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Pulmonary vein isolation is the electrophysiological endpoint of complete conduction block at the level of the veno-atrial junction and must be explicitly distinguished from encircling PV ablation which frequently does not result in isolation. The prerequisites for successful PV isolation include a knowledge of the individual anatomy of the PVs and the left atrium, appropriate positioning of circular mapping catheters, and a knowledge of the electrophysiology of PV activation, in addition to effective ablation tools. Excessive ablation, and possibly complications, can be avoided by the recognition of non-PV myocardial contributions to electrograms recorded from within the PVs. The posterior wall of the left atrial appendage contributes far-field electrograms to recordings from all or nearly all left superior PVs, the low anterior left atrium to 80% of left inferior PV recordings and the superior vena cava to 23% of right superior PV recordings. Recognition of these far-field components is feasible and accurate in sinus rhythm as well as during ongoing atrial fibrillation. Finally, the creation of temporally stable PV isolation remains a currently unsolved problem although prolonged post isolation surveillance, may be helpful.

Background— The long-QT and Brugada syndromes are important substrates of malignant ventricular arrhythmia. The feasibility of mapping and ablation of ventricular arrhythmias in these conditions has not been reported. Methods and Results— Seven patients (4 men; age, 38±7 years; 4 with long-QT and 3 with Brugada syndrome) with episodes of ventricular fibrillation or polymorphic ventricular tachycardia and frequent isolated or repetitive premature beats were studied. These premature beats were observed to trigger ventricular arrhythmias and were localized by mapping the earliest endocardial activity. In 4 patients, premature beats originated from the peripheral right (1 Brugada) or left (3 long-QT) Purkinje conducting system and were associated with variable Purkinje-to-muscle conduction times (30 to 110 ms). In the remaining 3 patients, premature beats originated from the right ventricular outflow tract, being 25 to 40 ms ahead of the QRS. The accuracy of mapping was confirmed by acute elimination of premature beats after 12±6 minutes of radiofrequency applications. During a follow-up of 17±17 months using ambulatory monitoring and defibrillator memory interrogation, no patients had recurrence of symptomatic ventricular arrhythmia but 1 had persistent premature beats. Conclusion— Triggers from the Purkinje arborization or the right ventricular outflow tract have a crucial role in initiating ventricular fibrillation associated with the long-QT and Brugada syndromes. These can be eliminated by focal radiofrequency ablation.

In 1964, Gordon Moe described the multiple wavelet hypothesis [1] based upon a computer model and proposed that the following factors-size and mass of the tissue, conduction velocity as well as refractory periods all modulated the ability to sustain atrial ~brillation. The probability of sustenance was proportional to the number of simultaneous wavelets. Later experimental data from Allessie et al provided evidence of the reentrant nature of this arrhythmia with the estimation that only 4 to 6 simultaneous wavelets were suf~cient to maintain AF in their model [2]. Intraoperative mapping studies from Cox’s group con~rmed the _eeting nature of wavelets both in time and location, precluding the use of mapping to guide ablative surgical therapy [3]. In contrast, however spatial disparities of complex electrical activity have been reported recently in both atria during AF. Li et al reported a disorganization of atrial electrograms on the posterior wall in both atria (“type III AF”) which reorganized anteriorly towards a type I AF [4] while Jais et al found that trabeculated regions in the right atrium exhibited temporally less frequent complex electrograms in comparison to the smooth walled region extending till the crista terminalis. In particular, electrograms recorded from the majority of the left atrium were complex except near the appendage again a trabeculated region (Fig. 1). Shah et al explored the electrical activity of great veins derived from atrial muscle ~bers in the venous walls. A spike like activity recorded from the superior vena cava was dissociated in 14 and followed the right atrial activity in one out of 15 patients during AF [6]. In contrast, activity in the pulmonary veins (notably the superior ones) could be recorded up to 5 cm inside and could track the left atrial activity at a high rate thus indicating a better coupled interface with the LA.

