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J Am Coll Cardiol, 2005; 45:1871-1877, doi:10.1016/j.jacc.2005.02.070
© 2005 by the American College of Cardiology Foundation
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PRECLINICAL STUDY

Rapid and Stable Re-Entry Within the Pulmonary Vein as a Mechanism Initiating Paroxysmal Atrial Fibrillation

Sunny S. Po, MD, PhD*,*, Yuhua Li, PhD{dagger}, David Tang, MS{dagger}, Hong Liu, PhD{dagger}, Ning Geng, MD{ddagger}, Warren M. Jackman, MD*, Benjamin Scherlag, PhD*, Ralph Lazzara, MD* and Eugene Patterson, PhD§

* Cardiac Arrhythmia Research Institute, Department of Medicine, Oklahoma City, Oklahoma
{dagger} College of Engineering, School of Electrical and Computer Engineering, University of Oklahoma, Norman, Oklahoma
{ddagger} Cardiology Department, 2nd Affiliated Hospital of China Medical University, Shenyang, China
§ Department of Veterans Affairs Medical Center, Oklahoma City, Oklahoma

Manuscript received December 23, 2004; revised manuscript received February 9, 2005, accepted February 22, 2005.

* Reprint requests and correspondence: Dr. Sunny S. Po, 1200 Everett Drive, ET-6E103, Oklahoma City, Oklahoma 73104. (Email: sunny-po{at}ouhsc.edu).


   Abstract
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 Abstract
Methods
 Results
 Discussion
 References
 
OBJECTIVES: We investigated the hypothesis that re-entrant pulmonary vein (PV) tachycardias may serve as a mechanism for initiating and sustaining paroxysmal atrial fibrillation (PAF).

BACKGROUND: The mechanisms of rapid repetitive discharges from the PV initiating PAF remain incompletely understood. Pulmonary vein myocardial sleeves appear to provide a favorable substrate for re-entry formation.

METHODS: The electrophysiologic properties of canine PV sleeves were investigated using a combination of high-resolution optical mapping (n = 5) and extracellular bipolar and intracellular microelectrode recordings (n = 56) in a superfused PV preparation.

RESULTS: From the left atrium to distal PV, there was progressive shortening of the action potential (AP) duration, reduction in AP and bipolar electrogram amplitude, and depolarization of resting membrane potentials. Sustained PV tachycardias were induced exclusively in the presence of acetylcholine (10–7 to 10–6 mol/l, n = 12). Sustained PV tachycardias were rapid (mean cycle length = 93 ± 15 ms), regular, and capable of induction, termination, and resetting by single extrastimuli. Re-entry as the mechanism underlying PV tachycardias was confirmed by optical mapping (n = 5). Acetylcholine also reduced the slope of the AP restitution curve and suppressed AP alternans (n = 6). Importantly, PV tachycardias exhibited 1:1 conduction into the atrium at short cycle lengths (<100 ms), emphasizing the potential role of re-entrant PV tachycardia in atrial fibrillation.

CONCLUSIONS: Pulmonary veins provide a favorable substrate for re-entry formation. Heterogeneity of the electrophysiologic properties and marked abbreviation of action potential duration and refractoriness by acetylcholine combine to produce rapid and stable re-entrant PV tachycardias. Elevated parasympathetic tone and re-entrant PV tachycardia may serve as a mechanism underlying the perpetuation of PAF.

Abbreviations and Acronyms
  ACH = acetylcholine
  AF = atrial fibrillation
  APD = action potential duration
  CL = cycle length
  DI = diastolic interval
  DS = distal pulmonary vein sleeve
  LA = left atrium/atrial
  PS = proximal pulmonary vein sleeve
  PV = pulmonary vein
  Rt = steepest slope of the action potential restitution curve

Rapid repetitive discharges from the pulmonary veins (PVs) frequently initiate atrial fibrillation (AF), but the underlying mechanisms are yet to be clarified (1). It is known that left atrial (LA) muscle extends onto PVs as myocardial sleeves. Histology of the PV sleeves revealed muscle fibers oriented spirally, circumferentially, and longitudinally to the axis of the PVs, and the fibers were frequently separated by connective tissue (2,3). We hypothesized that the PV myocardial sleeve forms a fertile substrate for re-entrant arrhythmias. When the action potential duration (APD) and refractoriness are markedly abbreviated by acetylcholine (ACH), rapid and stable re-entrant PV tachycardias may act to initiate and perpetuate AF.

