Adjacent Left Atrium Research Articles

Structural and electro-anatomical characterization of the equine pulmonary veins: implications for atrial fibrillation

Introduction/objectivesSpontaneous pulmonary vein (PV) activity triggers atrial fibrillation (AF) in humans. Although AF frequently occurs in horses, the origin remains unknown. This study investigated the structural and electro-anatomical properties of equine PVs to determine the potential presence of an arrhythmogenic substrate. Animals, materials and methodsEndocardial three-dimensional electro-anatomical mapping (EnSite Precision) using high-density (HD) catheters was performed in 13 sedated horses in sinus rhythm. Left atrium (LA) access was obtained retrogradely through the carotid artery. Post-mortem, tissue was harvested from the LA, right atrium (RA), and PVs for histological characterization and quantification of ion channel expression using immunohistochemical analysis. ResultsGeometry, activation maps, and voltage maps of the PVs were created and a median of four ostia were identified. Areas of reduced conduction were found at the veno-atrial junction. The mean myocardial sleeve length varied from 28 ± 13 to 49 ± 22 mm. The PV voltage was 1.2 ± 1.4 mV and lower than the LA (3.4 ± 0.9 mV, P < 0.001). The fibrosis percentage was higher in PV myocardium (26.1 ± 6.6%) than LA (14.5 ± 5.0%, P = 0.003). L-type calcium channel (CaV1.2) expression was higher in PVs than LA (P = 0.001). T-type calcium channels (CaV3.3), connexin-43, ryanodine receptor-2, and small conductance calcium-activated potassium channel-3 was expressed in PVs. ConclusionsThe veno-atrial junction had lower voltages, increased structural heterogeneity and areas of slower conduction. Myocardial sleeves had variable lengths, and a different ion channel expression compared to the atria. Heterogeneous properties of the PVs interacting with the adjacent LA likely provide the milieu for re-entry and AF initiation.

Early and Delayed Alteration of Atrial Electrograms Around Single Radiofrequency Ablation Lesion.

Purpose: The acute effect of radiofrequency (RF) ablation includes local necrosis and oedema. We investigated the spatiotemporal change of atrial electrograms in the area surrounding the site of single standardized pulse of RF energy.Methods: The study enrolled 12 patients (45–67 years, 10 males) with paroxysmal atrial fibrillation (AF) undergoing ablation procedure with irrigated-tip ablation catheter and 3D navigation. The high-density mapping/remapping (129 ± 63 points) within the circular area with radius of ~10 mm, centered at the pre-specified posterior left pulmonary vein antrum ablation site was performed at baseline, immediately after single RF energy delivery (25 W, 30 s, 20 ml/min) and after 30 min waiting period. Bipolar voltages of atrial electrograms (A-EGM-biV) were averaged within the central and 12 adjacent left atrium segments and their relative change was studied.Results: After the ablation, overall A-EGM-biV within the mapping zone (3.51 ± 1.89 mV at baseline) reduced to 2.83 ± 1.77 mV (immediately) and to 2.68 ± 1.58 mV (after 30 min waiting period). In per-segment pair-wise comparison, we observed highly significant change in A-EGM-biV that extended up to the distance of 8.8 mm from the lesion core. The maximum early A-EGM-biV attenuation by 39–49% (P < 0.001) was registered in segments adjacent to pulmonary vein ostia. The subsequent (delayed) A-EGM-biV reduction by 17–24% (P < 0.05) was observed in opposite direction from the lesion center.Conclusions: Significant alteration of atrial electrograms was detectable rather distant from the central lesion. Spatiotemporal development of ablation lesion was eccentric/asymmetric. While acute A-EGM-biV reduction can be attributed predominantly to direct thermal injury, delayed effects are probably due to oedema progression.

Inequalities for Left Atrial Ablation.

