Canine Pulmonary Veins Research Articles

Effect of autonomic influences to induce triggered activity in muscular sleeves extending into the coronary sinus of the canine heart and its suppression by ranolazine

Extrasystoles arising from the muscular sleeves associated with the pulmonary veins (PV), superior vena cava (SVC), and coronary sinus (CS) are known to precipitate atrial fibrillation (AF). The late sodium channel current (INa ) inhibitor ranolazine has been reported to exert antiarrhythmic effects in canine PV and SVC sleeves by suppressing late phase 3 early and delayedafter depolarization (EAD and DAD)-induced triggered activity induced by parasympathetic and/or sympathetic stimulation. The current study was designed to extend our existing knowledge of the electrophysiological and pharmacologic properties of canine CS preparations and assess their response to inhibition of late INa following autonomic stimulation. Transmembrane action potentials were recorded from canine superfused CS using standard microelectrode techniques. Acetylcholine (ACh, 1 µM), isoproterenol (Iso, 1 µM), high calcium ([Ca2+ ]o = 5.4 mM), or a combination were used to induce EADs, DADs, and triggered activity. Action potentials (AP) recorded from the CS displayed short and long AP durations (APD), with and without phase 4 depolarization (n = 19). Iso induced DAD-mediated triggered activity. The combination of sympathetic and parasympathetic agonists resulted in late phase 3 EAD-induced triggered activity in all CS preparations. Ranolazine (5-10 µM) suppressed late phase 3 EAD- and DAD-induced triggered activity in 8 of 8 preparations. Subthreshold stimulation induced a prominent hyperpolarization that could be suppressed by atropine. Our results suggest theimportant role of parasympathetic innervation in the activity of the CS. Autonomic influences promote DAD- and late phase-3-EAD-mediated triggered activity in canine CS, thus generating extrasystolic activity capable of initiating atrial arrhythmias. Ranolazine effectively suppresses these triggers.

Biophysical and molecular comparison of sodium current in cells isolated from canine atria and pulmonary vein.

The collar of the pulmonary vein (PV) is the focal point for the initiation of atrial arrhythmias, but the mechanisms underlying how PV cells differ from neighboring left atrial tissue are unclear. We examined the biophysical and molecular properties of INa in cells isolated from the canine pulmonary sleeve and compared the properties to left atrial tissue. PV and left atrial myocytes were isolated and patch clamp techniques were used to record INa. Action potential recordings from either tissue type were made using high-resistance electrodes. mRNA was determined using quantitative RT-PCR and proteins were determined by Western blot. Analysis of the action potential characteristics showed that PV tissue had a lower Vmax compared with left atrial tissue. Fast INa showed that current density was slightly lower in PV cells compared with LA cells (-96±18.7 pA/pF vs. -120±6.7 pA/pF, respectively, p<0.05). The recovery from inactivation of INa in PV cells was slightly slower but no marked difference in steady-state inactivation was noted. Analysis of late INa during a 225-ms pulse showed that late INa was significantly smaller in PV cells compared to LA cells at all measured time points into the pulse. These results suggest PV cells have lower density of both peak and late INa. Molecular analysis of Nav1.5 and the four beta subunits showed lower levels of Nav1.5 as well as Navβ1 subunits, confirming the biophysical findings. These data show that a lower density of INa may lead to depression of excitability and predispose the PV collar to re-entrant circuits under pathophysiological conditions.