Shortening of APD in response to increases in heart rate, known as APD restitution, is an important characteristic of cardiac tissues (4). The properties of restitution are usually assessed by analyzing the restitution curve, the nonlinear relationship between the APD and the preceding diastolic interval. The restitution hypothesis proposes that when cardiac tissue has a restitution curve with a slope >1, manifestations of instability such as AP alternans and wave break may occur, leading to fibrillation (5). Because PV firing is known to initiate AF, we hypothesized that PVs may have restitution properties supporting fibrillation inside the PVs.


   Methods
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 Abstract
 Methods
Results
 Discussion
 References
 
Tissue preparation and electrophysiologic recordings.   All studies were performed in accordance with the guideline of the American Physiological Society in protocols approved by the institutional animal care and use committee. Adult male mongrel dogs weighing 20 to 30 kg were anesthetized with intravenous sodium pentobarbital (30 mg/kg). For studies using extracellular bipolar electrode or intracellular microelectrode recordings, the heart was removed and rinsed in Tyrode’s solution (in 10–3 mol/l: NaCl, 130; KCl, 4.05; MgCl2, 1.0; NaHCO3, 20; NaH2PO4, 1.0; glucose, 5.5 and CaCl2, 1.35; pH = 7.4) bubbled with 95% oxygen and 5% CO2. The left or right superior PV was removed. The superfused preparation included 3 to 4 mm of LA myocardium and PV tissue 8 to 15 mm distal to the PV-LA junction. Adipose tissue was removed from the epicardial surface, and the thickness of the preparation from the distal segment of PV without visible myocardial sleeve (DS) to PV-LA junction was <1 mm to minimize tissue ischemia. The preparation was cut open along the anterior wall of PV and pinned either epicardial side down or endocardial side down to allow study of the endocardial or epicardial surface, respectively (Fig. 1A). Bipolar electrograms (filtered between 0.1 and 1,000 Hz) were recorded from three sites using 0.1-mm diameter Teflon-coated silver wires 1 mm apart. Pacing (2 ms duration stimuli at 2x to 3x diastolic threshold) was utilized to stimulate the preparation using a Grass S-88 stimulator (Grass Medical Instruments, Quincy, Massachusetts). Action potentials were recorded using glass microelectrodes filled with 3 mol/l KCl.



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  		Figure 1 A superfused left superior pulmonary vein (PV) preparation viewed from the endocardial surface (A) and action potentials recorded using the microelectrode technique (B, endocardial; C, epicardial), and optical mapping (D, endocardial). (A) LA, PS, and DS indicate left atrium, proximal PV with visible myocardial sleeves, and distal PV without visible myocardial sleeves, respectively. Black squares delineate the PV-LA junction. (B to D) All recordings were performed at a pacing cycle length of 1 s. Notice progressive changes of action potential duration and action potential amplitude as the recording electrodes move from LA to DS. Insets illustrate the bipolar electrograms (at different gains) recorded in corresponding regions.

 
Optical mapping.   For optical mapping, the left circumflex artery was cannulated immediately after excision of the heart and perfused with oxygenated Tyrode’s solution containing 5 x 10–6 mol/l of di-4-ANEPPS at 35°C (Molecular Probe, Eugene, Oregon) for 20 min. The very proximal segment of the circumflex artery was ligated over the cannula. The left anterior descending artery, along with all the ventricular branches of the circumflex artery, was ligated to enhance the flow toward the PVs and LA.

A wavelength selective optical mapping setup was designed and implemented in accordance with the fluorescence characteristics of di-4-ANEPPS (6). The optical setup was designed to operate in different optical magnification modes for either a higher spatial resolution or a larger field of coverage. A charge-coupled device-based digital detector was custom developed and integrated with the optical setup to acquire fluorescence signals. Comprehensive measurements were conducted and showed that this prototype system offers a wide dynamic range (12-bit digitization) and a high temporal resolution (approximately 2 ms). With 20 mm x 20 mm field coverage, the system offers a moderate spatial resolution (128 pixels x 128 pixels, 0.156 mm/pixel). With smaller field coverage, a higher spatial resolution can be achieved (0.11 mm/pixel).

