Proactive esophageal cooling protects against thermal insults during high-power short-duration radiofrequency cardiac ablation.

BACKGROUND: Proactive cooling with a novel cooling device has been shown to reduce endoscopically identified thermal injury during radiofrequency (RF) ablation for the treatment of atrial fibrillation using medium power settings. We aimed to evaluate the effects of proactive cooling during high-power short-duration (HPSD) ablation. METHODS: A computer model accounting for the left atrium (1.5 mm thickness) and esophagus including the active cooling device was created. We used the Arrhenius equation to estimate the esophageal thermal damage during 50 W/ 10 s and 90 W/ 4 s RF ablations. RESULTS: With proactive esophageal cooling in place, temperatures in the esophageal tissue were significantly reduced from control conditions without cooling, and the resulting percentage of damage to the esophageal wall was reduced around 50%, restricting damage to the epi-esophageal region and consequently sparing the remainder of the esophageal tissue, including the mucosal surface. Lesions in the atrial wall remained transmural despite cooling, and maximum width barely changed (<0.8 mm). CONCLUSIONS: Proactive esophageal cooling significantly reduces temperatures and the resulting fraction of damage in the esophagus during HPSD ablation. These findings offer a mechanistic rationale explaining the high degree of safety encountered to date using proactive esophageal cooling, and further underscore the fact that temperature monitoring is inadequate to avoid thermal damage to the esophagus.

A safe, simple technique for transseptal catheterization.

Transseptal catheterization is required for atrial fibrillation ablation and many ablations for atrial tachycardias, left atrial flutters, and accessory pathways. Using a Brockenbrough needle or other specialized device adds time, expense, and risk of potential complications such as atrial or aortic perforation, pericardial effusion, and tamponade to these procedures. We present a simple, low-risk technique for transseptal catheterization.

Direct Current Ablation of Deep Substrate Arrhythmia.

Direct-current ablation has been reinvestigated in animal models with considerably good outcomes and safety margins. Its modified version using biphasic energy lowers the current density further, minimizing its complications. We report a first-in-human ablation of ventricular tachycardia using biphasic direct current with short-term success and no procedural complications. (Level of Difficulty: Intermediate.).

Esophageal cooling for protection during left atrial ablation: a systematic review and meta-analysis.

PURPOSE: Thermal damage to the esophagus is a risk from radiofrequency (RF) ablation of the left atrium for the treatment of atrial fibrillation (AF). The most extreme type of thermal injury results in atrio-esophageal fistula (AEF) and a correspondingly high mortality rate. Various strategies for reducing esophageal injury have been developed, including power reduction, esophageal deviation, and esophageal cooling. One method of esophageal cooling involves the direct instillation of cold water or saline into the esophagus during RF ablation. Although this method provides limited heat-extraction capacity, studies of it have suggested potential benefit. We sought to perform a meta-analysis of published studies evaluating the use of esophageal cooling via direct liquid instillation for the reduction of thermal injury during RF ablation. METHODS: We searched PubMed for studies that used esophageal cooling to protect the esophagus from thermal injury during RF ablation. We then performed a meta-analysis using a random effects model to calculate estimated effect size with 95% confidence intervals, with an outcome of esophageal lesions stratified by severity, as determined by post-procedure endoscopy. RESULTS: A total of 9 studies were identified and reviewed. After excluding preclinical and mathematical model studies, 3 were included in the meta-analysis, totaling 494 patients. Esophageal cooling showed a tendency to shift lesion severity downward, such that total lesions did not show a statistically significant change (OR 0.6, 95% CI 0.15 to 2.38). For high-grade lesions, a significant OR of 0.39 (95% CI 0.17 to 0.89) in favor of esophageal cooling was found, suggesting that esophageal cooling, even with a low-capacity thermal extraction technique, reduces the severity of lesions resulting from RF ablation. CONCLUSIONS: Esophageal cooling reduces the severity of the lesions that may result from RF ablation, even when relatively low heat extraction methods are used, such as the direct instillation of small volumes of cold liquid. Further investigation of this approach is warranted, particularly with higher heat extraction capacity techniques.

Protecting the esophagus from thermal injury during radiofrequency ablation with an esophageal cooling device.

