A simplified differential pacing technique for the evaluation of bidirectional cavo-tricuspid isthmus block during ablation of typical atrial flutter.

PURPOSE: Bidirectional block of the cavo-tricuspid isthmus (CTI) is an established endpoint of CTI-dependent atrial flutter (AFl) ablation. Differential pacing has been used to evaluate the CTI block. The purpose of this study is to describe a modified differential pacing technique to evaluate the CTI block. METHODS: Sixty-two patients underwent radiofrequency (RF) ablation of CTI-dependent AFl. The acute endpoints were non-inducibility of the AFl, and verification of the bidirectional CTI block by our methodology. Pacing was performed in the CS with an ablation catheter positioned immediately lateral to the CTI ablation line, and then 1-2 cm more laterally. The stimulus-to-ablation catheter atrial electrogram intervals were measured at these sites (StimCS-Abl1 and StimCS-Abl2, respectively). Pacing with the ablation catheter also was performed at these 2 sites, and the stimulus-to-CS electrogram intervals (StimABL1-CS and StimABL2-CS) were measured. The criteria for the bidirectional block were StimCS-Abl1 > StimCS-Abl2, and StimABL1-CS > StimABL2-CS. Clinical efficacy was defined as freedom from recurrent AFl during follow-up. RESULTS: Following 12.2 ± 3.7 min of RF delivery across the CTI, intervals were StimCS-Abl1 = 181.2 ± 22.7 ms and StimABL1-CS = 181.0 ± 23.6 ms, and StimCS-Abl2 = 152.2 ± 26.5 ms and StimABL2-CS = 151.2 ± 22.7 (P < 0.001). Atrial flutter was rendered not inducible in all patients, and no procedural complications were encountered. During the next 15.9 ± 0.7 months, two patients were lost to follow-up, and among the 62 other patients, one (1.7%) had flutter recurrence. CONCLUSIONS: The bidirectional CTI block can be assessed quickly and easily using only the ablation and CS catheters for differential pacing.

Stepwise Approach for Ventricular Tachycardia Ablation in Patients With Predominantly Intramural Scar.

OBJECTIVES: The goal of this study was to assess the value of a stepwise, image-guided ablation approach in patients with cardiomyopathy and predominantly intramural scar. BACKGROUND: Few reports have focused on catheter-based ventricular tachycardia (VT) ablation strategies in patients with predominantly intramural scar. METHODS: The study included patients with predominantly intramural scar undergoing VT ablation. A stepwise strategy was performed consisting of a localized ablation guided by conventional mapping criteria followed by a more extensive ablation if VT remained inducible. The extensive ablation was guided by the location and extent of intramural scarring on delayed enhanced-cardiac magnetic resonance imaging. A historical cohort who did not undergo additional extensive ablation was identified for comparison. A novel measurement, the scar depth index (SDI), indicating the percent area of the scar at a given depth, was correlated with outcomes. RESULTS: Forty-two patients who underwent stepwise ablation (median age 61 years [interquartile range: 55 to 69 years], 35 male patients, median left ventricular ejection fraction 36.0% [25.0% to 55.0%], ischemic [n = 4] or nonischemic cardiomyopathy [n = 38]) were followed up for a median of 17 months (8 to 36 months). A stepwise approach resulted in a 1-year freedom from VT, death, or cardiac transplantation of 76% (32 of 42). Patients who underwent additional extensive ablation had a lower risk of events than a clinically similar historical cohort (N = 19) (hazard ratio: 0.30; 95% CI: 0.13 to 0.68; p < 0.004). SDI>5mm was associated with worse long-term outcomes (hazard ratio: 1.03; 95% CI: 1.01 to 1.06%; p = 0.03), SDI>5mm >16.5% was associated with failed ablation (area under the curve: 0.84; 95% CI: 0.71 to 0.97). CONCLUSIONS: Stepwise ablation using delayed enhanced-cardiac magnetic resonance guidance is a novel approach to VT ablation in patients with predominantly intramural scarring. The SDI correlates with immediate procedural and long-term outcomes.

Targeting Noninducible Clinical Ventricular Tachycardias in Patients With Prior Myocardial Infarctions Based on Stored Electrograms.