Correctable image distortions or variations that can obscure the important details were minimized before image analysis. These image distortions are usually caused by system components such as vignetting of the lenses and inhomogeneities of illumination. A commonly used flat fielding correction was performed on each of the original digital images. The pixel values of the resultant images therefore reflected accurately the strength of the fluorescence signal to be measured.

APD restitution.   Action potential duration restitution was assessed from the microelectrode recordings. Multiple sites in the preparation were examined before ACH administration. A dynamic restitution protocol (7) was implemented by delivering a pacing train at an initial cycle length (CL) of 1,500 ms. The pacing CL was gradually shortened after steady state was achieved at each CL. The pacing CL was progressively reduced to a minimum of 40 ms to ensure stable 1:1 capture at short CLs. Identical pacing protocols were applied to each region (LA, PS, and DS) (Fig. 1A). The relationship between the APD90 and diastolic interval was analyzed by constructing an APD restitution curve, in which the APD90 of the n ² 1th APD (APDN²1) was plotted against the preceding diastolic interval, DIN. The DIN was determined by subtracting the preceding APDN from the pacing CL. An exponential curve was used to fit the relationship between APDN²1 and DIN (Graphpad Prism, San Diego, California). Rt, the steepest slope of the exponential curve (restitution curve), was calculated by a linear regression of the steepest part of the exponential curve preceding loss of 1:1 capture.

Statistics
Data are expressed as the mean value ± SE. Differences between groups were determined by analysis of variance for single or repeated measures as appropriate. Student-Newman-Keuls test was used to determine differences between individual groups.


   Results
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 Methods
 Results
Discussion
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Basic electrophysiologic properties of PVs.   A total of 56 left or right superior PV preparations were studied using both bipolar and microelectrode recordings. The preparations typically remained healthy with stable and consistent electrophysiologic properties for 1 to 3 h. The thickness of the preparation from DS to the PV-LA junction was <1 mm based on histology studies (data not shown). The size of the superfused PV preparation was approximately 20 x 12 mm, incorporating PV sleeves up to 15 mm from the PV-LA junction (Fig. 1A). Despite the absence of visible myocardium in DS as viewed from the endocardial surface, the recording of electrograms and action potentials indicates the presence of myocardium. The LA, PS, and DS exhibited distinctly different electrophysiologic properties. Figures 1B and 1C illustrate representative action potentials recorded from the endocardial aspect (Fig. 1B) or epicardial aspect (Fig. 1C). As the recording sites moved from LA toward DS, the amplitude and duration of AP were reduced and resting membrane potentials were depolarized (Table 1). The DS action potential exhibited a triangular morphology lacking phase 2. The parameters presented in Table 1 were composite data from all experiments, grouped together by: 1) the presence (PS) or absence (DS) of visible PV sleeves on the endocardial surface, and 2) proximal (LA) or distal (PS) to the apparent PV-LA junction. There was no statistical difference in the electrophysiologic characteristics between the left and right superior PVs (data not shown) or between the endo- and epicardial sleeves (Table 1). Optical mapping of the endocardial surface was performed in five preparations, showing similar distributions of differences in APD (Fig. 1D).



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  		Table 1 Basic Electrophysiologic Properties of Pulmonary Veins

 
Re-entry and automatic rhythms.   Figures 2A and 2B illustrate the presence of functional conduction block and the propensity to re-entry formation. Only nonsustained tachycardia (3 to 12 beats; mean CL = 132 ± 12 ms) could be induced in PS or DS in the baseline state in 15 of 25 preparations. Automatic rhythms (40 ± 11 beats/min; from a maximal diastolic potential of –52 ± 6 mV) were observed in only 3 of 56 preparations. Figure 3A illustrates an example of the automatic rhythm (cycle length = 1,150 ms) originating from DS. This rhythm was not suppressed by overdrive pacing from DS (data not shown). No automatic rhythm was induced after burst pacing or by administration of ACH (10–6 mol/l) or isoproterenol (10–9 to 10–8 mol/l) in 20 preparations tested.



