Irene H. Stevenson

Electrophysiological and electrocardiographic characteristics of focal atrial tachycardia originating from the pulmonary veins: acute and long-term outcomes of radiofrequency ablation.

Background—The objective of this study was to describe the electrophysiological characteristics, anatomic distribution, and long-term outcome after focal ablation (RFA) of pulmonary vein (PV) atrial tachycardia (AT). Both atrial fibrillation (AF) and AT may be due to a rapidly firing focus in the PVs. Whether these represent two aspects of the same process is unknown. Methods and Results—Twenty-seven patients with 28 PV(16%) ATs of a consecutive series of 172 undergoing RFA for focal AT are reported. The mean age was 39±16 years, with symptoms for 9±14 years resistant to 1.7±0.8 medications. AT occurred spontaneously or with isoproterenol in all patients and was not inducible with PES in any. The distribution of PV ATs was right superior PV, 11; left superior PV, 11; left inferior PV, 5; and right inferior PV, 1; 26of 28 foci (93%) were ostial. RFA was successful in 28 of 28 PV ATs acutely. RFA was focal in 25 of 28, with PV isolation of a single target vein in 3. There were 4 recurrences at a mean of 3.3 months. Repeat RFA was performed in all 4 and successful in 3 of 4. All but one recurrence occurred from the same site. Long-term success was achieved in 26 of 27 (96%) patients at mean follow-up of 25±22 months. No patients have had subsequent development of AF or AT from a different site. Conclusions—PV AT has a distribution similar to PV AF, with a propensity to upper veins. However, the majority of foci are ostial, and only a small percentage occur from deep in the PV. Focal RFA is associated with high long-term success, with freedom from both AT from other sites and from AF. PV AT is a localized process and therefore may be different from PV AF.

The right ventricular outflow tract : The road to septal pacing

Background: Pacing from the right ventricular apex is associated with long‐term adverse effects on left ventricular function. This has fuelled interest in alternative pacing sites, especially the septal aspect of the right ventricular outflow tract (RVOT). However, it is a common perception that septal RVOT pacing is difficult to achieve.

Right ventricular outflow tract pacing: radiographic and electrocardiographic correlates of lead position.

Objective: To characterize the pacing site in an unselected series of patients undergoing right ventricular outflow tract (RVOT) lead placement and investigate the role of the electrocardiogram (ECG) in predicting implantation.

Atrial electrophysiology is altered by acute hypercapnia but not hypoxemia: implications for promotion of atrial fibrillation in pulmonary disease and sleep apnea.

BACKGROUND Chronic pulmonary disease and sleep apnea have been associated with the development of atrial fibrillation (AF). OBJECTIVE The purpose of this study was to characterize the atrial electrical changes that occur with hypercapnia and hypoxemia and to determine their role in AF development. METHODS Seventeen sheep (6 control, 5 hypercapnia, 6 hypoxemia) underwent open chest electrophysiologic evaluation under autonomic blockade. A 64-electrode endocardial basket catheter was positioned in the right atrium, and 2 x 128 electrode epicardial plaques were sutured to the right atrial and left atrial appendages to determine atrial refractoriness (effective refractory period [ERP]) at 9 sites and 5 cycle lengths, conduction time to fixed points on each plaque, and AF vulnerability. RESULTS Hypercapnia was associated with a 152% lengthening of ERP from baseline and increased conduction time. ERPs rapidly returned to baseline, but recovery of conduction was delayed at least 117 +/- 24 minutes following resolution of hypercapnia. AF vulnerability was reduced during hypercapnia (with increased ERP) but increased significantly with subsequent return to eucapnia (when ERP normalized but conduction time remained prolonged). No significant changes in ERP, atrial conduction time, or AF vulnerability occurred in hypoxemic or control groups. CONCLUSION Differential recovery of ERP and conduction that occurs following hypercapnia might account for the increased vulnerability to AF observed in the phase after return to eucapnia. This may explain in part the increased prevalence of AF in pulmonary disease and sleep apnea.

