Multiple sources initiating atrial fibrillation from a single pulmonary vein identified by a circumferential catheter

Electrophysiological Evaluation of Pulmonary Vein Isolation

Since the pulmonary veins (PVs) were identified as a major source of AF triggers, ablation strategies targeting the PVs have evolved from focal ablation inside the PVs to wide area circumferential PV isolation (PVI) which at this juncture is the standard approach. Despite the widespread popularity of PVI, a universal definition is lacking. While "entrance block" is a generally accepted endpoint for PVI, the role of "exit block" has yet to be determined. Inexcitability of the circular ablation line has been introduced as a promising additional endpoint for PVI and was associated with an improved clinical outcome in a randomized trial. Correct interpretation of PV electrograms during an ablation procedure is critical in terms of efficacy and safety. A variety of electrophysiological techniques help to correctly differentiate components of complex PV electrograms. Resumption of PV conduction after initially successful PVI leading to AF recurrence remains a major problem and confirmation of bi-directional conduction block does not exclude reversible tissue damage along the ablation line. Prolongation of post-PVI monitoring and application of provocative procedures such as the administration of adenosine after initial PVI to unmask dormant PV conduction may improve clinical outcome although there is lack of valid data supporting these strategies. This article aims on clarifying the electrophysiological criteria for complete pulmonary vein isolation and the explain the importance of this cornerstone in almost all atrial fibrillation ablation procedures.

Maze Procedures for Atrial Fibrillation, From History to Practice

Atrial fibrillation may result in significant symptoms, (systemic) thrombo-embolism, as well as tachycardia-induced cardiomyopathy with cardiac failure, and consequently be associated with significant morbidity and mortality. Nowadays symptomatic atrial fibrillation can be treated with catheter-based ablation, surgical ablation or hybrid approaches. In this setting a fairly large number of surgical approaches and procedures are described and being practised. It should be clear that the Cox-maze procedure resulted from building up evidence and experience in different steps, while some of the present surgical approaches and techniques are being based only on technical feasibility with limited experience, rather than on a process of consequent methodology. Some of the issues still under debate are whether or not the maze procedure can be limited to the left atrium or even to isolation of the pulmonary veins or that bi-atrial procedures are indicated, whether or not cardiopulmonary bypass is to be applied and which route of exposure facilitates an optimal result. In addition, maze procedures are not procedures guide by electrophysiological mapping. At least in theory not in all patients all lesions of the maze procedures are necessary. A history and aspects of current practise in surgical treatment of atrial fibrillation is presented.

High-density epicardial mapping of the pulmonary vein-left atrial junction in humans: insights into mechanisms of pulmonary vein arrhythmogenesis

BACKGROUND

The pulmonary veins (PVs) and the PV-LA (left atrium) junction are established sources of triggers initiating atrial fibrillation. In addition, they have been implicated in the maintenance of arrhythmia.

OBJECTIVE

To undertake high-density electrophysiological characterization of the right superior PV-LA junction in humans.

METHODS

Mapping was performed in 18 patients without a history of atrial fibrillation undergoing cardiac surgery. A high-density epicardial plaque was positioned at the anterior right superior pulmonary vein covering 3 regions: LA, PV-LA junction, and the PV. Isochronal maps were created during (1) sinus rhythm (SR); (2) LA pacing (LA-Pace); (3) PV pacing (PV-Pace); (4) LA programmed electrical stimulation (LA-PES); and (5) PV programmed electrical stimulation (PV-PES). Regional differences in conduction slowing/conduction block (CS/CB) and the prevalence of fractionated signals (FS) and double potentials (DPs) were assessed.

