Tristram D. Bahnson

Radiofrequency catheter ablation for the treatment of human type 1 atrial flutter. Identification of a critical zone in the reentrant circuit by endocardial mapping techniques.

BackgroundRecent studies of human type 1 atrial flutter demonstrated reentry in the right atrium and an area of slow conduction in the low posteroseptal right atrium. Direct-current catheter ablation of this area has been only moderately successful in preventing recurrence. Therefore, we performed endocardial activation mapping and entrainment pace mapping during atrial flutter to determine the critical site for radiofrequency ablation of this arrhythmia Methods and ResultsTwelve consecutive patients (seven men and five women; age, 21–73 years) with type 1 atrial flutter (mean cycle length, 253±39 msec) underwent right atrial endocardial activation and entrainment pace mapping using standard transvenous catheter techniques to localize the atrial flutter reentrant circuit, the area of slow conduction, and the exit site from the area of slow conduction. Upon identifying appropriate sites, radiofrequency energy (16–29 W) was applied via a 4-mm tipped catheter. Activation mapping of atrial flutter revealed a counterclockwise reentrant wave front originating just inferior or posterior to the coronary sinus ostium, proceeding superiorly in the atrial septum to the right atrial free wall, then inferiorly toward the tricuspid annulus and finally medially between the inferior vena cava and the tricuspid annulus, where low-amplitude fragmented electrical activity was noted. Entrainment pace mapping from this area produced an exact P wave match to atrial flutter on 12-lead ECG with a long (>40 msec) stimulus-to-P interval indicating slow conduction, whereas pacing just inferior or posterior to the coronary sinus ostium produced an exact P wave match with a short stimulus-to-P interval (<40 msec), presumably identifying the exit site from the area of slow conduction. Radiofrequency energy (one to 14 applications) was effective in terminating and preventing reinduction of atrial flutter in 10 patients. In two patients, atrial flutter was not terminated during radiofrequency energy application but during subsequent pacing attempts. Sites where ablation was successful, located just inferior or posterior to the coronary sinus ostium, were characterized by discrete electrograms with activation times of −20 to −50 msec before P wave onset and exact entrainment pace maps with a stimulus-to-P interval of 20 to 40 msec, consistent with the exit site from the area of slow conduction. Follow-up (mean, 16±9 weeks; range, 2–31 weeks) revealed recurrence of the original atrial flutter in two patients, one of whom underwent repeat ablation without further recurrence, self-limited infrequent recurrence of a new atrial flutter or atrial fibrillation in three suppressed by β-blocker or digoxin, and no recurrence in seven Conclusions1) Radiofrequency energy applied to a critical area in the atrial flutter reentrant circuit, inferior or posterior to the coronary sinus ostium, will terminate and prevent arrhythmia reinduction. 2) Long-term follow-up in a larger series of patients will be required to confirm efficacy of this technique, although short-term results look promising.

Assessment of Myocardial Scarring Improves Risk Stratification in Patients Evaluated for Cardiac Defibrillator Implantation

OBJECTIVES We tested whether an assessment of myocardial scarring by cardiac magnetic resonance imaging (MRI) would improve risk stratification in patients evaluated for implantable cardioverter-defibrillator (ICD) implantation. BACKGROUND Current sudden cardiac death risk stratification emphasizes left ventricular ejection fraction (LVEF); however, most patients suffering sudden cardiac death have a preserved LVEF, and many with poor LVEF do not benefit from ICD prophylaxis. METHODS One hundred thirty-seven patients undergoing evaluation for possible ICD placement were prospectively enrolled and underwent cardiac MRI assessment of LVEF and scar. The pre-specified primary endpoint was death or appropriate ICD discharge for sustained ventricular tachyarrhythmia. RESULTS During a median follow-up of 24 months the primary endpoint occurred in 39 patients. Whereas the rate of adverse events steadily increased with decreasing LVEF, a sharp step-up was observed for scar size >5% of left ventricular mass (hazard ratio [HR]: 5.2; 95% confidence interval [CI]: 2.0 to 13.3). On multivariable Cox proportional hazards analysis, including LVEF and electrophysiological-study results, scar size (as a continuous variable or dichotomized at 5%) was an independent predictor of adverse outcome. Among patients with LVEF >30%, those with significant scarring (>5%) had higher risk than those with minimal or no (≤5%) scarring (HR: 6.3; 95% CI: 1.4 to 28.0). Those with LVEF >30% and significant scarring had risk similar to patients with LVEF ≤30% (p = 0.56). Among patients with LVEF ≤30%, those with significant scarring again had higher risk than those with minimal or no scarring (HR: 3.9; 95% CI: 1.2 to 13.1). Those with LVEF ≤30% and minimal scarring had risk similar to patients with LVEF >30% (p = 0.71). CONCLUSIONS Myocardial scarring detected by cardiac MRI is an independent predictor of adverse outcome in patients being considered for ICD placement. In patients with LVEF >30%, significant scarring (>5% LV) identifies a high-risk cohort similar in risk to those with LVEF ≤30%. Conversely, in patients with LVEF ≤30%, minimal or no scarring identifies a low-risk cohort similar to those with LVEF >30%.

