Atrial fibrosis helps select the appropriate patient and strategy in catheter ablation of atrial fibrillation: a DE-MRI guided approach.

UNLABELLED: MRI for AF Patient Selection and Ablation Approach. INTRODUCTION: Left atrial (LA) fibrosis and ablation related scarring are major predictors of success in rhythm control of atrial fibrillation (AF). We used delayed enhancement MRI (DE-MRI) to stratify AF patients based on pre-ablation fibrosis and also to evaluate ablation-induced scarring in order to identify predictors of a successful ablation. METHODS AND RESULTS: One hundred and forty-four patients were staged by percent of fibrosis quantified with DE-MRI, relative to the LA wall volume: minimal or Utah stage 1; <5%, mild or Utah stage 2; 5-20%, moderate or Utah stage 3; 20-35%, and extensive or Utah stage 4; >35%. All patients underwent pulmonary vein (PV) isolation and posterior wall and septal debulking. Overall, LA scarring was quantified and PV antra were evaluated for circumferential scarring 3 months post ablation. LA scarring post ablation was comparable across the 4 stages. Most patients had either no (36.8%) or 1 PV (32.6%) antrum circumferentially scarred. Forty-two patients (29%) had recurrent AF over 283 ± 167 days. No recurrences were noted in Utah stage 1. Recurrence was 28% in Utah stage 2, 35% in Utah stage 3, and 56% in Utah stage 4. Recurrence was predicted by circumferential PV scarring in Utah stage 2 and by overall LA wall scarring in Utah stage 3. No recurrence predictors were identified in Utah stage 4. CONCLUSIONS: Circumferential PV antral scarring predicts ablation success in mild LA fibrosis, while posterior wall and septal scarring is needed for moderate fibrosis. This may help select the proper candidate and strategy in catheter ablation of AF.

Detection and quantification of left atrial structural remodeling with delayed-enhancement magnetic resonance imaging in patients with atrial fibrillation.

BACKGROUND: Atrial fibrillation (AF) is associated with diffuse left atrial fibrosis and a reduction in endocardial voltage. These changes are indicators of AF severity and appear to be predictors of treatment outcome. In this study, we report the utility of delayed-enhancement magnetic resonance imaging (DE-MRI) in detecting abnormal atrial tissue before radiofrequency ablation and in predicting procedural outcome. METHODS AND RESULTS: Eighty-one patients presenting for pulmonary vein antrum isolation for treatment of AF underwent 3-dimensional DE-MRI of the left atrium before the ablation. Six healthy volunteers also were scanned. DE-MRI images were manually segmented to isolate the left atrium, and custom software was implemented to quantify the spatial extent of delayed enhancement, which was then compared with the regions of low voltage from electroanatomic maps from the pulmonary vein antrum isolation procedure. Patients were assessed for AF recurrence at least 6 months after pulmonary vein antrum isolation, with an average follow-up of 9.6+/-3.7 months (range, 6 to 19 months). On the basis of the extent of preablation enhancement, 43 patients were classified as having minimal enhancement (average enhancement, 8.0+/-4.2%), 30 as having moderate enhancement (21.3+/-5.8%), and 8 as having extensive enhancement (50.1+/-15.4%). The rate of AF recurrence was 6 patients (14.0%) with minimal enhancement, 13 (43.3%) with moderate enhancement, and 6 (75%) with extensive enhancement (P<0.001). CONCLUSIONS: DE-MRI provides a noninvasive means of assessing left atrial myocardial tissue in patients suffering from AF and might provide insight into the progress of the disease. Preablation DE-MRI holds promise for predicting responders to AF ablation and may provide a metric of overall disease progression.

Magnetic resonance imaging-confirmed ablative debulking of the left atrial posterior wall and septum for treatment of persistent atrial fibrillation: rationale and initial experience.

