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Radiofrequency ablation of the inferior vena cava-tricuspid valve isthmus in common atrial flutter

Endocardial mapping has suggested that common atrial flutter (AF) is based on right atrial reentry surrounding the inferior vena cava (IVC). The isthmus between the IVC and the tricuspid valve (TV) appears essential to close the circuit. To test this hypothesis, radiofrequency was applied to the IVC-TV isthmus, with catheter electrodes, in 9 patients with AF. Mapping confirmed a right atrial circuit surrounding the IVC in all. In 4 patients another type of AF was induced that followed the circuit in the opposite direction. Radiofrequency interrupted AF in all patients. Multiple endocardial recordings showed that interruption was due to activation block at the point of application. Radiofrequency produced very brief or sustained, atrial fibrillation in 2 patients, which resulted in sinus rhythm. AF recurred in 4 patients with the same activation pattern and was interrupted again with radiofrequency in the IVC-TV isthmus in 3. AF was noninducible in 7 patients after 1 to 4 sessions. AF-free periods of 2 to 18 months without drugs were observed after radiofrequency, but 2 patients had paroxysmal atrial fibrillation. These results confirm that the IVC-TV isthmus is an essential part of the AF circuit. Ablation of this area may be of therapeutic value, but technical improvements are needed. Long-term efficacy of the procedure is uncertain.

Validation of double-spike electrograms as markers of conduction delay or block in atrial flutter☆

Recent mapping studies of atrial flutter have shown that fragmented electrograms can be found in most cases from the posterior, posteroseptal and posterolateral walls of the right atrium. The fragmentation pattern most often consists of a double spike. To further assess double-spike electrograms as a possible marker of conduction delay, bipolar electrograms were continuously recorded during atrial overdrive pacing of common flutter from the right atrium (7 patients) and from the proximal coronary sinus (5). Baseline double-spike separation of 50 to 130 ms was unchanged in 1 patient and slightly increased (5 to 25 ms) in 4 by coronary sinus pacing. The electrogram sequence was unchanged and the surface morphology was similar to that of basal flutter. Right atrial pacing decreased double-spike separation by 25 to 85 ms from basal values of 45 to 175 ms (23 to 83%), suggesting fusion in the area of fragmented electrograms. These findings suggest that double-spike electrograms represent activation on both sides of a conduction delay zone. The changes induced in these electrograms by pacing from the anterior right atrium and the coronary sinus are consistent with flutter circuits rotating counterclockwise (frontal plane) in the posterior right atrial wall in common atrial flutter.

Catheter ablation vs. antiarrhythmic drug treatment of persistent atrial fibrillation: a multicentre, randomized, controlled trial (SARA study)

Background Catheter ablation (CA) is a highly effective therapy for the treatment of paroxysmal atrial fibrillation (AF) when compared with antiarrhythmic drug therapy (ADT). No randomized studies have compared the two strategies in persistent AF. The present randomized trial aimed to compare the effectiveness of CA vs. ADT in treating persistent AF. Methods and results Patients with persistent AF were randomly assigned to CA or ADT (excluding patients with long-standing persistent AF). Primary endpoint at 12-month follow-up was defined as any episode of AF or atrial flutter lasting >24 h that occurred after a 3-month blanking period. Secondary endpoints were any atrial tachyarrhythmia lasting >30 s, hospitalization, and electrical cardioversion. In total, 146 patients were included (aged 55 ± 9 years, 77% male). The ADT group received class Ic (43.8%) or class III drugs (56.3%). In an intention-to-treat analysis, 69 of 98 patients (70.4%) in the CA group and 21 of 48 patients (43.7%) in the ADT group were free of the primary endpoint (P = 0.002), implying an absolute risk difference of 26.6% (95% CI 10.0–43.3) in favour of CA. The proportion of patients free of any recurrence (>30 s) was higher in the CA group than in the ADT group (60.2 vs. 29.2%; P < 0.001) and cardioversion was less frequent (34.7 vs. 50%, respectively; P = 0.018). Conclusion Catheter ablation is superior to medical therapy for the maintenance of sinus rhythm in patients with persistent AF at 12-month follow-up. Clinical Trial Registration Information NCT00863213 (http://clinicaltrials.gov/ct2/show/NCT00863213).