BACKGROUND: Ablation of postinfarction ventricular tachycardia (VT) has been shown to reduce VT recurrence and decrease mortality. However, VT recurrence can occur despite extensive ablation procedures. The lack of inducibility of clinical VTs during ablation procedures remains problematic and may be in part responsible for VT recurrences. In this prospective study, we targeted documented but noninducible clinical VTs based on stored implantable cardioverter-defibrillator (ICD) electrograms. METHODS: Radiofrequency ablation was performed in a consecutive group of 66 postinfarction patients (mean age, 67.5±9.2 years; men, 61; mean left ventricular ejection fraction, 25.1±10.8%) in whom clinical VTs were not inducible during an ablation procedure. In the first 33 patients (control group), only inducible VTs were targeted, and in the second 33 patients, noninducible clinical VTs were also targeted by pace-mapping based on stored ICD-electrograms (ICD-electrogram-guided ablation group). Procedural and clinical outcomes were compared at 24 months post-ablation. RESULTS: VT recurred in 5 patients (15%) in whom the ICD-electrogram-guided approach was performed and in 13 patients (39%) in the control group. Freedom from recurrent VT was higher (log-rank P=0.04) in the ICD-electrogram-guided group, but there was no difference in ventricular fibrillation or in total mortality between both groups. CONCLUSIONS: Ablation guided by pace-mapping of noninducible postinfarction clinical VTs based on ICD-electrograms is feasible and reduces the risk of recurrent VT.

Postinfarction Myocardial Calcifications on Cardiac Computed Tomography: Implications for Mapping and Ablation in Patients With Nontolerated Ventricular Tachycardias.

BACKGROUND: Postinfarction ventricular tachycardia (VT) generally involves myocardial fibers surrounded by scar. Calcification of scar tissue has been described, but the relationship between calcifications within endocardial scar and VTs is unclear. The purpose of this study was to assess the prevalence of myocardial calcifications as detected by cardiac computed tomography (CT) and the benefit for mapping and ablation focusing on nontolerated VTs. METHODS: Fifty-six consecutive postinfarction patients had a cardiac CT performed before a VT ablation procedure. Another 56 consecutive patients with prior infarction without VT who had cardiac CTs served as a control group. RESULTS: Myocardial calcifications were identified in 39 of 56 patients (70%) in the postinfarction group with VT, compared with 6 of 56 patients (11%) in the control group without VT. Calcifications were associated with VT when compared with a control group. A calcification volume of 0.538 cm3 distinguished patients with calcification-associated VT from patients without calcification-associated VTs (area under the curve, 0.87; sensitivity, 0.87; specificity, 0.88). Myocardial calcifications corresponded to areas of electrical nonexcitability and formed a border for reentry circuits for 49 VTs (33% of all VTs for which target sites were identified) in 24 of 39 patients (62%) with myocardial calcifications. A nonconfluent calcification pattern was associated with VT target sites independent of calcification volume ( P=0.01). CONCLUSIONS: Myocardial calcifications detected by cardiac CT in patients with prior infarction are associated with VT. The calcifications correspond to areas of unexcitability and represent a fixed boundary of reentry circuits that can be visualized by CT. Calcifications correspond to effective ablation sites in >1/3 of patients with postinfarction VT.

The relationship between the P wave and local atrial electrogram in predicting conduction block during catheter ablation of cavo-tricuspid isthmus-dependent atrial flutter.

PURPOSE: The endpoint for radiofrequency catheter ablation (RFA) of cavo-tricuspid isthmus (CTI)-dependent atrial flutter (AFL) is complete conduction block along the CTI. The purpose of this study is to evaluate the utility of the temporal relationship between the P wave and the local atrial electrograms in determining complete CTI block. METHODS: RFA of CTI was performed in 125 patients (age 63 ± 11 years). During pacing from the coronary sinus (CS), the intervals from the peak of the P wave (Ppeak) in lead V1 to the second component of the local atrial electrogram (A2) along the ablation line (Ppeak-A2) and from the end of the P wave (Pend) to A2 (Pend-A2) were investigated before and after complete block in the first 100 patients (training set). In the next 25 patients (validation set), Ppeak-A2 and Pend-A2 intervals were prospectively assessed to determine CTI block. RESULTS: The mean Ppeak-A2 and Pend-A2 immediately before complete block were - 15±24 and - 39±23 ms compared to 49 ± 17 and 21 ± 16 ms after CTI block (P < 0.0001). Ppeak-A2 ≥ 20 ms and Pend-A2 ≥ 0 ms predicted CTI block with 98% sensitivity and 95% specificity and 96% sensitivity and 100% specificity, respectively. In the validation set, the positive and negative predictive values of Ppeak-A2 ≥ 20 ms or Pend-A2 ≥ 0 ms were 100 and 96%, respectively. The diagnostic accuracy was 98%. CONCLUSIONS: During pacing from the CS, the temporal relationship between the P wave in lead V1 and A2 is a simple and reliable indicator of complete block during RFA of CTI-AFL.

