An annotation-independent algorithm based on electrogram characteristics to guide the identification of ventricular tachycardia isthmuses in patients with structural heart disease.

BACKGROUND: Criteria such as electrograms voltage or late potentials have been largely utilized in the past to help identify areas of substrate maps that are within the ventricular tachycardia (VT) isthmus; yet their specificity and positive predictive value are quite low. The Lumipoint fractionation tool of the Rhythmia system illuminates regions with fractionated electrograms irrespective of their timing and annotation. We aimed to ascertain whether the use of this tool can rapidly identify areas within VT isthmuses from substrate maps. METHODS: Thirty patients with structural cardiomyopathy in whom a complete right ventricular-paced substrate map and a full reconstruction of the diastolic isthmus during VT could be obtained were enrolled. The VT isthmus border was projected on each substrate map to verify whether the areas illuminated by Lumipoint fell within those borders. The behavior of the electrograms detected at the illuminated areas of the substrate maps was studied during a right ventricular drive train and extra stimulus protocol: if the near field potentials showed a delayed conduction after a single extra stimulus, defined as a minimum of 10 ms increase of the time interval between the far field and the near field activation measured during the drive train, the electrogram was said to have a "decremental" behavior. RESULTS: The logistic analysis showed that areas with fractionated electrograms illuminated by the Lumipoint software and showing the greatest decremental behavior fell within the VT isthmus borders (OR = 1.66, CI: 1.41-1.75, p<0.001; OR=1.57 CI: 1.32-1.72, p<0.001, respectively) with a sensitivity, specificity, and positive predictive value of 87%, 96%, and 97%, respectively. CONCLUSIONS: Fractionated electrograms illuminated by the automated Lumipoint software on right ventricular-paced substrate maps showing the greatest decremental behavior fall within the VT isthmus borders with a probability of 0.97, irrespective of their timing, annotation, or voltage, without any need for subjective assessment of their involvement in slow conduction areas.

Combining contact force and local impedance to treat idiopathic premature ventricular contractions from the outflow tracts: impact of ablation strategy on outcomes.

BACKGROUND: Contact force (CF)-sensing catheters have not proved superior to standard catheters in the ablation of premature ventricular contractions (PVCs) from the right and left ventricular outflow tract (RVOT, LVOT). In this context, the utility of measuring local impedance (LI) is not known. We aimed to ascertain whether the use of a catheter combining LI and CF information was associated with superior outcomes in comparison with other catheter technologies. METHODS: We compared three groups of 40 propensity-matched patients with PVCs from the OTs, ablated by means of different catheter technologies: a CF-plus LI-featured catheter, an LI-featured catheter, and a standard irrigated catheter. RESULTS: The CF + LI group displayed a significantly lower risk of PVC recurrence than the standard ablation group (HR, 0.22; 95%CI, 0.07-0.71; p = 0.01). In the CF + LI group, LI drop and RF time were the only predictors of successful lesions (OR = 1.19, CI: 1.13-1.26, p < 0.001; OR = 1.06 CI: 1.01-1.07, p = 0.044, respectively). In the coronary cusps, unlike the RVOT/LVOT region, CF was not associated with LI drop (p = 0.48), and RF duration showed a linear relationship with LI drop (p < 0.001). CONCLUSIONS: The use of ablation catheters that combine CF and LI information is associated with increased success in the RF ablation of PVCs from the OTs. LI drop is the most important predictor of effective lesions, but its behavior depends on the ablation site: in the coronary cusps, unlike the RVOT/LVOT region, longer RF application times are needed in order to achieve LI drops associated with successful outcomes. REGISTRY AND REGISTRATION NO. OF THE STUDY/TRIAL: NCT03793998.

One-year outcomes in patients undergoing very high-power short-duration ablation for atrial fibrillation.

