Colette M. Guiraudon

Chronic Rapid Atrial Pacing Structural, Functional, and Electrophysiological Characteristics of a New Model of Sustained Atrial Fibrillation

BACKGROUND Despite the clinical importance of atrial fibrillation (AF), the development of chronic nonvalvular AF models has been difficult. Animal models of sustained AF have been developed primarily in the short-term setting. Recently, models of chronic ventricular myopathy and fibrillation have been developed after several weeks of continuous rapid ventricular pacing. We hypothesized that chronic rapid atrial pacing would lead to atrial myopathy, yielding a reproducible model of sustained AF. METHODS AND RESULTS Twenty-two halothane-anesthetized mongrel dogs underwent insertion of a transvenous lead at the right atrial appendage that was continuously paced at 400 beats per minute for 6 weeks. Two-dimensional echocardiography was performed in 11 dogs to assess the effects of rapid atrial pacing on atrial size. Atrial vulnerability was defined as the ability to induce sustained repetitive atrial responses during programmed electrical stimulation and was assessed by extrastimulus and burst-pacing techniques. Effective refractory period (ERP) was measured at two endocardial sites in the right atrium. Sustained AF was defined as AF > or = 15 minutes. In animals with sustained AF, 10 quadripolar epicardial electrodes were surgically attached to the right and left atria. The local atrial fibrillatory cycle length (AFCL) was measured in a 20-second window, and the mean AFCL was measured at each site. Marked biatrial enlargement was documented; after 6 weeks of continuous rapid atrial pacing, the left atrium was 7.8 +/- 1 cm2 at baseline versus 11.3 +/- 1 cm2 after pacing, and the right atrium was 4.3 +/- 0.7 cm2 at baseline versus 7.2 +/- 1.3 cm2 after pacing. An increase in atrial area of at least 40% was necessary to induce sustained AF and was strongly correlated with the inducibility of AF (r = .87). Electron microscopy of atrial tissue demonstrated structural changes that were characterized by an increase in mitochondrial size and number and by disruption of the sarcoplasmic reticulum. After 6 weeks of continuous rapid atrial pacing, sustained AF was induced in 18 dogs (82%) and nonsustained AF was induced in 2 dogs (9%). AF occurred spontaneously in 4 dogs (18%). Right atrial ERP, measured at cycle lengths of 400 and 300 milliseconds at baseline, was significantly shortened after pacing, from 150 +/- 8 to 127 +/- 10 milliseconds and from 147 +/- 11 to 123 +/- 12 milliseconds, respectively (P < .001). This finding was highly predictive of inducibility of AF (90%). Increased atrial area (40%) and ERP shortening were highly predictive for the induction of sustained AF (88%). Local epicardial ERP correlated well with local AFCL (R2 = .93). Mean AFCL was significantly shorter in the left atrium (81 +/- 8 milliseconds) compared with the right atrium 94 +/- 9 milliseconds (P < .05). An area in the posterior left atrium was consistently found to have a shorter AFCL (74 +/- 5 milliseconds). Cryoablation of this area was attempted in 11 dogs. In 9 dogs (82%; mean, 9.0 +/- 4.0; range, 5 to 14), AF was terminated and no longer induced after serial cryoablation. CONCLUSIONS Sustained AF was readily inducible in most dogs (82%) after rapid atrial pacing. This model was consistently associated with biatrial myopathy and marked changes in atrial vulnerability. An area in the posterior left atrium was uniformly shown to have the shortest AFCL. The results of restoration of sinus rhythm and prevention of inducibility of AF after cryoablation of this area of the left atrium suggest that this area may be critical in the maintenance of AF in this model.

Role of the Posterior Left Atrium and Pulmonary Veins in Human Lone Atrial Fibrillation Electrophysiological and Pathological Data From Patients Undergoing Atrial Fibrillation Surgery

Background—Surgery can eliminate atrial fibrillation (AF), but data confirming the rationale for specific lesion sets are lacking. We used postoperative electrophysiological studies to test the rationale and effects of operative pulmonary venous isolation. Methods and Results—Fourteen patients undergoing surgical pulmonary venous isolation for drug-refractory lone AF were studied. Successful isolation was confirmed postoperatively in 13 of 14 patients. Spontaneous sustained AF was recorded from the isolated pulmonary venous region (PVR) in 4 and was induced by extrastimulus testing in another. The remaining atrial region (RAR) was in sinus rhythm in 13 patients and nonsustained AF in 1. Atrial extrastimulus testing and burst pacing in the RAR failed to induce sustained AF. In follow-up, 1 patient developed paroxysmal AF, and electrical continuity between the PVR and RAR was confirmed. Isolation was achieved with radiofrequency ablation with no further AF. Another patient developed typical atrial flutter that required ablation. AF has not recurred in any patient at 25.1±11.9 months (range, 6 to 56 months) after surgery. Atrial histopathology was consistent with tachycardia-induced changes. Conclusions—Total electrical isolation of the PVR controlled AF with excellent clinical outcome and appeared necessary for success. The isolated PVR can sustain spontaneous or induced AF, whereas the considerably larger RAR does not. These data provide a sound rationale for PVR in eliminating AF.