INTRODUCTION: Though pulmonary vein (PV) isolation has been widely adopted for treatment of atrial fibrillation (AF), recurrence rates remain unacceptably high with persistent and longstanding AF. As evidence emerges for non-PV substrate changes in the pathogenesis of AF, more extensive ablation strategies need further study. METHODS: We modified our PV antrum isolation procedure to include abatement of posterior and septal wall potentials. We also employed recently described image-processing techniques using delayed-enhancement (DE) MRI to characterize tissue injury patterns 3 months after ablation, to assess whether each PV was encircled with scar, and to assess the impact of these parameters on procedural success. RESULTS: 118 consecutive patients underwent debulking procedure and completed follow-up, of which 86 underwent DE-MRI. The total left atrial (LA) radiofrequency delivery correlated with percent LA scarring by DE-MRI (r = 0.6, P < 0.001). Based on DE patterns, complete encirclement was seen in only 131 of 335 PVs (39.1%). As expected, Cox regression analysis showed a significant relationship between the number of veins encircled by delayed enhancement and clinical success (hazard ratio of 0.62, P = 0.015). Also, progressive quartile increases in postablation posterior and septal wall scarring reduced recurrences rates with a HR of 0.65, P = 0.022 and 0.66, P = 0.026, respectively. CONCLUSION: Pathologic remodeling in the septal and posterior walls of the LA helps form the pathogenic substrate for AF, and these early results suggest that more aggressive treatment of these regions appears to correlate with improved ablation outcomes. Noninvasive imaging to characterize tissue changes after ablation may prove essential to stratifying recurrence risk.

Modulation of the sinus rate during ventricular fibrillation.

BACKGROUND: During supraventricular and ventricular tachycardia, the arterial baroreflex predominates with minimal contribution from the cardiopulmonary reflex. To our knowledge, the role of the arterial baroreflex gain (BRG) during and immediately following termination of ventricular fibrillation (VF) has not been characterized. OBJECTIVE: We hypothesized that (1) arterial BRG correlated with sinus node cycle length (SNCL) changes during VF, and that (2) the greater the arterial BRG, the greater the blood pressure (BP) recovery following successful defibrillation. METHODS: Arterial BRG was assessed in 18 patients referred for the implantation of a defibrillator incorporating an atrial lead. The average SNCL was measured during the 5 seconds prior to VF induction and the last 5 seconds during VF before defibrillation. Percent SNCL change (%DeltaSNCL) was determined. Arterial BP recovery was calculated as the difference in mean BP following defibrillation compared to during VF. RESULTS: Arterial BRG ranged between -3 and 18 ms/mmHg. During VF, SNCL shortened in 11 patients (group A, mean %DeltaSNCL =-15%), and surprisingly lengthened in seven patients (group B, mean %DeltaSNCL = 5%). There was no correlation between %DeltaSNCL and arterial BRG. In fact, arterial BRG in group A was lower when compared with group B (P = 0.075). Similarly, there was no correlation between arterial BRG and BP recovery. CONCLUSIONS: We found no correlation between arterial BRG and %DeltaSNCL during VF, or BP recovery following defibrillation. Our findings of SNCL lengthening in 7 of 18 patients suggest that in some patients, arterial BRG plays a minor role during VF with a greater contribution from the cardiopulmonary BRG.

Atrial fibrillation ablation in patients with therapeutic international normalized ratios.

AIMS: Pulmonary vein antrum isolation (PVAI) plays a pivotal role in the comprehensive treatment of atrial fibrillation (AF). The need for effective anticoagulation bridging following PVAI is associated with significant vascular complication rates and increased costs. We investigated the safety of PVAI in patients with therapeutic international normalized ratios (INR) the day of the procedure. METHODS: A case-control analysis was performed on patients who underwent PVAI with therapeutic INR (>2). Patients with normal preprocedure INR served as controls. The incidence of major and minor hematomas, fistulas, vascular injury, and cardiac perforation or tamponade were catalogued. PVAI was performed under fluoroscopic, electro-anatomical, and intracardiac echocardiographic guidance, with an open irrigation ablation technique. RESULTS: A total of 194 patients (mean age 64 +/- 12) were included; 87 patients underwent PVAI with therapeutic INR (cases) and 107 with normal INR (controls). Persistent AF was more prevalent than paroxysmal AF in the therapeutic INR group. The mean INR for cases was 2.8 +/- 0.7 compared to 1.4 +/- 0.3 in the control group (P < 0.01). All procedures were completed without acute complications. Two major adverse events were observed, one in each arm. No significant difference in terms of minor (6.5% vs. 5.7%, P = 0.23) or major (0.93% vs. 1.15%, P = 0.49) vascular events or bleeding was detected between the therapeutic INR and the control group. The combined endpoint of major and minor complications did not differ among groups (9.35% vs. 8.05%, P = 0.19). CONCLUSION: Atrial fibrillation ablation in patients with therapeutic INR on the day of a procedure appears to be safe and feasible. Expensive outpatient anti-coagulation bridging may be safely avoided in this type of population.