The role of chronic atrial stretch and atrial fibrillation on posterior left atrial wall conduction.

BACKGROUND The posterior left atrium (LA) is involved in the initiation and maintenance of atrial fibrillation (AF). OBJECTIVE The purpose of this study was to compare conduction patterns on the posterior LA in patients with mitral regurgitation (MR), with and without AF. METHODS Epicardial mapping of the posterior LA was performed in 23 patients undergoing cardiac surgery. Patients were included in one of three groups: Group A-patients in sinus rhythm with normal left ventricular function undergoing coronary artery bypass grafting, Group B-patients in sinus rhythm with MR undergoing mitral valve surgery, or Group C-patients in persistent AF with MR undergoing mitral valve surgery. Conduction patterns, regional conduction velocity, conduction heterogeneity, conduction anisotropy, and complex fractionated atrial electrograms (CFAEs) were assessed. RESULTS LA diameter was greater in patients in Groups C (57 +/- 4mm) and B (54 +/- 6mm) than in Group A (39 +/- 7 mm, P <0.01). Patients in Group C had a greater number of lines of conduction delay than Groups A and B (2.0 +/- 0.8 vs 1 +/- 0 and 1 +/- 0, P <0.05). The extent of conduction delay and conduction heterogeneity was greater in Group C than in Group B, which was greater than in Group A (P <0.05). The percentage of CFAEs that remained stable during AF was 61% +/- 17%. There was a significant correlation between CFAEs during AF and regions of slow conduction during pacing (R = 0.36, P <0.001). CONCLUSION Patients with MR, LA enlargement, and AF have more extensive regions of conduction slowing in the posterior LA. Anatomically constant lines of conduction delay in this region lead to circuitous wavefront propagation. During persistent AF, fractionated electrograms in the posterior LA are distributed to regions demonstrating slow conduction, and the majority remain stable over time.

Anatomically Determined Functional Conduction Delay in the Posterior Left Atrium Relationship to Structural Heart Disease

OBJECTIVES This study sought to characterize the conduction properties of the posterior left atrium (PLA) in patients with different forms of structural heart disease undergoing cardiac surgery. BACKGROUND The PLA plays an important role in the initiation and maintenance of atrial fibrillation. METHODS This study included 34 patients having elective cardiac surgery. There were 4 groups of patients: normal left ventricular (LV) function (coronary artery bypass grafting [CABG]); severe LV dysfunction (LVF/CABG); severe mitral regurgitation (MR); severe aortic stenosis (AS). Epicardial mapping of the PLA was performed in sinus rhythm and during differential pacing. Activation patterns, regional conduction velocity (CV), conduction heterogeneity, anisotropy, and total plaque activation time (TAT) were assessed. RESULTS Left atrial size in patients with LVF/CABG (47 +/- 7 mm) and MR (54 +/- 6 mm) was larger than patients with CABG (39 +/- 7 mm) and AS (42 +/- 6 mm; p < 0.05). During pacing, all patients developed a vertical line of conduction delay running between the pulmonary veins. The extent of this conduction delay was greater in patients with LVF/CABG and MR than patients with AS and CABG (p < 0.05). Conduction heterogeneity, anisotropy, and TAT were greater in patients with LVF/CABG and MR than patients with CABG (p < 0.05). These changes resulted in circuitous wave front propagation. CONCLUSIONS There is a line of functional conduction delay in a consistent anatomical location in the PLA in patients with structural heart disease. This is most marked in conditions associated with significant chronic atrial enlargement and leads to circuitous wave front propagation, suggesting a potential role in arrhythmogenesis.

Focal atrial tachycardias arising from the right atrial appendage: electrocardiographic and electrophysiologic characteristics and radiofrequency ablation.

Objective: To characterize the electrocardiographic and electrophysiological features and frequency of focal atrial tachycardia (AT) originating from the right atrial appendage (RAA).