RESULTS

A region of isochronal crowding representing CS/CB developed at the PV-LA junction in 84% of the maps. Three distinct activation patterns were seen. Pattern 1: Uniform SR activation without CS/CB. LA-Pace and PES caused 1 to 2 lines of isochronal crowding (CS/CB) at the PV-LA junction. Pattern 2: CS/CB occurred at the PV-LA junction in SR. LA/PV-Pace and LA/PV-PES caused an increase in CS/CB at the PV-LA junction with widely split DPs and FS. Pattern 3: A single incomplete line of CS at the PV-LA junction in SR. With LA/PV pacing and LA/PV-PES, multiple lines (≥3) of CS/CB developed at the PV-LA junction with evidence of circuitous activation and a marked increase in DPs and FS.

CONCLUSION

High-density epicardial mapping of the right superior pulmonary vein demonstrates marked functional conduction delay and circuitous activation patterns at the PV-LA junction, creating the substrate for reentry.

Catecholaminergic automatic activity in the rat pulmonary vein: electrophysiological differences between cardiac muscle in the left atrium and pulmonary vein

Ectopic activity in cardiac muscle within pulmonary veins (PVs) is associated with the onset and the maintenance of atrial fibrillation in humans. The mechanism underlying this ectopic activity is unknown. Here we investigate automatic activity generated by catecholaminergic stimulation in the rat PV. Intracellular microelectrodes were used to record electrical activity in isolated strips of rat PV and left atrium (LA). The resting cardiac muscle membrane potential was lower in PV [-70 +/- 1 (SE) mV, n = 8] than in LA (-85 +/- 1 mV, n = 8). No spontaneous activity was recorded in PV or LA under basal conditions. Norepinephrine (10(-5) M) induced first a hyperpolarization (-8 +/- 1 mV in PV, -3 +/- 1 mV in LA, n = 8 for both) then a slowly developing depolarization (+21 +/- 2 mV after 15 min in PV, +1 +/- 2 mV in LA) of the resting membrane potential. Automatic activity occurred only in PV; it was triggered at approximately -50 mV, and it occurred as repetitive bursts of slow action potentials. The diastolic membrane potential increased during a burst and slowly depolarized between bursts. Automatic activity in the PV was blocked by either atenolol or prazosine, and it could be generated with a mixture of cirazoline and isoprenaline. In both tissues, cirazoline (10(-6) M) induced a depolarization (+37 +/- 2 mV in PV, n = 5; +5 +/- 1 mV in LA, n = 5), and isoprenaline (10(-7) M) evoked a hyperpolarization (-11 +/- 3 mV in PV, n = 7; -3 +/- 1 mV in LA, n = 6). The differences in membrane potential and reaction to adrenergic stimulation lead to automatic electrical activity occurring specifically in cardiac muscle in the PV.

Anatomic approach for ganglionic plexi ablation in patients with paroxysmal atrial fibrillation

There is evidence that parasympathetic denervation may prevent atrial fibrillation (AF) recurrences. This study aimed at applying an anatomic approach for ablation of atrial ganglionic plexi (GPs) in patients with paroxysmal AF. Nineteen patients with symptomatic, paroxysmal AF underwent anatomically guided radiofrequency ablation at the location of the 4 main left atrial GPs and were prospectively assessed for recurrence of AF or other atrial arrhythmia. This group was compared with 19 age- and gender-matched patients who previously underwent conventional circumferential pulmonary vein ablation. All ablation procedures were uneventful. Circumferential and GP ablations were accomplished with a radiofrequency delivery time of 28 +/- 5 versus 18 +/- 3 min (p <0.001) and a fluoroscopy time of 31 +/- 5 versus 18 +/- 5 min (p <0.001), respectively. Parasympathetic reflexes during radiofrequency ablation were elicited in 4 patients (21%). Arrhythmia recurred in 7 patients (37%) with circumferential ablation and 14 patients (74%) with GP ablation, during 1-year follow-up (p for log-rank test = 0.017). In 2 patients with GP ablation, left atrial flutters were documented in addition to AF during follow-up. Patients who underwent GP ablation had an almost 2.5 times higher risk of AF recurrence compared with those who underwent circumferential ablation (hazard ratio 2.6, 95% confidence interval 1.0 to 6.6, p = 0.038). In conclusion, anatomically guided GP ablation is feasible and safe in the electrophysiology laboratory, but this approach yields inferior clinical results compared with circumferential ablation.

