Physiology of slow pathway conduction during sinus rhythm: evidence from high density mapping within the triangle of Koch.

PURPOSE: To evaluate nature of AV nodal activation in patients with AVNRT using high density electro-anatomic mapping (HD-EAM). METHODS: HD-EAM was created in 30 patients with AVNRT from the triangle of Koch (ToK) in sinus rhythm (SR). Isochronal late activation maps (ILAM) were created. EAMs were analyzed for slow pathway (SPW) and fast pathway (FPW) activation. A pivot point (PP) was defined where FPW and SPW collided and pivoted back to the AV node (AVN). Conduction was assessed with programmed extrastimulus (PES) in 9 patients until FPW refractory period (ERP). The change in PP distance from the HIS (ΔPP) was measured in SR and PES. The ΔPP was compared to ΔAH. The PP was ablated and SR re-mapped. RESULTS: The FPW activates the His and moves inferiorly toward the coronary sinus (CS). Activation also enters the ToK near the CS and collides with the FPW which then pivots around a functional line of block (LOB) within the ToK and moves superiorly along the septal tricuspid annulus. PP electrograms are fractionated, low amplitude, and consistent with SPW potentials (Haissaguerre et al. in Circulation 85:2162-2175, 1992). During PES the PP moved superiorly until FPW ERP when only SPW activation occurs. Normalized ΔAH and ΔPR vs ΔPP was highly correlated p < 0.0001. Ablation at the PP was successful and associated with loss of SPW fusion and pivot. CONCLUSION: We conclude HD-EAM/ILAM provide a novel method for localizing the SPW in SR. This study provides further understanding of dual AV nodal physiology and may aid in targeting the SPW for ablation of AVNRT.

Epicardial bridge via the coronary sinus musculatures revealed by ultra-high-definition mapping.

Mapping and ablation of perimitral flutter, a macro-reentrant tachycardia, can be sometimes challenging. We describe a case of perimitral atrial flutter following the pulmonary vein isolation in which mitral isthmus ablation failed to terminate the arrhythmia due to epicardial-endocardial breakthrough via the muscle fibers of coronary sinus. Ultra-high-definition mapping system was utilized to locate the epicardial bridge, and spot ablation of the lesion subsequently terminated the arrhythmia.

Direct Current Ablation of Deep Substrate Arrhythmia.

Direct-current ablation has been reinvestigated in animal models with considerably good outcomes and safety margins. Its modified version using biphasic energy lowers the current density further, minimizing its complications. We report a first-in-human ablation of ventricular tachycardia using biphasic direct current with short-term success and no procedural complications. (Level of Difficulty: Intermediate.).

Air Entrapment Causing Inappropriate Shock From a Subcutaneous Implantable Cardioverter Defibrillator.

Subcutaneous implantable cardioverter defibrillator (S-ICD) is an accepted alternative to conventional transvenous devices. Their efficacy in arrhythmia management is comparable to ICDs. However, those devices also have limitations such as lack of anti-tachycardia pacing capability or higher occurrence of device oversensing associated with inappropriate shocks. Air entrapment inside one or more of subcutaneous pockets has been reported as one of uncommon causes of device malfunction. It is important to recognize the wandering or drifting baseline signals during device interrogation for timely diagnosis and appropriate treatment.

A new methodology for atrial flutter ablation by direct visualization of cavotricuspid conduction with voltage gradient mapping: a comparison to standard techniques.

AIMS: To demonstrate that critical conduction within the cavotricuspid isthmus (CTI) can be directly visualized by voltage gradient mapping and facilitate efficient ablation compared to standard techniques. METHODS AND RESULTS: Group 1 (1 operator, n = 11) ablated based upon contact voltage measurements and voltage gradient mapping. Ablation targeted low-voltage bridges (LVBs) within the CTI. Repeat maps were obtained following ablation. Group 2 (operators 2, 3, and 4 n = 35) utilized electroanatomic navigation and ablated by the creation of linear lesions from the tricuspid valve to the inferior vena cava. Demonstration of bidirectional block (BDB) was required in both groups. LVB were associated with CTI conduction in all Group A patients. LVB ablation terminated flutter, or created BDB. Following ablation, CTI voltage connections were absent in all patients. Compared with Group B, Group A had less radiofrequency (RF) lesions to atrial flutter (AFL) termination (P = 0.001), less total RF lesions (P = 0.0001), and less total RF time (P = 0.001). Group 1 had no recurrent AFL whereas Group 2 had three recurrences. (follow-up median of 231 ± 181 days). CONCLUSION: (i) Voltage gradient mapping visualized regions of critical CTI conduction, (ii) ablation of LVB terminated AFL and resulted in BDB, (iii) repeat mapping confirmed the absence of trans-isthmus voltage, and (iv) Compared with standard ablation, voltage gradient mapping decreases total RF lesions, lesions to AFL termination, and total RF time. Use of voltage gradient mapping can facilitate successful AFL ablation.

Direct visualization of the slow pathway using voltage gradient mapping: a novel approach for successful ablation of atrioventricular nodal reentry tachycardia.