Evolution and pharmacological modulation of the arrhythmogenic wave dynamics in canine pulmonary vein model

AimsAtrial fibrillation (AF), the commonest cardiac arrhythmia, has been strongly linked with arrhythmogenic sources near the pulmonary veins (PVs), but underlying mechanisms are not fully understood. We aim to study the generation and sustenance of wave sources in a model of the PV tissue.Methods and resultsA previously developed biophysically detailed three-dimensional canine atrial model is applied. Effects of AF-induced electrical remodelling are introduced based on published experimental data, as changes of ion channel currents (ICaL, IK1, Ito, and IKur), the action potential (AP) and cell-to-cell coupling levels. Pharmacological effects are introduced by blocking specific ion channel currents. A combination of electrical heterogeneity (AP tissue gradients of 5–12 ms) and anisotropy (conduction velocities of 0.75–1.25 and 0.21–0.31 m/s along and transverse to atrial fibres) can results in the generation of wave breaks in the PV region. However, a long wavelength (171 mm) prevents the wave breaks from developing into re-entry. Electrical remodelling leads to decreases in the AP duration, conduction velocity and wavelength (to 49 mm), such that re-entry becomes sustained. Pharmacological effects on the tissue heterogeneity and vulnerability (to wave breaks and re-entry) are quantified to show that drugs that increase the wavelength and stop re-entry (IK1 and IKur blockers) can also increase the heterogeneity (AP gradients of 26–27 ms) and the likelihood of wave breaks.ConclusionBiophysical modelling reveals large conduction block areas near the PVs, which are due to discontinuous fibre arrangement enhanced by electrical heterogeneity. Vulnerability to re-entry in such areas can be modulated by pharmacological interventions.

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

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. 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. 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. 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. 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.

Comparison of two ultrasonic coagulating shears in sealing pulmonary vessels

Ultrasonic cutting and coagulating devices have been used successfully in thoracic applications such as pulmonary resection or artery harvesting, but few studies have evaluated their use in sealing pulmonary vessels. In this study we compared two commercially available devices, Harmonic Ace+ (HAR, Ethicon Endo-Surgery, Inc., Cincinnati OH, USA) and Sono- Surg (SS, Olympus America, Center Valley, PA, USA), in a canine preclinical model. There were three sections to the study: acute, survival, and ex vivo (burst pressure). Hemostasis of sealed pulmonary arteries and veins was assessed for the initial application and during a simu- lated hypertensive crisis, both immediately after vessel sealing and after a survival period of 30 days. Other intraoperative measures were also evaluated, including transection time, tissue sticking, tissue tags, and char on the seal. Histological evaluation was performed both after initial sealing and after the survival period. Burst pressure of sealed vessels was measured ex vivo. For both devices, hemostasis was excellent, including those measurements made under simulated hypertensive crisis. There were no differences in any of the intraoperative measures or thermal damage evaluated histologically. Wound healing was normal. The burst pressures for ex vivo vessels sealed by HAR (median 619.2 mmHg) were significantly higher than those of SS (350.3 mmHg, P = 0.022). Both devices displayed acceptable characteristics in sealing canine pulmonary arteries and veins. The only difference observed was that HAR produced burst pressures 76.8% greater than SS, which may lead to a lower percentage of failures in the region of physiological interest. Use of ultrasonic devices in thoracic applications provides a high rate of initial hemostasis, supraphysiological burst pressures, and durable seals that heal normally.

Cardiomyocyte progenitors in a canine pulmonary vein model of persistent atrial fibrillation

This study aimed to discover the pathogenesis of focal atrial fibrillation (AF) originating from pulmonary veins by observing the histological structure and special cells in the canine pulmonary vein model of persistent atrial fibrillation. The pulmonary veins and the sinus node were obtained from 10 mongrel dogs (5 AF and 5 control group). Light microscopy, transmission electron microscopy, and immunohistochemistry were applied to transverse sections of each pulmonary vein and sinoatrial node. Morphological and distribution analyses were performed manually and automatically. Cardiomyocyte progenitor (CMPs) and interstitial cells of Cajal (ICCs) showing typical features of either very immature or developing cells were found in the pulmonary vein sections of all animals subjected to experimental AF but not in the control group. The cells were mainly identified in sections with a thick muscular sleeve. A positive immunostaining of CMPs was also demonstrated; the staining characteristic was similar to that of P cells in the sinoatrial node, suggesting that these cells may function in a pacemaker capacity. We demonstrated that pulmonary veins can host cardiac stem cell niches. Continuous rapid pacing can induce the differentiation of CMPs and ICCs, and CMPs may underlie the pacemaker activity of isolated pulmonary veins.

