation lesions of similar size using the modern cryoablation system with nitrous oxide as a refrigerant. While these findings suggest the potential to reduce the standard 4-minute application time, further studies are required to compare clinical efficacy.

Sensor-Based Navigation and CRT ImplantationIntroduction Cardiac resynchronization therapy (CRT) implant procedures are often complex and prolonged, resulting in substantial ionizing radiation (IR) exposure to the patient and operator. We assessed the impact of lower-dose fluoroscopy settings and a sensor-based electromagnetic tracking system (MediGuide™, MDG) on reducing IR exposure during CRT implantation. Methods A single-center 2-group cohort study was conducted on 348 consecutive patients, age 66.4 ± 11.0 years, 80.4% male, with CRT implant procedures from 2013 to 2015. Patients were arbitrarily assigned to MDG (N = 239) versus no MDG (N = 109) guidance. Lower-dose fluoroscopy settings were adopted in January 2015 (3 instead of 6 fps; 23 instead of 40 nGy/pulse; N = 101). Results Overall, MDG was associated with an 82.1% reduction in IR exposure (393 μGray·m2 vs. 2191 μGray·m2, P < 0.001). Lower-dose fluoroscopy resulted in a 59.5% reduction in IR-exposure without MDG (1055 μGray·m2 vs. 2608 μGray·m2, P < 0.001) and 81.8% reduction with MDG (108 μGray·m2 vs. 595 μGray·m2, P < 0.001). Low-dose fluoroscopy combined with MDG was associated with a 95.9% lower exposure to IR when compared to standard fluoroscopy without MDG (108 μGray·m2 vs. 2608 μGray·m2, P < 0.001). Procedures with MDG were shorter (96 minutes vs. 123 minutes, P < 0.001) and associated with a trend towards a higher success rate (94.6% vs. 89.0%, P = 0.062), with fewer coronary sinus cannulation failures (2.1% vs. 6.4%, P = 0.040). Conclusion Low-dose fluoroscopy settings are highly effective (>50%) in reducing IR exposure during CRT implant procedures. When combined with MDG, >95% reduction in IR exposure is achieved. Moreover, MDG shortens procedural duration and may improve acute procedural outcomes.

ECG and Cardiovascular Outcomes in AFBackground The association between standard parameters from a simple 12-lead ECG (i.e., QRS duration and PR, JT, and QT intervals) and adverse cardiovascular outcomes (cardiovascular mortality, all-cause mortality, arrhythmic mortality, and hospitalizations) in patients with a history of atrial fibrillation (AF) has not been previously studied. Methods and Results A pooled analysis of patient-level data was conducted on 5,436 patients, age 68.2 ± 8.3 years, 34.8% female, with a history of non-permanent AF randomized in AFFIRM and AF-CHF trials. The predictive value of ECG parameters was assessed in AF and sinus rhythm in multivariate Cox regression models. During a follow-up of 40.8 ± 16.3 months, QRS duration >120 milliseconds was independently associated with all-cause mortality (hazard ratio [HR] 1.46, 95% confidence interval [CI; 1.21–1.76] in AF, P 200 milliseconds) was independently associated with cardiovascular (HR 1.56, 95% CI [1.11–2.21], P = 0.010) and arrhythmic (HR 1.91, 95% CI [1.14–3.18], P = 0.004) mortality. The JT and QTc intervals were not predictive of mortality. Conclusions Simple parameters from standard ECGs are significantly and independently associated with adverse cardiovascular outcomes in patients with a history of AF.