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  		Figure 2 Wavefront propagation recorded by optical mapping. (A) The S1 (cycle length [CL] = 700 ms) wavefront propagated relatively fast and homogeneously across the preparation. (B) In contrast, the S2 (coupling CL = 225 ms) wavefront propagated slower and took a counterclockwise course as conduction block was encountered. The numeric sequence indicates progressive times of propagation. Arrows indicate the site of stimulation. Frames are 32 ms apart. White dots outline the margin of the preparation. Stars indicate the leading edge of wavefront. Abbreviations as in Figure 1.

 


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  		Figure 3 (A) Automaticity was associated with more depolarized membrane potential. Phase 4 depolarization was observed. The slow automatic rhythm (CL = 1,150 ms) failed to conduct into PS and LA. (B) Concentration-response relationship between percent of action potential duration (APD90) abbreviation and acetylcholine (ACH) concentrations. The concentration that produces 50% of the maximal effect (EC50) was 1.35 ± 0.53 x 10–7 mol/l (n = 12). (C) Concentration-response relationship between the incidence of induced sustained PV tachycardia (>2 s) and ACH concentrations. The EC50 was 3.80 ± 0.85 x 10–7 mol/l (n = 15). Other abbreviations as in Figures 1 and 2.

 
Marked shortening of APD was observed in all 46 preparations with exposure to ACH. A concentration-response curve of APD abbreviation by ACH was constructed (Fig. 3B), and ACH concentrations near the concentration that produces 50% of the maximal effect (EC50) (1.35 ± 0.53 x 10–7 mol/l) were then chosen for induction of arrhythmias. Pulmonary vein refractoriness was assessed by delivering a decremental pacing train from PS and measuring the longest pacing CL causing 2:1 block. In the presence of 10–7 mol/l of ACH, the 2:1 block CLs (in ms) at LA (158 ± 11), PS (143 ± 8), and DS (133 ± 7) were significantly shortened by ACH (LA, 119 ± 9; PS, 111 ± 7; DS, 101 ± 8; n = 10, p < 0.05 for all).

Multiple episodes of sustained tachycardias (>2 s; mean duration: 16.8 ± 7.1 s) were reproducibly induced by single extrastimuli in 12 of 15 preparations in the presence of ACH. As with APD shortening, ACH exerted a concentration-dependent effect on the ability to induce sustained PV tachycardias (Figs. 3B and 3C). Sustained PV tachycardias were typically rapid and regular (mean CL = 93 ± 15 ms); could be induced, reset, or terminated by early extrastimuli; and were never induced without significant shortening of the APD by ACH (Figs. 4A to 4C). During tachycardia, the action potential always repolarized to the resting membrane potential despite the short-tachycardia CL (Fig. 4B, horizontal line). Double potentials, suggesting conduction block associated with re-entry, were consistently recorded (Fig. 4C). Pulmonary vein tachycardias were reset by an extrastimulus delivered at PS or DS in six of six preparations, suggesting the presence of an excitable gap and re-entry (Fig. 4B). Re-entry as the mechanism underlying sustained PV tachycardias was consistent with the pattern of activation ascertained by optical mapping (n = 5) (Fig. 4D). Fibrillatory patterns of activations were not induced in any experiments with ACH concentrations up to 10–4 mol/l.



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  		Figure 4 Pulmonary vein tachycardias in ACH. (A) A representative episode of sustained tachycardia (CL = 75 ms) induced with a premature extrastimulus delivered at DS. (B) Dashed box highlighted in A. A premature beat delivered from PS during PV tachycardia advanced the next beat of tachycardia (interval = 45 ms), demonstrating a positive resetting response. (C) An example of double potentials (arrows) recorded during another episode of PV tachycardia originating in PS. (D) Wavefront propagation of PV tachycardia recorded by optical mapping. The trajectory of wavefront propagation took a repetitive clockwise course, verifying re-entry as the mechanism underlying the PV tachycardia, and also demonstrated that the entire re-entrant circuit was confined to PV. Note that the tachycardia circuit was oval (not circular), and the conduction velocity was not uniform along the circuit. Frames are 32 ms apart. *Indicates the leading edge of wavefront. White dots outline the margin of the preparation. ACH = 10–7 mol/l for all. Abbreviations as in Figures 1 through 3.

