Ventricular arrhythmias in the Chagas disease are not random phenomena: Long-term monitoring in Chagas arrhythmias.

BACKGROUND: Variability of ventricular arrhythmias among days in patients with Chagas disease is not detected by 24 hours of Holter monitoring. OBJECTIVE: To analyze whether ventricular arrhythmias are a random phenomenon or have a reproducible behavior in patients with Chagas cardiomyopathy. METHOD: Holter monitoring was recorded in 16 subjects with a mean age of 52 ± 8 years. They were clinically stable and had ventricular couplets, isolated premature ventricular contractions (PVCs), and nonsustained ventricular tachycardia (NSVT). The recordings occurred for 7 days. Hurst exponent (HE) evaluated randomness and predictability index (PI) and repeated analysis of variance (ANOVA) assessed reproducibility. RESULTS: The HE was significantly greater than 0.5 in all 16 patients, which confirms the nonrandomness of arrhythmias in this Chagas sample. The PI for ventricular couplets and isolated PVCs was, on average, 38% and 54%, respectively. ANOVA with repeated measurement showed significant differences in the daily frequency of ventricular couplets (n = 15, P ≤ .05), isolated PVC (n = 12, P ≤ .05), and NSVT (n = 7, P ≤ .05). CONCLUSION: Ventricular arrhythmias in Chagas cardiomyopathy are not random. Dissimilarities in arrhythmias frequency make unlikely that 24 hours of Holter recording can capture this variability.

'Choosing Wisely' culture among Brazilian cardiologists.

OBJECTIVE: (i) To describe how aligned the 'Choosing Wisely' concept is with the medical culture among Brazilian cardiologists and (ii) to identify predictors for physicians' preference for avoiding wasteful care. DESIGN: Cross-sectional study. SETTING: Brazilian Society of Cardiology. PARTICIPANTS: Cardiologists who agree to fill a web questionary. INTERVENTION: A task force of 12 Brazilian cardiologists prepared a list of 13 'do not do' recommendations, which were made available on the Brazilian Society of Cardiology website for affiliates to assign a supported score of 1 to 10 to each recommendation. MAIN OUTCOME MEASUREMENT: Score average for supporting recommendations. RESULTS: Of 14 579 Brazilian cardiologists, 621 (4.3%) answered the questionnaire. The top recommendation was 'do not perform routine percutaneous coronary intervention in asymptomatic individuals' (mean score = 8.0 ± 2.9) while the one with the lowest support was 'do not use an intra-aortic balloon pump in infarction with cardiogenic shock' (5.8 ± 3.2). None of the 13 recommendations presented a mean grade >9 (strong support); 7 recommendations averaged 7-8 (moderate support) followed by 6 recommendations with an average of 5-7 (modest support). Multivariate analysis independently identified predictors of the score attributed to the top recommendation; being an interventionist and time since graduation were both negatively associated with support. CONCLUSIONS: (i) The support of Brazilian cardiologists for the 'Choosing Wisely' concept is modest to moderate, and (ii) older generations and enthusiasm towards the procedure one performs may be factors against the 'Choosing Wisely' philosophy.

Prognostic value of real-time three-dimensional echocardiography compared to two-dimensional echocardiography in patients with systolic heart failure.

