Importance Pulmonary vein isolation remains the foundational ablation approach for atrial fibrillation (AF), yet outcomes in persistent AF remain suboptimal. Targeting low-voltage zones identified by electroanatomical mapping offers a promising strategy for enhancing ablation success. Objective To determine whether adjunctive individualized low-voltage zone ablation improves arrhythmia outcomes and health-related quality of life beyond pulmonary vein isolation alone in patients with persistent AF and significant low-voltage zones. Design, Setting, and Participants Multicenter randomized clinical trial with 12 months of follow-up conducted at 5 Swedish ablation centers between May 18, 2020, and April 9, 2026. Of 936 adult patients undergoing first-time ablation and voltage mapping for persistent AF, 209 with low-voltage zones of 3.0 cm 2 or greater were randomized. Interventions Following pulmonary vein isolation, patients with significant low-voltage zones were randomized to either receive individualized adjunctive low-voltage zone ablation (n = 102) or receive no further ablation (n = 107). Main Outcomes and Measures The primary outcome was freedom from documented atrial arrhythmia without antiarrhythmic drugs at 12 months after 1 or 2 ablation procedures within 6 months. Secondary outcomes were time to first recurrence after a single procedure without antiarrhythmic drugs, health-related quality of life, and safety. Results Among the 209 randomized patients (median age, 72 years; 109 females [52.2%]), the primary outcome was achieved more frequently in the pulmonary vein isolation plus low-voltage zone ablation group than in the pulmonary vein isolation alone group. Arrhythmia-free survival was achieved in 69 patients (67.6%) vs 40 patients (37.4%), respectively (unadjusted difference, 30.3% [95% CI, 17.4%-43.2%]; odds ratio, 3.5 [95% CI, 2.0-6.2]; P < .001). Time to first recurrence after a single ablation procedure without antiarrhythmic drugs also favored low-voltage zone ablation (hazard ratio, 0.4; 95% CI, 0.3-0.6; P < .001). Improvements in health-related quality of life were greater in the low-voltage zone ablation group, whereas rates of serious adverse events were similar between groups. Conclusions and Relevance Adjunctive low-voltage zone ablation added to pulmonary vein isolation improved rhythm outcomes and health-related quality of life without increasing serious adverse events in patients with persistent AF and significant low-voltage zones. These findings support a low-voltage zone–guided ablation strategy in this population. Trial Registration ClinicalTrials.gov Identifier: NCT04377594

Importance:Pulmonary vein isolation remains the foundational ablation approach for atrial fibrillation (AF), yet outcomes in persistent AF remain suboptimal. Targeting low-voltage zones identified by electroanatomical mapping offers a promising strategy for enhancing ablation success. Objective:To determine whether adjunctive individualized low-voltage zone ablation improves arrhythmia outcomes and health-related quality of life beyond pulmonary vein isolation alone in patients with persistent AF and significant low-voltage zones. Design, Setting, and Participants:Multicenter randomized clinical trial with 12 months of follow-up conducted at 5 Swedish ablation centers between May 18, 2020, and April 9, 2026. Of 936 adult patients undergoing first-time ablation and voltage mapping for persistent AF, 209 with low-voltage zones of 3.0 cm2 or greater were randomized. Interventions:Following pulmonary vein isolation, patients with significant low-voltage zones were randomized to either receive individualized adjunctive low-voltage zone ablation (n = 102) or receive no further ablation (n = 107). Main Outcomes and Measures:The primary outcome was freedom from documented atrial arrhythmia without antiarrhythmic drugs at 12 months after 1 or 2 ablation procedures within 6 months. Secondary outcomes were time to first recurrence after a single procedure without antiarrhythmic drugs, health-related quality of life, and safety. Results:Among the 209 randomized patients (median age, 72 years; 109 females [52.2%]), the primary outcome was achieved more frequently in the pulmonary vein isolation plus low-voltage zone ablation group than in the pulmonary vein isolation alone group. Arrhythmia-free survival was achieved in 69 patients (67.6%) vs 40 patients (37.4%), respectively (unadjusted difference, 30.3% [95% CI, 17.4%-43.2%]; odds ratio, 3.5 [95% CI, 2.0-6.2]; P < .001). Time to first recurrence after a single ablation procedure without antiarrhythmic drugs also favored low-voltage zone ablation (hazard ratio, 0.4; 95% CI, 0.3-0.6; P < .001). Improvements in health-related quality of life were greater in the low-voltage zone ablation group, whereas rates of serious adverse events were similar between groups. Conclusions and Relevance:Adjunctive low-voltage zone ablation added to pulmonary vein isolation improved rhythm outcomes and health-related quality of life without increasing serious adverse events in patients with persistent AF and significant low-voltage zones. These findings support a low-voltage zone-guided ablation strategy in this population. Trial Registration:ClinicalTrials.gov Identifier: NCT04377594.