Relation of daytime bradyarrhythmias with high risk features of sleep apnea.

Bradyarrhythmias (BA) have been reported in patients with sleep apnea (SA), but the incidence of SA in patients with BA remains unclear. A case-control study was conducted to assess the prevalence of high-risk features of SA in patients with documented BA on 24-hour Holter monitoring compared with patients without BA. Controls were age-matched patients selected from those with no evidence of BA on 24-hour Holter monitoring. BA were defined as the presence of pauses of >3 seconds, regardless of the mechanism, and/or heart rate <40 beats/min during presumed waking hours (8 a.m. to 8 p.m.). High-risk features of SA were determined by the Berlin Questionnaire, with positive results defined as having '2 of 3 positive high-risk categories. Body mass index (BMI), hypertension, beta-blocker use, and other underlying characteristics were cataloged. Nineteen patients with documented BA and 47 with no BA were identified. The mean ages and BMIs in the active and control groups were not statistically significant. High-risk features for SA were present in 57.8% of patients in the BA group compared with 21.3% in the control group (p = 0.003). After controlling for age, BMI, hypertension, and beta-blocker use, patients with BA were 6 times more likely to have high-risk features of SA compared with those without BA (logistic regression odds ratio 6.1, 95% confidence interval 1.5 to 24, p = 0.012). In conclusion, irrespective of BMI, age, and other underlying risk factors, the presence of daytime BA was highly associated with high-risk features of SA.

Heart rate variability measures during sinus rhythm predict cycle length entropy during atrial fibrillation.

INTRODUCTION: Several noninvasive measures of cardiac risk such as heart rate variability (HRV) cannot be used in patients with atrial fibrillation (AF). One promising exception is the measure of ventricular cycle length entropy (VCLE) where initial data suggest that a reduction in VCLE portends an increased risk of cardiac death in patients with chronic AF. In this study, we hypothesized that measures of short-term HRV during sinus rhythm would correlate with measures of cycle length entropy during paroxysms of AF. METHODS: We tested 25 Holter recordings of paroxysmal AF from the Physionet AF Prediction Database. We calculated HRV parameters including standard deviation of all NN intervals (SDNN), the root mean square root of the differences between adjacent NN intervals (RMSSD), standard deviation of 5-minute averages of NN intervals (SDANN), percentage of adjacent NN interval differences >50 ms (pNN50), and interbeat correlation coefficient (ICC) from 30 minutes of normal sinus rhythm, and entropy measures (the Shannon Informational Entropy [ShEn] and Average of Approximate Entropy [ApEn]) from 5 minutes of AF that occurred during the same 24-hour monitor. Pairwise correlations were used to assess associations, as regression residuals were normally distributed. RESULTS: The mean entropy measures during AF were: ShEn: 4.78 +/- 0.82, ApEn: 0.198 +/- 0.21. When assessed during the 30 minutes immediately preceding AF onset, ICC showed a significant negative correlation with both ShEn (r =-0.65, P < 0.001) and ApEn (r =-0.60, P < 0.01). RMSSD also correlated with both ShEn (r = 0.41, P = 0.04) and ApEn (r = 0.39, P = 0.05), but other HRV measures showed no correlation with VCLE during AF. CONCLUSION: Reductions in RMSSD or increases in ICC, two short-term HRV measures that are known to reflect parasympathetic function in sinus rhythm, are correlated with reductions in the entropy of ventricular response intervals during AF. Our findings suggest that entropy during AF may be modulated, in part, by vagal innervation.

Scatter in repolarization timing predicts clinical events in post-myocardial infarction patients.

BACKGROUND: Increased spatial and temporal dispersion of repolarization contributes to ventricular arrhythmogenesis. Beat-to-beat fluctuations in T-wave timing are thought to represent such dispersion and may predict clinical events. OBJECTIVE: The purpose of this study was to assess whether a novel noninvasive measure of beat-to-beat instability in T-wave timing would provide additive prognostic information in post-myocardial infarction patients. METHODS: We studied 678 patients from 12 hospitals with 32-lead 5-minute electrocardiogram recordings 6-8 weeks after myocardial infarction. Custom software identified R wave-to-T wave intervals (RTIs) and diastolic intervals (DIs). Repolarization scatter (RTI:DI(StdErr)) was then calculated as the standard error about the RTI:DI regression line. In addition, left ventricular ejection fraction (LVEF), short-term heart rate variability (HRV) parameters, and QT variability index were measured. Patients were followed for the composite endpoint of death or life-threatening ventricular arrhythmia. RESULTS: After a mean follow-up of 63 months, 134 patients met the composite endpoint. An RTI:DI(StdErr) >5.50 ms was associated with a 210% increase in arrhythmias or deaths (P <.001). After adjusting for LVEF, RTI:DI(StdErr) remained an independent predictor (P <.001). RTI:DI(StdErr) was also independent of short-term HRV parameters and the QT variability index. CONCLUSIONS: Increased repolarization scatter, a measure of high-frequency, cycle-length-dependent repolarization instability, predicts poor outcomes in patients after myocardial infarction.

