Electrophysiology of Pulmonary Veins

Bigeminal potentials in the pulmonary vein indicate arrhythmogenic trigger of atrial fibrillation

BACKGROUND

The pulmonary veins (PVs) have unique electrophysiological properties triggering and maintaining atrial fibrillation (AF). Bigeminal PV electrical activity (PV bigeminy) during sinus rhythm has been reported; however, its mechanisms and clinical implication remain unclear. We hypothesized that PV bigeminy indicates arrhythmogenic activities and influences clinical outcome.

METHODS AND RESULTS

We retrospectively analyzed electrophysiological studies in 465 patients with AF who underwent first session PV isolation (PVI). PV bigeminy was observed in 30 PVs of 23 patients (4.9% of patients). PV bigeminy was observed in left inferior PV (LIPV) in 15 patients, which was the most prevalent, followed by left superior in seven and right superior in seven and right inferior in one. In response to atrial extra stimulus, the second PV potentials (PV2) showed decremental conduction properties, suggesting reentrant mechanisms involved (n = 5). Interestingly, AF was initiated from the 23 PVs with bigeminy in 21 patients (76.7% of 30 PVs with bigeminy), spontaneously or in response to drugs, which was significantly more prevalent from the AF initiation rate from each PV in the control 442 patients (182 firings in 1290 PVs, 14.1%, P < .0001). PVI-based ablation was completed in the 23 patients with PV bigeminy and no recurrence was observed during 1-year follow-up, whereas four patients needed second sessions.

CONCLUSIONS

PV bigeminy is relatively rare but a unique electrophysiological finding in AF patients, suggesting reentrant substrate within the PV and/or surrounding tissue. PV bigeminy is a strong indicator of arrhythmogenic vein triggering AF, and ensures an excellent clinical outcome after PVI.

Depolarization of the Rat Atria in Experimental Simulation of the Holiday Heart Syndrome

In the study of the sequence of depolarization of the atrial subepicardium of rats in the short-term alcohol consumption model (the "Holiday heart" syndrome), the localization of the sources of atrial arrhythmias was determined for the first time. The difference in the excitation of the right and left atria was discovered: the right atrium is activated anterogradely from the sinoatrial node, whereas the left atrium is activated retrogradely from the ectopic focus located in the left auricular appendage.

Cardiac transmembrane ion channels and action potentials: cellular physiology and arrhythmogenic behavior

Cardiac arrhythmias are among the leading causes of mortality. They often arise from alterations in the electrophysiological properties of cardiac cells and their underlying ionic mechanisms. It is therefore critical to further unravel the pathophysiology of the ionic basis of human cardiac electrophysiology in health and disease. In the first part of this review, current knowledge on the differences in ion channel expression and properties of the ionic processes that determine the morphology and properties of cardiac action potentials and calcium dynamics from cardiomyocytes in different regions of the heart are described. Then the cellular mechanisms promoting arrhythmias in congenital or acquired conditions of ion channel function (electrical remodeling) are discussed. The focus is on human-relevant findings obtained with clinical, experimental, and computational studies, given that interspecies differences make the extrapolation from animal experiments to human clinical settings difficult. Deepening the understanding of the diverse pathophysiology of human cellular electrophysiology will help in developing novel and effective antiarrhythmic strategies for specific subpopulations and disease conditions.

Ion currents, action potentials, and noradrenergic responses in rat pulmonary vein and left atrial cardiomyocytes

The electrophysiological properties of pulmonary vein (PV)‐cardiomyocytes, and their responses to the sympathetic neurotransmitter, noradrenaline (NA), are thought to differ from those of the left atrium (LA) and contribute to atrial ectopy. The aim of this study was to examine rat PV cardiomyocyte electrophysiology and responses to NA in comparison with LA cells. LA and PV cardiomyocytes were isolated from adult male Wistar rat hearts, and membrane potentials and ion currents recorded at 36°C using whole‐cell patch‐clamp techniques. PV and LA cardiomyocytes did not differ in size. In control, there were no differences between the two cell‐types in zero‐current potential or action potential duration (APD) at 1 Hz, although the incidence of early afterdepolarizations (EADs) was greater in PV than LA cardiomyocytes. The L‐type Ca²⁺ current (I_CaL) was ~×1.5 smaller (p = .0029, Student's t test) and the steady‐state K⁺ current (I_Kss) was ~×1.4 larger (p = .0028, Student's t test) in PV than in LA cardiomyocytes. PV cardiomyocyte inward‐rectifier current (I_K1) was slightly smaller than LA cardiomyocyte I_K1. In LA cardiomyocytes, NA significantly prolonged APD₃₀. In PV cells, APD₃₀ responses to 1 μM NA were heterogeneous: while the mean percentage change in APD₃₀ was not different from 0 (16.5 ± 9.7%, n cells/N animals = 12/10, p = .1177, one‐sample t test), three cells showed shortening (‐18.8 ± 6.0%) whereas nine showed prolongation (28.3 ± 10.1%, p = .008, Student's t test). NA had no effect on I_K1 in either cell‐type but inhibited PV I_Kss by 41.9 ± 4.1% (n/N = 23/11 p < .0001), similar to LA cells. NA increased I_CaL in most PV cardiomyocytes (median × 2.2‐increase, p < .0001, n/N = 32/14, Wilcoxon‐signed‐rank test), although in 7/32 PV cells I_CaL was decreased following NA. PV cardiomyocytes differ from LA cells and respond heterogeneously to NA.