Objective:This study aimed to examine the incidence of atrial fibrillation in patients with an accessory pathway (AP) and its association with transient ischemic attack (TIA)/stroke as well as mortality over long-term follow-up. Methods:A total of 1,302 consecutive patients who underwent first-time ablation AP between 2005 and 2018 were included from the Karolinska Ablation Registry and followed up through the National Patient Registry and Cause of Death Registry. Results:Patients were 41.7 ± 15.7 years old and 60.9% were men. New-onset or recurrence of atrial fibrillation occurred in 111 patients (8.5%) after a follow-up of up to 10 years (median 6.8 years; interquartile range 3.9-9.9 years). Multivariable analysis revealed that a history of atrial fibrillation, hyperlipidemia, a higher BMI, and older age were independently associated with new-onset or recurrence of atrial fibrillation during follow-up. All-cause mortality and TIA/stroke occurred in 35 patients (2.7%) and 28 patients (2.2%) after a follow-up of 10 years, respectively. Multivariable analysis revealed that the occurrence of atrial fibrillation during follow-up was independently associated with both outcomes. Conclusion:In this large patient cohort with ablated APs, long-term follow-up revealed a high incidence of atrial fibrillation with 8.5%. Occurrence of atrial fibrillation during follow-up was independently associated with both all-cause mortality and TIA/stroke. Hence, closer monitoring for atrial fibrillation is advisable in patients with ablated APs, especially in those with a prior history of atrial fibrillation.

AIMS:Controversy remains as to whether the exercise stress test (EST) is sufficient for risk evaluation in patients with pre-excitation. This study aims to clarify the usefulness of EST in risk stratification in both asymptomatic and symptomatic patients presenting with pre-excitation. METHODS AND RESULTS:This prospective study includes consecutive asymptomatic and symptomatic patients with pre-excitation referred for risk assessment. All participants performed an incremental EST (bicycle) prior to an electrophysiology study (EPS). Primary data from the EST included loss of pre-excitation during exercise, and primary data from the EPS included the measurement of accessory pathway effective refractory period (APERP), shortest pre-excited RR interval (SPERRI), and inducible arrhythmia with the use of a beta-adrenergic receptor agonist if deemed necessary. One hundred and sixty-four patients (59 asymptomatic, 105 symptomatic) completed an EST and EPS. Forty-five patients (27%) demonstrated low-risk findings on EST, of which 19 were asymptomatic and 26 were symptomatic. Six patients with low-risk EST findings had SPERRI/APERP ≤ 250 ms at EPS, and two of them were asymptomatic. The sensitivity, specificity, positive predictive value, negative predictive value (NPV), and accuracy of low-risk EST for excluding patients with SPERRI/APERP ≤ 250 ms were 40, 91, 87, 51, and 60%, respectively. The number of patients with inducible arrhythmia at EPS was similar in the asymptomatic (36, 69%) and symptomatic (73, 61%) groups. CONCLUSION:Sudden loss of pre-excitation during EST has a low NPV in excluding high-risk APs. The EPS with the use of isoproterenol should be considered to accurately assess the risk of patients with pre-excitation regardless of symptoms (ClinicalTrials.gov Identifier: NCT03301935).