Fractionated atrial electrograms during sinus rhythm: Relationship to age, voltage, and conduction velocity

BACKGROUND Fractionated atrial electrograms (CFAEs) have been implicated in the mechanism of atrial fibrillation (AF). The prevalence and distribution of CFAEs in normal populations have not been clearly defined. OBJECTIVE This study sought to determine the influence of age on CFAEs and investigate the relationship between CFAEs and the underlying atrial substrate. METHODS Twenty-one patients without structural heart disease underwent electroanatomic mapping of their right atrium (RA). Patients were categorized into 3 groups according to age: group A, patients <30 years (25.1 +/- 3.1 years, n = 7); group B, patients between 31 and 59 years (51.7 +/- 10.3 years, n = 6); group C, patients >60 years (66.9 +/- 7.7 years, n = 8). The proportion of points with CFAEs was analyzed for the high and low septal RA, high and low lateral RA, and high and low posterior RA. The mean atrial voltage and conduction velocity were assessed in each of these regions. RESULTS The percentage of CFAEs was greater in group C (14.6% +/- 7.7%) than in group A (2.7% +/- 2.1%; P = 0.001). The percentage of CFAEs in group B (8.5% +/- 3.5%) was not significantly different from that in group A (P = 0.21) and group C (P = 0.14). The CFAEs were predominantly located in the posterior RA and high septal RA. There were significant correlations between the proportion of CFAEs and age (R = 0.72; P < 0.01), atrial voltage (R = -0.57; P < 0.01), and conduction velocity (R = -0.73; P < 0.001). CONCLUSION CFAEs increase with age and occur in regions of low atrial voltage and slowed conduction. The distribution of CFAE is predominantly along the posterior and high septal RA, regions where there are marked changes in myocardial fiber orientation. This suggests that the underlying myocardial architecture is the main influence on electrogram morphology.

The right ventricular outflow tract : A comparative study of septal, anterior wall, and free wall pacing

Background: There is marked heterogeneity in right ventricular outflow tract (RVOT) pacemaker lead placement using conventional leads. As a result, we have sought to identify a reproducible way of placing a ventricular lead onto the RVOT septum.

Effects of long-term omega-3 polyunsaturated fatty acid supplementation on paroxysmal atrial tachyarrhythmia burden in patients with implanted pacemakers: Results from a prospective randomised study

BACKGROUND Sino-atrial node disease and aging increase AF risk. We investigated if long-term fish oil supplementation reduces paroxysmal atrial tachycardia/fibrillation (AT/AF) burden in patients aged ≥60 years with sinoatrial node disease and dual chamber pacemakers. METHODS Following a run-in period of 6 months (p1) where AT/AF burden was logged,78 patients were randomised to control or fish oil group (total omega-3 6 g/d) and AT/AF burden evaluated after 6 months (p2; 39 controls, 39 fish oil) and 12 months (p3; 39 controls; 18 fish oil). A subset of 21 fish oil patients crossed over to controls in the final 6 months (crossover group). RESULTS Median AT/AF burden increased significantly in controls (1.5%, 3.2%, 4.3%, P<.001) but not in fish oil patients at 6 months (1.4% to 2%, P=.46) or those continuing for 12 months (1.5%, 0.98%, 1%, P=.16). Time to first episode of AT/AF >1 min was not significantly different between the groups (P=.9). There was a rebound increase in AT/AF burden in p3 in cross over patients (2.2% to 5.8%, P=.01) reaching a level similar to controls (crossover vs. controls, 5.8% vs. 4.3%, P=.63) and higher than those who continued fish oil for 12 months (crossover vs. continued intake 5.8% vs. 1.2%, P=.02). Fish oil patients had shorter duration episodes of AT/AF with no difference in frequency compared to controls. CONCLUSION Long-term fish oil supplementation did not suppress AT/AF burden but may have attenuated its temporal progression related to aging and sinus node disease.