Bruno Fischer

Elimination of atrioventricular nodal reentrant tachycardia using discrete slow potentials to guide application of radiofrequency energy

BackgroundAblation of the slow pathway has been performed to eliminate atrioventricular (AV) nodal reentrant tachycardia (AVNRT) either by a surgical approach or by using radiofrequency catheter technique guided by retrograde slow pathway activation mapping. From previous experience of midseptal and posteroseptal mapping, we were aware of the existence of peculiar slow potentials in most humans. Postulating their role in AVNRT, we studied these potentials and the effects of radiofrequency energy. Methods and ResultsSixty-four patients (mean age, 48±19 years) with the usual form ofAVNRT were studied. Slow, low-amplitude potentials were recorded when using the anterograde AV conducting system. Slow potentials occupied all (giving a continuum of electrograms) or some of the time between the atrial and ventricular electrograms. Their most specific patterns were their progressive response to increasing atrial rates, which resulted in a dramatic decline in amplitude and slope, a corresponding increase in duration, and a separation from preceding atrial potentials until the disappearance of any consistent activity. Slow potentials were recorded along a vertical band at the mid or posterior part of the septum near the tricuspid annulus. Radiofrequency energy applied at the slow potential site resulted in interruption of induced tachycardia within a few seconds and rendered tachycardia noninducible in all patients. A median of two impulses was delivered to each patient. In 69% of patients, postablation atrial stimulation cannot achieve a long atrial-His interval, which previously was critical for tachycardia induction or maintenance. No patient had AVNRT over a follow-up period of 1-16 months, and all had preserved AV conduction. In all except two patients, the PR interval was unchanged. In 47 patients, long-term electrophysiological studies confirmed the efficacy of ablation and the nonreversibility of results by isoproterenol; however, echo beats remained inducible in 40%1 of patients. ConclusionsAn area showing slow potentials is present at the perinodal region in humans. In patients with AVNRT, application of radiofrequency energy renders tachycardia noninducible through the preferential modification of the anterograde slow pathway. With present clinical methods, the exact origin and significance of these physiological potentials cannot be specified.

Electrophysiological effects of catheter ablation of inferior vena cava-tricuspid annulus isthmus in common atrial flutter

BACKGROUND The electrophysiological mechanisms for successful catheter ablation of atrial flutter (AFI) targeting the inferior vena cava-tricuspid annulus (IVC-TA) isthmus have not been determined. METHODS AND RESULTS Twenty patients with common AFI were studied. All had inducible common AFI, and 8 of them had both common and reverse AFI. Right atrial (RA) activation sequences were investigated during pacing from sites proximal (low lateral RA) and distal (proximal coronary sinus) to the IVC-TA isthmus both during entrainment of common or reverse AFI and during pacing in sinus rhythm. This was repeated after ablation. During pacing in sinus rhythm from the low lateral RA, the septum was activated by caudocranial and craniocaudal wave fronts. Similarly, during pacing from the proximal coronary sinus, the lateral RA was activated by two wave fronts. Catheter ablation of the IVC-TA isthmus induced dramatic changes in mapping due to the loss of caudocranial wave front in all but 1 patient. The septum and the lateral RA were activated by a single craniocaudal front as during entrainment of reverse or common AFI, respectively. After a follow-up of 8 +/- 2 months, common or reverse AFI occurred in 4 patients. Two had no or only unidirectional changes in the isthmus conduction induced by ablation. The other 2 had a late recovery of conduction. CONCLUSIONS The present study provides evidence that the mechanism of successful AFI ablation targeting the IVC-TA isthmus is local bidirectional conduction block. This change can be used as a new and complementary electrophysiological end point for the procedure. AFI recurrences are associated with failure to achieve a permanent block.

Radiofrequency catheter ablation of common atrial flutter in 80 patients.