Background Atrioventricular nodal re-entrant tachycardia (AVNRT) is the most common paroxysmal supraventricular tachycardia. We sought to investigate the incidence of atrial fibrillation in patients with electrophysiologically confirmed/ablated AVNRT and its association with transient ischemic attack (TIA)/stroke as well as mortality during long-term follow-up. Methods From the Karolinska Ablation Registry, 2855 consecutive patients with a first-time ablation for AVNRT between 2005 and 2018 were analyzed. Results Patients were 52.1 +/- 15.9 years old and 59.3% were women. During follow-up of up to 10 years (median 6.0 years; interquartile range 3.3 to 9.2 years), new onset or recurrence of atrial fibrillation occurred in 317 (11.1%) patients (incidence rate 19 cases per 1000 person-years). Excluding those with history of atrial fibrillation, new onset of atrial fibrillation occurred in 153 (6.1%) patients. In multivariable analysis, history of atrial fibrillation, arterial hypertension, history of TIA/stroke, and heart failure remained independently associated with new onset or recurrence of atrial fibrillation during follow-up. Death of any cause and TIA/stroke occurred in 141 (4.9%) patients and 107 (3.7%) patients, respectively. In multivariable analysis, occurrence of atrial fibrillation during follow-up remained independently associated with both outcomes. The prevalence of atrial fibrillation according to age at the end of follow-up was high among young patients (<60 years of age: 12.7%; 60-69 years of age: 10.6%). Conclusion In this large cohort of patients with diagnosed AVNRT, the incidence of atrial fibrillation was high (11.1%) during long-term follow-up. Occurrence of atrial fibrillation during follow-up remained independently associated with death for any cause as well as with TIA/stroke. Therefore, a closer monitoring for atrial fibrillation in patients with AVNRT including those at young age is advisable.

OBJECTIVE:Catheter ablation of atrial fibrillation effectively reduces symptomatic burden. However, its long-term effect on mortality and stroke is unclear. We investigated if patients with atrial fibrillation who undergo catheter ablation have lower risk for all-cause mortality or stroke than patients who are managed medically. METHODS:We retrospectively included 5628 consecutive patients who underwent first-time catheter ablation for atrial fibrillation between 2008 and 2018 at three major Swedish electrophysiology units. Control individuals with an atrial fibrillation diagnosis but without previous stroke were selected from the Swedish National Patient Register, resulting in a control group of 48 676 patients. Propensity score matching was performed to produce two cohorts of equal size (n=3955) with similar baseline characteristics. The primary endpoint was a composite of all-cause mortality or stroke. RESULTS:Patients who underwent catheter ablation were healthier (mean CHA2DS2-VASc score 1.4±1.4 vs 1.6±1.5, p<0.001), had a higher median income (288 vs 212 1000 Swedish krona [KSEK]/year, p<0.001) and had more frequently received university education (45.1% vs 28.9%, p<0.001). Mean follow-up was 4.5±2.8 years. After propensity score matching, catheter ablation was associated with lower risk for the combined primary endpoint (HR 0.58, 95% CI 0.48 to 0.69). The result was mainly driven by a decrease in all-cause mortality (HR 0.51, 95% CI 0.41 to 0.63), with stroke reduction showing a trend in favour of catheter ablation (HR 0.75, 95% CI 0.53 to 1.07). CONCLUSIONS:Catheter ablation of atrial fibrillation was associated with a reduction in the primary endpoint of all-cause mortality or stroke. This result was driven by a marked reduction in all-cause mortality.