AIMS: Ablation of atrioventricular nodal reentry tachycardia (AVNRT) has become treatment of choice because of a high success and low complication rate. Most ablations are successful in utilizing an anatomic approach, but anatomic variance, unusual pathway locations, or multiple pathways may complicate the procedure. Visualization of the slow pathway could expedite ablation success and enhance safety. Our purpose is to determine whether voltage gradient mapping can directly image the slow pathway and aid successful ablation of AVNRT. METHODS AND RESULTS: Three-dimensional voltage maps of the right atrial septum were constructed from intracardiac recordings obtained by contact mapping. Voltage values were adjusted until low-voltage bridging was observed within the Triangle of Koch. Forty-eight consecutive patients undergoing ablation for inducible AVNRT, underwent voltage gradient mapping. The slow pathway was identified in all 48 patients via its corresponding low-voltage bridge. Ablation of the slow pathway associated low-voltage bridges in 48 patients was successful in preventing reinduction following the first lesion in 43 of 48 patients. Five patients had multiple slow pathways and >1 lesion was required to prevent reinduction. Repeat mapping confirmed the absence of low-voltage connections previously observed in all 48 patients. CONCLUSION: Voltage gradient mapping can assist in visualization of the slow pathway. Ablation of the associated low-voltage bridge results in loss of slow pathway function and significant changes in the post-ablation voltage map. We conclude that voltage gradient mapping offers the ability to target the slow pathway for successful ablation.

Lack of a hypotensive effect with rapid administration of a new aqueous formulation of intravenous amiodarone.

Hypotension is the most frequent adverse event reported with intravenous amiodarone. Hypotension has been attributed to the vasoactive solvents of the standard formulation (Cordarone IV) and is not dose related, but related to the rate of infusion. Drug labeling calls for intravenous amiodarone to be administered over 10 minutes. A new aqueous formulation of amiodarone (Amio-Aqueous) does not contain vasoactive excipients and may be administered safely by rapid administration without hypotension. This hypothesis was tested using combined data of 4 clinical trials; each assessed the development of hypotension prospectively. Hypotension was defined as a 25% decrease in systolic blood pressure (BP), with the development of a systolic BP of <90 mm Hg or a systolic BP that decreased to <80 mm Hg. In all, 358 Amio-Aqueous and 225 lidocaine boluses were administered to 278 patients; 246 had ventricular tachycardia (VT) during drug administration. Hypotension developed in 11% of patients on Amio-Aqueous versus 19% on lidocaine (p = NS), all during VT; most resolved spontaneously with VT termination. With both drugs, hypotension persisted after VT termination in 1% of patients; the incidence of drug-related hypotension occurred in 2% of patients (1% had hypotension requiring treatment). The Amio-Aqueous was discontinued in 1% of patients, and lidocaine was discontinued in 2% of patients because of hypotension. We conclude that Amio-Aqueous is at least as safe as lidocaine in terms of causing hypotension when administered rapidly. This is a significant advantage over the standard amiodarone formulation, because Cordarone cannot be administered by rapid bolus owing to excipient-related hypotension.

Clinical investigation of a new dual-chamber implantable cardioverter defibrillator with improved rhythm discrimination capabilities.

INTRODUCTION: Despite continuing advances, inappropriate implantable cardioverter defibrillator (ICD) therapies in response to nonventricular tachyarrhythmias continue to cause patient discomfort and increased follow-up demands. METHODS AND RESULTS: We investigated the performance of a new dual-chamber ICD (Photon DR, St. Jude Medical), with specific attention to its arrhythmia discrimination and detection capabilities. The system uses a hierarchical approach to tachyarrhythmia classification utilizing a new AV Rate Branch feature and subsequently utilizing morphology analysis, onset, and stability criteria. The arrhythmia discrimination results from this study group were compared to historical control group data from a recent clinical investigation of single-chamber Contour MD (Morphology Discrimination) and Angstrom MD ICDs without the Rate Branch feature. Rhythm discrimination was evaluated by comparing ventricular tachycardia diagnosis sensitivity and specificity between the two groups. To determine whether the new discrimination scheme affected detection speed, median ventricular fibrillation (VF) detection and redetection times also were compared. The study group consisted of 107 patients, and the control group consisted of 161 patients. Use of the AV Rate Branch feature was associated with significant improvements in both sensitivity (100% vs 97.9%, P < 0.0001) and specificity (84% vs 55.7%, P = 0.0002) of ventricular tachycardia diagnosis. Use of the new scheme slightly but significantly accelerated VF detection times (2.8 vs 3.0 sec, P < 0.0001) and redetection times (1.3 vs 1.4 sec, P < 0.0001). Adverse events were typical for this patient population. CONCLUSION: Compared with earlier St. Jude Medical ICDs, the Photon DR ICD offers improved rhythm discrimination without compromising VF detection time.

Bachmann's bundle versus right atrial appendage capture.