Treatment Failures in AF-CHF Introduction Rate and rhythm control strategies for atrial fibrillation (AF) are not always effective or well tolerated in patients with congestive heart failure (CHF). We assessed reasons for treatment failure, associated characteristics, and effects on survival. Methods and Results A total of 1,376 patients enrolled in the AF-CHF trial were followed for 37 ± 19 months, 206 (15.0%) of whom failed initial therapy leading to crossover. Rhythm control was abandoned more frequently than rate control (21.0% vs. 9.1%, P < 0.0001). Crossovers from rhythm to rate control were driven by inefficacy, whereas worsening heart failure was the most common reason to crossover from rate to rhythm control. In multivariate analyses, failure of rhythm control was associated with female sex, higher serum creatinine, functional class III or IV symptoms, lack of digoxin, and oral anticoagulation. Factors independently associated with failure of rate control were paroxysmal (vs. persistent) AF, statin therapy, and presence of an implantable cardioverter–defibrillator. Crossovers were not associated with cardiovascular mortality (hazard ratio [HR] 1.11 from rhythm to rate control; 95% confidence interval [95% CI, 0.73–1.73]; P = 0.6069; HR 1.29 from rate to rhythm control; 95% CI, 0.73–2.25; P = 0.3793) or all-cause mortality (HR 1.16 from rhythm to rate control, 95% CI [0.79–1.72], P = 0.4444; HR 1.15 from rate to rhythm control, 95% [0.69, 1.91], P = 0.5873). Conclusions Rhythm control is abandoned more frequently than rate control in patients with AF and CHF. The most common reasons for treatment failure are inefficacy for rhythm control and worsening heart failure for rate control. Changing strategies does not impact survival.

Blood Pressure and Atrial Fibrillation Background Hypertension is an established risk factor for new-onset atrial fibrillation (AF). However, the relationship between blood pressure and recurrent AF is less well understood. Methods and Results A pooled analysis of patient-level data from AFFIRM and AF-CHF trials was conducted on all 2,715 patients with paroxysmal or persistent AF, 68 ± 8 years, 66% male, randomized to rhythm control and followed for 40.6 ± 16.5 months. We assessed the impact of a baseline systolic blood pressure (SBP; 140 mmHg [N = 777]) on recurrent AF and proportion of time spent in AF. In patients with LVEF >40% (N = 1,719), SBP was not associated with recurrent AF in multivariate regression analyses (P = 0.752). In contrast, in patients with LVEF ≤40% (N = 996), the AF recurrence rate was higher in those with an SBP >140 mmHg compared to 120–140 mmHg (hazard ratio 1.47; 95% CI [1.12–1.93], P = 0.005). The rate of recurrent AF was similar in patients with SBP 40% (P = 0.645). However, in patients with LVEF ≤40%, the adjusted mean proportion of time spent in AF was 17.2% if SBP was 140 mmHg (P = 0.025). Conclusion Systolic blood pressure is an important determinant of recurrent AF and overall AF burden in patients with left ventricular dysfunction (LVEF≤40%) but not in those with preserved ventricular function.

Amiodarone for Atrial Fibrillation Introduction Despite amiodarone's established safety profile in the setting of heart failure, it is unknown whether its impact on cardiovascular outcomes in patients with atrial fibrillation is modulated by left ventricular function. Methods and Results A pooled analysis of 3,307 patients (age 68.0 ± 0.2 years; 31.1% female) enrolled in AFFIRM and AF-CHF trials was conducted to assess the effect of rhythm control with amiodarone on cardiovascular outcomes, according to left ventricular systolic function. In amiodarone-treated patients (N = 1,107), freedom from recurrent atrial fibrillation was 84% and 45% at 1 and 5 years, respectively, with no differences according to left ventricular function (P = 0.8754). Similarly, the adjusted proportion of time spent in atrial fibrillation (15.0 ± 1.8%) did not vary according to ventricular function (P = 0.6094). Over 40.0 ± 0.3 months of follow-up, 1,963 (59.4%) patients required at least one hospitalization, 1,401 (42.6%) of whom had cardiovascular-related hospitalizations. Adjusted all-cause and cardiovascular hospitalization rates were similar with amiodarone versus rate control in all patients and in subgroups with and without severe left ventricular dysfunction. A total of 729 (22.0%) patients died, 498 (15.1%) from cardiovascular causes. Adjusted all-cause and cardiovascular mortality rates were similar with amiodarone versus rate control overall and in subgroups with and without severe left ventricular dysfunction. Conclusion Amiodarone's efficacy in maintaining sinus rhythm and reducing the burden of atrial fibrillation is similar in the presence or absence of severe left ventricular dysfunction. Rhythm control with amiodarone is associated with comparable hospitalization and mortality rates to rate control in patients with and without left ventricular dysfunction.