Great teaching value can come from showcasing an unusual phenomenon that serves as an aid to explain how best to approach mundane, common problems. In this installment of teaching rounds, Wakabayashi et al1 use an unusual activation sequence observed along the mitral annular atrial myocardium that was observed after ablation of the mitral isthmus to teach us about the pitfalls created by the complex terrain in the left atrium (LA). See Article Much of what we initially learned about linear ablation is from ablation of the cavotricuspid isthmus for typical right atrial flutter. Although this experience is helpful, we need to be alert to the fact that we cannot equate this relatively simple ablation approach to the complex-interlinked isthmus anatomy in the LA. In their approach to this complex and instructional case, the authors stress the initial importance of pulmonary vein isolation when approaching mitral isthmus–dependent flutter. Unlike the human inferior vena cava, the left lower pulmonary vein does not serve as an anchor point for ablation of the mitral isthmus. This is because of the myocardial sleeves that extend into this pulmonary vein. As a result, to truly anchor the mitral isthmus line and obtain isthmus block at this site, either the ablation needs to go into the pulmonary vein (which would have a prohibitive risk of pulmonary vein stenosis) or the pulmonary vein must be circumferentially isolated with LA ablation. The usual method for determining whether the pulmonary vein is indeed isolated …

Left Atrial Diverticula in Patients Referred for Radiofrequency Ablation of Atrial Fibrillation

Background— The anatomic features of left atrial diverticula (LAD) are still unclear in patients with atrial fibrillation (AF). The purpose of this study was to evaluate the prevalence and morphological characteristics of LAD in patients referred for radiofrequency transcatheter ablation of AF with dual-source computed tomography. Methods and Results— Dual-source computed tomography images were obtained in 214 patients referred for AF catheter ablation and 214 sex- and age-matched control subjects. Images were analyzed to determine the prevalence and morphological characteristics of LAD and their relationship with adjacent pulmonary veins and left atrial appendage. In AF patients 77 (36.0%) (95% confidence interval, 29.6–42.4%) had 90 LAD, whereas in control subjects 70 (32.7%) (95% confidence interval, 26.4–39.0%) had 81 LAD ( P =0.551). In patients with AF, LAD locations were right anterosuperior (47.8%), left anterosuperior (8.9%), left lateral (32.2%), interatrial septum (4.4%), right inferior (5.6%), and posterosuperior (1.1%) walls, respectively. The mean size of LAD was 5.3±2.9×5.6±3.3 mm. The wall of the LAD was much thinner than that of adjacent left atrium (0.89±0.46 versus 2.39±0.83 mm). Most LAD were located close to a pulmonary vein or atrial appendage ostium, with a mean distance of 8.7–13.1 mm. Conclusions— LAD are common, with a prevalence of 36.0% in patients with AF, which is not statistically greater than that in patients without AF. Thin-walled LAD are more commonly located on the superior anterior wall of left atrium and close to common ablation sites.

Pulmonary Venous Flow Assessed by Doppler Echocardiography in the Management of Atrial Fibrillation

Pulmonary venous blood flow (PVF) visualized by Doppler echocardiography exhibits a pulsatile behavior, which is related to left atrial pressure and function, mitral valve function, and left ventricular compliance. In atrial fibrillation (AF), the disappearance of atrial reverse flow, a decrease in systolic flow with a greater diastolic than systolic flow, a prolonged onset of systolic flow and the appearance of an early systolic reverse flow are characteristic findings. A reduction in systolic PVF expressed by reduced peak velocity, reduced velocity-time integral of systolic flow, and reduced systolic fraction of PVF has been found to be associated with reduced left atrial appendage flow, left atrial spontaneous echo contrast formation, frequency of AF paroxysms and propensity for AF recurrence following restoration of sinus rhythm. Ablation techniques targeting pulmonary vein ostia and adjacent left atrium are promising treatment options to cure AF. Monitoring the PVF response to and adjusting of ablation procedures has been suggested to optimize outcome and prevent complications such as pulmonary vein stenosis. In conclusion, assessment of PVF variables and patterns by Doppler echocardiography seems useful in the management of AF patients. Especially the reduction in systolic PVF may be used as marker for left atrial dysfunction which favors thrombus formation and AF reinitiation. Finally, PVF monitoring has the potential to an increasing role in AF ablation procedures.

Three-dimensional rotational angiography of the left atrium and esophagus—A virtual computed tomography scan in the electrophysiology lab?