Fragmented electrograms and continuous electrical activity in atrial flutter

Multiple endocardial bipolar electrograms were recorded in 13 patients with atrial flutter (AF) to locate areas of fragmented electrical activity. Stable fragmentation patterns were found in each case, covering between 36% and 100% of the flutter cycle. Double or triple spike patterns were common. The direction of atrial activation was approximately defined in 11 patients, and in all of them at least part of the areas showing fragmentation was included in the circuit. In 1 patient an area of continuous electrical activity was found. AF circuits appeared to be included in the right atrium in 12 patients and in the left atrium in 1 patient. During atrial stimulation changes in fragmented electrograms coincided with changes in AF pattern before its interruption, while restoration of stable AF after stimulation was accompanied by reappearance of previous stable fragmented electrograms. In 6 patients electrograms were recorded after sinus rhythm was reestablished, and all showed marked decreases or disappearance of fragmentation. It is concluded that fragmented electrograms are often found in AF and may be related to abnormal local conduction in relation to the reentrant activation circuits.

Atrial flutter mapping and ablation. I. Studying atrial flutter mechanisms by mapping and entrainment.

Endocardial mapping has led to a detailed knowledge of reentry mechanisms in atrial flutter. Multipolar and deflecting tip catheters allow recording local electrograms from multiple areas of the right atrium, and from the coronary sinus. In common flutter, with the typical “sawtooth” pattern, there is circular activation of the right atrium in a “counterclockwise” direction, descending in the anterior and lateral walls, and ascending in the septum and posterior wall. Superior and inferior vena cava, linked by a “line” of functional block in the posterolateral wall, make the central obstacle for circular activation. The cranial and caudal turning points are the atrial “roof,” and the isthmus between the inferior vena cava and the tricuspid valve. Complex conduction patterns, probably including slow conduction are detectable in the low septal area, around the coronary sinus. Atypical flutter, without the sharp negative deflections of common flutter, sometimes shows circular activation in the right atrium, rotating in the opposite direction of common flutter (clockwise). Other atypical flutters show no circular right atrial activation, and only partial data from coronary sinus activation, combined with the response to atrial stimulation (entrainment) allow the diagnosis of left atrial reentry, without a precise delimitation of the circuits. In patients having undergone cardiac surgery, atypical flutter may be based on reentry around surgical scars. To our knowledge, the mechanism of type II flutter has not been disclosed in humans.

RADIOFREQUENCY ABLATION OF ATRIAL FLUTTER

RF Ablation of Atrial Flutter. Activation mapping in common atrial flutter has shown circular (reentrant) activation of the right atrium around anatomic structures and areas of functional block. The direction of rotation is counterclockwise (in a frontal view), and in the low right atrium the myocardium between the inferior vena cava (IVC) and the tricuspid valve (TV) is critical to close the activation circle. The circuit can be interrupted by radiofrequency ablation of the myocardium between the TV and the IVC, and, in some cases, by ablation between the coronary sinus and TV. Flutter interruption does not mean complete isthmus ablation, as it may remain inducible, requiring further ablation. Despite attaining noninducibility, flutter may recur, and new procedures may be needed for complete ablation. Atrial fibrillation occurs in up to 30% of the cases during follow‐up but is generally well controlled with antiarrhythmic drugs that were ineffective in treating flutter before ablation. Some noncommon atrial flutters show circular right atrial activation in a reversed (clockwise) direction, with the same critical areas in the low right atrium, and in these isthmus ablation is effective. Other noncommon flutters have different substrates in the right or left atrium, and mapping has to define specific critical isthmuses as ablation targets in each case. Left atrial flutter circuits remain inaccessible to ablation.

Mechanisms of entrainment of human common flutter studied with multiple endocardial recordings.

BACKGROUND The mechanisms of common atrial flutter entrainment have not been directly studied in humans. METHODS AND RESULTS Endocardial mapping in six cases of common flutter showed large right atrial (RA) reentry circuits. Activation was craniocaudal in the anterolateral right atrium and caudocranial in the septum. The inferior vena cava-tricuspid isthmus (IVC-TV) closed the circuit. The high right atrium was paced at progressively shorter cycle lengths (CLs) in all, and the IVC-TV was paced in three cases. We recorded six to eight simultaneous RA electrograms from septum and anterior wall. Transient entrainment was recognized from all sites by capture of all electrograms at two or more paced CLs, with total or partial preservation of baseline flutter sequence and return to baseline after pacing. Antidromic circuit penetration was documented in five cases during high RA pacing and in one with IVC-TV pacing. Short CLs induced orthodromic conduction delays that resulted in a postpacing pause longer than basal flutter CL. ECG fusion with high RA pacing correlated poorly with antidromic septal penetration. This was related to overlap of orthodromic septal activation with anterior wall activation of the following cycle. Pacing disorganized flutter into a brief irregular rapid rhythm in two cases and atrial fibrillation in one case. In two cases, complete antidromic septal penetration led to sudden flutter interruption, and in another case it led to circuit inversion. CONCLUSIONS Direct recordings confirm orthodromic and antidromic penetration of flutter circuits by high and low RA pacing. Short CLs modify the circuit. Disorganization is the most common mode of flutter interruption.