Cryoballoon-Induced Phrenic Nerve Injury Introduction Hemi-diaphragmatic paralysis is the most common complication associated with cryoballoon ablation for atrial fibrillation, yet the histopathology of phrenic nerve injury has not been well described. Methods and Results A preclinical randomized study was conducted to characterize the histopathology of phrenic nerve injury induced by cryoballoon ablation and assess the potential for electromyographic (EMG) monitoring to limit phrenic nerve damage. Thirty-two dogs underwent cryoballoon ablation of the right superior pulmonary vein with the objective of inducing phrenic nerve injury. Animals were randomized 1:1 to standard monitoring (i.e., interruption of ablation upon reduction in diaphragmatic motion) versus EMG guidance (i.e., cessation of ablation upon a 30% reduction in the diaphragmatic compound motor action potential [CMAP] amplitude). The acute procedural endpoint was achieved in all dogs. Phrenic nerve injury was characterized by Wallerian degeneration, with subperineural injury to large myelinated axons and evidence of axonal regeneration. The degree of phrenic nerve injury paralleled the reduction in CMAP amplitude (P = 0.007). Animals randomized to EMG guidance had a lower incidence of acute hemi-diaphragmatic paralysis (50% vs 100%; P = 0.001), persistent paralysis at 30 days (21% vs 75%; multivariate odds ratio 0.12, 95% confidence interval [0.02, 0.69], P = 0.017), and a lesser severity of histologic injury (P = 0.001). Mature pulmonary vein ablation lesion characteristics, including circumferentiality and transmurality, were similar in both groups. Conclusion Phrenic nerve injury induced by cryoballoon ablation is axonal in nature and characterized by Wallerian degeneration, with potential for recovery. An EMG-guided approach is superior to standard monitoring in limiting phrenic nerve damage.

Ablation Time and Active Cryoballoon Deflation Introduction Optimal cryoballoon ablation parameters for pulmonary vein (PV) isolation remain to be defined. We conducted a randomized preclinical trial to compare 2- versus 4-minute ablation lesions and assess the safety of active (forced) cryoballoon deflation. Methods and Results Thirty-two dogs underwent PV isolation with a second-generation 23 mm cryoballoon catheter. The left superior (LSPV) and inferior (LIPV) PVs were randomized in a factorial design to (1) a single 2- versus 4-minute cryoapplication, and (2) passive versus active cryoballoon deflation. Animals were survived for 30 days, after which histopathologic analysis was performed. Acute PV isolation was attained in 89.8% of PVs after a single application (93.8% LSPV, 85.2% LIPV; P = 0.2823). Mean time to PV isolation was 29.5 ± 18.5 seconds. Although 4-minute lesions were associated with a thicker neointima than 2-minute lesions (223.8 μm versus 135.6 μm; P = 0.007), no differences were observed in procedural characteristics (freezing temperature, rewarming time), rates of acute PV isolation, or the achievement of complete circumferentially transmural lesions at 30 days (78.7% overall; 86.2% for 2 minutes vs 70.0% for 4 minutes; P = 0.285). Active deflation was associated with faster balloon rewarming but not with significant differences in mean or maximum neointimal thickness. Conclusion A single application with the second-generation cryoballoon catheter results in a high rate of PV isolation. The degree of vascular injury was not increased by active balloon deflation and no differences in acute efficacy or mature transmural circumferential lesions were observed with 2- versus 4-minute applications.