Comparative pharmacophysiology of vernakalant, ranolazine, and d-sotalol in canine pulmonary vein sleeve preparations: new flavors or same old taste?

Atrial fibrillation (AF) affects millions of people worldwide, and as longevity increases, the burden becomes greater.1 Triggers of AF often arise from the pulmonary veins (PVs), and there has been much emphasis on treating this arrhythmia by ablating these triggers. The use of antiarrhythmic drugs to suppress AF has been disappointing in that recurrence rates are high and side effects are common. Yet the search for newer antiarrhythmic agents continues. None so far have targeted the PVs in patients.

Cardiomyocyte progenitors in canine pulmonary veins model of persistent atrial fibrillation

BackgroundRecent studies suggested that various cell lineages exist within the pulmonary veins. However, the source and differentiation of such progenitor cells that may unmask a previously unknown source or mechanism...

A region-specific quantitative profile of autonomic innervation of the canine left atrium and pulmonary veins

The aim of the present study was to determine and quantify the cardiac autonomic innervation of the canine atria and pulmonary vein. Tissue specimens were taken from the canine pulmonary veins (PVs), posterior left atrium (PLA), left atrial roof (LAR), anterior left atrium (ALA), interatrial septum (IAS), and left atrial appendage (LAA) respectively for immunohistochemical analysis and nerve density determination. Both sympathetic and parasympathetic nerve densities decreased in the order: PLA>PV>IAS>LAR>ALA>LAA. For sympathetic nerve, multiple comparisons between any two regions showed a significant difference (P<0.05–P<0.01) except for PV vs. PLA, IAS vs. LAR, and LAR vs. ALA; for parasympathetic nerve, all the differences between any pair of regions were statistically significant (P<0.05–P<0.01) with the exception of PV vs. PLA, IAS vs. LAR, LAR vs. ALA, and ALA vs. LAA. For both nerve types, there was a decreasing gradient of nerve densities from the external to internal layer (P<0.001, for each comparisons). Nerve density at the ostia for either nerve type was significantly higher than at the distal segments of PVs (P<0.001). In summary, the LA and PVs are innervated by sympathetic and parasympathetic nerves in a regionally heterogeneous way, which may be important for the pathophysiological investigation and ablation therapy of atrial fibrillation (AF).

Antiarrhythmic Effects of Simvastatin in Canine Pulmonary Vein Sleeve Preparations

The purpose of this study was to determine the electrophysiologic effects of simvastatin in canine pulmonary vein (PV) sleeve preparations. Ectopic activity arising from the PV plays a prominent role in the development of atrial fibrillation. 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. 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. 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 losartan and enalapril in canine pulmonary vein sleeve preparations.

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. 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. 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. 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.

Activation of Isac promotes atrial fibrillation initiation and perpetuation: is this a stretch?

c s m Atrial fibrillation (AF) is a cardiac arrhythmia that results in a rapid and irregular activation of the atrial myocardium. In humans, activation rates during AF can be as high as 400–600 pulses per minute. About 2–5 million people in he United States are afflicted by AF, and the incidence of he arrhythmia increases with age, affecting 10% of the ctogenarian population. AF is the number one cause of hospitalization for arrhythmias, and its incidence is predicted to double in two decades. Yet the therapeutic management for F is challenging; antiarrhythmic drug therapies are partially ffective, some of which are proarrhythmic. Thus, AF is a ajor challenge in cardiac electrophysiology, and a large perentage of AF patients await novel therapies for the treatment f the arrhythmia. What are the mechanisms of initiation and perpetuation f AF? It is well established that disorders such as congesive heart failure, coronary artery disease, hypertension, and itral valve disease predispose the atrial myocardium to brillation. Furthermore, it has been demonstrated that there is structural, contractile, and electrical remodeling during AF and that this remodeling, in turn, exacerbates the rrhythmia. Nevertheless, a trigger is required for initiating AF. A consensus that has emerged from human and animal studies is that ectopic focal activities originating from areas around the pulmonary veins (PVs) serve as triggers for AF. For example, in one study by Chen et al, the lectrophysiological properties of the atria and the PV reion were examined in 79 patients with frequent episodes of aroxysmal AF. The electrophysiological properties of the V region were found to be different from those of the atria. t was also shown that ectopic beats originating from the PV egion could initiate AF. In another study, Hocini et al investigated the cellular architecture and electrical properties of the canine PV region to determine what may predispose the region to the initiation of arrhythmias. The investigators demonstrated that areas of activation delay correlated with sudden changes in the orientation of muscle

