Insights into the electrophysiology of ventricular tachycardia gained by the catheter ablation experience: "learning while burning"

[Historical developments in the diagnosis and treatment of pre-excitation syndromes (WPW)]

In 1930, Wolff, Parkinson and White described the syndrome that bears their names. The mechanisms of supraventricular tachycardias were analyzed by brilliant electrocardiography interpretation by Pick and Langendorf. Wellens and Durrer using electrophysiologic studies analyzed the tachycardia mechanism invasively. In Germany the group by Seipel and Breithardt as well as Neuss and Schlepper studied the tachycardia mechanisms and response to antiarrhythmic drugs invasively by electrophysiological studies. Following the first successful interruption of an accessory pathway by Sealy in 1967, surgeons and electrophysiologists cooperated in Germany. Two centers, Hannover and Düsseldorf were established. Direct current (DC) ablation of accessory pathways was introduced by Morady and Scheinman. Because of side effects induced by barotrauma of DC, alternative strategies were studied. In 1987, radiofrequency ablation was introduced and thereafter established as curative therapy of accessory pathways in all locations.

[History of catheter ablation]

After His bundle electrography was established in 1967, the step from invasive electrophysiologic diagnosis of arrhythmias to interventional treatment by catheter ablation was imminent. The time interval of 15 years between the diagnosis and treatment of arrhythmias was even shorter than the 19 years between the first selective coronary angiography in 1958 at the Cleveland Clinic in the USA and the first percutaneous coronary intervention in 1977 in Zurich. During each time period, a great amount of knowledge was gained in cardiac surgery, which proved to be very helpful for the development of the interventional treatment. The history of endovascular treatment is an impressive reminder that the preparation and support of cardiovascular surgeons and their handling of complications played a decisive role in the further development of cardiovascular internal medicine. The history of catheter ablation teaches us that the joint work of cardiologists and cardiovascular surgeons is of great importance for the choice and further development of the best possible treatment as for future development of the techniques of therapy.

Radiofrequency ablation of haemodynamically unstable ventricular tachycardia after myocardial infarction

OBJECTIVE

To determine whether radiofrequency (RF) ablation might have a role in haemodynamically unstable ventricular tachycardia.

METHODS

10 patients with a history of ventricular tachycardia producing haemodynamic collapse in whom drug treatment had failed and device therapy was rejected underwent RF ablation of ventricular tachycardia in sinus rhythm. The arrhythmogenic zone was defined on the basis of abnormal systolic movement, the presence of fragmentation (low amplitude, prolonged multiphasic electrograms), and pace mapping. RF lesions were delivered in power mode in linear fashion within the defined arrhythmogenic zone.

RESULTS

Success (no ventricular tachycardia inducible postablation or at retest) was achieved in six patients, possible success (a different ventricular tachycardia inducible at more aggressive stimulation) in three. In one patient, the procedure was abandoned because of poor catheter stability. There were no clinical events during a mean (SD) follow up period of 23 (10) months in any of the nine patients defined as definite or possible successes.

CONCLUSIONS

RF ablation for addressing haemodynamically unstable ventricular tachycardia opens the door for the wider use of catheter ablation for treating this arrhythmia.

Laser photoablation of experimental post-infarction ventricular tachycardia guided by three dimensional activation mapping

BACKGROUND AND OBJECTIVE

The purpose of this study was to evaluate the efficacy of epicardially delivered laser energy to ablate induced ventricular tachycardia in a post-infarction canine model.

STUDY DESIGN/MATERIALS AND METHODS

In 13 canines, the left anterior wall myocardial infarction was created. Five days later, 240 plunged electrodes were inserted into the heart. Three-dimensional ventricular activation sequences were analyzed on line by a computerized mapping system.

RESULTS

Sixteen sustained monomorphic ventricular tachycardias were reproducibly induced in 10 canines. Epicardially contacted Nd:YAG laser irradiated the areas of the final pathway in macro-reentrant activation and the impulse origin in focal excitation. Linear photocoagulation lesions (11-16 x 50-72 mm) were created. Seven macro-reentrant circuits and six of nine focal origins were eliminated (success rate 81%). Pathology showed that laser photocoagulation involved all surviving subepicardial and intramural fibers.

CONCLUSION

Epicardially delivered laser energy in conjunction with electrical activation mapping has a high probability of ablating post-infarction ventricular tachycardia.

Insights into the mechanism of sustained ventricular tachycardia after myocardial infarction in a closed chest porcine model using a multielectrode "basket" catheter

INTRODUCTION

Accurate analysis of the arrhythmia substrate is important for successful radiofrequency ablation of sustained ventricular tachycardia (VT) after myocardial infarction (MI).