 
Restitution properties.   All the values of Rt acquired from different recording sites were <1 (Figs. 5B and 5C). Although the values of Rt were significantly greater in LA and PS than in DS, the differences were eliminated by ACH, mainly by greater reduction of Rt in LA and PS (Fig. 5C). Action potential alternans, defined as a periodic change in AP that occurs every other beat, was observed in the PV in six preparations in the baseline state. Action potential alternans was completely suppressed by 10–7 mol/l ACH in all experiments (Fig. 5D).



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  		Figure 5 Restitution properties in ACH. (A) An example of APDs and diastolic intervals (DIs) measured using the dynamic restitution protocols (DI = 840 ms, APD90 = 160 ms) at a pacing CL of 1 s. (B) Representative AP restitution curves and Rt (the steepest slope of the restitution curve) from PS before (black circles, Rt = 0.75) and after (open circles, Rt = 0.22) exposure to ACH. Insert shows the linear regression (Rt) of the shortest DIs preceding refractoriness. Dashed line represents unitary slope. (C) Mean values and standard errors of Rt from LA (black), PS (striped), and DS (open) before and after ACH (n = 12). *p < 0.05 for comparisons before and after ACH. (D) Suppression of AP alternans by ACH at a pacing CL of 130 ms (recorded from PS). ACH = 10–7 mol/l for all. Other abbreviations as in Figures 1 through 3.

 

   Discussion
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 Abstract
 Methods
 Results
 Discussion
References
 
In the present study, rapid and stable re-entrant PV tachycardias were induced in the presence of ACH. Although PV tachycardias were not shown to induce AF because of the absence of significant atrial tissue, rapid PV tachycardias maintain 1:1 conduction into LA. This rapid rhythm may be capable of initiating AF in intact hearts.

Automaticity.   Automatic rhythms have been proposed as a possible mechanism underlying the spontaneous discharges of PVs (8–10). However, other investigators have reported conflicting results, failing to show rapid automatic rhythms in PVs (11,12). In our study, manipulation of experimental conditions such as burst pacing and exposure to isoproterenol or ACH induced only three episodes of subsequent slow automatic rhythms in 56 PV preparations (Fig. 3A). Moreover, the slow automatic rhythms failed to conduct to the PS and LA, indicating that automaticity alone in normal dog hearts may not be a critical element in the genesis of rapid PV firing. However, the extrasystole that initiates re-entry in AF patients could result from automaticity or triggered firing. The factors leading to automaticity or triggered firing could be absent in the PVs of normal dogs.

Electrophysiology of the PV sleeve.   Other investigators have reported different electrophysiologic properties between the PV and the LA and suggested that these discrepancies may contribute to arrhythmia formation in the PV (10–15). In this study, we observed a graded transition of electrophysiologic properties from LA to DS, supporting the observations from clinical electrophysiologic studies in which the effective refractory period of the distal PV is shorter than the PV-LA junction (13,14). In our study, encircling wavefronts resulting from conduction block induced by extrastimuli were observed in the baseline state, consistent with similar observations made in PV and ventricular myocardium (10,15,16), in which heterogeneity of APD causes dispersions and gradients of repolarization, setting the stage for conduction block and functional re-entry. Tissues with reduced coupling of myocardial fibers, such as PVs, would augment the intrinsic heterogeneities and enhance the repolarization gradient (17). Despite the presence of a favorable substrate for re-entry (12,18), no sustained PV tachycardia was induced in the baseline state, signifying the importance of additional factors for the initiation of AF.

A recent study demonstrated heterogeneity and anisotropic conduction within the PV and at the PV-LA junction in patients undergoing catheter ablation for PAF (14). Atrial fibrillation was initiated by re-entry between the distal PV and PV-LA junction or unstable re-entry inside the PV, supporting our hypothesis that re-entrant PV tachycardia is a potential mechanism initiating AF. The crucial role of PV tachycardias in AF was further demonstrated by other investigators (19,20), showing that immediate recurrence of AF can be caused by PV tachycardias and that short bursts of PV tachycardias are critical in maintaining AF.