Three-dimensional (3D) reconstruction of the heart and surrounding structures has been supplementing traditional two-dimensional imaging to guide diagnostic and therapeutic electrophysiologic procedures. Current methods using computed tomography (CT)/magnetic resonance imaging (MRI) reconstruction have certain limitations. We investigated the feasibility of rotational angiography (RA) combined with simultaneous esophagogram to create an intraprocedural 3D reconstruction of the left atrium (LA) and the esophagus. Rotational angiography was performed. Contrast was injected via a pigtail catheter positioned in the left or right pulmonary artery to achieve a levophase venous cycle opacification of the ipsilateral pulmonary veins and adjacent LA. Simultaneous administration of oral contrast allowed a 3D reconstruction of the esophagus in the same image. Qualitative and quantitative comparison between the intraprocedural 3D RA and a remote CT scan was performed in 11 consecutive patients undergoing ablation for atrial fibrillation. Adequate visualization of the pulmonary veins, adjacent posterior LA, and esophagus was achieved in 10 patients. Determination of pulmonary transit time to guide the initiation of RA resulted in better-quality imaging. A close correlation between 3D RA and CT was found. Based on close proximity between the LA and esophagus, the ablation procedure was modified in three patients. Three-dimensional RA of the LA and esophagus is a promising new method allowing intraprocedural 3D reconstruction of these structures comparable in quality to a CT scan. Further studies refining the method are justified because it could eliminate the need for CT/MRI scans before ablation.

Identifying far-field superior vena cava potentials within the right superior pulmonary vein

Far-field extra-pulmonary vein (PV) potentials originating from the left atrial appendage and adjacent left atrium have been identified within the left PVs, but no systematic study of extra-PV potentials within the right superior PV (RSPV) has been described. The purpose of this study was to prospectively analyze extra-PV contributions to RSPV potentials. In a consecutive, prospective series of 114 patients (96 men and 18 women; 56 +/- 10 years) undergoing electrophysiologically guided ostial PV isolation, residual potentials recorded with a circular mapping catheter in the RSPV after ostial isolation were analyzed. Their extra-PV origin was validated by mapping a site with identical timing (in sinus rhythm or atrial fibrillation) within the adjacent superior vena cava (SVC) where, in sinus rhythm, local pacing (until threshold amplitude) concealed the residual potential within the stimulus artifact because of very short activation timing. The timing of residual potentials with respect to surface ECG P-wave onset was measured and compared with the earliest timing of ablated RSPV potentials. Residual low-amplitude (mean 0.29 +/- 0.17 mV, range 0.07-0.65 mV) extra-PV potentials were recorded from the anterior and superior aspect of the RSPV in 3.6 +/- 1 bipoles in 26 (23%) patients (all men, 51 +/- 10 years) with a timing from sinus P-wave onset of 17 +/- 12 ms (range 0-40 ms) vs 52 +/- 9 ms (range 35-70 ms) for the earliest RSPV potential (P <.001, t-test). Extra-PV potentials all originated from the posterior aspect of the SVC. The SVC potential was identified during ongoing atrial fibrillation in eight patients and later confirmed in sinus rhythm. An extra-PV potential of SVC origin could be identified by timing earlier than 30 ms from onset of the sinus P wave, with sensitivity of 92%, specificity 100%, positive predictive value 100%, and negative predictive value 89%. Extra-PV potentials of right-sided SVC origin were recorded within the RSPV in 23% of patients and can be identified with high sensitivity and specificity by a timing within 30 ms of sinus P-wave onset. Recognizing these potentials can avoid unnecessary additional ablation and possibly PV stenosis or phrenic paralysis.

Mechanisms of recurrent atrial fibrillation after pulmonary vein isolation by segmental ostial ablation

Objectives The aim of this study was to determine the mechanisms responsible for recurrent atrial fibrillation (AF) after pulmonary vein isolation (PV) by segmental ostial ablation. Background Recovery of conduction into a previously isolated PV is a common observation when there is recurrent AF soon after segmental ostial ablation. However, the mechanisms of recurrent AF have been unclear. Methods A repeat ablation procedure was performed in 50 patients who had recurrent paroxysmal AF at a mean of 7 ± 6 months after segmental ostial ablation to isolate the PVs. During the repeat procedure, a ring catheter was inserted into each PV during sinus rhythm and AF to determine whether the veins were still isolated and, if not, whether there were PV tachycardias with a cycle length shorter than in the adjacent left atrium during AF. Results There was recovery of conduction over a previously ablated muscle fascicle in ≥1 PV in 49 patients (98%). There were 10 ± 2 episodes of PV tachycardia per minute in 36 (72%) of the 50 patients during AF. Repeat ablation was performed by segmental ostial ablation (23 patients) or by left atrial catheter ablation to encircle the left- and right-sided PVs 1 to 2 cm from the ostia, with additional ablation lines in the posterior left atrium and mitral isthmus (27 patients). At 6-month follow-up, among 23 patients who underwent repeat ablation by segmental ostial ablation, AF recurred in 4 (21%) of the 19 patients who had PV tachycardias and in 3 (75%) of the 4 patients who did not ( P = .03). Among the 27 patients who underwent left atrial ablation, AF recurred in 2 (12%) of the 17 patients who had PV tachycardias and in 1 (10%) of the 10 patients who did not ( P = 0.7). Conclusions Recovery of conduction in previously ablated muscle fascicles is a common finding in patients with recurrent AF after segmental ostial ablation. The efficacy of repeat segmental ostial ablation depends on the presence of PV tachycardias, whereas left atrial ablation is effective regardless of whether PV tachycardias are present or not during AF.