Correlation between computer tomography-derived scar topography and critical ablation sites in postinfarction ventricular tachycardia.

BACKGROUND: Myocardial wall thickness (WT) in patients with a prior myocardial infarction has been used to indicate scarring. However, the correlation of WT with sites critical to ventricular tachycardia (VT) has not been previously investigated. The purpose of this study was to correlate electroanatomic mapping data obtained during VT ablation with WT determined by cardiac computed tomography (CT). METHODS AND RESULTS: Cardiac CTs were performed in 15 consecutive patients (mean age 63 ± 10 years, 86% male, left ventricular ejection fraction 27 ± 12%) with a prior infarct referred for VT ablation. The CTs were registered to the electroanatomic maps obtained during the mapping procedure. Pacing was performed throughout the scar at sites with fractionated electrograms and isolated potentials. Ablation sites were identified by pace-mapping or entrainment-mapping and these sites were correlated with WT. Bipolar and unipolar voltage amplitude and bipolar electrogram width correlated with WT (correlation coefficient: 0.63, 0.65, and 0.41, respectively, P < 0.001). Ablation target sites were identified for 58 of 113 inducible VTs. The ablation target sites were located on CT-defined ridges (WT: 4.2 ± 1.2 mm) bordered by areas of thinning (WT: 2.6 ± 1.1 mm, P < 0.0001) in 14 of 15 patients. Ablation targets were found on ridges in 49 of 58 VTs (84%) for which target sites were identified. A total of 70 ridges were localized in the 15 patients. VT became noninducible postablation in 11 of 15 patients (73%). CONCLUSION: WT measured by CT identifies ridges of myocardial tissue that often are critical for postinfarction VT and that can be appropriate target sites for ablation.

Spectrum of atrial arrhythmias using the ligament of Marshall in patients with atrial fibrillation.

BACKGROUND: The role of the ligament of Marshall (LOM) in patients with atrial fibrillation (AF) has not been well defined. OBJECTIVE: The purpose of this study was to describe the role of the LOM in patients with AF and related arrhythmias. METHODS: Fifty-six patients (mean age 63 ± 11 years; persistent AF in 48 [86%]; ejection fraction 0.49 ± 0.13; left atrial diameter 4.7 ± 0.6 cm) with LOM-mediated arrhythmias were included. RESULTS: A LOM-pulmonary vein (PV) connection was present in 18 patients (32%) and was eliminated with radiofrequency (RF) ablation at the left lateral ridge or crux (n = 12), at the mitral annulus (n = 3), or with alcohol/ethanol (EtOH) ablation of the vein of Marshall (VOM; n = 3). A LOM-mediated atrial tachycardia (AT) was present in 13 patients (23%). Thirty-one patients with refractory mitral isthmus conduction were referred for potential EtOH ablation. In the 6 patients in whom VOM was injected during perimitral reentry, EtOH resulted in slowing in 3 patients and termination in 1 patient. In others, EtOH infusion resulted in complete isolation of the left-sided PVs and left atrial appendage. Repeat RF and adjunctive EtOH ablation of the VOM tended to be more effective in creating conduction block across the mitral isthmus than RF ablation alone (P = .057). CONCLUSION: The LOM is responsible for a variety of arrhythmia mechanisms in patients with AF and atrial tachycardia. It may be ablated at any point along its course, at the mitral annulus, at the lateral ridge/PV antrum, and epicardially in the coronary sinus and the VOM itself. EtOH ablation of the VOM may be an adjunctive strategy in patients with refractory perimitral reentry.

Ablation of paroxysmal atrial fibrillation using a second-generation cryoballoon catheter or contact-force sensing radiofrequency ablation catheter: A comparison of costs and long-term clinical outcomes.