Atrial flutter ablation in inducible patients during pulmonary vein atrum isolation: a randomized comparison.

BACKGROUND: The incidence of atrial flutter (AFL) post pulmonary vein antrum isolation (PVAI) in patients with atrial fibrillation (AF) is reported to be between 8% and 20%. The need for right or left AFL ablation during the initial PVAI procedure remains controversial. We prospectively compared mapping and ablation versus no ablative treatment of inducible AFL during PVAI. METHODS AND RESULTS: In 220 patients (167 men, mean age 56+/-15 years) with symptomatic AF presenting for PVAI, burst pacing from the high right atrium and coronary sinus was performed to determine AFL inducibility. A total of 25 patients with sustained (17 patients) or reproducible (eight patients) AFL were included in this study. Patients were randomized to mapping and ablation of AFL using the CARTO 3D mapping system (Biosense Webster, Diamond Bar, CA, USA) versus no further ablation. Typical AFL was induced in 48% of the patients. During a follow-up of 12+/-4 months, recurrences were determined by serial 48-h Holter and event monitors. Recurrence rates, time to recurrence, and AFL cycle length differences between both groups were not statistically significant. CONCLUSION: These data suggest that inducibility of AFL post PVAI does not predict long-term incidence of AFL. Moreover, this study demonstrates little benefit to mapping and ablation of these arrhythmias during the PVAI procedures.

High-density mapping and ablation of concealed low-voltage activity within pulmonary vein antra results in improved freedom from atrial fibrillation compared to pulmonary vein isolation alone.

BACKGROUND: Despite advancements, the goal of durable pulmonary vein isolation (PVI) in all patients undergoing ablation for atrial fibrillation (AF) remains elusive. New high-density mapping (HDM) allows detection of concealed low-voltage signals (CLVSs) that persist after PVI and may represent vulnerabilities in the lesion set. OBJECTIVE: The purpose of this study was to determine the incidence of CLVSs after PVI and the effect of CLVS ablation on outcomes. METHODS: We conducted a case control study comparing 150 patients undergoing HDM-guided PVI and subsequent CLVS mapping and ablation (39 redo, 111 de novo) against 452 historical controls undergoing traditional PVI alone. PVI was similarly performed and confirmed in both groups. RESULTS: Baseline characteristics were similar, except left atrial size was larger in the HDM-guided group. Acute PVI was achieved in nearly all patients in both groups. In the HDM group, 31 of 150 patients exhibited CLVS after luminal PVI, and all were subsequently eliminated. During mean follow-up of 320 days, after controlling for baseline characteristics, the HDM-guided group exhibited a hazard ratio of 0.19 in freedom from AF (P <.001). De novo patients exhibited a hazard ratio of 0.44 relative to redo patients in the HDM-guided group. Both subgroups exhibited significantly lower event rates compared to controls in log-rank analysis (P <.001). CONCLUSION: CLVSs are commonly identified with HDM after PVI, likely representing vulnerabilities in antral lesion sets. Ablation of these targets seems to significantly improve freedom from AF compared to PVI alone.

Randomized comparison between open irrigation technology and intracardiac-echo-guided energy delivery for pulmonary vein antrum isolation: procedural parameters, outcomes, and the effect on esophageal injury.