A permanent transvenous lead system for an implantable pacemaker cardioverter-defibrillator. Nonthoracotomy approach to implantation.

A transvenous lead system for implantable defibrillators would obviate a surgical thoracotomy and reduce the morbidity and mortality associated with implantation. We evaluated the clinical performance of a new nonthoracotomy lead system that included a defibrillation lead in the coronary sinus. At the time of defibrillator implantation, transvenous defibrillation leads were inserted percutaneously through the left subclavian vein into the right ventricular apex (RVA), superior vena cava (SVC), and distal coronary sinus (CS) under fluoroscopic guidance. A subcutaneous patch electrode (SQ) was also available if required. The first single- or dual-pathway electrode configuration that successfully terminated three of four ventricular fibrillation episodes using 18 J or less was implanted. Eleven men and three women aged 39-77 years (60.0 +/- 10.1 years) with left ventricular ejection fraction ranging from 16% to 63% (33.4 +/- 13.1%) were evaluated. Nine presented with ventricular tachycardia, three had ventricular fibrillation, and two had both. A totally transvenous lead system (RVA/CS/SVC) was implanted in seven patients (50%) with a mean defibrillation threshold of 15.6 +/- 2.9 J (10-18 J). Four patients received a partial transvenous lead system (RVA/CS/SQ). An effective nonthoracotomy lead system was not found in three patients; they received epicardial electrodes. After cumulative follow-up of 73 patient-months, nine patients remain alive and free of problems related to the implanted nonthoracotomy leads. One patient died of respiratory failure 3 months after defibrillator implant, and the leads from another patient were removed at 9 months because of bacterial infection. A transvenous lead system that includes a defibrillation lead in the coronary sinus is a safe, reliable, and, at least in the short term, effective nonthoracotomy approach for automatic defibrillator implantation.

The coronary sinus diverticulum: a pathologic entity associated with the Wolff-Parkinson-White syndrome.

Of 65 patients with posterior septal accessory pathways, 6 were found intraoperatively to have a previously unrecognized pathologic entity: a coronary sinus (CS) diverticulum in the posterior septal region. The CS diverticulum is a venous pouch within the left ventricular wall, with a neck opening into the CS. The pouch, 2 to 5 cm in diameter, has a deep wall corresponding to the left ventricular wall, with venous channel openings and a thin superficial wall made of myocardium. The CS diverticulum neck is 5 to 10-mm wide, opens into the CS and is proximal to the midcardiac vein. Using an epicardial approach during normothermic bypass, the neck of the CS diverticulum was identified, separated from the left ventricle and then closed. Accessory pathway conduction disappeared only after separation of the CS diverticulum neck. The accessory pathway is intimately related to the diverticulum. The latter is a bridge between the left ventricle and the right or left atrium. The accessory pathways associated with CS diverticula had short anterograde refractory periods and were associated with potentially malignant arrhythmias. An epicardial operative approach with division of the neck of the diverticulum is recommended when surgery is indicated.

The Pathology of Drug Resistant Lone Atrial Fibrillation in Eleven Surgically Treated Patients

Although atrial fibrillation (AF) is a common disease, there is relatively few publications on its associated pathology. Autopsy studies[1,2,3,4,5] report the lesions observed in a large variety of structural heart and systemic diseases causing multiple clinical presentations of AF (acute or chronic, permanent or paroxysmal). Others studies focuses on AF in rheumatic disease using autopsy examination[6] or biopsy studies[7,8] done during surgery for rheumatic mitral valve lesions. More recent works[9,10,11] address the problem of “lone” atrial fibrillation occurring in the absence of structural Heart Disease or of metabolic diseases. The pathological findings suggest that cardiomyopathic changes in the atria could be the anatomical substrate for the fibrillation. We report pathological findings in eleven cases of long-standing, drug-resistant AFs treated surgically with the Corridor operation[12–15].