ACH effects on PV tachycardia.   Administering ACH in a canine right atrial preparation, Schuessler et al. (21) demonstrated conduction block and macro-re-entry as a mechanism for ACH-induced atrial tachycardias. In the present study, sustained re-entrant PV tachycardias were induced exclusively in the presence of marked shortening of APD and refractoriness caused by ACH. The presence of double potentials, positive resetting responses, and the wavefront propagation recorded by optical mapping provides strong evidence that re-entry is the mechanism operative in ACH-induced PV tachycardias. It is plausible that marked abbreviation of APD and refractoriness shorten the wavelength of the tachycardia, allowing re-entry to be initiated and sustained in a substrate with poorly coupled myocardial fibers. Moreover, abbreviation of the refractoriness across the PV preparation facilitates 1:1 conduction into the LA at short CLs (<100 ms), which may manifest as rapid PV firing and trigger AF. Because parasympathetic innervation of the heart is typically heterogeneous with concentrated clusters of autonomic ganglia near each of the PVs (22), hyperactivity of these sites in vivo would likely introduce more dispersion in APD and refractoriness and further enhance the formation of re-entry within PVs.

It is known that ACH greatly enhances AF initiation (23). Recent studies from our laboratory (24) demonstrated that AF initiation was substantially enhanced by selective stimulation of the local cardiac parasympathetic nervous system. Parasympathetic nervous system activation as a critical element for AF initiation and maintenance was further emphasized by a recent report (25) describing a subgroup of AF patients exhibiting marked bradycardia and hypotension during radiofrequency current application to the LA in the vicinity of parasympathetic ganglionated plexi. This subgroup of patients enjoyed a success rate of 99% in eliminating symptomatic AF, attributed to ablation of the parasympathetic nerve elements.

Rapid re-entrant PV tachycardias conform to the rotor hypothesis for AF, in which a stable re-entrant source gives rise to fibrillatory conduction (26). Kalifa et al. (26) demonstrated that rotors at the PV-LA junction can be elicited by increased intra-atrial pressure. In that study, rotors at the PV-LA junction were faster than the rotors in the LA free wall and the waves propagated from PV-LA junction toward LA free wall as the intra-atrial pressure reached >10 cm H2O, suggesting that PV-LA junctions play a key role in AF caused by atrial dilation. Probably because of the limited size of our preparation, we observed only single stationary re-entrant circuits inside the PV, and fibrillation was never induced. Although our preparation contained only a small segment of LA, and induction of AF in the atrium was not investigated, it is conceivable that rapid PV tachycardias with 1:1 conduction into LA are capable of inducing AF, particularly in pathological conditions that elevate the parasympathetic tone. The induction of re-entry required close-coupled premature extrastimuli; the mechanism of spontaneous close-coupled beats has not been clarified, but apparent triggering by early afterdepolarization during repolarization of abbreviated APD has been described (8,24).

Restitution properties.   Greater values of Rt indicate a greater degree of APD shortening in response to a given reduction in DI, leading to marked variations in refractoriness, instability of re-entry, alternans, wave break, and fibrillation (27). Pharmacologic agents that reduce the value of Rt have been shown to be anti-fibrillatory (28). In our experiments, AP alternans in PV can be reproducibly induced at short-pacing CL, but fibrillation inside the PV was never observed. Despite the well-known effect of ACH on inducing AF, ACH appears to be, at least theoretically, antifibrillatory in the PV tissue, based on our observations in which ACH reduced Rt across the preparation and inhibited AP alternans in PV. Although the role of Rt as a predictor of fibrillation has been challenged by observations showing that ventricular fibrillation can occur with Rt <1 (7), our results showed that PVs do not exhibit restitution properties prone to fibrillation. Instead, the myocardial discontinuity and heterogeneity of the electrophysiologic properties of PV provide a fertile substrate for re-entry. Marked shortening of the APD and refractoriness by ACH allow a well-timed premature beat to initiate and maintain the re-entrant PV tachycardia. Reduction of Rt and suppression of AP alternans by ACH may stabilize the re-entry and enhance conduction into LA to initiate AF.

Conclusions.   Structural and functional nonuniformity of the PV provide a fertile substrate for re-entry formation. In the presence of ACH, rapid and sustained re-entrant PV tachycardias maintaining 1:1 conduction into LA at short cycle lengths can serve as a mechanism operative in rapid repetitive PV firing. A relatively "flat" restitution curve (slope <1) in the baseline state and further flattening of the curve by ACH possibly stabilize the PV tachycardia.