Heart failure (HF) is associated with morbidity and mortality. Real-time three-dimensional echocardiography (RT3DE) may offer additional prognostic data in patients with HF. The study aimed to evaluate the prognostic value of real-time three-dimensional echocardiography (RT3DE). This is a prospective study that included 89 patients with HF and left ventricular ejection fraction (LVEF) < 0.50 who were followed for 48 months. Left atrium and ventricular volumes and functions were evaluated by RT3DE. TDI and two-dimensional echocardiography parameters were also obtained. The endpoint was a composite of death, heart transplantation and hospitalization for acute decompensated HF. The mean age was 55 ± 11 years, and the LVEF was 0.32 ± 0.10. The composite endpoint occurred in 49 patients (18 deaths, 30 hospitalizations, one heart transplant). Patients with outcomes had greater left atrial volume (40 ± 16 vs. 32 ± 12 mL/m2; p < 0.01) and right ventricle diameter (41 ± 9 vs. 37 ± 8 mm, p = 0.01), worse total emptying fraction of the left atrium (36 ± 13% vs. 41 ± 11%; p = 0.03), LVEF (0.30 ± 0.09 vs. 0.34 ± 0.11; p = 0.02), right ventricle fractional area change (34.8 ± 12.1% vs. 39.2 ± 11.3%; p = 0.04), and greater E/e' ratio (19 ± 9 vs. 16 ± 8; p = 0.04) and systolic pulmonary artery pressure (SPAP) (50 ± 15 vs. 36 ± 11 mmHg; p < 0.01). In multivariate analysis, LVEF (OR 4.6; CI 95% 1.2-17.6; p < 0.01) and SPAP (OR 12.5; CI 95% 1.8-86.9; p < 0.01) were independent predictors of patient outcomes. LVEF and the SPAP were independent predictors of outcomes in patients with HF.

Validation of a novel sleep-quality questionnaire to assess sleep in the coronary care unit: a polysomnography study.

INTRODUCTION: The sleep of patients admitted to coronary care unit (CCU) may be compromised. A feasible and cost-effective tool to evaluate sleep in this scenario could provide important data. The aim of this study was to evaluate sleep with a questionnaire developed specifically for the CCU and to validate it with polysomnography (PSG). METHODS: Ninety-nine patients (68% male; 56 ± 10 years old) with acute coronary syndrome were included. PSG was performed within 36 h of admission. A specific 18-question questionnaire (CCU questionnaire) was developed and applied after the PSG. Cronbach's alpha test was used to validate the questionnaire. The Spearman test was used to analyze the correlation between the PSG variables and the questionnaire, and the Kruskal-Wallis test was used to compare the PSG variables among patients with good, regular, or poor sleep. RESULTS: The total sleep time was 265 ± 81 min, sleep efficiency 62 ± 18%, REM sleep 10 ± 7%, apnea/hypopnea index 15 ± 23, and the arousal index 24 ± 15. Cronbach's alpha test was 0.69. The CCU questionnaire showed correlation with the sleep efficiency evaluated by PSG (r: 0.52; p < 0.001). Sleep quality was divided into three categories according to the CCU questionnaire: patients with good sleep had a sleep efficiency of 72 ± 9%, better than those with a regular or poor sleep (60 ± 16% and 53 ± 20%, respectively; p < 0.01). CONCLUSION: The CCU questionnaire is a feasible and reliable tool to evaluate sleep in the CCU, showing correlation with the PSG sleep efficiency.

The impact of sleep duration in obstructive sleep apnea patients.

PURPOSE: Obstructive sleep apnea (OSA) is a risk factor for cardiovascular disease. Strong associations have been reported among sleep duration, hypertension, obesity, and cardiovascular mortality. The authors hypothesize that sleep duration may play a role in OSA severity. The aim of this study is to analyze sleep duration in OSA patients. METHODS: Patients who underwent overnight polysomnography were consecutively selected from the Sleep Clinic of Universidade Federal de São Paulo database between March 2009 and December 2010. All subjects were asked to come to the Sleep Clinic at 8:00 a.m. for a clinical evaluation and actigraphy. Anthropometric parameters such as weight, height, hip circumference, abdominal circumference, and neck circumference were also measured. RESULTS: One hundred thirty-three patients were divided into four groups based on total sleep time, sleep efficiency, sleep latency, and wake after sleep onset: very short sleepers (n = 11), short sleepers (n = 21), intermediate sleepers (n = 56), and sufficient sleepers (n = 45). Apnea-hypopnea index (AHI) was higher in very short sleepers (50.18 ± 30.86 events/h) compared with intermediate sleepers (20.36 ± 14.68 events/h; p = 0.007) and sufficient sleepers (23.21 ± 20.45 events/h; p = 0.02). Minimal and mean arterial oxygen saturation and time spent below 90 % oxygen saturation exhibited worse values in very short sleepers. After adjustment for gender, age, AHI, and body mass index, mean oxygen saturation was significantly associated to total sleep time (p = 0.01). CONCLUSIONS: In conclusion, the present study suggests that sleep duration may be associated to low mean oxygen saturation in OSA patients.