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.

Mechanisms by Which Adenosine Restores Conduction in Dormant Canine Pulmonary Veins

Adenosine acutely reconnects pulmonary veins (PVs) after radiofrequency application, revealing "dormant conduction" and identifying PVs at risk of reconnection, but the underlying mechanisms are unknown. Canine PV and left-atrial (LA) action potentials were recorded with standard microelectrodes and ionic currents with whole-cell patch clamp before and after adenosine perfusion. PVs were isolated with radiofrequency current application in coronary-perfused LA-PV preparations. Adenosine abbreviated action potential duration similarly in PV and LA but significantly hyperpolarized resting potential (by 3.9+/-0.5%; P<0.05) and increased dV/dt(max) (by 34+/-10%) only in PV. Increased dV/dt(max) was not due to direct effects on I(Na), which was reduced similarly by adenosine in LA and PV but correlated with resting-potential hyperpolarization (r=0.80). Adenosine induced larger inward rectifier K(+)current (I(KAdo)) in PV (eg, -2.28+/-0.04 pA/pF; -100 mV) versus LA (-1.28+/-0.16 pA/pF). Radiofrequency ablation isolated PVs by depolarizing resting potential to voltages positive to -60 mV. Adenosine restored conduction in 5 dormant PVs, which had significantly more negative resting potentials (-57+/-6 mV) versus nondormant (-46+/-5 mV, n=6; P<0.001) before adenosine. Adenosine hyperpolarized both, but more negative resting-potential values after adenosine in dormant PVs (-66+/-6 mV versus -56+/-6 mV in nondormant; P<0.001) were sufficient to restore excitability. Adenosine effects on resting potential and conduction reversed on washout. Spontaneous recovery of conduction occurring in dormant PVs after 30 to 60 minutes was predicted by the adenosine response. Adenosine selectively hyperpolarizes canine PVs by increasing I(KAdo). PVs with dormant conduction show less radiofrequency-induced depolarization than nondormant veins, allowing adenosine-induced hyperpolarization to restore excitability by removing voltage-dependent I(Na) inactivation and explaining the restoration of conduction in dormant PVs.

Arrhythmogenic Foci and the Mechanisms of Atrial Fibrillation

In this issue of the Circulation: Arrhythmia and Electrophysiology , Kurotobi et al1 determined the number of arrhythmogenic foci in atria provocable with isoproterenol infusion in patients with paroxysmal, persistent, and permanent atrial fibrillation (AF). The results show that persistent AF has more foci than paroxysmal AF. However, when AF persists for >12 months, the number of foci were reduced. The authors suggest that the increased number of foci probably is involved in the development of persistent AF. However, because this association is not observed for AF that persists for >12 months, the importance of these foci in AF maintenance remains unclear. Article see p 39 In ambulatory canine models, simultaneous sympathovagal discharges (rather than isolated sympathetic activation) are typical triggers of paroxysmal atrial tachycardia (AT) and AF.2,3⇓ These observations are explained by the late phase-3 early afterdepolarization (EAD), which depends on the coexistence of increased amplitude and duration of intracellular calcium (Cai) transient and the shortened action potential duration (APD).4,5⇓ Vagal stimulation shortens APD and therefore is needed to promote the late phase-3 EAD. In the Kurotobi study, however, arrhythmogenic foci were induced by isoproterenol alone, without the need of vagal stimulation or the use of parasympathomimetic agents. These results are different from that obtained in canine studies. The first possible explanation is that the pulmonary veins (PVs) naturally have shorter APDs with elevated (less negative) membrane potentials.6,7⇓ Rapid activation may further shorten the APD in the PVs.8 These changes are independent of the vagal tone. Jais et al9 reported the effective refractory periods of the PVs were shorter …