Various subtypes of phosphodiesterase inhibitors differentially regulate pulmonary vein and sinoatrial node electrical activities

Phosphodiesterase (PDE)3-5 are expressed in cardiac tissue and play critical roles in the pathogenesis of heart failure and atrial fibrillation. PDE inhibitors are widely used in the clinic, but their effects on the electrical activity of the heart are not well understood. The aim of the present study was to examine the effects of various PDE inhibitors on spontaneous cardiac activity and compare those effects between sinoatrial nodes (SANs) and pulmonary veins (PVs). Conventional microelectrodes were used to record action potentials in isolated rabbit SAN and PV tissue preparations, before and after administration of different concentrations (0.1, 1 and 10 µM) of milrinone (PDE3 inhibitor), rolipram (PDE4 inhibitor) and sildenafil (PDE5 inhibitor), with or without the application of isoproterenol (cAMP and PKA activator), KT5823 (PKG inhibitor) or H89 (PKA inhibitor). Milrinone (1 and 10 µM) increased the spontaneous activity in PVs by 10.6±4.9 and 16.7±5.3% and in SANs by 9.3±4.3 and 20.7±4.6%, respectively. In addition, milrinone (1 and 10 µM) induced the occurrence of triggered activity (0/8 vs. 5/8; P<0.005) in PVs. Rolipram increased PV spontaneous activity by 7.5±1.3-9.5±4.0%, although this was not significant, and did not alter SAN spontaneous activity. Sildenafil reduced spontaneous activity in PVs to a greater extent than that seen in SANs. Both KT5823 and H89 suppressed milrinone-increased PV spontaneous activity. In the presence of isoproterenol, milrinone did not alter isoproterenol-induced PV arrhythmogenesis, suggesting that the effects of PDE3 are mediated by the protein kinase G and protein kinase A signaling pathways. In conclusion, inhibitors of different PDE subtypes exert diverse electrophysiological effects on PV and SAN activities.

Comparative study of hyperpolarization-activated currents in pulmonary vein cardiomyocytes isolated from rat, guinea pig, and rabbit

Pulmonary vein (PV) cardiomyocytes have the potential to generate spontaneous activity, in contrast to working myocytes of atria. Different electrophysiological properties underlie the potential automaticity of PV cardiomyocytes, one being the hyperpolarization-activated inward current (I_h), which facilitates the slow diastolic depolarization. In the present study, we examined pharmacological characteristics of the I_h of PV cardiomyocytes in rat, guinea pig and rabbit. The results showed that guinea pig and rat PV cardiomyocytes possessed sizeable amplitudes of the I_h, and the I_h of guinea pig was suppressed by Cs⁺, a blocker of the hyperpolarization-activated cation current. However, the I_h of rat was not suppressed by Cs⁺, but by Cd²⁺, a blocker of the Cl⁻ current. The current density of the I_h of rabbit PV cardiomyocytes was significantly smaller than those of other species. This suggests that the ion channels that carry the I_h of PV cardiomyocytes differ among the animal species.

Gap junction modifiers regulate electrical activities of the sinoatrial node and pulmonary vein: Therapeutic implications in atrial arrhythmogenesis

BACKGROUND

Gap junction (GJ) dysfunctions predispose cardiac tissues to various arrhythmias. Sinoatrial node (SAN) and pulmonary veins (PVs) are closely related atrial dysrhythmia. This study evaluated whether GJ modifications modulate SAN and PVs electrical activities.

METHODS

Conventional microelectrodes were used to record action potentials in isolated rabbit SAN, PVs, and connected PV-SAN tissue preparations before and after heptanol (GJ inhibitor) and PQ1 (GJ enhancer) administration with and without isoproterenol. A whole-cell patch clamp was used to record the electrical activities before and after heptanol in single SAN and PV cardiomyocytes.

RESULTS

Heptanol (1, 3, and 10μM) reduced the spontaneous beating rates of isolated SAN preparations but not PVs. Heptanol (10μM) decelerated the SAN leading rhythm in the PV-SAN preparations and induced PV burst firings without (3 of 6, 50%) and with (6 of 6, 100%) isoproterenol (1μM). Heptanol (10μM) also reduced the spontaneous beating rates in single SAN cardiomyocyte, but not PV cardiomyocyte, with a decreased pacemaker current. PQ1 (50 and 500nM) treatment did not change the spontaneous beating rates in isolated SAN and PV preparations. In the connected PV-SAN preparations, PQ1 (500nM) did not induce any PV firing even having additional isoproterenol treatment (1μM). Moreover, PQ1 (500nM) prevented heptanol-induced electrical changes in SAN and PVs preparations.

CONCLUSION

GJ dysfunction modulates SAN and PV electrical activity, which may contribute to atrial arrhythmogenesis. GJ enhancer has a therapeutic potential in SAN dysfunction and atrial arrhythmogenesis.

The Electrical Characteristics and Clinical Significance of the Effect of Adenosine on Dissociated Activity after Circumferential Venous Isolation in Patients with Atrial Fibrillation

BACKGROUND

Dissociated activity can occur after circumferential thoracic vein isolation for treating atrial fibrillation (AF). However, its clinical significance and response to adenosine remain unclear.

METHODS

Fifty-three patients (10 women, 11 with non-paroxysmal AF, with mean age 54.4 ± 11.2 years) with slow dissociated activity after thoracic vein isolation for AF ablation were analyzed. Adenosine (12 mg) was injected intravenously into 30 patients, and the responses of the dissociated activities were recorded.

RESULTS

The clinical characteristics and the rate of recurrence did not differ between patients with and without dissociated activity. Dissociated activity was most frequently observed at the right superior pulmonary vein (PV) (61%), left superior PV (26%), right inferior PV (5%), left inferior PV (4%), and non-PV sites (4%). The locations of dissociated activities were associated with the AF trigger sites (p = 0.004). Adenosine injection decreased the cycle length of dissociated activity in 13 patients (group 1) and increased it in 17 patients (group 2). Dissociated activity disappeared in 7 patients (41%) (group 2) after adenosine injection. During the mean 33 ± 17 months of follow-up, group 2 patients had a lower AF recurrence rate (24%) than group 1 patients (62%) (p = 0.035).

CONCLUSIONS

The locations of dissociated activity were closely associated with the AF trigger sites. The responses to adenosine may predict AF recurrence in patients with dissociated activity.

KEY WORDS

Ablation; Atrial fibrillation; Dissociated activity.