Subxyphoid pleural drain confers lesser impairment in respiratory muscle strength, oxygenation and lower chest pain after off-pump coronary artery bypass grafting: a randomized controlled trial.

OBJECTIVE: To evaluate respiratory muscle strength, oxygenation and chest pain in patients undergoing off-pump coronary artery bypass (OPCAB) using internal thoracic artery grafts comparing pleural drain insertion site at the subxyphoid region versus the lateral region. METHODS: Forty patients were randomized into two groups in accordance with the pleural drain site. Group II (n = 19) -pleural drain exteriorized in the intercostal space; group (SI) (n = 21) chest tube exteriorized at the subxyphoid region. All patients underwent assessment of respiratory muscle strength (inspiratory and expiratory) on the pre, 1, 3 and 5 postoperative days (POD). Arterial blood gas analysis was collected on the pre and POD1. The chest pain sensation was measured 1, 3 and 5 POD. RESULTS: A significant decrease in respiratory muscle strength (inspiratory and expiratory) was seen in both groups until POD5 (P <0.05). When compared, the difference between groups remained significant with greater decrease in the II (P <0.05). The blood arterial oxygenation fell in both groups (P <0.05), but the oxygenation was lower in the II (P <0.05). Referred chest pain was higher 1, 3 and 5 POD in the II group (P <0.05). The orotracheal intubation time and postoperative length of hospital stay were higher in the II group (P <0.05). CONCLUSION: Patients submitted to subxyphoid pleural drainage showed less decrease in respiratory muscle strength, better preservation of blood oxygenation and reduced thoracic pain compared to patients with intercostal drain on early OPCAB postoperative.

Delayed enhancement cardiac magnetic resonance imaging can identify the risk for ventricular tachycardia in chronic Chagas' heart disease.

BACKGROUND: Invasive and non-invasive tests have been used to identify the risk of ventricular tachycardia (VT) in patients with chronic Chagas' heart disease (CCHD). Cardiac magnetic resonance imaging (CMRI) using the delayed enhancement (DE) technique can be useful to select patients with global or segmentary ventricular dysfunction, with high degree of fibrosis and at higher risk for clinical VT. OBJECTIVE: To improve the identification of predictors of VT in patients with CCHD. METHOD: This study assessed 41 patients with CCHD [30 (72%) males; mean age, 55.1 ± 11.9 years]. Twenty-six patients had history of VT (VT group), and 15 had no VT (NVT group). All patients enrolled had DE and segmentary ventricular dysfunction. In each case, the following variables were determined: left ventricular volume; percentage of ventricular wall thickness impairment in each segment; and DE distribution. RESULTS: No statistical difference regarding the DE volume between both groups was observed: VT group = 30.0 ± 16.2%; NVT group = 21.7 ± 15.7%; p = 0.118. The probability of VT was greater in the presence of two or more contiguous transmural fibrosis areas, and that was a predictive factor of clinical VT (RR 4.1; p = 0,04). Agreement between observers was 100% regarding that criterion (p < 0.001). CONCLUSION: The identification of two or more segments of transmural DE by use of CMRI is associated with the occurrence of clinical VT in patients with CCHD. Thus, CMRI improved risk stratification in the population studied.

Naproxen as prophylaxis against atrial fibrillation after cardiac surgery: the NAFARM randomized trial.