The standard 4-minute application time for transcatheter cryoablation was determined in the 1990s when the system employed less potent chlorofluorocarbon refrigerants. The current refrigerant, nitrous oxide, generates substantially colder temperatures, with a faster cooling rate.We conducted a preclinical study on 32 mongrel dogs with stratified randomization of right atrial, right ventricular, and left ventricular chambers to 2-minute versus 4-minute application times using 8-mm electrode tip cryocatheters (Freezor Max, Medtronic CryoCath LP, Montreal, Canada). Animals were sacrificed one month after the procedure. Three-dimensional morphometric analyses were conducted in a blinded fashion. A total of 193 identified ablation lesions were processed for histological analyses, 102 with 2-minute applications and 91 with 4-minute applications. Ablation lesion surface area (167.8 ± 21.6 mmSingle 2-minute and 4-minute application times result in catheter ablation lesions of similar size using the modern cryoablation system with nitrous oxide as a refrigerant. While these findings suggest the potential to reduce the standard 4-minute application time, further studies are required to compare clinical efficacy.

To evaluate the safety and outcomes of mitral isthmus (MI) linear ablation with temporary spot occlusion of the coronary sinus (CS). Background: CS blood flow cools local tissue precluding transmurality and bidirectional block across MI lesion.

Impact of PFO on LA Linear Ablation. Introduction: We investigated the impact of the mode of left atrial (LA) access via patent foramen ovale (PFO) versus transseptal (TS) puncture on LA linear lesions during atrial fibrillation (AF) ablation. Methods and Results: We investigated 139 (PFO: 25) consecutive patients who underwent mitral isthmus (MI) and/or LA roof linear ablation. Technical endpoint was completeness of linear lesions and duration of radiofrequency (RF) application. During the initial procedure, complete MI and LA roof blocks were created in 13 of 19 (68%) and 14 of 17 (82%) patients in the PFO group, and in 57 of 94 (61%) and 54 of 70 (74%) patients in the TS group, respectively (P = NS). There was no significant difference in RF durations at MI (11.1 ± 8.9 and 15.1 ± 7.6 minutes, P = 0.11), and LA roof (10.1 ± 3.5 and 8.3 ± 5.0 minutes, P = 0.21) between the 2 groups. Among 28 patients who underwent repeat linear ablation, complete MI and LA roof blocks were created in 3 of 4 (75%) and 0 of 1 (0%) patients in the PFO group, and in 16 of 21 (76%) and 7 of 10 (70%) patients in the TS group, respectively (P = NS). There was no significant difference in RF durations at MI (15.3 ± 8.3 and 19.5 ± 18.3 minutes, P = 0.71), and LA roof (19.0 and 10.3 ± 5.4 minutes, P = 0.19) between the 2 groups. Clinical outcomes at 12 months were also similar. Conclusion: There were no significant differences in the procedural success rates, durations of RF application, 12-month clinical outcomes, and complication rates of LA linear ablation between the PFO and TS groups. Accessing the LA via a PFO is not an unfavorable approach toward LA linear ablation. © 2011 Wiley Periodicals, Inc.

In our initial experience, a linear multielectrode catheter using duty-cycled bipolar and unipolar RF energy was inferior to conventional single point irrigated ablation in achieving LA linear block. However, successful linear block was obtained within a short period of time, when it was achieved.