BACKGROUND: The very high-power short-duration (vHPSD) temperature-controlled ablation (vHPSD) improves the efficiency of pulmonary vein isolation (PVI) procedures. We evaluated the procedural and 12-months outcomes in atrial fibrillation (AF) patients undergoing PVI by means of vHPSD ablation. In patients with AF or atrial tachyarrythmia (AT) recurrence undergoing a redo procedure the durability of the PVI was investigated. METHODS: Consecutive paroxysmal/persistent AF patients undergoing PVI with the vHPSD ablation strategy (90 W, for 4 s) were enrolled. The rate of PVI, first-pass isolation, acute reconnection, and procedural complications were evaluated. Follow-up examinations and EKG were scheduled at 3,6, and 12 months. In case of AF/AT recurrence, patients underwent a redo procedure. RESULTS: Overall, 163 AF patients (29 persistent and 134 paroxysmal) were enrolled. The PVI was reached in 100% of patients (88% at the first pass). The rate of acute reconnection was 2%. The radiofrequency, fluoroscopy and procedural times were respectively 5.5 ± 1 min, 9 ± 1 min and 75 ± 20 min. No death, tamponade nor steam pops occurred; however, 5 patients had vascular complications. The 12-months freedom from AF/AT recurrence was 86% in both paroxysmal and persistent patients. Overall, 9 patients underwent a redo procedure, and in 4 all veins were still isolated, whereas in 5 pulmonary vein reconnections were found. The PVI durability was 78%. No overt clinical complications were observed in the follow-up. CONCLUSIONS: The vHPSD ablation represents an effective and safe ablation strategy to achieve PVI. The 12-months follow-up showed high freedom from AF/AT recurrence and a good safety profile.

Prospective evaluation of local impedance drop to guide left atrial posterior wall ablation with high power.

BACKGROUND: Local impedance (LI) drop predicts acute conduction block during pulmonary vein isolation (PVI). Whether the LI drop predicts also the achievement of left atrial posterior wall isolation (LAPWI) in persistent atrial fibrillation (PersAF) patients is unknown. We evaluated the efficacy and the safety of LI drop-guided LAPW ablation by using high power (50 watts) and investigated the impact of ablation parameters on the LI drop. METHODS: We included consecutive PersAF patients underwent PVI and both roof line and floor line completion to achieve LAPWI with a novel contact force (CF)- and LI-featured catheter (IntellaNAV Stablepoint™). For each radiofrequency (RF) application, we targeted a LI drop of 25 ohms. RESULTS: Out of 30 patients, first-pass floor line block was achieved in 26 (87%) and first-pass roof line block in 17 (57%), resulting in first-pass LAPWI in 14 patients (47%). After touch-up ablations, LAPWI was achieved in 28 patients (93%) with endocardial ablation only. No procedural nor 1-month complications occurred. Overall, 877 RF applications were delivered: 787 ablation tags (89%) were associated with acute conduction block, while 90 (11%) were located at sites of acute gaps in either the roof or floor line. LI drop values were greater at segments with acute block than those with gaps (p < 0.001). At multivariable analysis, only LI drop and RF time remained independently associated with the acute block (p < 0.001; p = 0.001). CONCLUSIONS: LI drop-guided LAPWI at a fixed power of 50 W was effective and did not lead to complications. LI drop was the most important predictor of acute conduction block.

Dielectric-based tissue thickness measured during radiofrequency catheter ablation.

INTRODUCTION: A new dielectric-based method (KODEX-EPD mapping system, EPD Solutions, a Philips company) for measuring tissue thickness at the catheter-tissue interface has recently been developed. We reported preliminarydata on real-time catheter-based measuring myocardial wall thickness in vivo, during typical atrial flutter radio frequency ablation. METHODS AND RESULTS: The study population consisted of 12 consecutive patients, suffering from symptomatic paroxysmal or persistent cavo-tricuspid isthmus dependent, counter clockwise and clockwise AFL, under going a first catheter ablation between April 2021 and November 2021. The new KODEX-EPD function, Wall Viever, was used to calculate atrialwall thickness. The atrial wall thickness was significantly higher closeto the tricuspid annulus than close to the inferior vena cava (3.6 ± 0.5 mm vs 2.4 ± 0.3 mm, p < .001) and a trend towards a progressive decrease of atrial wall thickness was observed moving the mapping catheter from the tricuspidvalve to the inferior vena cava. CONCLUSIONS: Thenew KODEX-EPD function, Wall Viever, allowed us to assess atrial wall thickness during atrial flutter radio frequency ablation.