PURPOSE: We sought to assess the effect of naproxen versus placebo on prevention of atrial fibrillation after coronary artery bypass graft (CABG) surgery. METHODS: In this randomized, double-blind, placebo-controlled, single-center trial of 161 consecutive patients undergoing CABG surgery, patients received naproxen 275 mg every 12 hours or placebo at the same dosage and interval over 120 hours immediately after CABG surgery. The primary outcome was the occurrence of atrial fibrillation in the first 5 postoperative days. RESULTS: The incidence of postoperative atrial fibrillation was 15.2% (12/79) in the placebo versus 7.3% (6/82) in the naproxen group (P=.11). The duration of atrial fibrillation episodes was significantly lower in the naproxen (0.35 hours) versus placebo group (3.74 hours; P=.04). There was no difference in the overall days of hospitalization between placebo (17.23±7.39) and naproxen (18.33±9.59) groups (P=.44). Intensive care unit length of stay was 4.0±4.57 days in the placebo and 3.23±1.25 days in the naproxen group (P=.16). The trial was stopped by the data monitoring committee before reaching the initial target number of 200 patients because of an increase in renal failure in the naproxen group (7.3% vs 1.3%; P=.06). CONCLUSIONS: Postoperative use of naproxen did not reduce the incidence of atrial fibrillation but decreased its duration, in a limited sample of patients after CABG surgery. There was a significant increase in acute renal failure in patients receiving naproxen 275 mg twice daily. Our study does not support the routine use of naproxen after CABG surgery for the prevention of atrial fibrillation.

Correlation between heart rate control during exercise and exercise capacity in patients with chronic atrial fibrillation.

BACKGROUND: Rate control is an acceptable alternative to rhythm control in patients with chronic atrial fibrillation (AF). HYPOTHESIS: The aim of this study of AF patients was to understand the correlation between their exercise capacity and both heart rate (HR) and HR variation index during exercise. METHODS: The exercise capacity of 85 male patients with chronic AF was measured using a cardiopulmonary exercise test (CPX). Within this population, we compared the exercise tolerance of patients with a normal chronotropic response (maximal HR 85%-115% that of the maximal age-predicted HR during CPX) to those whose HR response exceeded this range. Two similar comparisons were made by dividing the subject population according to (1) whether or not their HR variation index (HRVI) during CPX exceeded 10 bpm/min, and (2) whether their HR during the 6-minute walk test exceeded 110 bpm. RESULTS: Patients with an HRVI not over 10 bpm/min showed higher maximal oxygen uptake compared to patients with a higher HRVI (26.7 ± 6.1 vs 22.8 ± 4.8 mL O(2) /kg/min, P = 0.002) and a longer distance walked during CPX (705.6 ± 200.3 vs 520.9 ± 155.5 m, P<0.001). No other significant influence on exercise capacity was seen. Multivariate regression analysis revealed that both the body mass index and the HRVI during CPX were independent predictors of the maximal oxygen uptake. CONCLUSIONS: Better HRVI control on CPX was correlated with better exercise capacity in patients with chronic AF.

Impact of corticosteroids on late growth of radiofrequency lesions in infant pigs: histopathological and electroanatomical findings.

AIMS: Corticosteroids attenuate late growth of radiofrequency (RF) lesions in the thigh muscle of infant rats. We sought to assess the impact of these drugs on the late growth of RF lesions in immature swine myocardium and to determine the electroanatomical mapping (EAM) characteristics of these lesions. METHODS AND RESULTS: Radiofrequency (60°C; 60 s) lesions were created in the right atrium (n = 2) and ventricle (n = 2) of 14 piglets (age 65 days; weight 5 kg) and 3 adults. Piglets were divided into: controls (n = 7) and treated (n = 7), receiving hydrocortisone (10 mg/kg iv after RF) and prednisone (1 mg/kg/day) for 29 days. After 8 months, animals were sacrificed for histological analysis. In four piglets, endocardial and epicardial voltage EAM were performed. In infant groups, the dimensions of atrial (11 ± 5 vs. 13 ± 7 mm) and ventricular (12 ± 3 vs. 11 ± 3 mm) lesions were similar. In adults, atrial (6 ± 1 mm) and ventricular (6 ± 1 mm) lesions were smaller. In controls, ventricular lesions depicted dense fibrosis and multiple strands of fibrous tissue extending from the lesion into normal muscle. Treated piglets revealed scars exhibiting less dense fibrosis with predominance of fibroadipose tissue and less collagen proliferation. Large atrial and ventricular low-voltage areas corresponding to the macroscopic lesions were identified in all animals. CONCLUSION: Radiofrequency lesions in infant pigs reveal late growth and invasion of normal muscle by intense collagen proliferation. Corticosteroids do not prevent late enlargement of the lesions but modulate the fibrotic proliferation. The expressive growth of the lesion may generate low-voltage areas detectable by EAM.