To study the association between timing and success of electrical cardioversion (ECV) for the treatment of early recurrences (ERs) of atrial fibrillation post pulmonary vein isolation (PVI) on long-term rhythm outcome. Data of 133 patients ablated for paroxysmal or persistent atrial fibrillation receiving ECV for ERs, i.e., atrial tachyarrhythmia recurrences within 90 days post ablation were analyzed. During 1-year follow-up, patients were screened for late recurrences (LRs), i.e., recurrences after the blanking period. In 114 patients (85.7%), ECV was successful compared to 19 patients (14.3%) with failed ECV. A higher body mass index (odds ratio (OR) 1.19 (95% CI 1.02–1.39), p = 0.029), a lower left ventricular ejection fraction (OR 1.07 (95% CI 0.99–1.15), p = 0.079), and performance of ECV > 7 days from ER onset (OR 2.99 (95% CI 1.01–8.87), p = 0.048) remained independently associated with ECV failure. During 1-year follow-up, the rate of LR was significantly higher among patients with failed ECV as compared to patients with successful ECV (hazard ratio (HR) 3.00 (95% CI, 1.79–5.03), p < 0.001). Patients with ECV performed > 7 days from ER onset had a significantly higher risk of developing LR as compared to patients with ECV performed within ≤ 7 days from ER onset (HR 1.73 (95% CI 1.15–2.62), p = 0.009). Performance of ECV > 7 days from ER onset (HR 1.76 (95% CI 1.16–2.67), p = 0.008) and failed ECV (HR 3.32 (95% CI 1.96–5.64), p < 0.001) remained independently associated with LR. A failed ECV and performance of ECV > 7 days from ER onset were independently associated with LR.

Background: Cryoablation (CRYO) of cavotricuspid isthmus (CTI)-dependent atrial flutter (AFL) has been shown to be non-inferior to radiofrequency ablation (RF) in terms of ablation success and is associated with less pain. However, procedural time has been significantly longer with CRYO compared to RF. A possible explanation for this could be that operators had less experience with CRYO than with RF. The purpose of this study was to test the hypothesis that in the hands of experienced operators, cryoablation of CTI-dependent AFL is effective with procedure-time similar to what is reported for RF. Methods: This prospective 2-center study included 184 patients with CTI-dependent AFL - median age 66 years (range 28-83), 159 men (86%). Cryoablation was performed using a 9 F, 8 mm tip catheter (Freezor MAX, Medtronic, Inc, MN, USA). Ablation endpoint was bidirectional CTI-block. Pain was evaluated with a visual analogue scale (VAS 0-10). All operators had experience of at least 25 previous CTI-ablations with CRYO. Results: The acute success rate was 89%. Procedural time including an observation period of 30 min, was 115 +/- 36 min which is similar to procedural times for RF in previous studies. Fluoroscopy time was 11 +/- 9 min. Cryoablation was perceived as almost pain- free by the patients, VAS (mean) 1.8 +/- 1.2. Success rate at 12-month follow-up (FU) was 88% in patients with primary success. No major adverse events occurred. Conclusions: Cryoablation of CTI-dependent AFL is effective, with a low level of procedure-related pain. In experienced hands, the procedure time in this prospective non-randomised trial seems to be in the level of reported procedure times for RF. The long-term relapse rate appears to be higher than for RF.

This study evaluates the incidence of procedural complications related to catheter ablation of atrial fibrillation (AF) to assess the potential feasibility and safety of same‐day discharge in a large cohort.