The tissue in the high intraatrial septum in the region of Bachmann's Bundle (BB) exhibits electrophysiological properties that differ from the right atrial appendage (RAA). As BB pacing emerges as an alternative to RAA pacing, the feasibility of using automatic capture recognition technology in this location should be examined. At implant, active-fixation leads were consecutively placed in the RAA, then the BB in 18 patients (55.5% men, mean age 77.1 +/- 9.1). There was no significant difference between BB and RAA in the average capture threshold (1.12 vs 1.77 V, P = 0.09), sensing threshold (3.85 vs 3.69 mV, P = 0.84), impedance (508 vs 529 Ohms, P = 0.64), evoked response (1.78 vs 1.67 mV, P = 0.83), and polarization (0.41 vs 0.46 mV, P = 0.84) between. The difference in tissue characteristics was not associated with a different evoked response measured by the ventricular capture recognition algorithm. Based on the analogous evoked response and polarization values, capture recognition technology designed for the atrium will most likely be applicable at both pacing sites.

Is Bachmann's Bundle the only right site for single-site pacing to prevent atrial fibrillation? Results of a multicenter randomized trial.

The site of atrial pacing influences atrial activation patterns. It is believed that disparities in atrial activation and repolarization are contributors to the development and recurrence of atrial arrhythmias. We hypothesized that pacing from Bachmann's Bundle would improve clinical outcomes in patients with paroxysmal atrial fibrillation compared to right atrial appendage pacing. Pacing from Bachmann's Bundle results in a significant reduction in P wave duration and improvement in biatrial activation symmetry compared to right atrial appendage pacing. Compared to right atrial appendage pacing, Bachmann's bundle pacing improves sinus rhythm (75% vs. 47% at two years, p < 0.01) in patients with a history of paroxysmal atrial fibrillation. Recent studies have confirmed the benefits of Bachmann's Bundle pacing on atrial activation and rhythm regulation. Thus, Bachman's Bundle should be considered the preferred site for atrial pacing in patients with a history of paroxysmal atrial fibrillation.

Intravenous lidocaine versus intravenous amiodarone (in a new aqueous formulation) for incessant ventricular tachycardia.

The effectiveness of intravenous amiodarone for the treatment of incessant (shock resistant) ventricular tachycardia (VT) has not been established. This study evaluated the efficacy of a water-soluble amiodarone preparation or lidocaine for the treatment of shock-resistant VT. The trial was a double-blinded parallel design. Patients were randomized to receive up to 2 boluses of either 150 mg intravenous amiodarone or 2 boluses of 100 mg lidocaine followed by a 24-hour infusion. If the first assigned medication failed to terminate VT, the patient was crossed over to the alternative therapy. Twenty-nine patients were randomized to the study (18 received amiodarone and 11 received lidocaine). There were no significant differences between groups with regard to baseline characteristics. Immediate VT termination was achieved in 14 patients (78%) with amiodarone versus 3 patients (27%) on lidocaine (p <0.05). After 1 hour, 12 patients (67%) on amiodarone and 1 patient (9%) on lidocaine were alive and free of VT (p <0.01). Amiodarone had a 33% drug failure rate, whereas there was a 91% drug failure rate for lidocaine. The 24-hour survival was 39% on amiodarone and 9% on lidocaine (p <0.01). Drug-related hypotension with aqueous amiodarone was less frequent than with lidocaine. This study found that amiodarone is more effective than lidocaine in the treatment of shock-resistant VT.

Determinants of first-shock success for atrial implantable cardioverter defibrillators.

INTRODUCTION: The aim of this study was to identify determinants of first-shock success for defibrillation of spontaneous atrial fibrillation (AF) in ambulatory patients with an atrial implantable cardioverter defibrillator (ICD). The determinants of first-shock success in ambulatory patients with atrial ICDs are unknown. METHODS AND RESULTS: We used the generalized estimating equation method to analyze determinants of first-shock success in 50 consecutive atrial ICD recipients in whom DFT+ (weakest shock that defibrillates on two consecutive trials) was determined at implant and spontaneous AF was shocked with shock strength > or = 2 x DFT+. DFT+ was 6.2 +/- 3.1 J. Of 470 first shocks, 407 were successful (generalized estimating equation 85%, confidence interval 79% to 90%). Determinants of first-shock success were use of coronary sinus electrode (univariate P = 0.02; multivariate P < 0.001, relative risk 5.0), absence of a Class III antiarrhythmic drug (univariate P = 0.06; multivariate P < 0.001, relative risk 3.2), absence of early recurrence of atrial fibrillation (ERAF; univariate P = 0.06; multivariate P = 0.02, relative risk 2.9), and longer duration of AF prior to shock > or = 3 hours (univariate: P = 0.02; multivariate P = NS). Sinus rhythm >1 minute persisted after 93% of first shocks in patients without documented ERAF but after only 58% of shocks in patients with documented ERAF (P < 0.001). CONCLUSION: Reducing ERAF is critical to achieving a clinically acceptable rate of persistent sinus rhythm after first shocks. For first shocks > or = 2 x DFT +, success is not increased by programming stronger shocks. Early cardioversion does not increase first-shock success.