Canine Model of Ischemia-Induced Ventricular Tachycardia.

INTRODUCTION: Despite advances in antiarrhythmia therapies, ventricular tachycardia (VT) is a leading cause of sudden cardiac death. Investigation into the characteristics and new treatments for this arrhythmia is required to improve outcomes and a reproducible model of VT would be useful in these endeavors. We therefore created a canine model of ischemia-induced VT. MATERIALS AND METHODS: A pacing lead was implanted in the right ventricle in canines (n = 13) and the left anterior descending artery was occluded in two locations for 2 h and subsequently released to create an ischemia-reperfusion injury. In the 10 dogs that survived the first 48 h following the initial study, a terminal study was conducted 4-7 d later and VT was induced using premature stimulation or burst pacing through the right ventricle lead. The arrhythmia was terminated using either antitachycardia pacing or a defibrillatory shock. Multiple inductions into sustained VT were attempted. RESULTS: Sustained VT was induced in eight of 10 dogs with an average cycle length of 335 ± 70 bpm. Multiple episodes of VT were induced. Episodes of VT exhibited different electrocardiogram morphologies and cycle lengths in individual animals. CONCLUSIONS: This canine model provides a consistent technique for inducing multiple episodes of sustained VT. It may be useful for investigating VT mechanisms and testing novel therapeutics and treatments for patients with VT.

Antitachycardia pacing at the His bundle is safer than conventional right ventricular antitachycardia pacing in a canine myocardial ischemic injury model.

INTRODUCTION: Antitachycardia pacing (ATP) is used to terminate ventricular tachycardia (VT) by delivering rapid, low energy pacing to the right ventricle (RV). Unfortunately, ATP is not effective against all VT episodes and can result in adverse outcomes, such as VT acceleration and degeneration into ventricular fibrillation (VF). Improving ATP is therefore desirable. Our objective was to compare the efficacy and safety of ATP delivered at the His bundle to traditional ATP. METHODS: Six dogs were anesthetized and pacing leads were implanted in the RV and His bundle. The left anterior descending artery was occluded for 2 h to create an ischemic injury. In a study 4-7 days later, a 128-electrode sock was placed snugly around the ventricles and VT was induced using rapid pacing. ATP was delivered from either the His bundle or RV lead, then attempted at the other location if unsuccessful. Success rates and instances of VT acceleration and degeneration into VF were calculated. RESULTS: We induced 83 runs of VT and attempted ATP 128 times. RV ATP was successful in 36% of attempts; His ATP was successful in 38% of attempts. RV ATP resulted in significantly more adverse outcomes. RV and His ATP induced VT acceleration in 9% and 3% of trains, respectively, and induced degeneration into VF in 5% and 1% of trains, respectively. CONCLUSION: His bundle ATP is safer, but not significantly more effective, than RV ATP.

A canine model of chronic ischemic heart failure.

Preclinical large animal models of chronic heart failure (HF) are crucial to both understanding pathological remodeling and translating fundamental discoveries into novel therapeutics for HF. Canine models of ischemic cardiomyopathy are historically limited by either high early mortality or failure to develop chronic heart failure. Twenty-nine healthy adult dogs (30 ± 4 kg, 15/29 male) underwent thoracotomy followed by one of three types of left anterior descending (LAD) coronary artery ligation procedures: group 1 (n = 4) (simple LAD: proximal and distal LAD ligation); group 2 (n = 14) (simple LAD plus lateral wall including ligation of the distal first diagonal and proximal first obtuse marginal); and group 3 (n = 11) (total LAD devascularization or TLD: simple LAD plus ligation of proximal LAD branches to both the right and left ventricles). Dogs were followed until chronic severe HF developed defined as left ventricular ejection fraction (LVEF) < 40% and NH2-terminal-prohormone B-type natriuretic peptide (NT-proBNP) > 900 pmol/L. Overall early survival (48-h postligation) in 29 dogs was 83% and the survival rate at postligation 5 wk was 69%. Groups 1 and 2 had 100% and 71% early survival, respectively, yet only a 50% success rate of developing chronic HF. Group 3 had excellent survival at postligation 48 h (91%) and a 100% success in the development of chronic ischemic HF. The TLD approach, which limits full LAD and collateral flow to its perfusion bed, provides excellent early survival and reliable development of chronic ischemic HF in canine hearts.NEW & NOTEWORTHY The novel total left anterior descending devascularization (TLD) approach in a canine ischemic heart failure model limits collateral flow in the ischemic zone and provides excellent early survival and repeatable development of chronic ischemic heart failure in the canine heart. This work provides a consistent large animal model for investigating heart failure mechanisms and testing novel therapeutics.

