Demonstration of an Excitable Gap in the Common Form of Atrioventricular Nodal Reentrant Tachycardia

Premature ventricular depolarizations were introduced during sustained atrioventricular nodal reentrant tachycardia ("slow-fast" type) in a single patient during electrophysiological study. Preexcitation of the atrium with retrograde His bundle capture occurred over an 85 msec range of coupling intervals between the last antegmde His bundle depolarization and the first retrograde His bundle depolarimtion associated luith the premature beat (H₁ - H₂ interval). The interval between the retrograde His bundle depolarization (H₂) and the retrograde atrial depolarization (A₂) remained constant over this 85 msec excitable gap as the H₁-H₂ interval decreased. This indicates the presence of fully excitable tissue luithin the retrograde fast pathway of the reentrant circuit during the tachycardia and demonstrates the utility of this technique for defining the extent and conduction properties of the excitable gap in reentrant arrhythmias     

Conduction Properties of the Crista Terminalis in Patients with Typical Atrial Flutter: Basis for a Line of Block in the Reentrant Circuit

Conduction Properties of the Crista Terminalis . Introduction: Previous mapping studies in patients with typical atrial flutter have demonstrated the crista terminalis to he a posterior harrier of the reentrant circuit forming a line of block. However, the functional role of the crista terminalis in patients with or without a history of atrial flutter is not well known. The aim of this study was to determine whether the conduction properties of the crista terminalis are different between patients with and those without a history of atrial flutter. Methods and Results: The study population consisted of 12 patients with clinically documented atrial flutter (group 1) and 12 patients with paroxysmal supraventricular tachycardia as well as induced atrial flutter (group 2). A 7-French, 20-pole, deflectable Halo catheter was positioned around the tricuspid annulus. A 7-French, 20-pole Crista catheter was placed along the crista terminalis identified by the recording of double potentials with opposite activation sequences during typical atrial flutter. After sinus rhythm was restored, pacing from the low posterior right atrium near the crista terminalis was performed at multiple cycle length to 2:1 atrial capture. No double potentials were recorded along the crista terminalis during sinus rhythm in both groups. In group 1, the longest pacing cycle length that resulted in a line of block with double potentials along the crista terminalis was 638 ± 119 msec. After infusion of propranolol, it was prolonged to 832 ± 93 msec without change of the interdeflection intervals of double potentials. In group 2, the longest pacing cycle length that resulted in a line of block with double potentials along the crista terminalis was 214 ± 23 msec. After infusion of procainamide, it was prolonged to 306 ± 36 msec with increase of interdeflection interval of double potentials. Conclusion: The crista terminalis forms a line of transverse conduction block during typical atrial flutter. Poor transverse conduction property in the crista terminalis may be the requisite substrate for clinical occurrence of typical atrial flutter.     

Reduction in Atrial Flutter Ablation Time by Targeting Maximum Voltage: Results of a Prospective Randomized Clinical Trial

Background: Radiofrequency ablation (RFA) of the cavotricuspid isthmus (CTI) is an established therapy for typical atrial flutter. Previous studies have demonstrated that the CTI is often composed of discrete muscle bundles, and evidence has suggested that these bundles correlate with high-voltage local electrograms in the tricuspid isthmus. This randomized, multicenter clinical trial was designed to prospectively compare the hypothesis that a maximum voltage-guided (MVG) technique targets critical conducting bundles in the isthmus, as reflected by a reduction in ablation requirements compared to the anatomical approach to atrial flutter ablation.
Methods: Bidirectional block was achieved in patients undergoing ablation for typical atrial flutter using 1 of 2 randomly assigned methods. The anatomical approach produced a contiguous line of ablation lesions from the inferior aspect of the tricuspid annulus to the inferior vena cava using a standard method. The MVG technique sequentially targeted the maximum voltage local electrograms in the CTI along a similar line.
Results: Sixty-nine patients were randomized, with mean age 63 ± 10 and 58 (84%) male. Among patients in the anatomic group (n = 34), mean ablation time was 11.2 ± 7.5 minutes compared to 5.9 ± 3.3 in the MVG group (n = 35) (P = 0.0026). A mean of 14.2 ± 9.7 ablation lesions were created in the anatomic group, and 7.9 ± 4.8 in the MVG group (P = 0.0042).
Conclusions: Ablation for atrial flutter using an MVG technique results in significantly less ablation requirements than the traditional approach, potentially by concentrating ablation lesions on the muscle bundles responsible for transisthmus conduction.     

Case Reports: Radiofrequency Catheter Ablation of Typical Atrial Flutter and the Atrioventricular Junction via the Superior Vena Caval Approach in a Patient with a Congenital Absence of an Inferior Vena Cava

The absence of an inferior vena cava is a rare congenital condition often without clinical significance. Alternative venous approaches are often needed to treat these patients. We report a case of successful ablation of both isthmus dependent flutter and the AV junction using the superior vena cava in a patient with an inferior vena cava anomaly.