Catheter ablation of atrial fibrillation

Atrial fibrillation is a common arrhythmia associated with significant morbidity including angina, heart failure and stroke. Medical therapy remains suboptimal with significant side effects and toxicities, as well as a high recurrence rate. Catheter ablation or modification of the atrio-ventricular node with pacemaker implantation provides rate control but subjects the patient to the risks of an implantable device and does nothing to reduce the risk of stroke. Pulmonary vein antrum isolation offers a nonpharmacologic means of restoring sinus rhythm, thereby eliminating the morbidity of atrial fibrillation and the need for anti-arrhythmic drugs.

Ectopic activity in the rat pulmonary vein can arise from simultaneous activation of alpha1- and beta1-adrenoceptors

BACKGROUND AND PURPOSE

Atrial fibrillation (AF) is the most common electrical cardiac disorder in clinical practice. The major trigger for AF is focal ectopic activity of unknown origin in sleeves of cardiac muscle that extend into the pulmonary veins. We examined the role of noradrenaline in the genesis of ectopic activity in the pulmonary vein.

EXPERIMENTAL APPROACH

Mechanical activity of strips of pulmonary vein isolated from male Wistar rats was recorded via an isometric tension meter. Twitch contractions of cardiac myocytes were evoked by electrical field stimulation in a tissue bath through which flowed Krebs-Heinseleit solution warmed to 36-37 degrees C and gassed with 95% O(2) 5% CO(2).

KEY RESULTS

The superfusion of noradrenaline induced ectopic contractions in 71 of 76 different isolated pulmonary veins. Ectopic contractions in the pulmonary vein were not associated with electrically evoked twitch contractions. The effect of noradrenaline on the pulmonary vein could be replicated by the simultaneous, but not separate, application of the alpha adrenoceptor agonist phenylephrine and the beta adrenoceptor agonist isoprenaline. The use of selective agonists and antagonists for adrenoceptor subtypes showed that ectopic activity in the pulmonary vein arose from the simultaneous stimulation of alpha(1) and beta(1) adrenoceptors. The application of noradrenaline to isolated strips of left atrium did not induce ectopic contractions (n=10). conclusions: These findings suggest an origin for ectopic activity in the pulmonary vein that requires activation of both alpha and beta adrenoceptors. They also open new perspectives towards our understanding of the triggering of AF.

Catheter Ablation Therapy for Atrial Fibrillation

Since cases were first reported in 1994, catheter ablation of atrial fibrillation has undergone rapid development and expansion. The procedure began as an attempt to recreate the Maze III operation with a catheter technique. Understanding the contribution of the pulmonary veins to the initiation and maintenance of atrial fibrillation led to dramatic changes in procedural technique. The segmental ostial and the circumferential approaches have emerged as the 2 dominant methods. Efforts continue in academic centers to better understand the pathophysiology of the arrhythmia and to further refine the ablation procedure to improve patient outcomes.

Creating Continuous Linear Lesions in the Atria: A Comparison of the Multipolar Ablation Technique Versus the Conventional Drag-and-Burn

INTRODUCTION

Catheter-based treatment of atrial fibrillation (AF) requires the isolation of the triggering foci as well as modification of the atria with substrate that sustains AF. The creation of linear lesions in the left atrium with standard radiofrequency ablative methods requires long procedural times with unpredictable results.

METHODS

The simultaneous delivery of phase-shifted radiofrequency energy from a multipolar catheter was compared to the conventional drag-and-burn technique for creating linear lesions in 10 dogs. Four atrial sites were targeted under intracardiac ultrasound and fluoroscopic guidance in each of 10 dogs. The conventional drag-and-burn technique or the multipolar phase-shifted ablation catheter was randomly applied for 60 seconds and compared.