New Pharmacological Agents for Arrhythmias

Despite advances in catheter ablation techniques and device-based therapies for cardiac arrhythmias, antiarrhythmic drugs remain essential components of any comprehensive therapeutic strategy. Antiarrhythmic drug therapy, however, has been limited by both incomplete efficacy and a substantial potential for cardiac and extracardiac toxicity. As a result, only a few new antiarrhythmic agents have successfully completed clinical development programs and reached routine clinical usage over the past 20 years. Antiarrhythmic drugs may be indicated for ventricular tachycardia, sudden death prevention, or specific types of supraventricular arrhythmia. Implantable cardioverter-defibrillator (ICD) therapy has evolved as the primary treatment for most life-threatening ventricular arrhythmias, and antiarrhythmic drugs for these rhythms are currently mostly used either as acute interventions or as adjuncts to chronic ICD therapy. Although numerous trials have evaluated the effect of antiarrhythmic drugs to decrease ICD shocks or therapies, such data have yet to provide the sole basis for approval for any new agent. At the same time, drug therapy for atrial arrhythmias is often limited by the drug’s simultaneous effects on the ventricles, which has led to efforts to identify ionic channel targets specific to or preferentially located in the atria. The sustained outward K+ current (IKur, encoded by the Kv 1.5 subunit), the acetylcholine-activated outward K+ current (IKAch), and both peak and late atrial Na+ currents have therefore become potential targets for antiarrhythmic drug developers.1–4 Another approach has been to seek agents that synergistically affect multiple channels simultaneously, resulting in a net beneficial effect while minimizing toxicity. Other nontraditional targets for drug therapy that do not directly involve ion channels have also emerged as our understanding of the mechanisms of arrhythmias has improved. As a result, several new compounds are now at or near completion of phase 3 clinical trials, and other promising …

Activating Autoantibodies to the Beta-1 Adrenergic and M2 Muscarinic Receptors Facilitate Atrial Fibrillation in Patients With Graves' Hyperthyroidism

We studied activating autoantibodies to beta-1 adrenergic receptors (AAbeta1AR) and activating autoantibodies to M2 muscarinic receptors (AAM2R) in the genesis of atrial fibrillation (AF) in Graves' hyperthyroidism. Atrial fibrillation frequently complicates hyperthyroidism. Both AAbeta1AR and AAM2R have been described in some patients with dilated cardiomyopathy and AF. We hypothesized that their copresence would facilitate AF in autoimmune Graves' hyperthyroidism. Immunoglobulin G purified from 38 patients with Graves' hyperthyroidism with AF (n=17) or sinus rhythm (n=21) and 10 healthy control subjects was tested for its effects on isolated canine Purkinje fiber contractility with and without atropine and nadolol. Immunoglobulin G electrophysiologic effects were studied using intracellular recordings from isolated canine pulmonary veins. Potential cross-reactivity of AAbeta1AR and AAM2R with stimulating thyrotropin receptor (TSHR) antibodies was evaluated before and after adsorption to Chinese hamster ovary cells expressing human TSHRs using flow cytometry and enzyme-linked immunosorbent assays. The frequency of AAbeta1AR and/or AAM2R differed significantly between patients with AF and sinus rhythm (AAbeta1AR=94% vs. 38%, p<0.001; AAM2R=88% vs. 19%, p<0.001; and AAbeta1AR+AAM2R=82% vs. 10%, p<0.001). The copresence of AAbeta1AR and AAM2R was the strongest predictor of AF (odds ratio: 33.61, 95% confidence interval: 1.17 to 964.11, p=0.04). Immunoglobulin G from autoantibody-positive patients induced hyperpolarization, decreased action potential duration, enhanced early afterdepolarization formation, and facilitated triggered firing in pulmonary veins by local autonomic nerve stimulation. Immunoadsorption studies showed that AAbeta1AR and AAM2R were immunologically distinct from TSHR antibodies. When present in patients with Graves' hyperthyroidism, AAbeta1AR and AAM2R facilitate development of AF.