METHODS AND RESULTS

A multielectrode "basket" catheter capable of endocardial recording and pacing was inserted percutaneously into the left ventricle of post-MI swine for analysis of the mechanism of sustained VT. Sustained VT was induced in 42 of 61 pigs that survived an acute MI produced by percutaneous transluminal coronary angioplasty balloon occlusion of the left anterior descending coronary artery and injection of agarose gel beads. A multielectrode "basket" catheter (Constellation) with 64 electrodes was inserted in 35 of these animals for analysis of the VT. Induced VT had a cycle length of 179 +/- 25 msec at control and 230 +/- 43 msec after administration of intravenous procainamide. Presystolic electrical activity was recorded from at least 1 of 32 bipolar pairs of electrodes at a mean 40.7 +/- 23.6 msec prior to QRS onset. Isolated mid-diastolic potentials were recorded in 26 of 35 animals. In 22 animals, there were multiple isolated potentials recorded from adjacent electrode pairs. Isochronal maps demonstrated that these potentials returned to the systolic site of origin. Resetting of sustained VT by single premature ventricular stimuli was observed in 6 of 12 animals. Entrainment with overdrive pacing was seen in 19 of 26 animals with induced VT. Concealed entrainment was observed in ten animals. The mean stimulus to QRS interval was 45 +/- 28 msec. Concealed entrainment was observed from adjacent electrode pairs with different stimulus to QRS intervals.

CONCLUSION

These data suggest that sustained VT in this model is due to reentry with an excitable gap. A multielectrode "basket" catheter is useful for analyzing the zone of slow conduction participating in the tachycardia circuit. Such analysis may provide useful information to guide successful catheter ablation of sustained VT after MI.

Efficacy of radiofrequency catheter ablation for ventricular tachycardia in healed myocardial infarction

Radiofrequency catheter ablation has been useful in the treatment of ventricular tachycardia (VT) in selected patients with healed myocardial infarction. Previous studies have demonstrated success rates of 60% to 96% for targeted VT morphologies; however, these studies included patients only after they have had successful mapping procedures and have received radiofrequency lesions. All patients referred for VT ablation from July 1992 to November 1996 were included in this analysis on an intention-to-treat basis. Ninety-five procedures were performed in 66 patients for 77 distinct presentations with tolerated, sustained VT. Fifty-five procedures were successful (58%) and 40 procedures failed. Reasons for procedural failure included failed radiofrequency application despite adequate VT mapping (21 procedures), no tolerated VT induced (12), and aborted procedures due to complications or technical difficulties (7). Fifty-five patients (71%) eventually had a successful VT ablation, although 10 required > 1 procedure. This analysis revealed factors that contribute to failure of VT ablation procedures in addition to inadequate mapping and lesion formation. Procedural difficulties, particularly the inability to induce tolerated VT, frequently prevent successful catheter ablation in patients who present with tolerated, sustained VT.

Insights into the electrophysiology of accessory pathway-mediated arrhythmias provided by the catheter ablation experience: "learning while burning, part III"

The success of catheter ablation has greatly improved the care of patients with paroxysmal tachycardias and has caused a revolution in the practice of electrophysiology. Some investigators have expressed that concern over procedural success in an increasingly interventional specialty threatens to eclipse attempts to understand the physiology of arrhythmia syndromes. Alternatively, due to the precise and directed nature of the lesions created with radiofrequency energy, catheter ablation procedures have allowed investigation to continue at a more focused level. In this article, the insights provided by the catheter ablation experience into the physiology of arrhythmias mediated by accessory AV pathways will be reviewed. Although the learning process was sometimes delayed by the nearly immediate success of radiofrequency catheter ablation, difficult situations have continued to renew efforts for understanding at a deeper level. Conscious attempts at "learning while burning" will provide the opportunity to investigate aspects of bypass tract physiology that remain incompletely characterized, such as partial response to therapy and late recurrence.

Insights into the electrophysiology of atrial arrhythmias gained by the catheter ablation experience: "learning while burning, Part II"

Although the development and wide-scale application of catheter ablative techniques has drastically changed the practice of electrophysiology, catheter ablation does not preclude physiologic investigation. On the contrary, given the precise and directed nature of this technique and the increased attention to detailed cardiac mapping that it requires, catheter ablation may be viewed as a tool to provide unique information about arrhythmia substrates. In this article, the insights provided by the catheter ablation experience into the pathophysiology of the focal atrial arrhythmias, atrial tachycardia, sinus node reentrant tachycardia, and inappropriate sinus tachycardia will be reviewed. Atrial arrhythmias were initially difficult to treat with ablative therapy, particularly because they can occur anywhere within the atria and the experience with mapping for surgical ablation was quite limited. A number of novel approaches to atrial mapping have been developed in response to this challenge, and presently, catheter ablation provides effective therapy for the majority of patients with focal atrial arrhythmias. In addition, deliberate attempts at "learning while burning" have already begun to enhance our understanding of the interaction of the structural and electrophysiologic aspects of the substrate for atrial arrhythmias.