RESULTS

Creating linear lesions using the simultaneous multipolar phase-shifted ablation catheter was on average 11.0 minutes faster (33.6 minutes vs 44.6 minutes, P < 0.01) than the drag-and-burn method. The fraction of the lesion length achieved using phase-shifted ablation compared to that intended was 23% greater (76% vs 53%, P < 0.01), and has less discontinuities (0.1 compared to 0.8 discontinuities/line, P < 0.003). There was no significant difference in either the lesion transmurality, or fluoroscopy times.

CONCLUSION

The simultaneous delivery of phase-shifted, radiofrequency energy using a multipolar catheter is more effective and efficient in producing linear lesions than the traditional drag-and-burn technique. Using the multipolar ablative method to create linear lesions may be a useful technique in the treatment of patients with substrate-mediated atrial fibrillation.

Prevalence of pulmonary vein disconnection after anatomical ablation for atrial fibrillation: consequences of wide atrial encircling of the pulmonary veins

AIMS

Anatomical and wide atrial encircling of the pulmonary veins (PVs) has been proposed as a cure of atrial fibrillation (AF). We evaluated the acute achievement of electrical PV isolation using this approach. In addition, the consequences of wide encircling of the PVs with isolation were assessed.

METHODS AND RESULTS

Twenty patients with paroxysmal AF were studied. Anatomically guided ablation was performed utilizing the CARTO system to deliver coalescent lesions circumferentially around each PV to produce a voltage reduction to <0.1 mV, with the operator blinded to recordings of circumferential PV mapping. After achieving the anatomical endpoint, the incidence of residual conduction and the amplitude and conduction delay of residual PV potentials were determined. Electrical isolation of the PV was then performed and the residual far-field potentials evaluated. Individual PV ablation was performed in all PVs. Anatomically guided PV ablation was performed for 47.3+/-11 min, after which 44 (55%) PVs were electrically isolated. In the remaining 45%, despite abolition of the local potential at the ablation site, PV potentials [amplitude 0.2 mV (range 0.09-0.75) and delay of 50.3+/-12.6 ms] were identified by circumferential mapping. After electrical isolation (12.2+/-11.7 min ablation), 55 (69%) PVs demonstrated far-field potentials; with a greater incidence (P=0.015) and amplitude (P=0.021) on the left compared with the right PVs. At 13.2+/-8.3 months follow-up, 13 patients (65%) remained arrhythmia-free without anti-arrhythmics. In four patients (20%), spontaneous sustained left atrial macrore-entry required re-mapping and ablation. Macrore-entry was observed to utilize regions around or bordering the previous ablation as its substrate.

CONCLUSION

Anatomically guided circumferential PV ablation results in apparently coalescent but electrically incomplete lesions with residual conduction in 45% of PVs. Wide encircling of the PVs was associated with left atrial macrore-entry in 20% of patients.

Identification of atrial tissue in pulmonary veins using intravascular ultrasound

BACKGROUND

Atrial fibrillation (AF) is initiated by ectopic beats originating in the sleeve of atrial tissue in pulmonary veins (PVs). Circumferential ablation of PVs can, thus, result in a cure of AF. Identification of this PV arrhythmogenic tissue has been exclusively on the basis of electrophysiologic recordings. The purpose of this study was to visualize this tissue using intravascular ultrasound (IVUS). Methods and results In all, 15 patients undergoing AF ablation had IVUS studies of their PVs. A total of 21 veins had a wall thickness less than 0.1 mm, whereas 31 veins had well-demarcated areas of thickening measuring 0.81 +/- 0.32 mm. Electrophysiologic recordings from these thickened areas showed typical high-frequency potentials associated with arrhythmogenic atrial tissue in the PVs. Ectopic beats initiating AF always originated from these areas. PVs without thickening on IVUS did not have these potentials.

CONCLUSIONS

IVUS permits visualization of atrial tissue in the PVs, and arrhythmogenic PVs are qualitatively and quantitatively different from nonarrhythmogenic PVs.