Control of rapid ventricular response by radiofrequency catheter modification of the atrioventricular node in patients with medically refractory atrial fibrillation.

BACKGROUND Pharmacological control of rapid ventricular response to atrial fibrillation may be difficult in some patients. Alternative treatments, including curative surgery or atrioventricular (AV) node ablation with pacemaker implantation, have significant potential morbidity. In view of evidence that dual AV nodal physiology may exist in a significant percentage of the population, even in those without AV nodal reentrant tachycardia, we postulated that control of ventricular response might be achieved by radiofrequency (RF) catheter ablation in the region of the AV nodal slow pathway with its short refractory period. METHODS AND RESULTS Ten patients underwent attempted AV node modification using a 4-mm-tipped electrode catheter positioned in the middle or posterior septum, between the His bundle and coronary sinus ostium on the tricuspid valve annulus. RF energy was applied at 16 to 30 W for up to 60 seconds, until average ventricular response fell below 100 beats per minute. Reduction of maximal ventricular response below 120 beats per minute was confirmed with atropine 1 mg IV. If required, additional ablations were performed progressively more posteriorly up to the coronary sinus ostium. Patients with successful AV node modification were discharged off AV node-blocking drugs and followed in the clinic at regular intervals. Twenty-four-hour ambulatory ECG recordings and/or treadmill stress tests were obtained before and after ablation for statistical comparison of maximum ventricular rate. Resting average ventricular rate was determined during electrophysiology study before and after ablation. In 7 of 10 patients (70%), maximum ventricular rate was reduced from a mean of 164 +/- 12 to 123 +/- 16 beats per minute (P < .01) and average ventricular rate from a mean of 128 +/- 11 to 83 +/- 10 beats per minute after ablation. Mean minimum ventricular rate was 54 +/- 11 beats per minute after ablation. These 7 patients have remained symptom free from rapid ventricular response for a mean of 14 +/- 8 months (range, 1 to 22). Three remain off all AV node-blocking drugs, 3 remain on digoxin alone, which was previously ineffective, and 1 remains on a beta-blocker for angina. In the 3 patients who did not respond to AV node modification, complete AV node ablation and permanent pacemaker implantation was performed in 2 and DC cardioversion after amiodarone loading was performed in 1. CONCLUSIONS RF catheter modification of AV node conduction is effective in controlling rapid ventricular response to atrial fibrillation in a significant percentage of medically refractory patients. A possible mechanism of RF modification of AV node conduction is AV nodal slow pathway ablation. Large-scale clinical trials will be needed to determine the overall efficacy and safety of this technique.

Real-Time Monitoring of Luminal Esophageal Temperature During Left Atrial Radiofrequency Catheter Ablation for Atrial Fibrillation: Observations About Esophageal Heating During Ablation at the Pulmonary Vein Ostia and Posterior Left Atrium

Introduction: Left atrial radiofrequency catheter ablation (RFA) is gaining acceptance as treatment for drug‐refractory atrial fibrillation (AF). This therapy has been associated with esophageal injury and atrioesophageal fistula formation causing death.

Pulmonary Vein Isolation Using the Visually Guided Laser Balloon: A Prospective, Multicenter, and Randomized Comparison to Standard Radiofrequency Ablation