Influence of heart rate on quality of life in patients with chronic atrial fibrillation.

BACKGROUND: Current criteria for rate control in atrial fibrillation (AF) treatment are empirical and based on a small amount of scientific data. HYPOTHESIS: This study was designed to analyze the influence of heart rate (HR, measured by the 6-minute walk test [6MWT] and 24-hour Holter monitoring) on quality of life (QoL). METHODS: A total of 89 male patients with chronic atrial fibrillation (AF) and resting HR < 90 bpm were included. QoL (assessed by the Short Form-36 Health Survey [SF-36] questionnaire) was compared among 3 groups of patients classified by HR testing results: group 1 had HR < or = 110 bpm on 6MWT and < or = 80 bpm on Holter monitor; group 2 had HR in the target area by 1 but not both tests; and group 3 had HR > 110 bpm on 6MWT and > 80 bpm on Holter monitor. RESULTS: There were significant differences among the 3 groups in physical and mental component summary scores (285.9 +/- 73.9; 276.6 +/- 80.8; 230.3 +/- 91.0, P = .035; and 319.8 +/- 70.2; 294.7 +/- 76.0; 255.0 +/- 107.1, P = .026, respectively).When the methods were analyzed separately, there was a significant difference on QoL in physical and mental summary scores in patients with maximal HR < or = 110 bpm on 6MWT in comparison with HR > 110 bpm (P = .04 and P = .01, respectively) and in the physical summary score in patients with average HR < or = 80 bpm on Holter monitor in comparison with HR > 80 bpm (P = .02). CONCLUSIONS: Holter monitoring and 6MWT should be performed as complementary methods to better predict QoL.

Validating a new quality of life questionnaire for atrial fibrillation patients.

BACKGROUND: Atrial fibrillation (AF) is the most common sustained arrhythmia in clinical practice, and has major impact on health-related quality of life, thus, there is a need for a specific instrument to assess AF symptoms and quality of life. METHODS: We developed and validated a specific questionnaire for quality of life in AF patients (QLAF) based on clinical manifestations (palpitation, breathlessness, dizziness and chest pain), and the usual treatments (medication, cardioversion and ablation). For validation, the new questionnaire was compared with the generic SF-36 questionnaire. Reproducibility was tested using 40 questionnaires administered by two different observers at distinct times and places. Responsiveness was evaluated based on variation of the QLAF score over time. RESULTS: There were a total of 462 questionnaires (231 SF-36 and 231 QLAF) administered at baseline, 3, 6, 9 and 12 months. Construct validity was demonstrated by the negative correlation between QLAF and SF-36 scores that was observed over the follow-up period. Analysis of internal consistency for reproducibility showed excellent Cronbach's alpha coefficients (inter- and intraobserver coefficients of 0.98 and 0.96, respectively). QLAF was responsive as indicated by significant differences in mean domain scores from the beginning to the end of follow-up. It took much less time to administer the QLAF than the SF-36 (3:08±0:33 min vs. 9:25±1:14 min, p<0.001). CONCLUSION: The QLAF questionnaire is easy to understand and can be administered rapidly in the outpatient setting. Furthermore, the QLAF score is valid and reproducible and responsive to a change in clinical status.

Effects of alcohol on atrial fibrillation: myths and truths.