PURPOSE: We sought to quantify the capabilities of a commercially available cooling device to protect the esophagus from RF injury in an animal model and develop a mathematical model to describe the system and provide a framework from which to advance this technology. METHODS: A series of ablations (10 W, duration 30-45 seconds) were performed directly on exposed swine esophagus. Control ablations were performed with static 37°C water, and treatment ablations were performed with water (range 5°C-37°C) circulating within the device. Mucosal lesions were evaluated visually and with target tissue histology. A mathematical model was then developed and compared against the experimental data. RESULTS: All 23 ablations (100%) performed under control conditions produced visible external esophageal lesions; 12 of these (52%) were transmural. Under treatment conditions, only 5 of 23 ablations (22%) produced visible external lesions; none (0%) were transmural. Transmurality of lesions decreased as circulating water temperature decreased, with absolute reduction ranging from 5.1% with the use of 37°C water (p=0.7) to 44.5% with the use of 5°C water (p<0.001). Comparison to the mathematical model showed an R^2 of 0.75, representing good agreement. CONCLUSION: Under worst-case conditions, with RF energy applied directly to the adventitial side of the esophagus, internal esophageal cooling with an esophageal cooling device provides significant protective effect from thermal injury. A mathematical model of the process provides a means to further investigate this approach to preventing esophageal injury during RF ablation and can serve to guide ongoing clinical investigations currently in progress.

Sex-Specific Associations of Oral Anticoagulant Use and Cardiovascular Outcomes in Patients With Atrial Fibrillation.

BACKGROUND: Sex-specific effectiveness of rivaroxaban (RIVA), dabigatran (DABI), and warfarin in reducing myocardial infarction (MI), heart failure (HF), and all-cause mortality among patients with atrial fibrillation are not known. We assessed sex-specific associations of RIVA, DABI, or warfarin use with the risk of MI, HF, and all-cause mortality among patients with atrial fibrillation. METHODS AND RESULTS: Medicare beneficiaries (men: 65 734 [44.8%], women: 81 135 [55.2%]) with atrial fibrillation who initiated oral anticoagulants formed the study cohort. Inpatient admissions for MI, HF, and all-cause mortality were compared between the 3 drugs separately for men and women using 3-way propensity-matched samples. In men, RIVA use was associated with a reduced risk of MI admissions compared with warfarin use (hazard ratio [95% confidence interval (CI): 0.59 [0.38-0.91]), with a trend towards reduced risk compared with DABI use (0.67 [0.44-1.01]). In women, there were no significant differences in the risk of MI admissions across all 3 anticoagulants. In both sexes, RIVA use and DABI use were associated with reduced risk of HF admissions (men: RIVA; 0.75 [0.63-0.89], DABI; 0.81 [0.69-0.96]) (women: RIVA; 0.64 [0.56-0.74], DABI; 0.73 [0.63-0.83]) and all-cause mortality (men: RIVA; 0.66 [0.53-0.81], DABI; 0.75 [0.61-0.93]) (women: RIVA; 0.76 [0.63-0.91], DABI; 0.77 [0.64-0.93]) compared with warfarin use. CONCLUSIONS: RIVA use and DABI use when compared with warfarin use was associated with a reduced risk of HF admissions and all-cause mortality in both sexes. However, reduced risk of MI admissions noted with RIVA use appears to be limited to men.

Survey of physician experience, trends and outcomes with atrial fibrillation ablation.

OBJECTIVE: We evaluated the prevalence, trends, outcomes and the general experience of physicians performing atrial fibrillation ablation (AF-ABL) in the United States (US). BACKGROUND: AF-ABL is a non-pharmacological and potentially curative therapy for AF. Success rates for AF-ABL have been reported to be between 80 and 90%. Although there are numerous clinical trial addressing this therapy little is known about the general status of AF-ABL in clinical practice. METHODS: We administered a mailed survey to the physician members of a professional arrhythmia society (Heart Rhythm Society, formerly known as the North American Society of Pacing and Electrophysiology) who practiced in the US (n = 1843). RESULTS: There were 304 responses, 66% (n = 204) performed ABL and 30% (n = 92) performed AF-ABL. The study group performed a total of 5,592 AF-ABL from 2000 to 2003, out of 72,575 total ABL procedures during the same time period. There was a four-fold increase in the number of AF-ABL between 2000 and 2003 (2000: 628 vs. 2003: 2,575). In the same period, the self-reported short and long-term success rates of AF-ABL improved an average of 18 +/- 4% (p < or = 0.001). In 2003 the average self-reported one-month, one-year, and two-year success rates were: 71 +/- 4%, 66 +/- 5%, 63 +/- 6% respectively. The predicted five-year success was 60 +/- 4%. The average procedure took 4.5 +/- 0.4 hours. Physicians reported that approximately 29 +/- 4% of their patents were potential candidates for AF-ABL. CONCLUSIONS: AF-ABL is becoming a much more common procedure in the US. Over the last four years the perceived short and long term success rates of AF-ABL have improved. Success rates in this survey are 10 to 20% lower than those reported in the recent clinical trials.