Shorter distance between the esophagus and the left atrium is associated with higher rates of esophageal thermal injury after radiofrequency ablation.

BACKGROUND: Esophageal thermal injury (ETI) is a known and potentially serious complication of catheter ablation for atrial fibrillation. We intended to evaluate the distance between the esophagus and the left atrium posterior wall (LAPW) and its association with esophageal thermal injury. METHODS: A retrospective analysis of 73 patients who underwent esophagogastroduodenoscopy (EGD) after LA radiofrequency catheter ablation for symptomatic atrial fibrillation and pre-ablation magnetic resonance imaging (MRI) was used to identify the minimum distance between the inner lumen of the esophagus and the ablated atrial endocardium (pre-ablation atrial esophageal distance; pre-AED) and occurrence of ETI. Parameters of ablation index (AI, Visitag Surpoint) were collected in 30 patients from the CARTO3 system and compared with assess if ablation strategies and AI further impacted risk of ETI. RESULTS: Pre-AED was significantly larger in patients without ETI than those with ETI (5.23 ± 0.96 mm vs. 4.31 ± 0.75 mm, p < .001). Pre-AED showed high accuracy for predicting ETI with the best cutoff value of 4.37 mm. AI was statistically comparable between Visitag lesion markers with and without associated esophageal late gadolinium enhancement (LGE) detected by postablation MRI in the low-power long-duration ablation group (LPLD, 25-40 W for 10-30 s, 393.16 [308.62-408.86] vs. 406.58 [364.38-451.22], p = .16) and high-power short-duration group (HPSD, 50 W for 5-10 s, 336.14 [299.66-380.11] vs. 330.54 [286.21-384.71], p = .53), respectively. CONCLUSION: Measuring the distance between the LA and the esophagus in pre-ablation LGE-MRI could be helpful in predicting ETI after LAPW ablation.

Short-term natural course of esophageal thermal injury after ablation for atrial fibrillation.

INTRODUCTION: Esophageal injury is rare but potentially a devastating complication of atrial fibrillation (AF) ablation. The goal here was to provide insight into the short-term natural history of esophageal thermal injury (ETI) after radiofrequency catheter ablation (RFCA) for AFby esophagogastroduodenoscopy (EGD). METHODS: We screened patients who underwent RFCA for AF and EGD based on esophageal late gadolinium enhancement (LGE) in postablation magnetic resonance imaging. Patients with ETI diagnosed with EGD were included. We defined severity of ETI according to Kansas City classification: type 1: erythema; type 2: ulcers (2a: superficial; 2b deep); type 3 perforation (3a: perforation; 3b: perforation with atrioesophageal fistula [AEF]). Repeated EGD was performed within 1-14 days after the last EGD if recommended and possible until any certain healing signs (visible reduction in size without deepening of ETI or complete resolution) were observed. RESULTS: ETI was observed in 62 of 378 patients who underwent EGD after RFCA. Out of these 62 patients with ETI, 21% (13) were type 1, 50% (31) were type 2a and 29% (18) were type 2b at the initial EGD. All esophageal lesions, but one type 2b lesion that developed into an AEF, showed signs of healing in repeated EGD studies within 14 days after the procedure. The one type 2b lesion developing into an AEF showed an increase in size and ulcer deepening in repeat EGD 8 days after the procedure. CONCLUSION: We found that all ETI which did not progress to AEF presented healing signs within 14 days after the procedure and that worsening ETI might be an early signal for developing esophageal perforation.

Important factors in left atrial posterior wall isolation using 28-mm cryoballoon ablation for persistent atrial fibrillation-Block line or isolation area?