Alcohol is the most consumed drug worldwide. Both acute and chronic alcohol use have been associated with cardiac arrhythmias, in particular atrial fibrillation, or so-called 'holiday heart syndrome'. Epidemiological, clinical and experimental studies have attempted to elucidate the mechanisms involved in this association. However, because most of these studies have shown conflicting results, the connection between ethanol and atrial arrhythmias remains controversial. Historical, epidemiological and pharmacological aspects of alcohol, as well as recent concepts on atrial fibrillation are reviewed. We then examine the literature and provide a critical point of view on the still elusive association between alcohol and atrial fibrillation.

Effects of corticosteroid therapy on the long-term outcome of radiofrequency lesions in the Swine caval veins.

BACKGROUND: We explored the angiographic and pathological effects of corticosteroids on the long-term outcome of radiofrequency (RF) ablation lesions in the swine caval veins. METHODS: Under fluoroscopy guidance, a single linear RF lesion (4-mm tip, 60 degrees C, 180 seconds) was created in each vena cava (from +/-2 cm into the vein to the venoatrial junction) of 20 anesthetized minipigs (35+/- 2 kg). Three groups were studied: acute (n = 4), killed 1 hour after RF; control (n = 8), sacrificed 83+/- 1 days after RF; and pigs (n = 8) receiving hydrocortisone (400 mg i.v. after RF) and prednisone (25 mg po for 30 days), killed 83+/- 1 days post-RF. Angiography was performed before, immediately after ablation, and at follow-up. Then, animals were sacrificed for histological analysis. RESULTS: Mild (<40%) or moderate (41-70%) acute luminal narrowing occurred in 19/20 (95%) inferior veins and in 13/20 (65%) superior veins. Severe (>70%) stenosis and occlusions were not noted. At follow-up, in both chronic groups, mean vessel diameters returned to baseline and progression of luminal narrowing did not occur in any vein. Of note, superior and inferior vena cava angiographic diameter for control and treated pigs did not differ. The same was observed for the cross-sectional luminal area. Acute lesions displayed transmural coagulative necrosis whereas chronic lesions revealed marked fibrosis. Histological findings were similar in controls and treated pigs. CONCLUSION: In this model, mild and moderate stenosis, occurring immediately after ablation, seems to resolve over time. Corticosteroids do not affect the long-term outcome of such RF lesions in the caval veins.

Incremental shuttle and six-minute walking tests in the assessment of functional capacity in chronic heart failure.

BACKGROUND: The incremental shuttle test presents some theoretical advantages over the six-minute walk test in chronic heart failure (CHF), including better standardization and less dependency on collaboration. OBJECTIVES: The present study evaluated test-retest repeatability, test accuracy in predicting a peak oxygen consumption (VO(2)) of 14 mL/kg/min or less, as well as the prognostic value of both walking tests in stable CHF patients. METHODS: Sixty-three patients (44 men; New York Heart Association functional class II to IV) underwent an incremental treadmill exercise test and, on another day, the walk test in duplicate. RESULTS: Patients showed well-preserved functional capacity according to the distance walked in both tests (six-minute walk test 491+/-94 m versus incremental shuttle walk test 422+/-119 m; P<0.001). Interestingly, the six-minute and incremental shuttle walk test differences in distance walked were higher in more disabled patients. The mean bias +/-95% CI of the within-test differences were similar (7+/-40 m and 8+/-45 m, respectively). Peak VO(2), but not distance walked in either test, was associated with survival (P<0.05). CONCLUSIONS: The incremental shuttle walk test showed similar repeatability and accuracy in estimating peak VO(2) compared with the six-minute walk test in CHF patients. Direct measurement of peak VO(2), however, remains superior to either walking test in predicting survival--at least in patients with well-preserved functional capacity.

Influence of pleurotomy on pulmonary function after off-pump coronary artery bypass grafting.