BACKGROUND Balloon catheters have been designed to facilitate pulmonary vein (PV) isolation in patients with paroxysmal atrial fibrillation (AF). The visually guided laser balloon (VGLB) employs laser energy to ablate tissue under direct visual guidance. OBJECTIVES This study compared the efficacy and safety of VGLB ablation with standard irrigated radiofrequency ablation (RFA) during catheter ablation of AF. METHODS Patients with drug-refractory paroxysmal AF were enrolled in a multicenter, randomized controlled study of PV isolation using either the VGLB or RFA (control). The primary efficacy endpoint was freedom from protocol-defined treatment failure at 12 months, including symptomatic AF occurring after the 90-day blanking period. The primary efficacy and safety endpoints were powered for noninferiority. RESULTS A total of 353 patients (178 VGLB, 175 control) were randomized at 19 clinical sites. The mean procedure, ablation, and fluoroscopy times were longer with VGLB compared with controls. The primary efficacy endpoint was met in 61.1% in the VGLB group versus 61.7% in controls (absolute difference -0.6%; lower limit of 95% confidence interval [CI]: -9.3%; p = 0.003 for noninferiority). The primary adverse event rate was 11.8% in the VGLB group versus 14.5% in controls (absolute difference -2.8%; upper limit of 95% CI: 3.5; p = 0.002 for noninferiority), and was mainly driven by cardioversions. Diaphragmatic paralysis was higher (3.5% vs. 0.6%; p = 0.05), but PV stenosis was lower (0.0% vs. 2.9%; p = 0.03) with VGLB. CONCLUSIONS Despite minimal prior experience, the safety and efficacy of VGLB ablation proved noninferior to RFA for the treatment of paroxysmal AF. (Pivotal Clinical Study of the CardioFocus Endoscopic Ablation System-Adaptive Contact [EAS-AC] [HeartLight] in Patients With Paroxysmal Atrial Fibrillation [PAF] [HeartLight]; NCT01456000).

Efficacy of adjunctive ablation of complex fractionated atrial electrograms and pulmonary vein isolation for the treatment of atrial fibrillation: a meta-analysis of randomized controlled trials

AIMS Although useful, percutaneous left atrial ablation for pulmonary vein isolation (PVI) does not eliminate atrial fibrillation (AF) in all patients. The ablation of complex fractionated atrial electrograms (CFAEs) has been proposed as an adjunctive strategy to improve the maintenance of sinus rhythm after PVI. Our objective was to analyse the efficacy of adjunctive CFAE ablation. METHODS AND RESULTS We meta-analysed six randomized controlled trials (total, n=538) using random-effects modelling to compare PVI (n=291) with PVI plus CFAE ablation (PVI+CFAE) (n=237). The primary outcome was freedom from AF or other atrial tachyarrhythmias (ATs) after a single ablation with or without antiarrhythmic drugs. Following a single ablation, PVI+CFAE improved the odds of freedom from any AF/AT compared with PVI alone (odds ratio 2.0, 95% confidence interval 1.04-3.8, P=0.04) at ≥3-month follow-up. There was moderate heterogeneity among trials (I2=63.0%). Complex fractionated atrial electrogram ablation significantly increased mean procedural (178.5±66.9 vs. 331.5±92.6 min, P<0.001), mean fluoroscopy (59.5±22.2 vs. 115.5±35.3 min, P<0.001), and mean radiofrequency (RF) energy application times (46.9±36.6 vs. 74.4±43.0 min, P<0.001). CONCLUSIONS Pulmonary vein isolation followed by adjunctive CFAE ablation is associated with increased freedom from AF after a single procedure. Adjunctive CFAE ablation increased procedural, fluoroscopy, and RF application times, and the risk/benefit profile of adjunctive CFAE ablation deserves further evaluation with additional studies and longer-term follow-up.

Intracardiac acoustic radiation force impulse imaging: A novel imaging method for intraprocedural evaluation of radiofrequency ablation lesions

BACKGROUND Arrhythmia recurrence after cardiac radiofrequency ablation (RFA) for atrial fibrillation has been linked to conduction through discontinuous lesion lines. Intraprocedural visualization and corrective ablation of lesion line discontinuities could decrease postprocedure atrial fibrillation recurrence. Intracardiac acoustic radiation force impulse (ARFI) imaging is a new imaging technique that visualizes RFA lesions by mapping the relative elasticity contrast between compliant-unablated and stiff RFA-treated myocardium. OBJECTIVE To determine whether intraprocedure ARFI images can identify RFA-treated myocardium in vivo. METHODS In 8 canines, an electroanatomical mapping-guided intracardiac echo catheter was used to acquire 2-dimensional ARFI images along right atrial ablation lines before and after RFA. ARFI images were acquired during diastole with the myocardium positioned at the ARFI focus (1.5 cm) and parallel to the intracardiac echo transducer for maximal and uniform energy delivery to the tissue. Three reviewers categorized each ARFI image as depicting no lesion, noncontiguous lesion, or contiguous lesion. For comparison, 3 separate reviewers confirmed RFA lesion presence and contiguity on the basis of functional conduction block at the imaging plane location on electroanatomical activation maps. RESULTS Ten percent of ARFI images were discarded because of motion artifacts. Reviewers of the ARFI images detected RFA-treated sites with high sensitivity (95.7%) and specificity (91.5%). Reviewer identification of contiguous lesions had 75.3% specificity and 47.1% sensitivity. CONCLUSIONS Intracardiac ARFI imaging was successful in identifying endocardial RFA treatment when specific imaging conditions were maintained. Further advances in ARFI imaging technology would facilitate a wider range of imaging opportunities for clinical lesion evaluation.