AIM:Data on ablation for atypical recurrent atrioventricular nodal reentry tachycardia (AVNRT) and long-term follow-up are generally sparse. Furthermore, the rate of recurrence and safety of cryoablation for atypical AVNRT has not been established. We compared patients cryoablated for atypical AVNRT and typical AVNRT during long-term follow-up.METHODS:All patients (n = 2612) who underwent catheter ablation for AVNRT at the Karolinska University Hospital between January 2009 and August 2019 were analyzed. A total of 91 patients undergoing first-time cryoablation for atypical AVNRT were included. A control group with first-time cryoablation for typical AVNRT was matched in a 1:1 ratio. Patients were followed-up for recurrences for a median of 5.0 years (interquartile range: 3.1-7.5 years).RESULTS:After 5 years, AVNRT recurrence occurred in 10 patients (11.0%) in the atypical AVNRT group and in 8 patients (8.8%) in the typical AVNRT group (hazard ratio: 1.31 [95% confidence interval: 0.52-3.32]; p = 0.568). The duration of the index procedure was significantly longer for atypical compared to typical AVNRT ablation (132.1 ± 49.2 min vs. 110.1 ± 38.8 min; p = 0.001). Transient AV blocks occurred in a similar fashion in the atypical compared to typical group (11 [12.1%] vs. 4 [4.9%]; p = 0.103). However, no ablation induced persistent AV block developed in either group.CONCLUSION:Cryoablation for atypical AVNRT showed similar rate of recurrences and safety compared to typical AVNRT during long-term follow-up.

Purpose Cather ablation is known to influence the autonomic nervous system. This study sought to investigate the association of sinus heart rate pre-/post-ablation and recurrences in patients with atrial fibrillation undergoing pulmonary vein isolation (PVI). Methods Between January 2012 and December 2017, data of 482 patients undergoing their first PVI were included. Sinus heart rate was recorded before (PRE), directly post-ablation (POST) and 3 months post-ablation (3 M). All patients were screened for atrial tachyarrhythmia recurrences during the one-year follow-up. Results In the total study cohort, the mean resting sinus heart rate at PRE [mean 57.9 bpm (95% CI 57.1–58.7 bpm)] increased by over 10 bpm to POST [mean 69.4 bpm (95% CI 68.5–70.3 bpm); p < 0.001] followed by a slight decrease at 3 M [mean 67.3 bpm (95% CI 66.4–68.2 bpm)] but still remaining higher compared to PRE ( p < 0.001). This pattern was observed in patients with and without recurrences at POST and 3 M (both p < 0.001 compared to PRE). However, at 3 M the mean sinus heart rate was significantly lower in patients with compared to patients without recurrences ( p = 0.031). In this regard, patients with a heart rate change < 11 bpm (PRE to 3 M) or, as an alternative parameter, patients with a heart rate < 60 bpm at 3 M had a significantly higher risk of recurrences compared to the remaining patients (Hazard ratio (HR) 1.82 (95% CI 1.32–2.49), p < 0.001 and HR 1.64 (95% CI 1.20–2.25), p = 0.002, respectively). Conclusion Our study confirms the impact of PVI on cardiac autonomic function with a significant sinus heart rate increase post-ablation. Patients with a sinus heart rate change < 11 bpm (PRE to 3 M) are at higher risk for recurrences during one-year post-PVI.

OBJECTIVE The preferential sites for focal atrial tachycardia (FAT) are mainly in the right atrium in both sexes. However, a limited number of studies have indicated that sex differences in the localization of FAT. This study investigated possible sex differences in the distribution of FAT in a large cohort of patients referred for ablation. METHODS From 2004 to 2019, 487 patients (298 women) were referred to our institution for ablation of FAT. A standard electrophysiological study was conducted, and isoproterenol or atropine was given when needed. Conventional catheter mapping, electroanatomic contact mapping, and noncontact mapping were used to assess the origin of ectopic atrial tachycardia. RESULTS Overall, 451 foci were successfully ablated in 436 patients (90%). Although the foci located along the crista terminalis were more common in women than in men (42% vs. 29%; p=0.023), the opposite were found in the foci located along the tricuspid annulus (5% vs. 11%; p=0.032) and the right atrial appendage (RAA) (1% vs. 3%; p=0.032). Other locations were similarly distributed in men and women. In addition, the presence of persistent FAT was more frequent in men than in women (22% vs. 5%; p<0.001). Finally, the difference in the induction pattern of FAT was also remarkable between sexes. CONCLUSION The distribution of FAT in women and men is different. In addition, persistent FAT seems more often in men than in women. The different distribution, persistency, and induction pattern of FAT should be considered in the successful management of this type of tachycardia.