BACKGROUND: This study evaluated the influence of pleurotomy on pulmonary function after off-pump coronary artery bypass grafting (CABG) using the left internal thoracic artery (LITA). METHODS: Thirty patients were prospectively allocated into two groups: 15 patients with an opened left pleural cavity (OP group) and 15 patients with an intact pleural cavity (IP group). Bedside pulmonary function tests were recorded preoperatively and on postoperative days 1, 3, and 5. Arterial blood gas analyses and ratio of partial pressure of arterial oxygen (PaO2/fraction of inspired oxygen (FiO2) ratio were evaluated preoperatively and on postoperative day 1. RESULTS: A significant decrease of pulmonary function was observed in both groups until postoperative day 5. When compared with the percentage of the preoperative value, the forced vital capacity was significantly lower in the OP group than in the IP group on postoperative days 1 (33.3% +/- 8.3% versus 49.1% +/- 8.4%, p < 0.001), 3 (45.4% +/- 7.0% versus 62.1% +/- 8.6%, p < 0.001), and 5 (56.1% +/- 8.7% versus 77.5% +/- 11.6%, p < 0.001). Similar results were found for forced expiratory volume in 1 second on postoperative days 1 (35.7% +/- 8.6% versus 50.0% +/- 9.8%, p < 0.001), 3 (48.4% +/- 7.0% versus 61.5% +/- 9.02%, p < 0.001) and 5 (58.8% +/- 8.5% versus 75.9% +/- 10.2%, p < 0.001). The PaO2 value and the PaO2/FiO2 ratio dropped on postoperative day 1 in both groups (p < 0.05), with a higher fall in the OP group (p < 0.05). Orotracheal intubation time (p = 0.012) and hospital stay (p = 0.002) were lower in the IP group. CONCLUSIONS: Off-pump CABG using the LITA, independently of pleural opening, induced a significant reduction in early postoperative pulmonary function. However, the patients undergoing pleurotomy demonstrated more pronounced pulmonary dysfunction.

Epicardial radiofrequency ablation of ventricular myocardium: factors affecting lesion formation and damage to adjacent structures.

UNLABELLED: We evaluated the factors affecting epicardial radiofrequency (RF) lesion formation in normal ventricular myocardium. In 16 dogs, a minithoracotomy was made and a sheath was placed in the pericardial space. Standard ablation lesions (4-mm tip catheter; 70 ( composite function) C/60 seconds) were created in each ventricle under fluoroscopy guidance (n = 7) or hand-held with direct visualization of the catheter to assure optimal electrode-tissue contact (n = 6). In the latter, thermally-shielded (TS) electrodes (50% tip surface along its 4 mm length) were used in 3/6 dogs. Catheter tip (4 mm) irrigation (13 mL/minutes; 40 ( composite function) C/60 seconds) was employed with conventional techniques in 3 additional dogs. RESULTS: With optimal electrode-tissue contact (11 lesions), power (3.4 +/- 2.3 W vs. 16 +/- 13 W; p < 0.001) and pacing thresholds (0.2 +/- 0.0 mA vs. 3.6 +/- 5.7 mA; p = 0.004) were lower than standard RF (25 lesions). However, lesion dimensions were similar and transmural lesions did not occur (depth 2.8 +/- 1.1 mm vs. 3.0 +/- 1.5 mm). Catheter irrigation allowed high power outputs (43 +/- 6.1 W; p < 0.001) generating transmural lesions, 5/9 (55%), depth 6.4 +/- 2.1 mm. At constant power (2 W), catheter-tip temperature (52 +/- 5.2( composite function) C vs. 57 +/- 6.6( composite function) C; p = NS) and lesion (10 in each group) dimensions were similar for conventional and TS electrodes, but damage to parietal pericardium and lungs occurred with conventional electrodes only (70% vs. 0% p = 0.02). CONCLUSION: Standard epicardial RF ablation does not produce deep lesions and exhibits a significant energy loss probably due to poor electrode-tissue contact. Catheter irrigation allows delivery of high power outputs to the epicardium consistently creating deeper lesions than standard ablation. TS electrodes may reduce damage to neighboring structures during epicardial RF ablation.