OBJECTIVES The purpose of this study was to evaluate the efficacy and safety of radiofrequency catheter ablation of common atrial flutter and to determine the optimal target sites in a large series of patients. BACKGROUND Recent studies report the efficacy of radiofrequency current application in the low right atrial region to interrupt and prevent recurrences of common atrial flutter. However, larger groups of patients are required to confirm the efficacy of this technique and to specify the target sites. METHODS Two different approaches were used to target the ablation site in 80 consecutive patients. In the first 50 patients, target sites were localized using both anatomic landmarks and electrophysiologic variables. Three anatomic landmarks were used: area 1 = between the tricuspid valve and inferior vena cava orifice; area 2 = between the tricuspid valve and coronary sinus ostium; area 3 = between the inferior vena cava and coronary sinus. The electrophysiologic criterion was to ablate when there was a stable atrial electrogram during the plateau phase. In the next 30 patients we assessed the effect of application of radiofrequency energy in a single line in area 1, 2 or 3 in groups of 10 patients. RESULTS Overall atrial flutter was interrupted and rendered noninducible after a single session in 72 patients (90%) and could not be interrupted in 8 (10%). The mean (+/- SD) number of radiofrequency applications was 12 +/- 8. After a mean (+/- SD) follow-up of 20 +/- 8 months, recurrences occurred in 14 patients (17%). The location of the final successful site in the first group of 50 patients was in area 1 in 39%, area 2 in 36% and area 3 in 25%. In the next 30 patients, when lines of radiofrequency lesions were placed at several sites, they produced success rates of 70%, 40% and 10% at areas 1, 2 and 3, respectively. CONCLUSIONS Radiofrequency catheter ablation of atrial flutter can be performed with a high success rate and is safe. The highest success rate is achieved with radiofrequency energy applied in the isthmus between the inferior vena cava orifice and tricuspid valve.

Successful Irrigated-Tip Catheter Ablation of Atrial Flutter Resistant to Conventional Radiofrequency Ablation

BACKGROUND Catheter ablation of typical right atrial flutter is now widely performed. The best end point has been demonstrated to be bidirectional isthmus block. We investigated the use of irrigated-tip catheters in a small subset of patients who failed isthmus ablation with conventional radiofrequency (RF) ablation. METHODS AND RESULTS Of 170 patients referred for ablation of common atrial flutter, conventional ablation of the cavotricuspid isthmus with >21 applications failed to create a bidirectional block in 13 (7.6%). An irrigated-tip catheter ablation was performed on identified gaps in the ablation line according to a protocol found to be safe in animals: a moderate flow rate of 17 mL/min and temperature-controlled (target, 50 degrees C) RF delivery with a power limit of 50 W. Bidirectional isthmus block was achieved in 12 patients by use of a mean delivered power of 40+/-6 W with a single application in 6 patients and 2 to 6 applications in the other 6. No side effects occurred during or after the procedure. CONCLUSIONS Irrigated-tip catheter ablation is safe and effective for achieving cavotricuspid isthmus block when conventional RF energy has failed.

Radiofrequency catheter ablation of left lateral accessory pathways via the coronary sinus.

BackgroundThe purpose of this study was to describe a new technique for catheter ablation of left lateral accessory pathways (APs) by radiofrequency energy applied at the epicardium through the coronary sinus wall using a unipolar configuration. Methods and ResultsIn an overall group of 212 patients with left lateral APs, multiple endocardial ablation attempts of the AP were unsuccessful in eight patients. The mean±SD cumulative duration of previous attempts was 12±9 hours, using DC shocks and/or radiofrequency energy applied both at the atrial and/or ventricular AP insertions. Epicardial AP insertion was determined by bipolar and unipolar unfiltered distal electrograms by scanning the coronary sinus with a steerable 6F or 7F catheter with a 4-mm distal electrode. The local atrial to ventricular electrogram amplitude ratio was 03–1.6. At the ablation site, the catheter tip was slightly deflected toward the annulus to increase both the ventricular component of electrograms and contact with the epicardium. In four patients, epicardial electrogram timings were earlier than endocardial ones. The AP was ablated in seven of the eight patients with 20–30 W applied for 10–60 seconds. No complications occurred except a marked nonspecific pain during radiofrequency energy application; however, the catheter remained adherent to the coronary sinus wall, and its withdrawal was performed during a new radiofrequency application to decrease the risk of coronary sinus rupture. After ablation, echocardiograms, coronary artery angiograms, and levophase coronary sinus angiograms showed no abnormality in all patients except two who had a probable mural thrombus in the coronary sinus. AP conduction remained abolished for 1–10 months of follow-up in seven patients. ConclusionsRadiofrequency catheter ablation of left lateral APs can be achieved effectively and relatively safely via the mid or distal coronary sinus when endocardial approaches are unsuccessful.