Non-HLA-linked hemochromatosis in a Chinese woman

SummaryA 55-year-old Chinese woman is described with severe iron overload similar in degree and distribution to that seen in hereditary hemochromatosis in the Causasian population. Autopsy findings confirmed severe iron overload in the liver, pancreases, skin, heart, and endocrine organs. Hepatic iron concentration was 482 μmol/g with a hepatic iron index of 8.8. There was no history of thalassemia, transfusions, or alcohol abuse. Pedigree analysis revealed two HLA identical brothers that had no clinical or biochemical evidence of iron overload. This case is an unsual example of severe iron overload in a non-Causasian kindred and may represent a non-HLA-linked form of iron overload.

Anatomical pitfalls during encircling cryoablation of the left atrium for atrial fibrillation therapy in the pig

We previously published encircling endocardial cryo-isolation of the pulmonary vein (PV) region. This study documented mechanisms of isolation failure using CARTO® mapping. Cryo-isolation used a modified Surgifrost® introduced via a Universal Cardiac Introducer® on the left atrial appendage. Of five pigs, two had incomplete isolation and repeat mapping: Activation was over Bachmann’s bundle (BB) in one and the coronary sinus (CS) in the other. Repeat cryoablation failed to eliminate gaps. Histologically, the BB gap had nonlesioned sub-epicardial fibres and thick fat covering the cryolesioned BB: fat protecting the epicardium from cryoablation. The inferior gap had a large CS, and a thick myocardium bridging the isthmus: myocardial thickness and CS thermal sink preventing transmural cryolesions. CARTO® mapping localized gaps. Although the CS is known to cause failure, its protective mechanism is not well documented. The BB gap is novel. These findings have important clinical implications for isolation of the PV region.

Anatomically guided surgery to the AV node. AV nodal skeletonization: experience in 46 patients with AV nodal reentrant tachycardia.

We report our combined experience with operative therapy for atrioventricular nodal tachycardia using an anatomically guided procedure. The operative rationale was to dissect the AV node with the intent of modifying perinodal tissues (skeletonization). The anterior septal and posterior septal regions were initially approached epicardially to facilitate endocardial dissection. Under normothermic cardiopulmonary bypass, the right atrial septum was mobilized and the intermediate AV node was exposed anterior to the tendon of Todaro. Ablation of concomitant accessory pathways was done prior to AV nodal skeletonization. Forty-six patients aged 9-71 years (mean 36) were operated upon. Five patients had accessory pathways in addition to AV nodal reentry. At electro-physiological study prior to discharge, no patient had an AV block although anterograde and retrograde Wenckebach cycle lengths were significantly prolonged. Ten patients had a retrograde AV block. The 46 patients were free of arrhythmia and not taking antiarrhythmic medication after a follow-up of 1-45 months (mean 17). Three patients had a recurrence of the tachycardia 10 days, 2 months and 7 months post-operatively, respectively. All patients had a subsequently successful reoperation.

Atrial flutter: lessons from surgical interventions (musing on atrial flutter mechanism).

We report our experience with seven patients who underwent direct surgical ablation of problematic common flutter. Intraoperative mapping was obtained in four patients. Surgical techniques varied over time. A circular incision of the right atrium was performed in the first patient. Two patients had epicardial cryoablation of the isthmus between the inferior vena cava and the tricuspid valve annulus. Four patients had extensive endocardial cryoablation of the isthmus. There were no immediate postoperative complications. One patient had atrial fibrillation 2 months postoperatively and underwent a corridor operation 1 year later. The other six patients are free of arrhythmias without antiarrhythmic drugs. Surgical ablation confirmed that the common form of atrial flutter is associated with a right atrial macroreentrant circuit. One of our intraoperative endocardial maps suggested that variant reentrant circuits can be associated with variant forms of flutter.

Operation for the Wolff-Parkinson-White syndrome in the Catheter ablation era

Catheter ablation has greatly altered surgical referral patterns for the Wolff-Parkinson-White syndrome. We describe 51 patients (aged 9 to 63 years; 35 male, 16 female) referred for operation from our institution and elsewhere between August 1990 and August 1993, coincident with the inception of our ablation program. During the same period, 375 patients with problematic Wolff-Parkinson-White syndrome had ablation procedures. Operation was the initial therapy in 26 patients, due to physician preference in 23 and the need for a concomitant cardiac operation in 3. Operation was related to ablation failure in 22 patients and was urgent in 3 patients. Previous ablation was not associated with added surgical difficulties, and all pathways were ablated intraoperatively on the first attempt using the epicardial approach. Visible epicardial lesions were observed in 8 patients at the site of the accessory pathway. In 2 patients, the lesions were remote to the atrioventricular ring. There was a striking significant increase in proportion of right free wall pathways after attempted ablation (27% versus 8%) as compared with the preablation era. We conclude that previous attempted ablation does not impair efficacy and safety of operative therapy. Operation remains a useful alternative for ablation failure and as a back-up for acute complications.