INTRODUCTION: Although noninferiority of cryoballoon ablation (CBA) and radiofrequency catheter ablation for antral pulmonary vein isolation (APVI) has been reported in patients with paroxysmal atrial fibrillation (PAF), it is not clear whether contact force sensing (CF-RFA) and CBA with the second-generation catheter have similar procedural costs and long-term outcomes. The objective of this study is to compare the long-term efficacy and cost implications of CBA and CF-RFA in patients with PAF. METHODS AND RESULTS: A first APVI was performed in 146 consecutive patients (age: 63 ± 10 years, men: 95 [65%], left atrial diameter: 42 ± 6 mm) with PAF using CBA (71) or CF-RFA (75). Clinical outcomes and procedural costs were compared. The mean procedure time was significantly shorter with CBA than with CF-RFA (98 ± 39 vs. 158 ± 47 minutes, P < 0.0001). Despite a higher equipment cost in the CBA than the CF-RFA group, the total procedure cost was similar between the two groups (P = 0.26), primarily driven by a shorter procedure duration that resulted in a lower anesthesia cost. At 25 ± 5 months after a single ablation procedure, 51 patients (72%) in the CBA, and 55 patients (73%) in the CF-RFA groups remained free from atrial arrhythmias without antiarrhythmic drug therapy (P = 0.84). CONCLUSIONS: The procedure duration was approximately 60 minutes shorter with CBA than CF-RFA. The procedural costs were similar with both approaches. At 2 years after a single procedure, CBA and CF-RFA have similar single-procedure efficacies of 72-73%.

Injection of cold saline for diagnosis of intramural ventricular arrhythmias.

BACKGROUND: The failure to identify a successful target site for catheter ablation despite extensive endocardial and epicardial mapping is a common feature for an intramural site of origin of a ventricular arrhythmia. OBJECTIVE: The purpose of this study was to assess whether transient suppression of premature ventricular complexes (PVCs) by injection of cold saline into the distal coronary venous system can identify an intramural focus. METHODS: Cold saline (room temperature) was injected through an irrigated-tip catheter into the distal coronary venous system in a consecutive series of 26 patients with frequent PVCs referred for catheter ablation. RESULTS: PVCs were temporarily suppressed in 11 of 26 patients during injection of cold saline. Extensive mapping suggested the presence of an intramural site of origin in 9 of 11 patients with PVC suppression by cold saline but in only 1 of 15 patients in whom PVCs were not suppressed. The suppression of PVCs by cold saline was associated with the presence of an intramural PVC focus with an accuracy of 88% (sensitivity 90%, specificity 88%, positive predictive value 82%, negative predictive value 93%, P = .0002). CONCLUSION: Temporary suppression of PVCs by cold saline infused into the distal coronary venous system and the perforator veins strongly suggests the presence of an intramural septal focus of the PVCs.

Single- and dual-site pace mapping of idiopathic septal intramural ventricular arrhythmias.

BACKGROUND: Pace mapping (PM) is used to identify the origin of ventricular arrhythmias (VAs). For intramural VAs, the site of origin often cannot be reached and therefore PM is less accurate. OBJECTIVE: The purpose of this study was to assess the value of single- and dual-site pace maps to differentiate intramural from nonintramural VAs. METHODS: In 18 consecutive patients with idiopathic intramural VAs, pace mapping was performed at 2 breakthrough sites in adjacent anatomic structures. Twelve-lead electrocardiograms of the 2 pace maps were averaged in MATLAB and compared (correlation coefficient [CC]) with the targeted VA. Dual-site pace mapping was performed in a control group of 18 patients with nonintramural VAs at the sites of earliest electrical activation and a breakthrough site in an adjacent anatomic location. RESULTS: Dual-site pace maps had a higher CC than did best single-site pace maps (0.87 ± 0.1 vs 0.81 ± 0.16; P = .02) in patients with intramural VAs. At the site of origin, single-site pace maps had a higher CC than did dual-site pace maps obtained from adjacent anatomic locations (0.93 ± 0.04 vs 0.89 ± 0.05; P = .0004) in patients with nonintramural VAs. Sensitivity, specificity, positive predictive value, and negative predictive value of dual-site pace maps for identifying an intramural VA were 89%, 82%, 84%, 88%, and 86%, respectively. Furthermore, the receiver operating characteristic curve analysis revealed that a CC cutoff value of ≤0.86 for a single-site pace map best differentiated intramural from nonintramural VAs. CONCLUSION: A higher CC value for a dual-site pace map obtained from the earliest breakthrough site as well as a CC cutoff value of ≤0.86 for a single-site pace map obtained from the site of earliest electrical activation can best differentiate intramural from nonintramural VAs.