Targeted ablation of residual pulmonary vein potentials in atrial fibrillation ablation through ultra-high-density mapping: Insights from the CHARISMA registry.

INTRODUCTION: Low-voltage activity beyond pulmonary veins (PVs) may contribute to the failure of ablation of atrial fibrillation (AF) in the long term. We aimed to assess the presence of gaps (PVG) and residual potential (residual antral potential [RAP]) within the antral scar by means of an ultra-high-density mapping (UHDM) system. METHODS: We studied consecutive patients from the CHARISMA registry who were undergoing AF ablation and had complete characterization of residual PV antral activity. The Lumipoint™ (Boston Scientific) map-analysis tool was used sequentially on each PV component. The ablation endpoint was PV isolation (PVI) and electrical quiescence in the antral region. RESULTS: Fifty-eight cases of AF ablation were analyzed. A total of 86 PVGs in 34 (58.6%) patients and 44 RAPs in 34 patients (58.6%) were found. In 16 (27.6%) cases, we found at least one RAP in patients with complete absence of PV conduction. RAPs showed a lower mean voltage than PVG (0.3 ± 0.2 mV vs. 0.7 ± 0.5 mV, p < .0001), whereas the mean number of electrogram peaks was higher (8.4 ± 1.4 vs. 3.2 ± 1.5, p < .0001). The percentage of patients in whom RAPs were detected through Lumipoint™ was higher than through propagation map analysis (58.6% vs. 36.2%, p = .025). Acute procedural success was 100%, with all PVs successfully isolated and RAPs completely abolished in all study patients. During a mean follow-up of 453 ± 133 days, 6 patients (10.3%) suffered an AF/AT recurrence. CONCLUSION: Local vulnerabilities in antral lesion sets were easily discernible by means of the UHDM system in both de novo and redo patients when no PV conduction was present.

Cavotricuspid isthmus ablation by means of very high power, short-duration, temperature-controlled lesions.

BACKGROUND: A very high-power short-duration (vHPSD) strategy of radiofrequency (RF) ablation aims to minimize conductive heating and increase resistive heating. We evaluated the feasibility, efficacy and safety of the vHPSD ablation of the cavotricuspid isthmus (CTI) in patients presenting with typical atrial flutter (AFL). METHODS: This prospective non-randomized study enrolled 28 consecutive patients (FAST Group) with typical AFL undergoing CTI ablation. The vHPSD ablation was performed applying 90 W, for 4 s, with an irrigation of 8 ml/min. Thirty consecutive patients who, previously, underwent CTI ablation by means of a contact force surrounding flow catheter guided by ablation index (500) served as control group (AI Group). RESULTS: In the FAST Group, the mean CTI length was 29 ± 6 mm, and the mean number of RF tags was 20 ± 9. The CTI bidirectional "first pass" block was reached in 25 (89%) patients. There were no major procedural complications. After a mean follow-up of 6 ± 2 months, one (3.5%) patient had arrhythmia recurrence. The vHPSD ablation was as effective as AI-guided ablation in achieving acute CTI block (rate of first pass 89% vs 93%, p = 0.59), with a shorter RF time (88 ± 40 s vs 492 ± 269 s, p < 0.001) and similar procedure (30 ± 4 min vs 34 ± 10 min, p = 0.5) and fluoroscopy time (103 ± 29 vs 108 ± 52 s, p = 0.7). At 8 months, the freedom from AFL recurrence was 96% in the FAST group and 97% in the AI group. CONCLUSIONS: Our preliminary data show that the vHPSD ablation represents an effective and safe ablation strategy to achieve bidirectional block for the treatment of typical AFL.