INTRODUCTION: We performed a prospective study to compare efficacy and safety of both open irrigation tip (OIT) technology with intracardiac echo (ICE)-guided energy delivery in patients presenting for PVAI. METHODS AND RESULTS: Fifty-three patients presenting for PVAI were randomized to ablation using an OIT catheter (Group 1, 26 patients; temperature and power were set at 50 degrees and 50 W, respectively, with a saline pump flow rate of 30 mL/min) or radiofrequency (RF) energy delivery under ICE guidance (Group 2, 27 patients; energy was titrated based on microbubbles formation). The mean procedure time and fluoroscopy exposure were lower in Group 1 (164 +/- 42 min and 7,560 +/- 2,298 microGray m2 vs 204 +/- 47 min and 12,240 +/- 4,356 microGray m2; P = 0.005 and 0.008, respectively). Moreover, the durations of RF lesions applied per PV antrum was lower in Group 1 compared with Group 2 (5.1 +/- 2.2 min vs 9.2 +/- 3.2 min, P = 0.03, respectively). Within 24 hours after PVAI in 35.7% (all erythema) of Group 1 and 57.1% (21.4% erythema and 35.7% necrosis) of Group 2, patients' esophageal wall changes were documented. After 14 +/- 2 months of follow up, recurrences were documented in 19.2% of Group 1 and 22.2% of Group 2 patients. CONCLUSION: Although both OIT and ICE-guided energy delivery possess a similar effect in treating AF, OIT seems to be superior in terms of achieving isolation and shortening fluoroscopy exposure. Moreover, a lower incidence of esophageal wall injury was observed utilizing OIT for PVAI.

Heart rate turbulence parameters correlate with post-premature ventricular contraction changes in muscle sympathetic activity.

BACKGROUND: Heart rate turbulence (HRT) has been shown to be vagally mediated with a strong correlation to baroreflex indices. However, the relationship between HRT and peripheral sympathetic nerve activity (SNA) after a premature ventricular contraction (PVC) remains unclear. OBJECTIVE: We sought to evaluate the relationship between HRT and the changes in peripheral SNA after PVCs. METHODS: We recorded postganglionic muscle SNA during electrocardiogram monitoring in eight patients with spontaneous PVCs. Fifty-two PVCs were observed and analyzed for turbulence onset (TO) and slope (TS). SNA was quantified during (1) the dominant burst after the PVC (dominant burst area) and (2) the 10 seconds after the dominant burst (postburst SNA). RESULTS: The mean TO was 0.1% +/- 4.6%, and the mean TS was 6.1 +/- 6.6. The dominant burst area negatively correlated with TO (r = -0.50, P = .0002). The postburst SNA showed a significant positive correlation with TO (r = 0.44, P = .001) and a negative correlation with TS (r = -0.42, P = .002). These correlations remained significant after controlling for either the PVC coupling interval or the left ventricular ejection fraction. CONCLUSIONS: Our findings highlight the relationship between perturbations in HRT and pathology in the sympathetic limb of the autonomic nervous system. Future studies are needed to evaluate the prognostic role of baroreflex control of sympathetic activity in patients with structural heart disease.

The effects of rate and irregularity on sympathetic nerve activity in human subjects.

BACKGROUND: We have recently shown that atrial fibrillation is associated with an increase in sympathetic nerve activity (SNA) compared with sinus rhythm. It remains unclear, however, whether these findings are true at various rates and whether the magnitude of sympathoexcitation is related to the degree of irregularity. OBJECTIVE: To determine the role of irregularity in mediating the SNA changes at various pacing rates. Univariate analysis showed that as the irregularity increased, SBP increased (r = 0.44, P < .001) but that MAP and DBP did not change significantly. METHODS: Using custom-made software, atrioventricular sequential pacing with predetermined rates (100, 120, and 140 bpm) and irregularities (standard deviation = 0%, 5%, 15%, and 25% of mean cycle length) was performed in 23 patients referred for electrophysiologic evaluation. Pacing at each rate/irregularity was performed for 2 minutes, with 2 minutes of recovery in between. Systolic, diastolic, and mean arterial blood pressure (SBP, DBP, and MAP), central venous pressure (CVP), and SNA were measured at baseline and during pacing. RESULTS: Univariate analysis showed that as the irregularity increased, SBP increased (r = 0.44, P < .001 but that MAP and DBP did not change significantly. A significant correlation was found between the pacing irregularity and SNA, with greater sympathoexcitation noted at greater degrees of irregularity (r = 0.2, P = .04). A five-variable linear model using DBP, MAP, CVP, and degree of pacing irregularity to predict SNA was highly statistically significant (r = 0.46, P < .001). After controlling for hemodynamic changes, for every 1% increase in irregularity, there was a 6.1% increase in SNA. CONCLUSION: We have shown that greater degrees of irregularity cause greater sympathoexcitation and that the effects of irregular pacing on SNA are independent of the hemodynamic changes.