Change in P wave morphology after convergent atrial fibrillation ablation

Convergent atrial fibrillation ablation involves extensive epicardial as well as endocardial ablation of the left atrium. We examined whether it changes the morphology of the surface P wave. We reviewed electrocardiograms of 29 patients who underwent convergent ablation for atrial fibrillation. In leads V₁, II and III, we measured P wave duration, area and amplitude before ablation, and at 1, 3 and 6 months from ablation.

After ablation, there were no significant changes in P wave amplitude, area, or duration in leads II and III. There was a significant reduction in the area of the terminal negative deflection of the P wave in V₁ from 0.38 mm² to 0.13 mm² (p = 0.03). There is also an acute increase in the amplitude and duration of the positive component of the P wave in V₁ followed by a reduction in both by 6 months. Before ablation, 62.5% of the patients had biphasic P waves in V₁. In 6 months, only 39.2% of them had biphasic P waves.

Hybrid ablation causes a reduction of the terminal negative deflection of the P wave in V₁ as well as temporal changes in the duration and amplitude of the positive component of the P wave in V₁. This likely reflects the reduced electrical contribution of the posterior left atrium after ablation as well as anatomical and autonomic remodeling. Recognition of this altered sinus P wave morphology is useful in the diagnosis of atrial arrhythmias in this patient population.

Histone deacetylase inhibition reduces pulmonary vein arrhythmogenesis through calcium regulation

Pulmonary veins (PVs) play a critical role in the pathophysiology of atrial fibrillation (AF). Histone deacetylases (HDACs) are vital to calcium homeostasis and AF genesis. However, the electrophysiological effects of HDAC inhibition were unclear. This study evaluated whether HDAC inhibition can regulate PV electrical activity through calcium modulation. Whole-cell patch-clamp, confocal microscopic with fluorescence, and Western blot were used to evaluate electrophysiological characteristics and Ca(2+) dynamics in isolated rabbit PV cardiomyocytes with and without MPT0E014 (a pan HDAC inhibitor), MS-275 (HDAC1 and 3 inhibitor), and MC-1568 (HDAC4 and 6 inhibitor) for 5~8h. Atrial electrical activity and induced-AF (rapid atrial pacing and acetylcholine infusion) were measured in rabbits with and without MPT0E014 (10mg/kg treated for 5 hours) in vivo. MPT0E014 (1 μM)-treated PV cardiomyocytes (n=12) had slower beating rates (2.1 ± 0.2 vs. 2.8 ± 0.1 Hz, p < 0.05) than control PV cardiomyocytes. However, control (n=11) and MPT0E014 (1 μM)-treated (n = 12) SAN cardiomyocytes had similar beating rates (3.2 ± 0.2 vs. 2.9 ± 0.3 Hz). MS-275-treated PV cardiomyocytes (n = 12, 2.3 ± 0.2 Hz), but not MC-1568-treated PV cardiomyocytes (n=14, 3.1 ± 0.3 Hz) had slower beating rates than control PV cardiomocytes. MPT0E014-treated PV cardiomyocytes (n=14) had a lower frequency (2.4 ± 0.6 vs. 0.3 ± 0.1 spark/mm/s, p < 0.05) of Ca(2+) sparks than control PV (n=17) cardiomyocytes. As compared to control, MPT0E014-treated PV cardiomyocytes had reduced Ca(2+) transient amplitudes, sodium-calcium exchanger currents, and ryanodine receptor expressions. Moreover, MPT0E014-treated rabbits had less AF and shorter AF duration than control rabbits. In conclusions, HDAC inhibition reduced PV arrhythmogenesis and AF inducibility with modulation on calcium homeostasis.

Depolarization of atrial epicardium near pulmonary veins orifices in hypertensive ISIAH rats

The formation of early activation regions was demonstrated in the area of the pulmonary vein orifice in hypertensive rats. The appearance of early activation zones on the dorsal side of the left atrium near the pulmonary veins simultaneously with the sinoatrial node in rats with arterial hypertension indicates the possibility of ectopic foci formation in the area of pulmonary vein sleeves.

Surgical options for treatment of atrial fibrillation

If we want to improve the outcomes, increase the success and reduce the complication rate of existing treatment strategies in concomitant and stand-alone atrial fibrillation (AF) procedures, we will have to increase our understanding of the pathophysiology, and of the disease, the limitations of current energy sources and ablation catheters, the different possible lesion sets, as well as improve communication between the electrophysiologist and cardiac surgeon. The technical limitations of percutaneous endocardial ablation procedures and the empirical techniques in surgical AF procedures necessitate new and innovative approaches. Surgeons should aim to improve the quality of the lesion set and minimize the invasiveness of existing techniques. The Maze procedure remains the basis upon which most of the more limited concomitant ablation procedures are and will be designed, but in stand-alone patients, recent progress has directed us towards either a single-step or sequential combined percutaneous endocardial procedure with a thoracoscopic epicardial procedure on the beating heart. A dedicated team of electrophysiologists and cardiothoracic surgeons can now work together to perform AF procedures. This can guide us to determine if there is an additional value of limiting the lesion set of the Maze procedure in concomitant surgery, and of an epicardial access in the treatment of stand-alone AF on the beating heart. If so, we will better understand which energy sources, lesion sets and surgical techniques are able to give us a three-dimensional knowledge and a three-dimensional treatment of AF. As a result, we can expect to obtain a higher single procedure long-term success rate with an acceptable low complication rate.

Antiarrhythmic effects of simvastatin in canine pulmonary vein sleeve preparations

OBJECTIVES

The purpose of this study was to determine the electrophysiologic effects of simvastatin in canine pulmonary vein (PV) sleeve preparations.

BACKGROUND

Ectopic activity arising from the PV plays a prominent role in the development of atrial fibrillation.

METHODS

Transmembrane action potentials were recorded from canine superfused left superior or inferior PV sleeves using standard microelectrode techniques. Acetylcholine (1 μM), isoproterenol (1 μM), high calcium ([Ca(2+)](o) = 5.4 mM), or a combination was used to induce early afterdepolarizations or delayed afterdepolarizations and triggered activity. Voltage clamp experiments were performed in the left atrium measuring fast and late sodium currents.