Termination of paroxysmal supraventricular tachycardia by tecadenoson (CVT-510),a novel A1-adenosine receptor agonist☆

OBJECTIVES The aim of this study was to evaluate tecadenoson safety and efficacy during conversion of paroxysmal supraventricular tachycardia (PSVT) to sinus rhythm. BACKGROUND Tecadenoson (CVT-510), a novel adenosine receptor (Ado R) agonist, selectively activates the A1 Ado R and prolongs atrioventricular (AV) nodal conduction at doses lower than those required to cause A2 Ado R-mediated coronary and peripheral vasodilation. Unlike adenosine, which non-selectively activates all four Ado R subtypes and produces unwanted effects, tecadenoson appears to terminate AV node-dependent supraventricular tachycardias without hypotension and bronchoconstriction. METHODS In this open-label, multicenter, dose escalation study, tecadenoson was administered to 37 patients (AV node re-entrant tachycardia, n = 29; AV re-entrant tachycardia, n = 8) with inducible PSVT sustained for > or =1 min during an electrophysiology study. Seven regimens (0.3 to 15 microg/kg) of up to two identical tecadenoson intravenous bolus doses were administered. RESULTS After the first or second bolus, PSVT converted to sustained sinus rhythm for > or =5 min in 86.5% (32/37) of the patients, with 91% (29/32) of the conversions occurring after the first bolus (most within 30 s), coincident with anterograde conduction block in the AV node. No effects on sinus cycle length (SCL) or systolic blood pressure were observed. The atrial-His (AH), but not the His-ventricular (HV) interval was prolonged up to 5 min after the final tecadenoson bolus, returning to baseline by 10 min. Tecadenoson was generally well tolerated. CONCLUSIONS In this study, tecadenoson rapidly terminated sustained PSVT by depressing AV nodal conduction without causing hypotension. After sinus rhythm restoration, there was minimal AH interval prolongation without HV interval or SCL prolongation.

Prevalence and clinical characteristics associated with left atrial appendage thrombus in fully anticoagulated patients undergoing catheter-directed atrial fibrillation ablation.

LAA Thrombus Among Anticoagulated AF Patients. Introduction: Catheter‐directed atrial fibrillation (AF) ablation is contraindicated among patients with left atrial appendage (LAA) thrombus. The prevalence of LAA thrombus among fully anticoagulated patients undergoing AF ablation is unknown.

Species variability in angiotensin receptor expression by cultured cardiac fibroblasts and the infarcted heart

Cardiac fibroblasts, an abundant cell of the left ventricle (LV), proliferate and synthesize collagen in the heart after acute injury and during pressure overload hypertrophy. From many studies, angiotensin II (ANG II) receptors have been implicated in promoting collagen formation by the rat cardiac fibroblast. The present study examined species variability in ANG II receptor expression. Cultured rat fibroblasts expressed 43,000 ± 15,000 ANG II (AT1-specific) receptors per cell (dissociation constant = 0.92 ± 0.34 nM), whereas rabbit and neonate human cardiac fibroblast cultures expressed few receptors. Angiotensin increased intracellular Ca2+ concentration in rats but not in rabbit or human cardiac fibroblasts and stimulated arachidonic acid release in rat but not rabbit fibroblasts. In situ, 6 days after coronary artery ligation, angiotensin receptor expression was increased 34.8 ± 13.4-fold in the infarcted area relative to the noninfarcted tissue in the rat LV, whereas rabbit hearts demonstrated only a 3.2 ± 1.6-fold increase in ANG II binding within the infarcted tissue. These species differences in receptor expression raise questions as to the role of angiotensin as a mediator of collagen formation across species and as a direct target of angiotensin-converting enzyme inhibitors to regulate cardiac fibroblast function.