Doppler evaluation of the descending aorta in patients with hypertrophic cardiomyopathy: potential for assessing the functional significance of outflow tract gradients and for optimizing pacemaker function.

UNLABELLED: We evaluated whether analysis of aortic flow could be useful for determining the functional significance of left ventricular outflow gradients and for optimizing pacing therapy in patients with hypertrophic cardiomyopathy (HOCM). METHODS: Doppler echocardiography was performed in 32 patients with HOCM. Eleven patients with pacemakers (PPM) also underwent treadmill and quality-of-life (QOL) testing in a randomized crossover trial (1 month of backup pacing (AAI at 30 beats per minute), 1 month with an atrioventricular interval (AVI) of 30 ms (DDD30), and 1 month with an "optimized" AVI (DDDop) that maximized the descending aortic Doppler velocity time integral. RESULTS: Patients with HOCM displayed a notch in the aortic Doppler flow profile. The location of the notch in systole corresponded with the development of the peak left ventricular outflow gradient. Aortic flow after the notch was variable ranging from 6-48% of the total flow. In patients with pacemakers, improved response to pacing was noted in those patients that developed the notch early in systole and had subsequent attenuation of aortic flow. Optimizing the AVI was associated with improved exercise tolerance (AAI: 4.6 +/- 2.3 min., DDD30: 5.5 +/- 2.2 min., and DDDop: 7.7 +/- 2.5 min.; p < 0.05) and improved QOL. CONCLUSIONS: Patients with HOCM have a notch in their aortic Doppler flow profile. The location of the notch correlates with the development of the peak left ventricular outflow gradient and flow after the notch is variable. Patients with an early notch and attenuated flow after the notch appear to have the greatest response to pacing therapy.

Atrial fibrillation ablation leads to long-term improvement of quality of life and reduced utilization of healthcare resources.

In some patients, rapid activation from one or several foci can lead to atrial fibrillation. This study evaluated long-term changes in quality of life and healthcare resource utilization in patients with atrial fibrillation treated by ablation of focal triggers. Thirty-three patients underwent ablation for paroxysmal atrial fibrillation. Health surveys (SF-36) were obtained at baseline, and after 1 year and 3 years of follow-up. Health care costs were measured for the 3 years before and after ablation. Ablation was successful in 82%, partially successful in 12% (no sustained episodes but on antiarrhythmic drug therapy), and unsuccessful in 6% of patients. The average number of ablation procedures was 1.6 +/- 0.6 per patient. After ablation, patients reported significantly improved quality of life in all SF-36 categories except bodily pain. Healthcare resource utilization was significantly reduced after ablation (Clinic visits: 7.4 +/- 2.5 per year vs. 1.1 +/- 0.6 per year, p < 0.05; Emergency room visits: 1.7 +/- 0.90 per year vs. 0.03 +/- 0.17 per year, p < 0.05; Hospitalization: 1.6 +/- 0.81 vs. 0, p < 0.05). Cost of healthcare (not including procedural costs) was significantly reduced after ablation (Pre-ablation: 1,920 +/- 889 dollars/year vs. post-ablation: 87 +/- 68 dollars/year; p < 0.01). Procedural cost of ablation was 17,173 +/- 2,466 dollars/patient. Ablation of focal triggers of atrial fibrillation is associated with a sustained improvement in quality of life. Although the initial cost of ablation is high, after ablation, utilization of healthcare resources is significantly reduced.

Reduced resident "code blue" experience in the era of quality improvement: new challenges in physician training.