Mechanism of immediate recurrences of atrial fibrillation after restoration of sinus rhythm.

An immediate recurrence of AF may occur after restoration of sinus rhythm. Although pulmonary vein (PV) isolation has been shown to prevent immediate recurrence of AF, the specific trigger for immediate recurrence of AF has not been described. In 89 consecutive patients (mean age 53 +/- 11 years) who had sinus rhythm restored by spontaneous or transthoracic cardioversion in the course of a PV isolation procedure, electrograms recorded within a PV and in the adjacent left atrium were analyzed to determine the mechanism of initiation of immediate recurrence of AF. Immediate recurrence of AF was defined as a recurrence of AF within 90 seconds after restoration of sinus rhythm. There were 124 episodes of immediate recurrence of AF at a mean of 18 +/- 23 seconds after cardioversion. Recordings within the PV that triggered the immediate recurrence of AF were available in 23 (19%) of the 124 immediate recurrence of AF episodes. Among these 23 episodes of immediate recurrence of AF, all (100%) were triggered by a burst of PV tachycardia (P < 0.001). The coupling interval and prematurity index (coupling interval/preceding sinus cycle length) of the premature depolarizations that did and did not trigger immediate recurrence of AF were 246 +/- 67 ms and 0.30 +/- 0.11 vs 378 +/- 117 ms and 0.49 +/- 0.16, respectively (P < 0.01). Immediate recurrence of AF was abolished by PV isolation. The mechanism of immediate recurrence of AF is a burst of PV tachycardia, not a single premature depolarization. Immediate recurrence of AF identifies patients with AF in whom the PVs may play a major role in the initiation of AF.

Characteristics of rapid rhythms recorded within pulmonary veins during atrial fibrillation.

Rapid rhythms often arise in the pulmonary veins during atrial fibrillation (AF). The activation patterns within pulmonary veins during these rapid rhythms are not well described. In 39 patients with paroxysmal AF, ostial recordings were obtained during AF in 110 pulmonary veins with a decapolar distal ring catheter. Pulmonary vein tachycardia (PVT) was defined as a pulmonary vein (PV) rhythm that had a cycle length shorter than at the adjacent left atrium. During AF, PVT was recorded in 93% of PV's, usually in the form of intermittent bursts that had a mean duration of 1,325 +/- 647 ms and mean cycle length of 125 +/- 20 ms. The mean cycle length of continuous PVT's (141 +/- 25) was longer than the mean cycle length of intermittent bursts of PVT (P < 0.05). The intermittent PVT's were associated with a shorter left atrial cycle length than were the continuous PVT's. In 90% of PVTs, complex activation patterns attributable to simultaneous recordings from two or more overlapping fascicles were present at a segment of the pulmonary vein ostium, and the mean cycle length of these recordings was 80 +/- 32 ms. PVT during AF is much more often intermittent than continuous. The relationship between PVT cycle length and left atrial cycle length suggests that PVT's influence the left atrium during AF. PVT must be distinguished from recordings within PV's that have a short cycle length as a result of simultaneous recordings from two or more overlapping fascicles.

Demonstration of electrical and anatomic connections between Marshall bundles and left atrium in dogs: implications on the generation of P waves on surface electrocardiogram.