The incidence and characteristics of dissociated arrhythmia confined to the pulmonary vein (PV) following disconnection have not been described in a large number of patients with paroxysmal atrial fibrillation.This was a prospective study of 152 patients (29 female, mean age 51 +/- 11 years) referred for catheter ablation of drug-refractory paroxysmal atrial fibrillation. Following ostial ablation, the rate and regularity of any dissociated venous activity was analyzed with and without isoproterenol infusion (to achieve a heart rate of 120-140 beats/min). Patients then were classified according to their venous dissociated activity. Group 1 consisted of patients in whom the dissociated PV spike had a slow rhythm1,200 ms. Group 2 consisted of patients with spontaneous repetitive dissociated discharges confined in the vein with a cycle length400 ms. A total of 384 PVs were ablated in 152 patients. Disappearance of all venous potentials was observed in 88% of the treated veins; at least one dissociated venous potential was observed in the remaining 12%. Group 1 activity was seen more often than group 2 (23 patients, mean cycle length 2,300 +/- 1,100 ms vs 13 patients, mean cycle length 179 +/- 77 ms). Dissociated PV arrhythmia was seen most often in the right superior PV (19%).Dissociation as the endpoint of PV disconnection was observed in 12% of PVs. Due to the capricious nature of this activity, the actual incidence is almost certainly higher. The dissociated venous rhythm usually is slow and, less commonly, is rapid and repetitive.

Left atrial flutters are not as common as peri-tricuspidian circuits. Their systematic study is much more recent and had greatly benefited from the use of 3 D mapping systems. Reentry has been demonstrated as being the mechanism but the circuits are not stereotypical like in the right atrium. Multiple macroreentrant circuits with one or more loops have been described as well as small re-entrant circuits. The complexity and variability of these circuits is related to the presence of zone of block, slow conduction and electrically silent areas. They create the conditions for the arrhythmia maintenance as they stabilize the circuit and prevent short circuiting. Most of the patients with left atrial flutter have an underlying structural heart disease, but their arrhythmia is amenable to curative catheter ablation.

The pulmonary veins (PVs) have been shown to trigger paroxysmal atrial fibrillation. The relationship of anatomical dimensions versus arrhythmogenicity has not been assessed.The diameters of four PVs were measured by selective PV angiography before ablation in 39 consecutive patients (23 male, mean age 46 years) with only one (25 patients) or two (14 patients) arrhythmogenic PVs (ArPVs). After ablation of ArPVs, no patient had recurrence of atrial fibrillation from the remaining PVs. Comparisons were performed variously between ArPV and non-ArPV, and within and across both groups.ArPVs were distributed as follows; left superior PV: 40%, left inferior PV: 28%, right superior PV: 26%, and right inferior PV: 6%. Statistical comparisons showed that (1) Triggers of atrial fibrillation were located in the largest PV in 72% of patients, (2) For each PV, the mean diameter of ArPV was significantly larger than that of non-ArPV (p0.05), (3) No significant difference was observed in the diameter of the four different ArPVs (range 16.2 +/- 1.3 to 17.2 +/- 4.4).In patients with atrial fibrillation initiated from one or two ArPVs, the diameters of ArPVs were significantly larger than those of non-ArPVs irrespective of the specific PV concerned, which might imply a possible role of PV dilatation in the arrhythmogenesis.

Pulmonary vein ostial ablation with the aim of electrically isolating the arrhythmogenic tissue is the commonest ablation strategy for AF. Attempts are being made to simplify pulmonary vein isolation by creating 3D versions of the atrial anatomy, and robotic as well as remote catheter navigation has been developed. Single shot circular ablation devices, using RF, ultrasound, cryo and laser energy, are under evaluation. Despite these different innovations, the most commonly used technique is the composite multiple point ablation lesion created with a fundamentally simple radiofrequency energy delivering ablation catheter. The high recurrence rate and low efficacy of current ablation procedures may be traced in large part to the inherent variability in individual lesion size with this technology. Real-time measurement of catheter tip contact force may allow electrophysiologists to avoid both ineffective lesions because of insufficient contact and complications due to excessive contact force. Currently, fiber-optic as well as electro-magnetic sensor based technologies offer the most precise real-time measurement although impedance and friction based measures are also available. The greatest experimental and clinical experience is with the fiber-optic technology, with more than 700 human patients. Three prospective human studies are underway evaluating the correlation between contact force and acute as well as chronic efficacy in isolating the pulmonary veins. This technology may help reduce re-do procedure rates for atrial fibrillation and also improve procedural safety.