RESULTS

Under steady-state conditions, simvastatin (10 nM, n = 9) induced a small increase in action potential duration measured at 85% repolarization and a significant decrease in action potential amplitude, take-off potential, and maximum rate of rise of action potential upstroke at the fastest rates. The V(max) decreased from 175.1 ± 34 V/s to 151.7 ± 28 V/s and from 142 ± 47 V/s to 97.4 ± 39 V/s at basic cycle lengths of 300 and 200 ms, respectively. Simvastatin (10 to 20 nM) eliminated delayed afterdepolarizations and delayed afterdepolarization-induced triggered activity in 7 of 7 PV sleeve preparations and eliminated or reduced late-phase 3 early afterdepolarizations in 6 of 6 PV sleeve preparations. Simvastatin (20 nM) did not affect late or fast sodium currents measured using voltage clamp techniques.

CONCLUSIONS

Our data suggest that in addition to its upstream actions to reduce atrial structural remodeling, simvastatin exerts a direct antiarrhythmic effect by suppressing triggers responsible for the genesis of atrial fibrillation.

Antiarrhythmic effects of the highly selective late sodium channel current blocker GS-458967

BACKGROUND

Previous studies have shown that late sodium channel current (INa) blockers such as ranolazine can exert antiarrhythmic effects by suppressing early and delayed afterdepolarization (EAD and DAD)-induced triggered activity.

OBJECTIVE

To evaluate the electrophysiological properties of GS-458967 (GS967), a potent and highly selective late INa blocker, in canine Purkinje fibers (PFs) and pulmonary vein (PV) and superior vena cava (SVC) sleeve preparations.

METHODS

Transmembrane action potentials were recorded from canine PFs and PV and SVC sleeve preparations by using standard microelectrode techniques. The rapidly activating delayed rectifier potassium channel current blocker E-4031 (2.5-5 µM) and the late INa agonist ATX-II (10 nM) were used to induce EADs in PFs. Isoproterenol (1 µM), high calcium ([Ca(2+)]o = 5.4 mM), or their combination was used to induce DADs and triggered activity.

RESULTS

In PFs, GS967 (10-300 nM) caused a significant concentration-dependent reduction in action potential duration without altering the maximum rate of rise of the action potential upstroke, action potential amplitude, or resting membrane potential at any rate studied (basic cycle lengths of 1000, 500, and 300 ms) or concentration evaluated (n = 5; P < .05). GS967 (30-100 nM) abolished EADs and EAD-induced triggered activity elicited in PFs by exposure to E-4031 (n = 4) or ATX-II (n = 4). In addition, GS967 reduced or abolished DADs and suppressed DAD-induced triggered activity elicited in PFs (n = 4) and PV (n = 4) and SVC (n = 3) sleeve preparations by exposure to isoproterenol, high calcium, or their combination.

CONCLUSIONS

Our data suggest that the selective inhibition of late INa with GS967 can exert antiarrhythmic effects by suppressing EAD- and DAD-mediated extrasystolic activity in PFs and PV and SVC sleeve preparations.

Atrial fibrillation in the elderly: the potential contribution of reactive oxygen species

Atrial fibrillation (AF) is the most commonly encountered cardiac arrhythmia, and is a significant source of healthcare expenditures throughout the world. It is an arrhythmia with a very clearly defined predisposition for individuals of advanced age, and this fact has led to intense study of the mechanistic links between aging and AF. By promoting oxidative damage to multiple subcellular and cellular structures, reactive oxygen species (ROS) have been shown to induce the intra- and extra-cellular changes necessary to promote the pathogenesis of AF. In addition, the generation and accumulation of ROS have been intimately linked to the cellular processes which underlie aging. This review begins with an overview of AF pathophysiology, and introduces the critical structures which, when damaged, predispose an otherwise healthy atrium to AF. The available evidence that ROS can lead to damage of these critical structures is then reviewed. Finally, the evidence linking the process of aging to the pathogenesis of AF is discussed.

Electrical activity of the mouse pulmonary vein myocardium

We recorded the electrical activity from the myocardial layer of isolated mouse pulmonary veins with the glass microelectrode technique. Spontaneous electrical activity was observed in about half of the preparations, which appeared either as constant firing or as repetitive bursts. Noradrenaline enhanced, while acetylcholine reduced, automatic activity. The action potentials evoked in quiescent preparations showed a resting membrane potential less negative than the atria and an extremely rapid early repolarization followed by a late plateau. The present study revealed that the mouse pulmonary vein myocardium shows diverse electrical activity, which is influenced by autonomic neurotransmitters.

Comparison of electrophysiological and antiarrhythmic effects of vernakalant, ranolazine, and sotalol in canine pulmonary vein sleeve preparations

BACKGROUND

Vernakalant (VER) is a relatively atrial-selective antiarrhythmic drug capable of blocking potassium and sodium currents in a frequency- and voltage-dependent manner. Ranolazine (RAN) is a sodium-channel blocker shown to exert antiarrhythmic effects in pulmonary vein (PV) sleeves. dl-Sotalol (SOT) is a β-blocker commonly used in the rhythm-control treatment of atrial fibrillation. This study evaluated the electrophysiological and antiarrhythmic effects of VER, RAN, and SOT in canine PV sleeve preparations in a blinded fashion.

METHODS

Transmembrane action potentials were recorded from canine superfused PV sleeve preparations exposed to VER (n = 6), RAN (n = 6), and SOT (n = 6). Delayed afterdepolarizations were induced in the presence of isoproterenol and high-calcium concentrations by periods of rapid pacing.

RESULTS

In PV sleeves, VER, RAN, and SOT (3-30 μM) produced small (10-15 ms) increases in action potential duration. The effective refractory period, diastolic threshold of excitation, and the shortest S(1)-S(1) cycle length permitting 1:1 activation were significantly increased by VER and RAN in a rate- and concentration-dependent manner. VER and RAN significantly reduced V(max) in a concentration- and rate-dependent manner. SOT did not significantly affect the effective refractory period, V(max), diastolic threshold of excitation, or the shortest S(1)-S(1) cycle length permitting 1:1 activation. All 3 agents (3-30 μM) suppressed delayed afterdepolarization-mediated triggered activity induced by isoproterenol and high calcium.