Rate and rhythm control strategies for atrial fibrillation (AF) are not always effective or well tolerated in patients with congestive heart failure (CHF). We assessed reasons for treatment failure, associated characteristics, and effects on survival.A total of 1,376 patients enrolled in the AF-CHF trial were followed for 37 ± 19 months, 206 (15.0%) of whom failed initial therapy leading to crossover. Rhythm control was abandoned more frequently than rate control (21.0% vs. 9.1%, P0.0001). Crossovers from rhythm to rate control were driven by inefficacy, whereas worsening heart failure was the most common reason to crossover from rate to rhythm control. In multivariate analyses, failure of rhythm control was associated with female sex, higher serum creatinine, functional class III or IV symptoms, lack of digoxin, and oral anticoagulation. Factors independently associated with failure of rate control were paroxysmal (vs. persistent) AF, statin therapy, and presence of an implantable cardioverter-defibrillator. Crossovers were not associated with cardiovascular mortality (hazard ratio [HR] 1.11 from rhythm to rate control; 95% confidence interval [95% CI, 0.73-1.73]; P = 0.6069; HR 1.29 from rate to rhythm control; 95% CI, 0.73-2.25; P = 0.3793) or all-cause mortality (HR 1.16 from rhythm to rate control, 95% CI [0.79-1.72], P = 0.4444; HR 1.15 from rate to rhythm control, 95% [0.69, 1.91], P = 0.5873).Rhythm control is abandoned more frequently than rate control in patients with AF and CHF. The most common reasons for treatment failure are inefficacy for rhythm control and worsening heart failure for rate control. Changing strategies does not impact survival.

Hypertension is an established risk factor for new-onset atrial fibrillation (AF). However, the relationship between blood pressure and recurrent AF is less well understood.A pooled analysis of patient-level data from AFFIRM and AF-CHF trials was conducted on all 2,715 patients with paroxysmal or persistent AF, 68 ± 8 years, 66% male, randomized to rhythm control and followed for 40.6 ± 16.5 months. We assessed the impact of a baseline systolic blood pressure (SBP;120 mmHg [N = 1,008], 120-140 mmHg [N = 930],140 mmHg [N = 777]) on recurrent AF and proportion of time spent in AF. In patients with LVEF40% (N = 1,719), SBP was not associated with recurrent AF in multivariate regression analyses (P = 0.752). In contrast, in patients with LVEF ≤40% (N = 996), the AF recurrence rate was higher in those with an SBP140 mmHg compared to 120-140 mmHg (hazard ratio 1.47; 95% CI [1.12-1.93], P = 0.005). The rate of recurrent AF was similar in patients with SBP120 mmHg compared to 120-140 mmHg (hazard ratio 1.15; 95% CI [0.92-1.43], P = 0.225). Consistently, the proportion of time spent in AF was not influenced by SBP in patients with LVEF40% (P = 0.645). However, in patients with LVEF ≤40%, the adjusted mean proportion of time spent in AF was 17.2% if SBP was120 mmHg, 15.4% for SBP 120-140 mmHg, and 24.0% for SBP140 mmHg (P = 0.025).Systolic blood pressure is an important determinant of recurrent AF and overall AF burden in patients with left ventricular dysfunction (LVEF≤40%) but not in those with preserved ventricular function.

Despite amiodarone's established safety profile in the setting of heart failure, it is unknown whether its impact on cardiovascular outcomes in patients with atrial fibrillation is modulated by left ventricular function.A pooled analysis of 3,307 patients (age 68.0 ± 0.2 years; 31.1% female) enrolled in AFFIRM and AF-CHF trials was conducted to assess the effect of rhythm control with amiodarone on cardiovascular outcomes, according to left ventricular systolic function. In amiodarone-treated patients (N = 1,107), freedom from recurrent atrial fibrillation was 84% and 45% at 1 and 5 years, respectively, with no differences according to left ventricular function (P = 0.8754). Similarly, the adjusted proportion of time spent in atrial fibrillation (15.0 ± 1.8%) did not vary according to ventricular function (P = 0.6094). Over 40.0 ± 0.3 months of follow-up, 1,963 (59.4%) patients required at least one hospitalization, 1,401 (42.6%) of whom had cardiovascular-related hospitalizations. Adjusted all-cause and cardiovascular hospitalization rates were similar with amiodarone versus rate control in all patients and in subgroups with and without severe left ventricular dysfunction. A total of 729 (22.0%) patients died, 498 (15.1%) from cardiovascular causes. Adjusted all-cause and cardiovascular mortality rates were similar with amiodarone versus rate control overall and in subgroups with and without severe left ventricular dysfunction.Amiodarone's efficacy in maintaining sinus rhythm and reducing the burden of atrial fibrillation is similar in the presence or absence of severe left ventricular dysfunction. Rhythm control with amiodarone is associated with comparable hospitalization and mortality rates to rate control in patients with and without left ventricular dysfunction.