Fluoroscopy and contrast media use in cryoballoon ablation of atrial fibrillation using a novel imaging system.

Pulmonary vein (PV) isolation using cryoballoon (CB) catheter is generally characterized by a high radiation and contrast media exposure. A new dielectric imaging system (KODEX-EPD imaging system) allows pulmonary vein (PV) occlusion assessment without dye use. The purpose of this study was to verify the feasibility of reducing the radiation and dye use during CB ablation in patients with atrial fibrillation (AF) using the new dielectric imaging system. In a retrospective, single center study, we enrolled 34 consecutive patients with paroxysmal AF divided in two groups: 17 patients in Conventional Group underwent the procedure under fluoroscopy guidance before the new system introduction, while 17 patient in KODEX-EPD Group underwent the procedure under fluoroscopy and KODEX-EPD imaging system guidance. There were no differences in any clinical and anatomical characteristics between the two study groups. Overall procedure time was comparable between the two groups (69 [IQR 63-98] min in Conventional Group vs. 65 [IQR 58-74] min in KODEX-EPD Group, p = 0.16), while fluoroscopy time (8 [IQR 5-9] min vs. 11 [IQR 9-12] min, p = 0.014) and dye use (35 [IQR 28-45] ml vs. 70 [IQR 57-83] ml, p < 0.001) were significantly lower in the KODEX-EPD Group. No 30-day complications were observed. At 12-month follow-up 7/37 (19%) patients had an atrial arrhythmias recurrence, without any difference between the two study groups (17.6% vs. 23.5%, p = 0.68). The use of a new dielectric imaging system allowed a significantly reduction in radiation exposure and dye use during CB ablation in patients with AF.

In vivo biophysical characterization of very high power, short duration, temperature-controlled lesions.

INTRODUCTION: A very high-power short-duration (vHPSD) strategy of radiofrequency (RF) ablation aims to minimize conductive heating and increase resistive heating. This study aimed to clarify the contribution of contact force (CF) and temperature and their interrelationship in making an adequate lesion with the vHPSD catheter. METHODS: We enrolled 46 consecutive patients undergoing first catheter ablation for atrial fibrillation (AF). The vHPSD ablation was performed applying 90 W, for 4 s, with an irrigation of 8 ml/min. During an application, an impedance drop (ID) ≥10 Ω was regarded as an adequate lesion formation. RESULTS: The mean procedural time was 95 ± 15 min. First-pass isolation was reached in 89% of patients and at the end of the procedure all pulmonary veins were isolated. No steam pop nor procedural complication occurred. A total of 3829 qualified RF points were analyzed and the median values of ID, CF and maximum temperature were respectively 10.6 (IQR 8.6-13.1) Ohm, 9 (5.8-13.8) g, 46.8 (44.1-49.8) °C. The mean ID significantly increased in parallel with the increasing CF as well as with the increasing maximum temperature. In the multivariable analysis only the CF and the maximum temperature were independent predictors of ID. From receiver operating characteristic curve analysis, a CF of 8 g and a maximum temperature of 47°C are the optimal cutoff discriminatory value for adequate lesion formation. CONCLUSIONS: The vHPSD ablation is highly effective and safe. The CF and the maximum temperature are independent predictors of adequate lesion formation assessed by means of ID.

Occlusion tool software for pulmonary vein occlusion verification in atrial fibrillation cryoballoon ablation.