CONCLUSIONS

In canine PV sleeves, the effects of VER and RAN were similar and largely characterized by concentration- and rate-dependent depression of sodium-channel-mediated parameters, which were largely unaffected by SOT. All 3 agents demonstrated an ability to effectively suppress delayed afterdepolarization-induced triggers of atrial arrhythmia.

Nonpharmacologic management of atrial fibrillation: role of the pulmonary veins and posterior left atrium

Nonpharmacologic approaches for the management of atrial fibrillation are rapidly emerging as the mainstay for definitive management of this arrhythmia. Over the past several years, numerous studies reported in the literature have highlighted various aspects of the pathophysiologic mechanisms underlying atrial fibrillation. The purpose of this review is to place the current approaches being used for arrhythmia management in the context of the current knowledge of about arrhythmia mechanisms.

Added value of transoesophageal echocardiography during transseptal puncture performed by inexperienced operators

AIMS

Transseptal puncture (TP) appears to be safe in experienced hands; however, it can be associated with life-threatening complications. The aim of our study was to demonstrate the added value of routine use of transoesophageal echocardiography (TEE) for the correct positioning of the transseptal system in the fossa ovalis, thus potentially preventing complications during fluoroscopy-guided TP performed by inexperienced operators.

METHODS AND RESULTS

Two hundred and five patients undergoing pulmonary vein isolation procedure (PVI) for drug-resistant paroxysmal or persistent atrial fibrillation were prospectively included. When the operator (initially blinded to TEE) assumed that the transseptal system was in a correct position according to fluoroscopical landmarks, the latter was then checked with TEE unblinding the physician. If necessary, further refinement of the catheter position was performed. Refinement >10 mm, or in case of catheter pointing directly at the aortic root or posterior wall were considered as major repositioning. Thirty-four patients required major repositioning. Regression analysis revealed age (P: 0.0001, Wald: 12.9, 95% confidence interval: 1.04-1.16), left atrial diameter (P: 0.01, Wald: 6.6, 95% confidence interval: 1.04-1.34), previous PVI (P: 0.01, Wald: 6.3, 95% confidence interval: 1.31-8.76), and atrial septal thickness (P: 0.03, Wald: 4.5, 95% confidence interval: 1.05-3.4) as independent predictors of major revision with TEE.

CONCLUSION

Routine 2D TEE in addition to traditional fluoroscopic TP appears to be very useful to guide the TP assembly in a correct puncture position and thus, to avoid TP-related complications. However, further randomized prospective comparative studies are necessary to support these suggestions.

Effects of chronic omega-3 polyunsaturated fatty acid supplementation on human pulmonary vein and left atrial electrophysiology in paroxysmal atrial fibrillation

Omega-3 polyunsaturated fatty acids in fish oils may have antifibrillatory effects; however, their electrophysiologic effects in paroxysmal atrial fibrillation (PAF) remain unknown. The aim of this study was to investigate the effects of chronic fish oil supplementation on human pulmonary vein (PV) and left atrial electrophysiology in PAF. Patients with PAF undergoing PV isolation were randomized ≥1 month before their procedure into a control group (n = 18) or a fish oil group (n = 18) in an unblinded fashion. The latter were supplemented with fish oil 6 g/day for a mean of 40 ± 12 days. Pulmonary venous and left atrial effective refractory periods (ERPs), PV conduction, and susceptibility to AF initiated within PVs were assessed. Compared to the control group, the fish oil group had (1) longer left-sided (p = 0.002) and right-sided (p = 0.001) pulmonary venous ERPs; (2) less dispersion of pulmonary venous ERPs (left PVs p = 0.001, right PVs p = 0.07); (3) longer left atrial ERPs (p = 0.02); (4) no difference in pulmonary venous conduction; (5) lower incidence of AF initiated from PVs during ERP testing (77% vs 31%, p = 0.02); and (6) prolongation of mean AF cycle length (p = 0.009) and shortest AF cycle length in PVs (p = 0.04). In conclusion, patients with PAF chronically supplemented with fish oils exhibit distinctive electrophysiologic properties including prolonged pulmonary venous and left atrial ERPs and decreased susceptibility to initiation AF from within PVs. These changes may in part explain the antifibrillatory effect of chronic omega-3 polyunsaturated fatty acid supplementation in patients with PAF.

Antiarrhythmic effects of losartan and enalapril in canine pulmonary vein sleeve preparations

INTRODUCTION

Angiotensin-converting enzyme (ACE) inhibitors and angiotensin II-receptor blockers (ARBs) are prototypes of "upstream" therapy for the management of atrial fibrillation (AF). Ectopic activity arising from the PV sleeves plays a prominent role in the development of AF.

METHODS

Transmembrane action potentials were recorded from canine superfused left superior or inferior PV sleeves using standard microelectrode techniques. Acetylcholine (ACh, 1 μM), isoproterenol (1 μM), high calcium ([Ca(2+)](o) = 5.4 mM) or a combination was used to induce early or delayed afterdepolarizations (EADs or DADs) and triggered activity.

RESULTS

The ARB losartan (1 μM, n = 5) and the ACE inhibitor enalapril (10 μM, n = 5) produced no significant change in action potential duration, maximum rate of rise of action potential upstroke (V(max)), action potential amplitude or take-off potential at basic cycle lengths of 200 to 2000 ms. Losartan (1 μM) and enalapril (10-20 μM) markedly attenuated or suppressed EADs and DAD-induced triggered activity elicited by exposure of the PV sleeves to ACh, isoproterenol or high calcium following rapid pacing in 6 of 6 (losartan) and 4 of 5 (enalapril) PV sleeve preparations. Neither losartan nor enalapril altered Ca(2+) or K(+) channel currents in enzymatically-dissociated atrial myocytes at these concentrations.