Hemi-diaphragmatic paralysis is the most common complication associated with cryoballoon ablation for atrial fibrillation, yet the histopathology of phrenic nerve injury has not been well described.A preclinical randomized study was conducted to characterize the histopathology of phrenic nerve injury induced by cryoballoon ablation and assess the potential for electromyographic (EMG) monitoring to limit phrenic nerve damage. Thirty-two dogs underwent cryoballoon ablation of the right superior pulmonary vein with the objective of inducing phrenic nerve injury. Animals were randomized 1:1 to standard monitoring (i.e., interruption of ablation upon reduction in diaphragmatic motion) versus EMG guidance (i.e., cessation of ablation upon a 30% reduction in the diaphragmatic compound motor action potential [CMAP] amplitude). The acute procedural endpoint was achieved in all dogs. Phrenic nerve injury was characterized by Wallerian degeneration, with subperineural injury to large myelinated axons and evidence of axonal regeneration. The degree of phrenic nerve injury paralleled the reduction in CMAP amplitude (P = 0.007). Animals randomized to EMG guidance had a lower incidence of acute hemi-diaphragmatic paralysis (50% vs 100%; P = 0.001), persistent paralysis at 30 days (21% vs 75%; multivariate odds ratio 0.12, 95% confidence interval [0.02, 0.69], P = 0.017), and a lesser severity of histologic injury (P = 0.001). Mature pulmonary vein ablation lesion characteristics, including circumferentiality and transmurality, were similar in both groups.Phrenic nerve injury induced by cryoballoon ablation is axonal in nature and characterized by Wallerian degeneration, with potential for recovery. An EMG-guided approach is superior to standard monitoring in limiting phrenic nerve damage.

Introduction: Despite widespread clinical use, ablation lesions produced by cryocatheters with 6 and 8 mm electrode-tips have not been fully characterized. We, therefore, sought to quantify and compare lesion dimensions and thrombus formation with 4, 6, and 8 mm electrode-tip cryocatheters. Methods and Results: By means of a randomized factorial design, 72 ablation lesions were created in atrial and ventricular chambers of adult miniature swine at a mean temperature of 79.9 ± 4.0°C. By histological morphometric analysis, the overall lesion depth was 4.3 ± 2.1 mm, surface area 61.3 (28.7, 116.0) mm2, and volume 130.2 (62.7, 231.3) mm3. Cryolesions produced by all electrode-tip sizes were well circumscribed, with intact endothelial cell layers, and absence of thrombus. Colder temperatures generated lesions of greater surface area (P = 0.0061) and volume (P = 0.0080), but not depth. Depths were similar between the three electrode-tips. However, surface areas produced by 8 mm catheters were 91.7 mm2 larger on average (176.7% increase, P = 0.0003) than 4 mm and 72.3 mm2 greater (101.3% increase, P = 0.0144) than 6 mm catheters. The 8 and 6 mm catheters yielded mean lesion volumes 252.6 mm3 (248.3% increase, P = 0.0041) and 115.9 mm3 (113.9% increase, P = 0.0670) larger than 4 mm catheters. Greater variability in surface area and volume were observed with 8 mm catheters. Conclusion: Longer electrode-tip cryocatheters produce larger lesions of similar depth, with intact endothelial layers and absence of thrombosis. Surface areas and volumes may be particularly sensitive to catheter tip-to-tissue contact angles with larger electrodes, as reflected by greater variability with 8 mm tips.