BACKGROUND: Optimal pulmonary vein (PV) occlusion, usually verified with selective contrast injection, is mandatory to obtain an effective PV isolation during cryoballoon (CB) ablation. AIM OF THE STUDY: The purpose of this study was to verify the feasibility and the accuracy of a new dielectric sensing system in assessing PV occlusion during CB ablation in patients with atrial fibrillation (AF). METHODS: We enrolled 28 consecutive patients with paroxysmal or persistent AF. After transseptal access, a detailed image reconstruction of left atrium and PVs was achieved with an octapolar or decapolar mapping catheter (Achieve catheter, Medtronic Inc.) and KODEX-EPD system (EPD Solutions, a Philips company). The degree of PV occlusion with the inflated Arctic Front Advance Cryoballoon (Medtronic Inc.) was verified using the new "occlusion tool" software module (EPD Solutions, a Philips company) and compared to an angiogram obtained with contrast medium injection in each PV. RESULTS: A total of 105 PV CB occlusion were tested. The new occlusion tool software module showed a 91% sensitivity and 76% specificity in assessing a complete PV occlusion verified with contrast medium injection. The positive predictive value was 80%, and the negative predictive value was 88.6%. Mean procedure time was 81 ± 17 minutes. Mean fluoroscopy time was 6 ± 2 minutes. No 30-day complications were observed. CONCLUSION: The new dielectric imaging system was able to assess the degree of PV occlusion during a CB ablation with good sensitivity and specificity.

A novel local impedance algorithm to guide effective pulmonary vein isolation in atrial fibrillation patients: Preliminary experience across different ablation sites from the CHARISMA pilot study.

INTRODUCTION: Recently, a novel technology able to measure local impedance (LI) and tissue characteristics has been made available for clinical use. This analysis explores the relationships among LI and generator impedance (GI) parameters in atrial fibrillation (AF) patients. Characterization of LI among different ablation spots and procedural success were also evaluated. METHODS AND RESULTS: Consecutive patients undergoing AF ablation from the CHARISMA registry at five Italian centers were included. A novel radiofrequency (RF) ablation catheter with a dedicated algorithm (DIRECTSENSE™) was used to measure LI and to guide ablation. The ablation endpoint was pulmonary vein (PV) isolation. We analyzed 2219 ablation spots created around PVs in 46 patients for AF ablation. The mean baseline tissue impedance was 105.8 ± 14 Ω for LI versus 91.8 ± 10 Ω for GI (p < .0001). Baseline impedance was homogenous across the PV sites and proved higher in high-voltage areas than in intermediate- and low-voltage areas and the blood pool (p < .001). Both LI and GI displayed a significant drop after RF delivery, and absolute LI drop values were significantly larger than GI drop values (14 ± 8 vs. 3.7 ± 5 Ω, p < .0001). Every 5-point increment in LI drop was associated with successful ablation (odds ratio = 3.05, 95% confidence interval: 2.3-4.1, p < .0001). Conversely, GI drops were not significantly different comparing successful versus unsuccessful sites (3.7 ± 5 vs. 2.8 ± 4 Ω, p = .1099). No steam pops or major complications occurred during or after the procedures. By the end of the procedures, all PVs had been successfully isolated in all patients. CONCLUSIONS: The magnitude of the LI drop was more closely associated with effective lesion formation than the GI drop.

Design and rationale of the Impact of MultiPoint pacing in CRT patients with reduced RV-to-LV delay (IMAGE-CRT) study.