Study limitations.   The possibility of artificial PV re-entry caused by experimentally created boundaries or ischemia merits consideration. In optical mapping experiments, the re-entrant wavefront was clearly not forced to turn around at the edge of the preparation, and tachycardia could be induced only with ACH, indicating that conduction block and re-entry were intrinsic electrophysiologic properties of the PV (Figs. 2A and 2B). The thickness of the preparation from the DS to the PV-LA junction was <1 mm, and there was no evidence of ischemia in this superfused preparation based on stable electrograms, resting membrane potentials, and refractoriness. Although the mean CL of PV tachycardia was slightly longer than what was reported by Kalifa et al. (93 ms vs. 80 ms) (26), the difference is likely due to different experimental conditions (ACH administration vs. increased intra-atrial pressure) rather than ischemia of our preparation.

Mapping of the action potential propagation on the endocardial and epicardial surfaces of PV illustrated substantial differences, resulting from differently oriented myocardial fibers (10). We elected to optically map the endocardial surface of the PV sleeve to circumvent the problem associated with the epicardial fat that interferes with the acquisition of fluorescent signals. To ensure the legitimacy of this approach, electrophysiologic properties of the endo- and epicardial surfaces were compared, showing no electrophysiologic differences in the corresponding regions between the two surfaces (Table 1). Therefore, we assume that the same arrhythmia mechanism can be operative in both the endo- and epicardial sleeves. In addition, the vast majority of clinical studies of PV electrophysiology were conducted using endocardial recordings, which further justify our study focusing on the endocardial PV electrophysiology. Another advantage of our experimental preparation is that it exhibits minimal motion artifact; excitation-contraction uncouplers such as diacetyl monoxime or cytochalasin-D, known for affecting cardiac electrophysiology, were not used.


   Footnotes
 
This work was supported by grants 0450143Z from the American Heart Association; K23HL069972 from the National Heart, Lung, and Blood Institute; and a Whitaker Bioengineering Seed Grant.


   References
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 Discussion
 References
 