CONCLUSIONS

Our data suggest that in addition to their "upstream" effects to reduce atrial structural remodeling, ACE inhibitors and ARBs exert a "direct" antiarrhythmic effect by suppressing triggers responsible for the genesis of AF and other atrial arrhythmias.

Noninvasive characterization of epicardial activation in humans with diverse atrial fibrillation patterns

BACKGROUND

Various mechanisms of atrial fibrillation (AF) have been demonstrated experimentally. Invasive methods to study these mechanisms in humans have limitations, precluding continuous mapping of both atria with sufficient resolution. In this article, we present continuous biatrial epicardial activation sequences of AF in humans using noninvasive electrocardiographic imaging (ECGI).

METHODS AND RESULTS

In the testing phase, ECGI accuracy was evaluated by comparing ECGI with co-registered CARTO images during atrial pacing in 6 patients. Additionally, correlative observations from catheter mapping and ablation were compared with ECGI in 3 patients. In the study phase, ECGI maps during AF in 26 patients were analyzed for mechanisms and complexity. ECGI noninvasively imaged the low-amplitude signals of AF in a wide range of patients (97 procedural success). Spatial accuracy for determining initiation sites from pacing was 6 mm. Locations critical to maintenance of AF identified during catheter ablation were identified by ECGI; ablation near these sites restored sinus rhythm. In the study phase, the most common patterns of AF were multiple wavelets (92), with pulmonary vein (69) and non-pulmonary vein (62) focal sites. Rotor activity was seen rarely (15). AF complexity increased with longer clinical history of AF, although the degree of complexity of nonparoxysmal AF varied widely.

CONCLUSIONS

ECGI offers a noninvasive way to map epicardial activation patterns of AF in a patient-specific manner. The results highlight the coexistence of a variety of mechanisms and variable complexity among patients. Overall, complexity generally increased with duration of AF.

Electrophysiologic and antiarrhythmic effects of AZD1305 in canine pulmonary vein sleeves

The objective of this study was to examine the electrophysiologic and antiarrhythmic effects of the new antiarrhythmic agent tert-butyl (2-[7-[2-(4-cyano-2-fluorophenoxy)ethyl]-9-oxa-3,7-diazabicyclo[3.3.1]non3-yl]ethyl)carbamate (AZD1305) in canine pulmonary vein (PV) sleeve preparations isolated from untreated and long-term amiodarone-treated animals. Ectopic activity arising from PV sleeves plays a prominent role in the development of atrial fibrillation (AF). Delayed afterdepolarizations (DADs) and late phase 3 early afterdepolarizations (EADs), originating from the PV have been proposed as potential triggers in initiation of AF. Action potentials were recorded from canine superfused PV sleeves using standard microelectrode techniques. Acetylcholine (1 microM), isoproterenol (1 microM), or their combination was used to induce EADs, DADs, and triggered activity (TA). The effects of AZD1305 (0.1-10 microM) were evaluated in PV sleeve preparations isolated from untreated and amiodarone-treated (40 mg/kg daily for 6 weeks) dogs. AZD1305 (0.1-10 microM, 30 min) significantly prolonged action potential duration and reduced excitability. Abbreviating basic cycle length from 1000 to 300 ms resulted in a decrease of V(max) from 314 +/- 79 to 251 +/- 55 V/s (Delta = -20%) in control and from 177 +/- 53 to 76.5 +/- 33 V/s (Delta = -57%) after AZD1305 (n = 6, p < 0.05). AZD1305 markedly attenuated or suppressed DADs and DAD-induced TA, but not late phase 3 EADs. AZD1305-induced attenuation of excitability, leading to activation failure at much longer cycle lengths, was much more pronounced in PV from amiodarone-treated dogs. Potent effects of AZD1305 to depress excitability, prolong action potential duration, and suppress DAD-induced triggered activity in canine PV sleeve preparations may be effective in suppressing triggers responsible for the genesis of AF and other atrial arrhythmias.

Oxidative stress on pulmonary vein and left atrium arrhythmogenesis

BACKGROUND

Oxidative stress and pulmonary veins (PVs) play critical roles in the pathophysiology of atrial fibrillation. The purpose of the present study was to investigate whether oxidative stress and antioxidant agents can change the electrophysiological characteristics of the left atrium (LA) and PVs.

METHODS AND RESULTS

Conventional microelectrodes were used to record the action potentials (APs) in isolated rabbit PV and LA specimens before and after H(2)O(2) administration with or without ascorbic acid or N-mercaptopropionyl-glycine (N-MPG, a free radical .OH scavenger). H(2)O(2) (0.02 and 0.2 mmol/L) decreased the PV spontaneous rates from 2.0+/-0.1 Hz to 1.6+/-0.1 Hz, and 1.7+/-0.1 Hz (n=10, P<0.05), but H(2)O(2) (2 mmol/L) increased PV spontaneous rates from 2.0+/-0.1 Hz to 2.8+/-0.2 Hz. H(2)O(2) easily induced PV burst firing and early afterdepolarizations, but not in the LA. H(2)O(2) shortened the AP duration and increased the contractile force to a greater extent in the LA than in PVs. In addition, the H(2)O(2)-induced PV burst firing and increasing spontaneous rates were suppressed or attenuated by pretreatment with ascorbic acid (1 mmol/L) or N-MPG (10 mmol/L).

CONCLUSIONS

H(2)O(2) significantly changed the electrophysiological characteristics of PV and LA through activation of free radicals and may facilitate the occurrence of atrial fibrillation.

Comparison of non-gated vs. electrocardiogram-gated 64-detector-row computed tomography for integrated electroanatomic mapping in patients undergoing pulmonary vein isolation

AIMS

To compare non-gated vs. electrocardiogram (ECG)-gated 64-detector-row computed tomography (MDCT) of the left atrium (LA) for integrated electroanatomic mapping (EAM) in patients with paroxysmal atrial fibrillation (AF).