Comparison of radiofrequency catheter ablation of drivers and circumferential pulmonary vein isolation in atrial fibrillation: a noninferiority randomized multicenter RADAR-AF trial.

BACKGROUND Empiric circumferential pulmonary vein isolation (CPVI) has become the therapy of choice for drug-refractory atrial fibrillation (AF). Although results are suboptimal, it is unknown whether mechanistically-based strategies targeting AF drivers are superior. OBJECTIVES This study sought to determine the efficacy and safety of localized high-frequency source ablation (HFSA) compared with CPVI in patients with drug-refractory AF. METHODS This prospective, multicenter, single-blinded study of 232 patients (age 53 ± 10 years, 186 males) randomized those with paroxysmal AF (n = 115) to CPVI or HFSA-only (noninferiority design) and those with persistent AF (n = 117) to CPVI or a combined ablation approach (CPVI + HFSA, superiority design). The primary endpoint was freedom from AF at 6 months post-first ablation procedure. Secondary endpoints included freedom from atrial tachyarrhythmias (AT) at 6 and 12 months, periprocedural complications, overall adverse events, and quality of life. RESULTS In paroxysmal AF, HFSA failed to achieve noninferiority at 6 months after a single procedure but, after redo procedures, was noninferior to CPVI at 12 months for freedom from AF and AF/AT. Serious adverse events were significantly reduced in the HFSA group versus CPVI patients (p = 0.02). In persistent AF, there were no significant differences between treatment groups for primary and secondary endpoints, but CPVI + HFSA trended toward more serious adverse events. CONCLUSIONS In paroxysmal AF, HFSA failed to achieve noninferiority at 6 months but was noninferior to CPVI at 1 year in achieving freedom of AF/AT and a lower incidence of severe adverse events. In persistent AF, CPVI + HFSA offered no incremental value. (Radiofrequency Ablation of Drivers of Atrial Fibrillation [RADAR-AF]; NCT00674401).

Bundle-Branch Reentry and the Postpacing Interval After Entrainment by Right Ventricular Apex Stimulation: A New Approach to Elucidate the Mechanism of Wide-QRS-Complex Tachycardia With Atrioventricular Dissociation

Background —Diagnosis of bundle-branch reentry ventricular tachycardia (BBR-VT) by the standard approach is challenging, and this may lead to nonrecognition of this tachycardia mechanism. Because the postpacing interval (PPI) after entrainment has been correlated with the distance from the pacing site to the reentrant circuit, BBR-VT entrainment by pacing from the right ventricular apex (RVA) should result in a PPI similar to the tachycardia cycle length (TCL). This factor may differentiate BBR-VT from other mechanisms of wide-QRS-complex tachycardia with AV dissociation, such as myocardial reentrant VT (MR-VT) or AV nodal reentrant tachycardia (AVNRT), in which the circuit is usually located away from the RVA. Methods and Results —Transient entrainment by RVA pacing was attempted in 18 consecutive BBR-VTs and finally achieved in 13. Results were compared with those found in 59 consecutive MR-VTs and 50 consecutive AVNRTs. The mean PPI−TCL difference was significantly (P <0.0001) shorter in the BBR-VT group (9±11 ms) than in the MR-VT (109±48 ms) and the AVNRT (150±29 ms) groups. No BBR-VT showed a PPI−TCL >30 ms (range −12 to 24 ms). Except for 2 MR-VTs, no MR-VT (range 21 to 211 ms) or AVNRT (range 100 to 215 ms) showed a PPI−TCL <30 ms. Conclusions —A PPI−TCL >30 ms, after entrainment by RVA stimulation, makes BBR-VT unlikely. Conversely, a PPI−TCL <30 ms is suggestive of BBR-VT but should lead to further investigation by use of conventional criteria.

Catheter Ablation of Atrial Flutter Circuits

Atrial flutter (AF) mapping has shown circular activation in the right atrium (RA), wilh a “counterclockwise” rotation in a frontal view. The myocardial isthmus between the inferior vena cava and the tricuspid valve (IVC‐T) closes the activation circuit in its caudal end. The reproducibility of this activafion pattern, and the fact that some “rare” AF with a “clockwise” rotation of activation use the same circuit, suggests that reentry is greatly facilitated by the anatomical arrangement of the caudal end of the RA. This suggested that ablation of the IVC‐T isthmus may interrupt AF and prevent its recurrence. We have applied radiofrequency (RF) current to the IVC‐T isthmus in nine patients, producing sudden interruption of activation at this point in five (all those treated with large surface electrode catheters). in three others, RF produced acceleration or disorganization, leading to interruption. Preliminary follow‐up data suggest a favorable effect on AF recurrence, either by preventing it, or by making antiarrhythmic drugs effective.