BACKGROUND: Cardiac resynchronization therapy (CRT) is an established treatment in patients with heart failure and prolonged QRS duration. A biventricular device is implanted to achieve faster activation and more synchronous contraction of the ventricles. Despite the convincing effect of CRT, 30-40% of patients do not respond. We decided to investigate the role of multipoint pacing (MPP) in a selected group of patients with right ventricle (RV)-to-left ventricle (LV) intervals less than 80 ms that do not respond to traditional CRT. METHODS: We will enrol 248 patients in this patient-blinded, observational, clinical study aiming to investigate if MPP could decrease LV end-systolic volume (ESV) in patients with RV-to-LV interval less than 80 ms. MPP will be activated ON at implant in patients with RV-to-LV delay less than 80 ms and OFF in RV-to-LV at least 80 ms. At follow-up the activation of MPP will be related to CRT response. The primary study endpoint will be the responder rate at 6 months, defined as a decrease in LV ejection fraction, LV end-diastolic volume, LV end-systolic volume (LVESV) at least 15% from baseline. Secondary outcomes include 12 months relative percentage reduction in LVESV and a combined clinical outcome measure of response to CRT defined as the patient being alive, no hospitalization due to heart failure, and experiencing an improvement in New York Heart Association functional class (Composite-Score). CONCLUSION: Reducing the nonresponder rate continues to be an important goal for CRT.If an increase in reverse remodelling can be achieved by MPP, this study supports the conduct of larger trials investigating the role of MPP on clinical outcomes in selected patients treated, right now, only with traditional CRT. TRIAL REGISTRATION: ClinicalTrials.gov, NCT02713308. Registered on 18 March 2016.

Safety and efficacy of atrial fibrillation ablation guided by Ablation Index module.

PURPOSE: Reconnection of pulmonary veins (PVs) remains common following radiofrequency catheter ablation for atrial fibrillation (AF). Ablation Index (AI) is a novel ablation quality marker that incorporates stability, contact force (CF), time, and power in a weighted formula. Its use seems to improve lesion durability. This is a prospective, single-arm registry to investigate on the safety and mid-term efficacy of AF ablation guided by the AI. METHODS: One hundred fifty-six consecutive patients (mean age 58 ± 10 years, 49% males, 44% with structural heart disease) referred for paroxysmal (124) or persistent (32) AF underwent antral PV isolation using a surround flow CF-sensing catheter guided by the AI. Radiofrequency was delivered targeting interlesion distance ≤ 6 mm and Ablation Index of 330-350 at posterior wall and 400-450 at anterior wall. RESULTS: Mean overall procedure time was 95 ± 30 min with a mean fluoroscopy time of 5 ± 6 min. Mean ablation time was 26 ± 10 min, 627/628 targeted PV were isolated. One pericardial effusion and two groin hematomas were reported; none required intervention. During a mean follow-up of 14 ± 6 months, 17 (10.8%) (9% paroxysmal AF vs 22% persistent AF, p = 0.09) patients had an atrial arrhythmia recurrence. CONCLUSIONS: PV ablation guided by AI resulted feasible, achieving a high rate of isolated PVs, with a low complication rate, and allowed a high single-procedure arrhythmia-free survival at 14 months.

Highly complicated lead extraction procedure in patient with previous early orthotopic heart transplantation: A first case report.

We report a first case of a highly complicated lead extraction in a young man who previously underwent orthotopic heart transplantation (OHT).Lead extraction in transplanted patients may be a feasible and safe procedure in order to maintain a low infective risk and to preserve alternative vascular access sites.

High-resolution mapping and ablation of recurrent left lateral accessory pathway conduction.

Proper localization of the anatomical target during ablation of the accessory pathways (AP) and the ability to detect clear AP potentials on the ablation catheter are crucial for successful AP ablation. We report a case of recurring AP conduction that was finally eliminated using a novel ablation catheter equipped with high-resolution mini-electrodes. Smaller and closer electrodes result in high mapping resolution with less signal averaging and cancellation effects. Owing to improved sensitivity, the new catheter seems effective in detecting fragmented and high frequency signals, thus allowing more effective radiofrequency application and improving ablation success.

Radiation Dose is Significantly Reduced by Use of Contact Force Sensing Catheter During Circumferential Pulmonary Vein Isolation.

The creation of a durable radiofrequency (RF) lesion depends on several parameters, including catheter tip electrode size and composition, tip orientation, temperature, RF pulse duration, power, blood flow, and catheter to tissue contact. The development of new contact force (CF) sensor catheters has allowed the measurement of the tip to tissue CF during the RF ablation procedure. Here, we describe the clinical experience obtained using CF catheters for atrial fibrillation ablation, with a specific focus on the impact of CF technology on acute procedural data (procedure and fluoroscopy time).