Value of Cardiac Magnetic Resonance Imaging in Patients With Failed Ablation Procedures for Ventricular Tachycardia.

BACKGROUND: Ventricular tachycardia (VT) in patients with cardiomyopathy originates in scar tissue. Intramural or epicardial scar may result in ineffective ablation if mapping and ablation are limited to the endocardium. The purpose of this study was to investigate whether preprocedural magnetic resonance imaging (MRI) is beneficial in patients with failed endocardial VT ablations in determining an appropriate ablation strategy. METHODS AND RESULTS: A cardiac MRI was performed in 20 patients with a failed ablation procedure and cardiomyopathy (nonischemic n = 12, ischemic n = 8). A subsequent ablation strategy was determined by a delayed enhanced MRI (DE-MRI) and an epicardial subxyphoid access was planned only in patients with epicardial or intramural free-wall scar. MRIs were performed in all patients with or without an implanted cardioverter defibrillator (ICD). The location of scar tissue in the MRI predicted the origin of VT in all patients. In 9/20 patients an epicardial procedure was performed based on the result of the MRI. An endocardial procedure was performed in the remaining 11 patients who had either endocardial or septal scarring and one patient in whom the MRI only showed artifact. Five patients remained inducible postablation and four patients had VT recurrence within a follow-up period of 17 ± 22 months. All of the latter patients had an intramural scar pattern. CONCLUSIONS: Imaging with DE-MRI prior to VT ablation in patients with previously failed endocardial ablation procedures is beneficial in identifying an ablation strategy, helps to focus on an area of interest intraprocedurally, and provides valuable outcomes information.

Coexistent Types of Atrioventricular Nodal Re-Entrant Tachycardia: Implications for the Tachycardia Circuit.

BACKGROUND: There is evidence that atypical fast-slow and typical atrioventricular nodal re-entrant tachycardia (AVNRT) do not use the same limb for fast conduction, but no data exist on patients who have presented with both typical and atypical forms of this tachycardia. We compared conduction intervals during typical and atypical AVNRT that occurred in the same patient. METHODS AND RESULTS: In 20 of 1299 patients with AVNRT, both typical and atypical AVNRT were induced at electrophysiology study by pacing maneuvers and autonomic stimulation or occurred spontaneously. The mean age of the patients was 47.6±10.9 years (range, 32-75 years), and 11 patients (55%) were women. Tachycardia cycle lengths were 368.0±43.1 and 365.8±41.1 ms, and earliest retrograde activation was recorded at the coronary sinus ostium in 60% and 65% of patients with typical and atypical AVNRT, respectively. Thirteen patients (65%) displayed atypical AVNRT with fast-slow characteristics. By comparing conduction intervals during slow-fast and fast-slow AVNRT in the same patient, fast pathway conduction times during the 2 types of AVNRT were calculated. The mean difference between retrograde fast pathway conduction during slow-fast AVNRT and anterograde fast pathway conduction during fast-slow AVNRT was 41.8±39.7 ms and was significantly different when compared with the estimated between-measurement error (P=0.0055). CONCLUSIONS: Our data provide further evidence that typical slow-fast and atypical fast-slow AVNRT use different anatomic pathways for fast conduction.

Noninducibility in postinfarction ventricular tachycardia as an end point for ventricular tachycardia ablation and its effects on outcomes: a meta-analysis.

BACKGROUND: Although ventricular tachycardia (VT) ablation is a widely used therapy for patients with VT, the ideal end points for this procedure are not well defined. We performed a meta-analysis of the published literature to assess the predictive value of noninducibility of postinfarction VT for long-term outcomes after VT ablation. METHODS AND RESULTS: We performed a systematic review of MEDLINE (1950-2013), EMBASE (1988-2013), the Cochrane Controlled Trials Register (Fourth Quarter, 2012), and reports presented at scientific meetings (1994-2013). Randomized controlled trials, case-control, and cohort studies of VT ablation were included. Outcomes reported in eligible studies were freedom from VT/ventricular fibrillation and all-cause mortality. Of the 3895 studies evaluated, we identified 8 cohort studies enrolling 928 patients for the meta-analysis. Noninducibility after VT ablation was associated with a significant increase in arrhythmia-free survival compared with partial success (odds ratio, 0.49; 95% confidence interval, 0.29-0.84; P=0.009) or failed ablation procedure (odds ratio, 0.10; 95% confidence interval, 0.06-0.18; P<0.001). There was also a significant reduction in all-cause mortality if patients were noninducible after VT ablation compared with patients with partial success (odds ratio, 0.59; 95% confidence interval, 0.36-0.98; P=0.04) or failed ablation (odds ratio, 0.32; 95% confidence interval, 0.10-0.99; P=0.049). CONCLUSIONS: Noninducibility of VT after VT ablation is associated with improved arrhythmia-free survival and all-cause mortality.