METHODS AND RESULTS

Twenty-nine consecutive patients with paroxysmal AF underwent MDCT prior to pulmonary vein isolation (PVI). All patients were in sinus rhythm both during CT imaging and PVI. Multi-detector-row computed tomography was performed in 15 patients without ECG-gating (non-gated MDCT) and in 14 patients with retrospective ECG-gating (ECG-gated MDCT). Image quality of LA reconstructions from MDCT was rated on a five-point scale (from 1 = excellent to 5 = segmentation failed). Registration error between LA geometry obtained from EAM and MDCT was calculated as the mean distance between EAM points and MDCT surface. In all patients, LA was successfully segmented from MDCT data. The segmentation process took 2:31 +/- 0:54 min for non-gated MDCT and 2:36 +/- 0:47 min for ECG-gated MDCT (P = 0.8). Image quality scores of LA reconstructions from non-gated and ECG-gated MDCT were 1.3 +/- 0.6 and 1.4 +/- 0.7, respectively (P = 0.76). There was no significant difference in the registration error between non-gated and ECG-gated MDCT (1.8 +/- 0.2 vs. 1.9 +/- 0.3 mm, respectively; P = 0.6). The radiation dose of non-gated MDCT was significantly lower compared with ECG-gated MDCT (4.6 +/- 1.4 vs. 13.4 +/- 3.6 mSv, respectively; P < 0.001).

CONCLUSION

Non-gated MDCT depicts LA with appropriate image quality for integrated EAM, while exposing patients to substantially lower radiation dose compared with ECG-gated MDCT.

Synergistic electrophysiologic and antiarrhythmic effects of the combination of ranolazine and chronic amiodarone in canine atria

BACKGROUND

Amiodarone and ranolazine have been characterized as inactivated- and activated-state blockers of cardiac sodium channel current (I(Na)), respectively, and shown to cause atrial-selective depression of I(Na)-related parameters. This study tests the hypothesis that their combined actions synergistically depress I(Na)-dependent parameters in atria but not ventricles.

METHODS AND RESULTS

The effects of acute ranolazine (5 to 10 micromol/L) were studied in coronary-perfused right atrial and left ventricular wedge preparations and superfused left atrial pulmonary vein sleeves isolated from chronic amiodarone-treated (40 mg/kg daily for 6 weeks) and untreated dogs. Floating and standard microelectrode techniques were used to record transmembrane action potentials. When studied separately, acute ranolazine and chronic amiodarone caused atrial-predominant depression of I(Na)-dependent parameters. Ranolazine produced a much greater reduction in V(max) and much greater increase in diastolic threshold of excitation and effective refractory period in atrial preparations isolated from amiodarone-treated versus untreated dogs, leading to a marked increase in postrepolarization refractoriness. The drug combination effectively suppressed triggered activity in pulmonary vein sleeves but produced relatively small changes in I(Na)-dependent parameters in the ventricle. Acetylcholine (0.5 micromol/L) and burst pacing induced atrial fibrillation in 100% of control atria, 75% of ranolazine-treated (5 micromol/L) atria, 16% of atria from amiodarone-treated dogs, and in 0% of atria from amiodarone-treated dogs exposed to 5 micromol/L ranolazine.

CONCLUSIONS

The combination of chronic amiodarone and acute ranolazine produces a synergistic use-dependent depression of I(Na)-dependent parameters in isolated canine atria, leading to a potent effect of the drug combination to prevent the induction of atrial fibrillation.

Spontaneous onset of atrial fibrillation

Most commonly, atrial fibrillation is triggered by rapid bursts of electrical impulses originating in the myocardial sleeves of pulmonary veins (PVs). However, the nature of such bursts remains poorly understood. Here, we propose a mechanism of bursting consistent with the extensive empirical information about the electrophysiology of the PVs. The mechanism is essentially non-local and involves the spontaneous initiation of non-sustained spiral waves in the distal end of the muscle sleeves of the PVs. It reproduces the experimentally observed dynamics of the bursts, including their frequency, their intermittent character, and the unusual shape of the electrical signals in the pulmonary veins that are reminiscent of so-called early afterdepolarizations (EADs).

Atrial fibrillation: cure or treat?

Controversies exist with regard to the optimal management of atrial fibrillation (AF). Restoration and maintenance of sinus rhythm is a desirable goal in AF patients because the prevention of recurrences may improve cardiac function, relieve symptoms and should reduce the likelihood of adverse events. Pharmacological therapy for AF has been disappointing with unacceptable rates of AF recurrence and other proarrhythmic sequelae. Recent studies suggested that potential benefit of sinus-rhythm maintenance with respect to mortality may have been neutralized by harmful effects of currently available antiarrhythmic therapies. Because of the inefficacy and dangers with nonablative therapies currently available for maintaining sinus rhythm, alternative treatments are certainly desirable. Curative treatment of atrial fibrillation with catheter ablation is now a legitimate option for a large number of patients. In several studies AF ablation has consistently been demonstrated to be superior to antiarrhythmic medications for the maintenance of sinus rhythm. Nevertheless, many aspects of the therapy are still controversial and large-scale prospective studies are needed to confirm the efficacy and safety of this approach.

Potent antiarrhythmic effects of chronic amiodarone in canine pulmonary vein sleeve preparations

OBJECTIVES

To examine the effects of chronic amiodarone on the electrophysiology of canine pulmonary vein (PV) sleeve preparations and left ventricular wedge preparation.

BACKGROUND

Amiodarone is commonly used for the treatment of ventricular and supraventricular arrhythmias. Ectopic activity arising from the PV plays a prominent role in the development of atrial fibrillation (AF).

METHODS

Standard microelectrode techniques were used to evaluate the electrophysiological characteristics of superfused PV sleeve (left superior or inferior) and arterially perfused left ventricular (LV) wedge preparations isolated from untreated and chronic amiodarone-treated dogs (amiodarone, 40 mg/kg daily for 6 weeks).