Long-term outcomes of CRT-PM versus CRT-D recipients.

OBJECTIVE: To compare the rates of all-cause mortality in recipients of cardiac resynchronization therapy devices without (CRT-PM) versus with defibrillator (CRT-D). METHODS: Between February 1999 and July 2004, 233 patients (mean age = 69 +/- 8 years, 180 men) underwent implantation of CRT-PM or CRT-D devices. New York Heart Association (NYHA) heart failure functional class II was present in 11%, class III in 69%, and class IV in 20% of patients; mean left ventricle ejection fraction (LVEF) was 26.5 +/- 6.5 %, 48% presented with idiopathic dilated cardiomyopathy and 49% with ischemic heart disease. Cox multiple variable regression analysis was performed in search of predictors of death. RESULTS: The clinical characteristics of the 117 CRT-PM and 116 CRT-D recipients were similar, except for LVEF (28.2 +/- 6.2% vs 25.0 +/- 6.5%, respectively; P < 0.001), and ischemic versus nonischemic etiology of heart failure (41% vs 56%, respectively P = 0.02). Over a mean follow-up of 58 +/- 15 months, no significance difference in overall mortality rate was observed between the two study groups. Male sex, NYHA functional class IV, and atrial fibrillation at implant were significant predictors of death. CONCLUSIONS: There was no difference in long-term survival rate among patients with CRT-D versus CRT-PM, although CRT-D more effectively lowered the sudden death rate. Male sex, NYHA functional class IV, and atrial fibrillation predicted the worst prognosis.

Long-term performance of coronary sinus leads used for cardiac resynchronization therapy.

BACKGROUND: Little is known regarding the long-term performance of coronary sinus (CS) leads, which have an effect on the longevity of cardiac resynchronization therapy (CRT) systems. METHODS: This study included 109 patients (79 men) whose mean age was 68 +/- 9 years, New York Heart Association (NYHA) functional class 3.2 +/- 0.5, and left ventricular ejection fraction 25.6 +/- 6.6%, and who underwent CRT (n = 45) or CRT-D (n = 64) systems implants for management of idiopathic (53%), ischemic (40%), or miscellaneous (7%) dilated cardiomyopathy. Unipolar (n = 57) or bipolar (n = 52) leads were placed into the CS venous system. RESULTS: At implant, no significant difference was observed between unipolar and bipolar leads with respect to mean sensing performance (14 +/- 6 mV vs 14 +/- 8 mV, P = 0.97), pacing impedance (875 +/- 234 ohms vs 943 +/- 331 ohms, P = 0.24), and stimulation energy threshold (2 +/- 3.2 muJ vs 1.13 +/- 1.5 muJ, P = 0.08). At a median follow-up of 33 months, a significant decrease in stimulation impedance and increase in stimulation energy threshold was observed with unipolar (689 +/- 122 vs 875 +/- 234 ohms, P < 0.01, and 8.34 +/- 10.4 muJ vs 2 +/- 3.2 muJ, P < 0.001, respectively) as well as with bipolar (735 +/- 268 ohms vs 943 +/- 331 ohms, P < 0.01, and 4.81 +/- 9.92 vs 1.13 +/- 1.5 muJ, P = 0.02, respectively) leads. No significant difference in sensing performance was observed with either type of lead (10 +/- 5 mV vs 14 +/- 6 mV and 10 +/- 6 mV vs 14 +/- 8 mV, respectively). At long-term follow-up, no significant difference among any sensing or stimulation parameter was observed between unipolar and bipolar leads. CONCLUSIONS: At long-term follow-up, a significant increase in the energy required for stimulation was observed, whereas sensing performance remained unchanged. The increase in energy capture threshold was less marked with bipolar than with unipolar leads.