INTRODUCTION: Left atrial (LA) roof ablation using the cryoballoon technique, combined with pulmonary vein isolation (PVI), has been reported to be beneficial for ablation therapy in patients with persistent atrial fibrillation (AF). Left posterior wall ablation also results in improved patient outcomes. However, the contribution of these techniques to the success of cryoballoon ablation (CBA) treatment of AF is not known. The present study examined the influence of the roofline block and isolation area on outcomes after CBA. METHODS AND RESULTS: We enrolled 78 patients with persistent AF. LA roof ablation was performed using a 28-mm cryoballoon with a single freezing of 3 minutes at each region (median number of freezes: 4) after PVI. After CBA, bipolar voltage amplitude mapping was performed during sinus rhythm using the NavX mapping system. Patients were divided into two subgroups according to the voltage and activation map: the roof-conduction (n = 46) and roofline-block groups (n = 32). Atrial tachyarrhythmia recurred in 20 patients of the conduction group and 4 patients of the roofline-block group. The rate of 12-month freedom from tachyarrhythmia after a single ablation procedure was 78% (95% confidence interval [CI], 60%-89%) in the roofline-block group and 45% (95% CI, 30%-60%) in the conduction group (P = .048). Cox proportional hazard analysis revealed that the isolated area was not a significant predictor of recurrence (hazard ratio, 0.94; 95% CI, 0.86-1.02; P = .15). CONCLUSION: Creating a complete roofline block is the major factor predicting the maintenance of sinus rhythm in patients with persistent AF.

Novel use of a 3-dimensional mapping system in cryoablation of right-sided and septal accessory pathways: playback ablation.

PURPOSE: Despite recent advances in the treatment of eliminating accessory pathways (APs), catheter-induced mechanical block (bump) of APs has been reported to result in a less favorable outcome with high primary failure and recurrence rates. The real bump site cannot always be precisely reapproached under fluoroscopy so physicians can perform ablation to a location different from where the mechanical block was encountered. In this paper, we describe this novel use of a 3-dimensional (3D) mapping system (playback ablation) with a case series. METHODS: The EnSite Velocity system (St. Jude Medical, St. Paul, MN, USA), a 3D mapping system, has a unique function that records the positional information of catheters in a 3D geometric map and the local potential of catheters continuously. This function enables physicians to specify the bump site in a 3D geometric map and apply ablation to the bump site even if the catheter moves away from the bump site. RESULTS: This technique helped us eliminate APs in two patients with bump of APs, and they have been free of preexcitation and arrhythmias without the use of anti-arrhythmic drugs for more than 3 months. CONCLUSIONS: This technique may contribute to improving long-term success in patients with mechanical block of APs.

A relation between ablation area and outcome of ablation using 28-mm cryoballon ablation: Importance of carina region.

INTRODUCTION: Pulmonary vein isolation (PVI) with wide antral ablation leads to better outcomes in atrial fibrillation ablation therapy, but the ablation area is relatively small during cryoballoon ablation (CBA). The present study tested the hypothesis that wide ablation can lead to better outcomes in CBA. METHODS AND RESULTS: Ninety-six patients with atrial fibrillation were enrolled (paroxysmal 76%, 64.1 ± 11.7 years). All patients underwent preprocedural computed tomography and the PV diameter at left atrial PV junction was measured. PV isolation was performed using a 28-mm CB for 3 minutes with single freezing. Sinus rhythm bipolar voltage amplitude maps with the NavX mapping system were generated after ablation. According to the voltage map, patients were divided into 3 subgroups (68 in the extensive isolation group, 17 in the individual isolation group, and 10 in the incomplete isolation group). Atrial tachyarrhythmias recurred in 9 patients of the extensive isolation group and 6 in the individual isolation group. The rate of 12-month freedom from tachyarrhythmia after a single ablation procedure was 84% (95% confidence interval [C.I.], 72%-91%) in the extensive group and 57% (95% C.I., 28%-78%) in the individual group (P = 0.048). Multiple logistic regression analyses revealed that maximal PV diameter was the only predictor to achieve extensive PVI (odds ratio, 1.57; 95% C.I. 1.08-2.29 P = 0.018). CONCLUSION: Extensive isolation is superior to individual isolation for achieving freedom from atrial arrhythmia in long term follow-up by CBA. Evaluating PV diameter at the left atrial PV junction is essential for applying CBA.