  1. Haissaguerre M, Jais P, Shah DC, et al. Spontaneous initiation of atrial fibrillation by ectopic beats originating in the pulmonary veins N Engl J Med 1998;339:659-666.[Abstract/Free Full Text]
  2. Saito T, Waki K, Becker AE. Left atrial myocardial extension onto pulmonary veins in humansanatomic observations relevant for atrial arrhythmias. J Cardiovasc Electrophysiol 2000;11:888-894.[ISI][Medline]
  3. Ho SY, Cabrera JA, Tran VH, et al. Architecture of the pulmonary veinsrelevance to radiofrequency ablation. Heart 2001;86:265-270.[Abstract/Free Full Text]
  4. Nolasco JB, Dahlen RW. A graphic method for the study of alternation in cardiac action potentials J Appl Physiol 1968;25:191-196.[Free Full Text]
  5. Weiss J, Chen PS, Qu Z, et al. Electrical restitution and cardiac fibrillation J Cardiovasc Electrophysiol 2002;13:292-295.[CrossRef][ISI][Medline]
  6. Loew LM. Mechanism and principles of voltage-sensitive fluorescenceIn: Rosenbaum D, Jalife J, editors. Optical Mapping of Cardiac Excitation and Arrhythmias. Armonk, NY: Futura Publishing Inc; 2001. pp. 33-46.
  7. Banville I, Chattipakorn N, Gray R. Restitution dynamics during pacing and arrhythmias in isolated pig hearts J Cardiovasc Electrophysiol 2004;15:455-463.[CrossRef][ISI][Medline]
  8. Chen Y, Chen S, Chang M, et al. Arrhythmogenic activity of cardiac muscle in pulmonary veins of the dogimplication for the genesis of atrial fibrillation. Cardiovasc Res 2000;48:265-273.[Abstract/Free Full Text]
  9. Honjo H, Boyett MR, Niwa R, et al. Pacing-induced spontaneous activity in myocardial sleeves of pulmonary veins after treatment with ryanodine Circulation 2003;107:1937-1943.[Abstract/Free Full Text]
  10. Arora R, Verheule S, Luis S, et al. Arrhythmogenic substrate of the pulmonary veins assessed by high-resolution optical mapping Circulation 2003;107:1816-1821.[Abstract/Free Full Text]
  11. Ehrlich JR, Cha TJ, Zhang L, et al. Cellular electrophysiology of canine pulmonary vein cardiomyocytesaction potential and ionic current properties. J Physiol 2003;551:801-813.[Abstract/Free Full Text]
  12. Hocini M, Ho S, Kawara T, et al. Electrical conduction in canine pulmonary veinselectrophysiological and anatomic correlation. Circulation 2002;105:2442-2448.[Abstract/Free Full Text]
  13. Jais P, Hocini M, Macle L, et al. Distinctive electrophysiological properties of pulmonary vein in patients with atrial fibrillation Circulation 2002;106:2479-2485.[Abstract/Free Full Text]
  14. Kumagai K, Ogawa M, Noguchi H, et al. Electrophysiological properties of pulmonary veins assessed using a multielectrode basket catheter J Am Coll Cardiol 2004;43:2281-2289.[Abstract/Free Full Text]
  15. Hamabe A, Okuyama Y, Miyauchi Y, et al. Correlation between anatomy and electrical activation in canine pulmonary veins Circulation 2003;107:1550-1555.[Abstract/Free Full Text]
  16. Laurita KR, Rosenbaum DS. The interdependence of modulated dispersion and tissue structure in the mechanism of unidirectional block Circ Res 2000;87:922-928.[Abstract/Free Full Text]
  17. Laurita KR, Rosenbaum DS. Restitution, repolarization and alternans as arrhythmogenic substratesIn: Zipes DP, Jalife J, editors. Cardiac Electrophysiology. From Cell to Bedside. Philadelphia, PA: Saunders; 2004. pp. 232-241.
  18. Verheule S, Wilson EE, Arora R, et al. Tissue structure and connexin expression of canine pulmonary veins Cardiovasc Res 2002;55:727-738.[Abstract/Free Full Text]
  19. Oral H, Ozaydin M, Tada H, et al. Mechanistic significance of intermittent pulmonary vein tachycardia in patients with atrial fibrillation J Cardiovasc Electrophysiol 2002;13:645-650.[CrossRef][ISI][Medline]
  20. Chugh A, Ozaydin M, Scharf C, et al. Mechanism of immediate recurrences of atrial fibrillation after restoration of sinus rhythm Pacing Clin Electrophysiol 2004;27:77-82.[CrossRef][Medline]
  21. Schuessler RB, Grayson TM, Bromberg BI, et al. Cholinergically mediated tachyarrhythmias induced by a single extrastimulus in the isolated canine right atrium Circ Res 1992;71:1254-1267.[Abstract/Free Full Text]
  22. Armour JA, Murphy DA, Yuan BX, et al. Gross and microscopic anatomy of the human intrinsic cardiac nervous system Anat Rec 1997;247:289-298.[CrossRef][Medline]
  23. Rosenshtraukb LV, Fedorov VV, Sharifov OF. Cholinergic atrial fibrillationIn: Zipes DP, Jalife J, editors. Cardiac Electrophysiology. From Cell to Bedside. Philadelphia, PA: Saunders; 2004. pp. 306-316.
  24. Schauerte P, Scherlag B, Patterson E, et al. Focal atrial fibrillationexperimental evidence for a pathophysiologic role of the autonomic nervous system. J Cardiovasc Electrophysiol 2001;12:592-599.[CrossRef][ISI][Medline]
  25. Pappone C, Santinelli V, Manguso F, et al. Pulmonary vein denervation enhances long-term benefit after circumferential ablation for paroxysmal atrial fibrillation Circulation 2004;109:327-334.[Abstract/Free Full Text]
  26. Kalifa J, Jalife J, Zaitisev AV, et al. Intra-atrial pressure increases rate and organization of waves emanating from the superior pulmonary veins during atrial fibrillation Circulation 2003;108:668-671.[Abstract/Free Full Text]
  27. Weiss JN, Chen PS, Qu Z, et al. Ventricular fibrillationhow do we stop the wave from breaking?. Circ Res 2000;87:1103-1107.[Abstract/Free Full Text]
  28. Garfinkel A, Kim H, Voroshilovsky O, et al. Preventing ventricular fibrillation by flattening cardiac restitution Proc Natl Acad Sci USA 2000;97:6061-6066.[Abstract/Free Full Text]



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