Iatrogenic cardiac tamponades are a rare but dreaded complication of invasive electrophysiology procedures (EPs). Their long-term impact on clinical outcomes is unknown. This study analyzed the risk of death or serious cardiovascular events in patients suffering from EP related cardiac tamponade requiring pericardiocentesis during long-term follow-up. Out of 19997 invasive EPs at our university hospital between January 1998 and September 2018, all patients with EP related periprocedural cardiac tamponade were identified (n=60) and matched (1:3 ratio) to a control group (n=180). After a follow-up of 5 years, the composite primary end point - death from any cause, acute myocardial infarction, TIA/stroke and hospitalization for heart failure – occurred in significantly more patients in the tamponade than in the control group (12 patients (20.0%) vs 19 patients (10.6%); Hazard ratio (HR) 2.53 (95% CI, 1.15–5.58); p=0.021). This was mainly driven by a higher incidence of TIA/stroke in the tamponade than in the control group (HR 3.75 (95% CI, 1.01–13.97); p=0.049). Death from any cause, acute myocardial infarction and hospitalization for heart failure did not show a significant difference between the groups. Hospitalization for pericarditis occurred in significantly more patients in the tamponade than in the control group (HR 36.0 (95% CI, 4.68–276.86); p=0.001). Patients with EP related cardiac tamponade are at higher risk for cerebrovascular events during the first two weeks and hospitalization for pericarditis during the first months after index procedure. Despite the increased risk for early complications tamponade patients have a good long-term prognosis without increased risk for mortality or other serious cardiovascular events. Type of funding source: Foundation. Main funding source(s): German Research Foundation

AIMS:To investigate the significance of early recurrence (ER) of atrial tachyarrhythmias after pulmonary vein isolation (PVI) on the development of late recurrence (LR) and to redefine the blanking period during which an ER is considered nonspecific.METHODS:Data of 713 patients undergoing their first PVI for paroxysmal or persistent atrial fibrillation between January 2012 and December 2017 were included. All patients were followed-up for 12 months according to clinical and outpatient routine and were screened for any atrial tachyarrhythmia lasting >30 seconds occurring during the first 3 months postablation (ER) and after the 3 months blanking period (LR).RESULTS:Patients with ER compared to those without ER had significantly more LR (74.5% vs 16.5% vs, P < .001). The occurrence of ER during the first, second and third months showed increasing LR rates of 35.2%, 67.9%, and 94.8%, respectively (P < .001). Receiver operator characteristic analysis revealed a blanking period of 46 days with the highest sensitivity (68.1%) and specificity (96.5%). Later timing and longer time span of ER were independent predictors for LR in multivariable analysis.CONCLUSION:ER is a strong predictor for LR. Our study advocates a shortening of the post-PVI blanking period followed by a "gray zone" up to 3 months where individualized therapeutic decisions based on additional risk factors should be considered. We suggest that the ER time span might serve as such a predictor identifying patients at the highest risk for LR.