Potent Antiarrhythmic Effects of Chronic Amiodarone in Canine Pulmonary Vein Sleeve Preparations

To examine the effects of chronic amiodarone on the electrophysiology of canine pulmonary vein (PV) sleeve preparations and left ventricular wedge preparation. 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). 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). 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. The results point to potent effects of chronic amiodarone to preferentially suppress arrhythmogenic substrates and triggers arising from the PV sleeves of the dog.

Development of cardiomyopathy and atrial tachyarrhythmias associated with activating autoantibodies to beta-adrenergic and muscarinic receptors

A 71-year-old male with well-controlled hypertension developed atrial tachyarrhythmias in 2002 and a restrictive cardiomyopathy in 2006 to 2007. Sera from 1992, 2001, and 2006 to 2008 demonstrated activating autoantibodies against β-adrenergic (AAβAR) and M2 muscarinic receptors (AAM2R). These sera have been characterized for bioactivity using in vitro assays of cardiac contractility and automaticity using a canine cardiac Purkinje fiber assay as well as protein kinase assay activation in H9c2 cells. These assays demonstrated concurrent positive βAR and inhibitory M2R effects that were blocked by nadolol and atropine, respectively. In a canine pulmonary vein atrial sleeve preparation, sera diluted 1:100 produced atrial hyperpolarization that was blocked by atropine. Atrial tachyarrhythmias developed in 2002 in the presence of a persistent bradycardia. Serial echocardiograms demonstrated progressive diastolic dysfunction in the absence of cardiac hypertrophy between 2006 and 2007. A dual-chamber pacemaker was installed with combined βAR (nadolol) and M2<3R (oxybutynin) blockade, resulting in marked suppression of atrial ectopy and improved diastolic function. The estimated pulmonary artery pressure decreased and exercise tolerance returned. Blood pressure has remained normal with β-blockade. AAβAR and AAM2R prospectively influenced atrial and ventricular function in this patient, and specific receptor blockade was associated with improved cardiac function.

Chronic left atrial volume overload abbreviates the action potential duration of the canine pulmonary vein myocardium via activation of IK channel

Electrophysiological properties of the pulmonary vein myocardium were assessed in a canine chronic atrioventricular block model resulting in left atrial volume overload. Five chronic atrioventricular block dogs and five sham-operated dogs were used. The heart was removed two months after a surgical procedure causing atrioventricular block, when atrial structural remodeling was established. Standard microelectrode penetrations were made with glass microelectrodes to obtain action potential signals of left atrium and pulmonary vein myocardia. The resting membrane potential in the pulmonary vein was more positive than that in the left atrium (− 69 mV vs − 74 mV) in both animal groups. The action potential duration at 50% repolarization of the pulmonary vein was shorter in the chronic atrioventricular block dogs than in the sham-operated dogs (38 ms vs 63 ms), whereas no significant difference was detected in the action potential duration of the left atrium between the two animal groups (67 ms vs 61 ms). The action potential duration of the pulmonary vein in the chronic atrioventricular block dogs was prolonged by charybdotoxin but not by iberiotoxin. Such prolongation was not observed in the normal pulmonary vein. These results suggest that long-term left atrial dilatation shortened the action potential duration of pulmonary vein myocardium, which may be associated with activation of the intermediate conductance Ca 2+-activated K + channel (IK channel).