The muscle bundles within the ligament of Marshall (LOM) are electrically active. The importance of these muscle bundles (Marshall bundle [MB]) to atrial activation and the generation of the ECG P wave is unclear. We used optical mapping techniques to study epicardial activation patterns in isolated perfused left atrium in four dogs. In another seven dogs, P waves were studied before and after in vivo radiofrequency (RF) ablation of the connection between coronary sinus (CS) and the LOM. Computerized mapping was performed before and after RF ablation. Optical mapping studies showed that CS pacing resulted in broad wavefronts propagating from the middle and distal LOM directly to the adjacent left atrium (LA). Serial sections showed direct connection between MB and LA near the orifice of the left superior pulmonary vein in two dogs. In vivo studies showed that MB potentials were recorded in three dogs. After ablation, the duration of P waves remained unchanged. In the other four dogs, MB potentials were not recorded. Computerized mapping showed that LA wavefronts propagated to the MB region via LA-MB connection and then excited the CS. After ablation, the activation of CS muscle sleeves is delayed, and P wave duration increased from 65.3 +/- 14.9 msec to 70.5 +/- 17.2 msec (P = 0.025). In about half of the normal dogs, MB provides an electrical conduit between LA free wall and CS. Severing MB alters the atrial activation and lengthens the P wave. MB contributes to generation of the P wave on surface ECG.

Identification of left atrial origin of ectopic tachycardia during right atrial mapping: analysis of double potentials at the posteromedial right atrium.

The high posteromedial right atrium is adjacent to the left atrium near the right superior pulmonary vein. We hypothesized that analysis of electrograms at this site could distinguish left from right atrial tachycardia. Atrial mapping was performed in 16 patients with left atrial origin ectopic tachycardia (11 patients with right superior pulmonary vein origin and 5 patients with other left atrial tachycardias). During left atrial tachycardia, earliest right atrial activation was recorded at the high posterior right atrium in 14 of 16 patients. At all of these 14 early sites, double potentials were recorded during tachycardia. The first potential was a far-field signal from left atrium as indicated by the following: (1) during sinus beats, the timing of the two potentials reversed such that the left atrial one was late; (2) ablation at the right atrial site did not decrease the amplitude of the first potential, but did decrease the amplitude of the second potential; and (3) the timing of activation at the adjacent left atrium agreed with that of the first potential. In the 11 right superior pulmonary vein tachycardias, the first potential was markedly earlier than the p wave onset, but in left atrial tachycardias with other origins it was later. In a control group of six patients with pacing to simulate right atrial tachycardia, double potentials were recorded in the posterior right atrium, but the timing of components did not reverse during sinus rhythm. For some left atrial ectopic tachycardias, particularly those originating from the right superior pulmonary vein, recognition of left versus right atrial origin can be accomplished during right atrial mapping by analysis of double potentials in the posteromedial right atrium.

Electrical conduction between the right atrium and the left atrium via the musculature of the coronary sinus.

The purpose of this study was to determine whether the coronary sinus (CS) musculature has electrical connections to the right atrium (RA) and left atrium (LA) and forms an RA-LA connection. Six excised dog hearts were perfused in a Langendorff preparation. A 20-electrode catheter (2-4-2-mm spacing center to center) was placed along the CS. Excision of the pulmonary veins provided access to the LA, and a second 20-electrode catheter was placed along the LA endocardium opposite the CS catheter. An incision opened the CS longitudinally, and microelectrodes were inserted into the CS musculature and adjacent LA myocardium. Continuous CS musculature was visible along a 35+/-9-mm length of the CS beginning at the ostium. During lateral LA pacing, CS electrodes recorded double potentials, a rounded, low-frequency potential followed by a sharp potential. The rounded initial potential propagated in the lateral-to-septal direction and represented "far-field" LA activation (timing coincided with adjacent LA potentials and with action potentials recorded from microelectrodes in adjacent LA cells). The sharp potential represented CS activation (timing coincided with action potentials recorded from CS musculature). A distal LA-CS connection (earliest sharp potential in the CS during lateral LA pacing) was located 26+/-7 mm from the ostium. During RA pacing posterior to the CS ostium, CS electrodes recorded septal-to-lateral activation of the high-frequency potential, with slightly later activation of the rounded potential (LA activation). Incisions surrounding the CS ostium isolating the ostium from the RA had no effect on the CS musculature and LA potentials during RA pacing within the isolated segment containing the CS ostium. RA pacing outside the isolated segment delayed activation of the CS musculature until after LA activation, confirming that the RA-CS connection was located in the region of the CS ostium as well as confirming the presence of the LA-CS connection. In canine hearts, the CS musculature is electrically connected to the RA and the LA and forms an RA-LA connection.