PURPOSE: Emergency resuscitation or "code blue" is a clinical event through which responding medical residents gain experience and proficiency. A retooling of practice has occurred at academic medical centers since the emergence of quality improvement initiatives and resident duty hours limits. The authors investigated how these changes may impact code blue frequency and resident opportunities to gain clinical experience. METHOD: The authors conducted a single-center, retrospective (2002-2009) review of monthly code blue frequency. They compared code blue frequency with corresponding monthly first-year internal medicine resident call schedules (2002-2008 academic years). Using a Monte Carlo simulation they estimated annual code blue experience, and using Poisson regression, they estimated annual trends in resident code blue experience. RESULTS: The authors detected a 41% overall reduction in code blue events between 2002 and 2008; code blue events decreased by 13% annually (P < .001). These trends persisted, even after accounting for hospital census fluctuations: Rates fell from approximately 12 code blue events/1,000 admissions in 2002 to 3.8 events/1,000 in 2008. Overall, the model of code blue frequency and resident call schedules shows a dramatic reduction in the predicted number of code blue experiences, falling from 29 events (empirical 95% CI 18-40) in academic year 2002 to 5 events (CI 1-9) in 2008. CONCLUSIONS: Physicians-in-training at one facility are seeing far fewer code blue events than their predecessors. Whether current numbers of in-hospital code blue events are sufficient to provide adequate experience without supplemental practice for trainees is unclear.

Transvenous access to the pericardial space: an approach to epicardial lead implantation for cardiac resynchronization therapy.

BACKGROUND: Percutaneous access to the pericardial space (PS) may be useful for a number of therapeutic modalities including implantation of epicardial pacing leads. We have developed a catheter-based transvenous method to access the PS for implanting chronic medical devices. METHODS: In eight pigs, a transseptal Mullins sheath and Brockenbrough needle were introduced into the right atrium (RA) from the jugular vein under fluoroscopic guidance. The PS was entered through a controlled puncture of the terminal anterior superior vena cava (SVC) (n = 7) or right atrial appendage (n = 1). A guidewire was advanced through the transseptal sheath, which was then removed leaving the wire in PS. The guidewire was used to direct both passive and active fixation pacing leads into the PS. Pacing was attempted and lead position was confirmed by cine fluoroscopy. Animals were sacrificed acutely and at 2 and 6 weeks. RESULTS: All animals survived the procedure. Pericardial effusion (PE) during the procedure was hemodynamically significant in four of the eight animals. At necropsy, lead exit sites appeared to heal without complication at 2 and 6 weeks. Volume of pericardial fluid was 10.8 +/- 6.2 mL and appeared normal in four of the six chronic animals. Moderate fibrinous deposition was observed in two animals, which had exhibited significant over-procedural PE. CONCLUSIONS: Access to the PS via a transvenous approach is feasible. Pacing leads can be negotiated into this region. The puncture site heals with the lead in place. Further development should focus on eliminating PE and performing this technique in appropriate heart failure models.

Electromechanical analysis of infarct border zone in chronic myocardial infarction.

To test the hypothesis that alterations in electrical activation sequence contribute to depressed systolic function in the infarct border zone, we examined the anatomic correlation of abnormal electromechanics and infarct geometry in the canine post-myocardial infarction (MI) heart, using a high-resolution MR-based cardiac electromechanical mapping technique. Three to eight weeks after an MI was created in six dogs, a 247-electrode epicardial sock was placed over the ventricular epicardium under thoracotomy. MI location and geometry were evaluated with delayed hyperenhancement MRI. Three-dimensional systolic strains in epicardial and endocardial layers were measured in five short-axis slices with motion-tracking MRI (displacement encoding with stimulated echoes). Epicardial electrical activation was determined from sock recordings immediately before and after the MR scans. The electrodes and MR images were spatially registered to create a total of 160 nodes per heart that contained mechanical, transmural infarct extent, and electrical data. The average depth of the infarct was 55% (SD 11), and the infarct covered 28% (SD 6) of the left ventricular mass. Significantly delayed activation (>mean + 2SD) was observed within the infarct zone. The strain map showed abnormal mechanics, including abnormal stretch and loss of the transmural gradient of radial, circumferential, and longitudinal strains, in the region extending far beyond the infarct zone. We conclude that the border zone is characterized by abnormal mechanics directly coupled with normal electrical depolarization. This indicates that impaired function in the border zone is not contributed by electrical factors but results from mechanical interaction between ischemic and normal myocardium.