RESULTS

In PV sleeves, chronic amiodarone (n = 6) induced a significant increase in action potential duration at 90% repolarization (APD90) and a significant use-dependent reduction in Vmax leading to 1:1 activation failure at long cycle lengths (basic cycle length of 124 +/- 15 ms in control vs 420 +/- 320 ms after chronic amiodarone [P < 0.01]). Diastolic threshold of excitation increased from 0.3 +/- 0.2 to 1.8 +/- 0.7 mA (P < 0.01). Delayed and late phase 3 early afterdepolarizations and triggered activity could be induced in PV sleeve preparations using acetylcholine (ACh, 1 microM), high calcium ([Ca2+]o = 5.4 mM), isoproterenol (Iso, 1 microM), or their combination in 6 of 6 untreated PV sleeves, but in only 1 of 5 chronic amiodarone-treated PV sleeve preparations. Vmax, conduction velocity, and 1:1 activation failure were much more affected in PV sleeves versus LV wedge preparations isolated from amiodarone-treated animals.

CONCLUSIONS

The results point to potent effects of chronic amiodarone to preferentially suppress arrhythmogenic substrates and triggers arising from the PV sleeves of the dog.

Mechanical characterization of rabbit pulmonary vein sleeves in in vitro intact ring preparation

BACKGROUND

Pulmonary vein (PV) sleeves, composed of cardiomyocytes, play certain roles in arrhythmogenesis. In the literature, it has been frequently reported that PV sleeves possess intrinsic spontaneous pacemaking activity and triggered activity in normal dogs and rabbits. In contrast, other research groups presented totally opposite findings which showed absence of such pacemakers in dogs, rabbits and rats. The present study was designed to clarify this puzzle and contradiction.

METHODS

A novel methodology using in vitro experimentation was used to examine the electromechanical activity of whole segments of PV sleeves. The ring preparation was composed of a small piece of left atrial (LA) free wall, PV ostium and sleeve from rabbits. A circumferential contraction of the PV sleeve was measured when the preparation was electrically driven from the LA free wall. Mechanical force of the ring preparation was measured using a force transducer. The action potentials were recorded using conventional intracellular recording technique in strip preparation.

RESULTS

In 15 rabbits, no spontaneous pacemaking activity or triggered activity was found in the in vitro ring preparation of PV sleeve. The circumferential contraction of PV sleeves was external calcium-dependent. Frequency-force relation displayed a negative staircase at 0.1-0.5 Hz and a positive staircase at 1-5 Hz. Post-rest potentiation was prominent between 15 s and 120 s. Intracellular action potential recording did not display any automaticity or triggered activity in PV sleeves.

CONCLUSION

In an intact ring preparation of rabbit PV sleeves, intrinsic spontaneous pacemaking activity or triggered activity was not found.

Antiarrhythmic effects of ranolazine in canine pulmonary vein sleeve preparations

BACKGROUND

Ectopic activity arising from the pulmonary veins (PV) plays a prominent role in the development of atrial fibrillation (AF).

OBJECTIVE

This study sought to determine the electrophysiological effects of ranolazine in canine PV sleeve preparations.

METHODS

Transmembrane action potentials were recorded from canine superfused left superior or inferior PV sleeves using standard microelectrode techniques. Acetylcholine (ACh, 1 microM), isoproterenol (1 microM), high calcium ([Ca(2+)](o) = 5.4 mM) or a combination was used to induce early or delayed afterdepolarizations (EADs or DADs) and triggered activity.

RESULTS

Ranolazine (10 microM) significantly accentuated use-dependent depression of maximal rate of increase of action potential upstroke (V(max)). Reducing basic cycle length (BCL) from 2000 to 200 ms resulted in a decrease of V(max) from 279 +/- 58 to 146 +/- 23 V/s (47.7%) in control subjects and from 241 +/- 71 to 72 +/- 63 V/s (70.2%) after 10 microM ranolazine (n = 4, P <.05). Ranolazine slightly abbreviated action potential duration, but induced significant rate-dependent prolongation of effective refractory period due to development of postrepolarization refractoriness (n = 6, P <.05). Ranolazine (10 microM) caused loss of excitability resulting in 2:1 activation failure at BCLs <or= 200 ms (n = 3) and suppressed late phase 3 EADs, DADs, and triggered activity elicited by exposure of the PV sleeves to Ach + isoproterenol, or high [Ca(2+)](o) + rapid pacing (n = 11).

CONCLUSION

Ranolazine causes marked use-dependent inhibition of sodium channel activity leading to prolongation of effective refractory period, conduction slowing, and block as well as suppression of late phase 3 EAD and DAD-mediated triggered activity in canine PV sleeves. Our data suggest that ranolazine may be useful in suppressing AF triggers arising from the PV sleeves.

Swelling activated chloride currents in the electrical activity of pulmonary vein cardiomyocytes

BACKGROUND

Pulmonary veins (PVs) contain cardiomyocytes with a high arrhythmogenicity for inducing atrial fibrillation. The swelling-activated outwardly rectifying Cl(-) currents (I(Cl,swell)) are important in the electrical activity of cardiomyocytes. This study was to investigate whether I(Cl,swell) play a role in the PV electrophysiological characteristics.

MATERIALS AND METHODS

A whole-cell patch clamp was used to investigate the action potentials and I(Cl,swell) in isolated rabbit single PV and atrial cardiomyocytes during immersion in isotonic (290-300 mosm L(-1)) and hypotonic (220-230 mosm L(-1)) solutions. The cell length and cell width were measured using confocal microscopy.

RESULTS

Hypotonic solution induced larger I(Cl,swell) in the PV cardiomyocytes with pacemaker activity than those in the PV cardiomyocytes without pacemaker activity or atrial cardiomyocytes. Hypotonic solution shortened the action potential duration and increased the cell width to a greater extent in the PV cardiomyocytes than in the atrial cardiomyocytes. Moreover, hypotonic solution decreased the PV firing with a decrease in the transient inward currents and delayed after depolarizations.

CONCLUSIONS

These findings suggest that the I(Cl,swell) plays an important role in the electrical activity of the PV cardiomyocytes.