Characteristics of intramural scar in patients with nonischemic cardiomyopathy and relation to intramural ventricular arrhythmias.

BACKGROUND: Ventricular arrhythmias have been described to originate from intramural locations. Intramural scar can be assessed by delayed-enhanced MRI, but MRIs cannot be performed on every patient. The objective of this study was to assess the value of voltage mapping to detect MRI-defined intramural scar and to correlate the scar with ventricular arrhythmias. METHODS AND RESULTS: In 15 consecutive patients (3 women; age 55±16 years; ejection fraction, 49±13%) with structural heart disease, intramural scar was detected by delayed-enhanced MRI. All patients underwent endocardial unipolar and bipolar voltage mapping guided by the registered intramural scar. Scar volume by MRI was 11.7±8 cm3 with a scar thickness of 4.6±0.7 mm and a preserved endocardial/epicardial rim of 3.3±1.6 and 4.8±2.6 mm, respectively. Endocardial bipolar voltage was 1.6±1.73 mV at the scar, 2.12±2.15 mV in a 1 cm perimeter around the scar, and 2.83±3.39 mV in remote myocardium without scar. The corresponding unipolar voltage was 4.94±3.25, 6.59±3.81, and 8.32±3.39 mV, respectively (P<0.0001). Using receiver-operator characteristic curves, a unipolar cut-off value of 6.78 mV (area under the curve, 0.78) and a bipolar cut-off value of 1.55 mV (area under the curve, 0.69) best separated endocardial measurements overlying scar as compared with areas not overlying a scar. At least 1 intramural ventricular arrhythmia was eliminated in all but 2 patients in this series. CONCLUSIONS: Intramural scar can be detected by unipolar and bipolar voltage, unipolar voltage being more useful. Mapping and ablation of intramural arrhythmias originating from an intramural focus can be accomplished.

Endocardial ablation of postinfarction ventricular tachycardia with nonendocardial exit sites.

BACKGROUND: Most infarct-related ventricular tachycardias (VTs) have an exit site that can be targeted by endocardial ablation. However, some VT reentry circuits have an exit site that is intramural or epicardial. Even these circuits may have an endocardial component that can be endocardially ablated. OBJECTIVE: To assess the prevalence of postinfarction VTs with a nonendocardial exit site that can be successfully eliminated by endocardial ablation. METHODS: Twenty-eight consecutive patients with postinfarction VT (27 men, age 69 ± 8 years, ejection fraction 0.25% ± 0.15%) were referred for VT ablation. A total of 213 VTs were inducible (cycle length 378 ± 100 ms). Pace mapping was performed throughout the scar, and critical sites were identified for 137 VTs (64.5%). Critical sites identified by entrainment mapping and/or pace mapping were divided into exit and nonexit sites depending on the stimulus-QRS/VT cycle length ratio (S-QRS/VT CL ≤ 0.3 vs>0.3). RESULTS: Endocardial exit sites (S-QRS/VTCL ≤ 0.3) were identified for 100 of 137 VTs. Only critical nonexit sites were identified for 37 of 137 (27%) VTs. Nonexit sites were confined to a smaller area within the endocardium (1.81 ± 1.7 cm(2)) and were located within dense scar (0.28 ± 0.24 mV) further away from the border zone (2.05 ± 2.79 cm) than did the VT exit sites. Exit sites had a larger area of matching pace maps (3.86 ± 1.9 cm(2); P<.01) and were at a closer distance to the border zone (0.93 ± 1.06 cm; P<.01). A total of 133 of 137 VTs were ablated. The success rate was similar for VTs in which exit sites were targeted (n = 90 of 100) and VTs in which only nonexit sites were targeted (n = 36 of 37) (P = .83). CONCLUSIONS: In about one-third of postinfarction VTs for which critical sites were identified, the exit site was not endocardial. Critical nonexit sites that are effective for ablation are often within dense scar at a distance from the border zone and can be missed if only the border zone is targeted.

The impact of age on the atrial substrate: insights from patients with a low scar burden undergoing catheter ablation of persistent atrial fibrillation.