AIMS:The transseptal approach is used for left atrial access during the ablation of atrial fibrillation (AF) and other left-sided arrhythmia substrates. Transseptal puncture (TP) is commonly performed with fluoroscopic guidance, contrast injection, and pressure monitoring. In many centres, additional techniques [intracardiac echocardiography (ICE), transoesophageal echocardiography (TEE), radiofrequency needle] are used to facilitate TP but its use adds costs. In this retrospective study, we studied the safety and complication rate when TP was routinely done with fluoroscopic guidance, contrast injection, and pressure monitoring using ICE or TEE only in selected cases. METHODS AND RESULTS:This study analysed 4690 consecutive TP performed between 2000 and 2015: 3408 (72.6%) were ablation of AF, left-sided atrial flutter, or left-sided atrial tachycardia (non-AP group); 1153 (24.6%) were ablation of left-sided accessory pathway, AP group; and 129 (2.8%) were ablation of ventricular tachycardia. Transseptal puncture was done under fluoroscopy, pressure monitoring, and commonly using contrast media injection. In 27 procedures, ICE or TEE was used to guide the TP. We found 34 tamponades (Tx) that required pericardial drainage of which 28 (0.59%) could possibly be TP related and six could not. The total complication rate for all Tx was 0.72%. A higher rate of tamponades was observed in the AF (non-AP) group than in the AP group (0.88 vs. 0.17%, P < 0.02). The highest rate of tamponades was registered during the operators 51-100 cases, 1.3%, and decreased to 0.4% in cases 101-200, P = 0.04. CONCLUSION:TP can safely be done under fluoroscopy and pressure monitoring without routine use of additional techniques. With experience, operators should be able to further decrease complication rate.

Purpose: The transseptal approach is used for ablation of atrial fibrillation (AF) and other left sided substrates. Transseptal puncture (TP) is commonly done with fluoroscopic guidance and pressure monitoring. Intracardiac echocardiography (ICE) is in many centers routinely used to guide TP but adds costs. In this retrospective study we investigated the safety and complication rate when TP routinely was done without ICE. Aims: 1) To assess the safety of TP with fluoroscopic guidance and pressure monitoring without routine use of additional techniques. 2) To assess the importance of experience for safe TP. Methods: 4610 consecutive TP between 2000 and 2015 were analyzed. 3405 (74%) were ablation for AF, left sided atrial flutter or left sided atrial tachycardia (non AP group), 1076 (23%) were for left sided accessory pathway (AP group) and 129 (3%) were for ablation of ventricular tachycardias. TP was done under fluoroscopy, pressure monitoring, and commonly contrast injection. For 20 procedures ICE was used to guide the transseptal puncture. Conclusion: TP can safely be done under fluoroscopy and pressure monitoring without routine use of ICE. There is a learning curve with decreasing complication rate with experience.

Ablation Effectiveness and Biophysical Parameters Background There is a paucity of data on biophysical parameters during radiofrequency ablation of scar‐mediated ventricular tachycardia (VT). Methods and Results Data were collected from consecutive patients undergoing VT ablation with open‐irrigation. Complete data were available for 372 lesions in 21 patients. The frequency of biophysical parameter changes were: >10Ω reduction (80%), bipolar EGM reduction (69%), while loss of capture was uncommon (32%). Unipolar injury current was seen in 72% of radiofrequency applications. Both EGM reduction and impedance drop were seen in 57% and a change in all 3 parameters was seen in only 20% of lesions. Late potentials were eliminated in 33%, reduced/modified in 56%, and remained after ablation in 11%. Epicardial lesions exhibited an impedance drop (90% vs. 76%, P = 0.002) and loss of capture (46% vs. 27%, P < 0.001) more frequently than endocardial lesions. Lesions delivered manually exhibited a >10Ω impedance drop (83% vs. 71%, P = 0.02) and an EGM reduction (71% vs. 40%, P < 0.001) more frequently than lesions applied using magnetic navigation, although loss of capture, elimination of LPs, and a change in all 3 parameters were similarly observed. Conclusions VT ablation is inefficient as the majority of radiofrequency lesions do not achieve more than one targeted biophysical parameter. Only one‐third of RF applications targeted at LPs result in complete elimination. Epicardial ablation within scar may be more effective than endocardial lesions, and lesions applied manually may be more effective than lesions applied using magnetic navigation. New technologies directed at identifying and optimizing ablation effectiveness in scar are clinically warranted.