Electrophysiological demonstration of dissociation of pulmonary vein potentials through electroanatomically guided circumferential ablation

A 57-year-old woman with frequent isolated and repetitive premature atrial contractions initiating paroxysmal atrial fibrillation, underwent electrophysiological study and catheter ablation. A real-time three-dimensional map of the left atrium was reconstructed using a nonfluoroscopic navigation system. By means of a deflectable decapolar catheter, the left superior pulmonary vein (PV) was identified as the arrhythmogenic vein, and PV potentials were found in the left inferior and right superior veins. Ablation was performed under electroanatomic guidance. After circumferential ablation outside the PV ostia, dissociation of PV potentials was obtained in the left superior vein, and PV potentials were eliminated in the other two veins.

Circumferential mapping and electric isolation of pulmonary veins in patients with atrial fibrillation

Information about the clinical efficacy and complications of the circumferential mapping and isolation of the pulmonary veins (PVs) in patients with atrial fibrillation (AF) is still limited. The present study included 75 patients (mean age 58 +/- 11 years, 20 women) with paroxysmal (n = 69) or persistent AF (n = 6). Mapping of PVs was performed with a circumferential mapping catheter. After preferential PV-left atrium (LA) electric inputs were defined, radiofrequency ablation was performed until complete isolation of the PVs from the LA was achieved. A total of 226 PVs were mapped; 195 (86%) showed typical PV potentials. Complete isolation of PVs from the LA was achieved in 173 PVs (89%). Detailed follow-up, including 7-day Holter monitoring at 1, 4, 9, and 12 months after intervention was performed. If AF reoccurred, PVs were mapped and reisolated. After a mean follow-up period of 230 +/- 133 days, 38 of 75 patients (51%) were in sinus rhythm. At 1, 4, and 9 months of follow-up, 31 of 65 patients (48%), 36 of 53 patients (68%, p = 0.04 as compared with the first month), and 21 of 28 patients (75%, p = 0.025 as compared with the first month), respectively, were in sinus rhythm. During follow-up, 30 patients (40%) underwent a second ablation procedure due to recurrence. Recurrences were related to resumption of PV muscle-left atrial conduction (27 patients) and/or extra PV foci (12 patients) or nonablated PVs (8 patients). Complications occurred in 17 patients (22%). PV stenosis was detected in 13 patients (25% to 50% in 7 patients and >50% in 6 patients). Pericardial effusion occurred in 4 patients. It was concluded that isolation of the PV from the LA is moderately effective in the prevention of AF recurrence and could be associated with serious acute and long-term complications.

A new radiofrequency thermal balloon catheter for pulmonary vein isolation

OBJECTIVES

We sought to evaluate whether porcine pulmonary vein (PV) isolation (PVI) can be produced by ablation using our novel radiofrequency (RF) thermal balloon catheter (RBC).

BACKGROUND

It has been proposed that PVI can prevent focal atrial fibrillation (AF) originating in or close to the PV.

METHODS

The RBC is composed of a 12F main shaft, a 4F inner tube and a balloon. Inside the balloon, there is a unipolar coil electrode with a thermocouple sensor mounted along the tube, the former to deliver RF energy (13.56 MHz) and the latter to monitor the temperature. After the presence of a PV potential was confirmed, the RBC was safely inserted into the left atrium (LA) by the trans-septal approach. Once the balloon was inflated and optimally wedged at the junction between the PV and LA, RF energy was applied for 5 min. Radiofrequency catheter ablation (RFA) was repeated up to three times, until elimination of the PV potential or dissociation between the LA and PV was observed. Finally, each heart was examined histologically.

RESULTS

In 18 PVs that had PV potentials, PVI was performed, resulting in success in 15 (success rate 83%, 95% confidence interval [CI] 58.0% to 96.3%; failure rate 17%, 95% CI 3.7% to 42.0%). After successful PVI, the PV potentials completely disappeared and the histologic examination revealed circumferential, transmural necrosis around the PV trunks. No major complications, such as PV stenosis or macroscopic thrombosis, were observed.

CONCLUSIONS

The RBC was useful for PVI.