BACKGROUND: Advancing age is a strong risk factor for the development of atrial fibrillation (AF). However, its impact on the left atrial (LA) substrate in patients is not well defined. METHODS: Forty-seven patients underwent catheter ablation of persistent AF. Bipolar electrograms from the LA were recorded for voltage analysis. The AF cycle length was determined by averaging the cycle lengths of ten fibrillatory ("f") waves on lead V(1). The mean amplitude of the same ten "f" waves was also determined. The ablation strategy consisted of pulmonary vein isolation, electrogram guided, and linear ablation. RESULTS: There was an inverse relationship between the mean bipolar LA voltage and age (R = -0.58; P < 0.0001). There was a direct relationship between AF cycle length and age (R = 0.74; P < 0.0001). There was an inverse relationship between amplitude of the "f" waves and age (R = -0.62; P < 0.0001). Areas of scar were found in 15 of the 47 patients (32%). AF cycle length was longer in patients with vs. those without scar (183 ± 20 vs. 151 ± 15 ms; P < 0.0001). Advancing age was the only predictor of LA scar (OR, 1.32; 95% CI, 1.11-1.58; P < 0.01). Forty patients (85%) remain arrhythmia-free without antiarrhythmic medications after a mean follow-up of 18 ± 10 months. Neither age nor LA scar was associated with outcome. CONCLUSIONS: In patients undergoing ablation of persistent AF, advancing age makes for a complex LA substrate that is characterized by areas of low voltage/scar, and yet is associated with a lower AF frequency. LA scar did not seem to impact outcome in this small study.

Delayed-enhanced MR scar imaging and intraprocedural registration into an electroanatomical mapping system in post-infarction patients.

Post-infarction arrhythmias are most often confined to scar tissue. Scar can be detected by delayed-enhanced cardiac magnetic resonance. The purpose of this study was to assess the feasibility of pre-procedural scar identification and intraprocedural real-time image registration with an electroanatomical map in 23 patients with previous infarction and ventricular arrhythmias (VAs). Registration accuracy and cardiac magnetic resonance/electroanatomical map correlations were assessed, and critical areas for VA were correlated with the presence of scar. With a positional registration error of 3.8 ± 0.8 mm, 86% of low-voltage points of the electroanatomical map projected onto the registered scar. The delayed-enhanced cardiac magnetic resonance-defined scar correlated with the area of low voltage (R = 0.82, p < 0.001). All sites critical to VAs projected on the registered scar. Selective identification and extraction of delayed-enhanced cardiac magnetic resonance defined scar followed by registration into a real-time mapping system are feasible and help to identify and display the arrhythmogenic substrate in post-infarction patients with VAs.

Septal involvement in patients with post-infarction ventricular tachycardia: implications for mapping and radiofrequency ablation.

OBJECTIVES: The purpose of this study was to assess the prevalence of the re-entry circuit within the interventricular septum in post-infarction patients referred for ventricular tachycardia (VT) ablation. BACKGROUND: Post-infarction ventricular tachycardia can involve the endocardial myocardium, the intramural myocardium, the epicardium, or the His Purkinje system. METHODS: Among 74 consecutive patients with recurrent post-infarction VT, 33 patients (45%) were identified in whom the critical part of the VT involved the interventricular septum. A total of 206 VTs were induced in these 33 patients. In 46 of the 206 VTs, a critical component was identified in the interventricular septum. The critical isthmus of the re-entry circuit was identified by entrainment mapping, activation mapping, or pace-mapping. RESULTS: In 32 of 46 VTs (70%), the critical component of the re-entry circuit was confined to the endocardium. In 9 of 46 VTs (20%), the critical component involved the Purkinje system, and in 5 of 46 VTs (11%), an intramural area was critical. Entrainment and/or pace-mapping helped to identify critical areas of endocardial VTs as well as VTs involving the Purkinje fibers, but neither of these mapping techniques localized intramural VTs. Electrocardiographic characteristics were specific for each of the septal locations. All VTs mapped to the interventricular septum were acutely successfully ablated. VTs recurred in 9 of 33 patients with septal VTs during a mean follow-up period of 40 ± 20 months. CONCLUSIONS: Post-infarction VT involving the interventricular septum can involve the endocardial muscle, Purkinje fibers, or intramural muscle fibers. Electrocardiographic characteristics differ depending on the type of tissue involved.