Cardiovascular Implantable Electronic Device Infections: Risk Scoring and Role of Antibiotic Envelope in Prevention.

Cardiac implantable electronic device (CIED) has been increasingly used with expanding indications in patients with cardiac diseases. There is substantial evidence to suggest of their role in improving outcomes in patients with and without heart failure. Complications of the device implantation including infections are associated with increased morbidity and mortality and also substantial financial burden to the society. Several clinical characteristics have been recognized as risk factors for the occurrence of the infections. Considering that infections occur in the presence of multiple risk factors acting together, scoring systems have been developed in identifying patients at risk. Despite preventive measures, the rates of infections associated with CIEDs have increased over the last decade. Recent studies have documented the role of implantable antibiotic eluting pouches in reducing infections in patients undergoing CIED implantation. The present review will address the risk scoring systems studied and also address the role of antibiotic pouch and the recent patents in developing this technology.

Favorable changes in cardiac geometry and function following gastric bypass surgery: 2-year follow-up in the Utah obesity study.

OBJECTIVES: The objective of this study was to test the hypothesis that gastric bypass surgery (GBS) would favorably impact cardiac remodeling and function. BACKGROUND: GBS is increasingly used to treat severe obesity, but there are limited outcome data. METHODS: We prospectively studied 423 severely obese patients undergoing GBS and a reference group of severely obese subjects that did not have surgery (n = 733). RESULTS: At a 2-year follow up, GBS subjects had a large reduction in body mass index compared with the reference group (-15.4 ± 7.2 kg/m(2) vs. -0.03 ± 4.0 kg/m(2); p < 0.0001), as well as significant reductions in waist circumference, systolic blood pressure, heart rate, triglycerides, low-density lipoprotein cholesterol, and insulin resistance. High-density lipoprotein cholesterol increased. The GBS group had reductions in left ventricular (LV) mass index and right ventricular (RV) cavity area. Left atrial volume did not change in GBS but increased in reference subjects. In conjunction with reduced chamber sizes, GBS subjects also had increased LV midwall fractional shortening and RV fractional area change. In multivariable analysis, age, change in body mass index, severity of nocturnal hypoxemia, E/E', and sex were independently associated with LV mass index, whereas surgical status, change in waist circumference, and change in insulin resistance were not. CONCLUSIONS: Marked weight loss in patients undergoing GBS was associated with reverse cardiac remodeling and improved LV and RV function. These data support the use of bariatric surgery to prevent cardiovascular complications in severe obesity.

Bipolar lumenless lead performance in children and adults with congenital heart disease.

BACKGROUND: Because of small size and anatomic variation, implantation of intracardiac leads for permanent pacing in pediatric and congenital heart disease (CHD) patients can be challenging. A novel 4.1F bipolar catheter-delivered lead offers potential advantages for this population. OBJECTIVE; The purpose of this study was to retrospectively evaluate this lead performance in this specific population. METHODS: We performed a retrospective descriptive analysis of all pediatric and adult CHD patients at a single center implanted with a 4.1F bipolar catheter-delivered active fixation pacemaker lead (Medtronic model 3830, Medtronic, Inc, Minneapolis, MN, USA). RESULTS: Over 10 months, 42 leads were implanted in 27 patients. Twenty-six atrial and 16 ventricular leads were placed. Patient ages were 1-28 years (mean 15 +/- 7), and weights were 7.8-104 kg (mean 51.5 +/- 26.6). Ventricular septal defect and D-transposition of great arteries were the most prevalent CHD diagnoses. Implant capture thresholds were 1.2 +/- 0.8 V at 0.5 ms in the atrium and 0.8 +/- 0.5 V at 0.5 ms in the ventricle. Implant sensing thresholds were 4.1 +/- 2.7 mV in the atrium and 12.1 +/- 4.9 mV in the ventricle. Phrenic nerve stimulation was avoided in all, and selective site pacing was achieved in most cases. Pacing and sensing thresholds remained stable during 90 +/- 52 days follow-up. No lead related complications, failures, or extractions were observed. CONCLUSIONS: In our single-center experience with pediatric and CHD patients, a novel small, catheter-delivered bipolar lead has proven safe and effective for atrial and ventricular pacing in acute and subacute time periods. Longer performance trends will be required to determine chronic efficacy.