Simplified Electrophysiologically Directed Catheter Ablation of Recurrent Common Atrial Flutter

BACKGROUND Despite verification of bidirectional conduction block after radiofrequency (RF) catheter ablation in the inferior vena cava (IVC)-tricuspid annulus (TA) isthmus, recurrence of common atrial flutter is relatively common. Although complete linear reablation is usually performed, we evaluated a simplified electrophysiological strategy selectively targeting recovered conducting isthmus tissue. METHODS AND RESULTS Twenty-one patients (18 men and 3 women, age, 54+/-10 years) with a recurrence of typical atrial flutter 6+/-7 months after an apparently successful catheter ablation in the IVC-TA isthmus prospectively underwent electrophysiologically targeted reablation during flutter. Sites with narrow electrograms or fractionated electrograms interposed between adjacent sites with double potentials considered to represent gaps were ablated without movement of the catheter. Mapping showed that 18 of 21 patients had a single gap. Successful ablation required a single application in 14 patients and, in the group as a whole, a median of one application (mean, 2+/-2; range, 1 to 11) with resultant bidirectional block in 13 of 16. A single narrow electrogram (duration, 48+/-6 ms; amplitude, 0.1+/-0.05 mV) was noted at the successful site in 11, whereas a fractionated electrogram (97+/-32 ms, 0.05+/-0.04 mV, P<.05) was noted in 9. There were four additional recurrences during a follow-up at 7+/-5 months; three were similarly ablated with a median of one pulse. CONCLUSIONS Transmural ablation lesions in the isthmus can be recognized during flutter by double potentials separated by an isoelectric interval. Postablation recurrent flutter is usually due to a single discrete recovered gap; this is represented by a single or a fractionated potential spanning the isoelectric interval of adjacent double potentials, which can be selectively targeted to minimize repeat ablation.

Frequency of recurrent atrial fibrillation after catheter ablation of overt accessory pathways

The effect of successful catheter ablation of overt accessory pathways on the incidence of atrial fibrillation (AF) was studied in 129 symptomatic patients with (n = 75) or without (n = 54) previous documented AF. Fourteen had had ventricular fibrillation. Factors predictive of recurrence were examined, including electrophysiologic parameters. Atrial vulnerability was defined as induction of sustained AF (greater than 1 minute) using single, then double, atrial extrastimuli at 2 basic pacing cycle lengths. When compared to patients with only reciprocating tachycardia, patients with clinical AF included more men (77 vs 54%, p = 0.008) and were older (35 +/- 12 vs 29 +/- 12 years, p = 0.01). They had a significantly shorter cycle length leading to anterograde accessory pathway block (252 +/- 42 vs 298 +/- 83 ms, p less than 0.001), greater incidences of atrial vulnerability (89 vs 24%, p less than 0.001) and subsequent need for cardioversion (51 vs 15%, p less than 0.001). After discharge, the follow-up period was 35 +/- 12 months (range 18 to 76); 7 patients with previous spontaneous AF (9%) had recurrence at a mean of 10 months after ablation. Age, presence of structural heart disease accessory pathway location, atrial refractory periods and accessory pathway anterograde conduction parameters were not predictive of AF recurrence. Persistence of atrial vulnerability after ablation was the only factor associated with further recurrence of AF. Atrial vulnerability was observed after ablation in only 56% of patients with previous AF versus 89% before ablation. It is concluded that successful catheter ablation of accessory pathways prevents further recurrence of AF in 91% of patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Usefulness of Isometric Exercise During Dobutamine Administration for Stress Echocardiography

An isometric exercise was performed by 170 consecutive patients at peak dose dobutamine, before atropine administration. The test was well tolerated, heart rate increased significantly during exercise, and atropine administration was avoided in 29% of patients.

Anatomical versus electrophysiological approaches for ablation of the slow pathway in patients with AV nodal reentrant tachycardia

Different approaches have been described [1–12] for ablating the slow ‘pathway’ (SP) in patients with atrioventricular nodal reentrant tachycardia (AVNRT). In one approach, electrogram patterns are used to identify the ablation site [1,4], whereas in the other approach, the ablating site is selected on anatomical criteria. Both approaches appear effective, but no study (except one preliminary abstract [8]) comparing the two techniques has been published. In the following study, we analyze the results of these different techniques and investigated the prevalence of electrogram patterns and their relation to a successful outcome in a series of 164 patients.