Luis R. Scott

Arrhythmogenic Substrate of the Pulmonary Veins Assessed by High-Resolution Optical Mapping

Background—It has recently been recognized that atrial fibrillation can originate from focal sources in the pulmonary veins (PVs). However, the mechanisms of focal atrial fibrillation have not been well characterized. We assessed the electrophysiological characteristics of the PVs using high-resolution optical mapping. Methods and Results—Coronary-perfused, isolated whole-atrial preparations from 33 normal dogs were studied. Programmed electrical stimulation was performed, and a 4-cm2 area of the PV underwent optical mapping of transmembrane voltage to obtain 256 simultaneous action potentials. Marked conduction slowing was seen at the proximal PV, compared with the rest of the vein, on both the epicardial (31.3±4.47 versus 90.2±20.7 cm/s, P =0.001) and endocardial (45.8±6.90 versus 67.6±10.4 cm/s, P =0.012) aspects. Pronounced repolarization heterogeneity was also noted, with action potential duration at 80% repolarization being longest at the PV endocardium. Nonsustained reentrant beats were induced with single extrastimuli, and the complete reentrant loop was visualized (cycle length, 155±30.3 ms); reentrant activity could be sustained with isoproterenol. Sustained focal discharge (cycle length, 330 to 1100 ms) was seen from the endocardial surface in the presence of isoproterenol; each focus was localized near the venous ostium. Conclusions—The normal PV seems to have the necessary substrate to support reentry as well as focal activity. Although reentry occurred more distally in the vein, focal activity seemed to occur more proximally.

Tissue structure and connexin expression of canine pulmonary veins

OBJECTIVE Rapid electrical activity in pulmonary veins (PVs) has been proposed as a mechanism for focal atrial fibrillation. The way in which the myocardial sleeve inside PVs can form a substrate for focal activity is not well understood. Therefore, we have studied tissue structure and connexin distribution at the veno-atrial transition in the dog. METHODS In adult mongrel dogs, the anatomy of the PV area was studied. Tissue structure in individual veins was assessed in formalin fixed sections using Massons Trichrome staining. Gap junction protein distribution was examined using antibodies against connexin40 (Cx40) and connexin43 (Cx43). The ultrastructure of myocytes in myocardial sleeves was studied using electron microscopy. RESULTS Individual PVs in the dog had a gross morphology similar to that observed in the human, with myocardial sleeves extending into the veins for 4-20 mm. In all veins examined, myocytes in myocardial sleeves had a normal atrial morphology and anti-desmin staining pattern. Cx43 was expressed throughout the sleeve at levels comparable to normal atrial myocardium. By contrast, Cx40 expression was lower in myocardial sleeves than in the rest of the left atrium. Myocytes in the sleeve, which were ultrastructurally similar to normal atrial myocytes, were predominantly organized in a circumferential pattern. CONCLUSIONS PVs in the dog and various canine models of heart disease will be a suitable model for (patho)physiology of the veno-atrial transition. Myocytes in myocardial sleeves are similar to normal atrial myocytes. The circumferential orientation of these myocytes may provide a substrate for rapid circular reentry.

Nontraditional Surgical Approaches for Implantation of Pacemaker and Cardioverter Defibrillator Systems in Patients With Limited Venous Access

BACKGROUND Indications for placement of implantable cardioverter-defibrillators (ICD) and pacemakers have expanded, and traditional transvenous implantation may not be feasible in patients with aberrant anatomy or venous obstruction. In these settings, successful lead placement has required innovative surgical approaches. A case series of successful placement of these systems in challenging patients is presented. METHODS A 2-year retrospective study of patients undergoing placement of minimally invasive epicardial pacing leads or ICD coils was performed. RESULTS Eleven patients underwent minimally invasive surgical placement of leads or coils. None were converted to open sternotomy. One required extension to minianterior thoracotomy. Causes of intravenous placement failure included aberrant anatomy with failure to access coronary sinus in 9 and venous occlusion in 2. Four patients had previous operations through a median sternotomy. Procedures included left video-assisted thoracoscopic (VATS) placement of a left ventricular epicardial lead in 8, left VATS conversion to minianterior thoracotomy left ventricular epicardial lead placement in 1, left VATS placement of ICD coil in 1, subxiphoid placement of a right ventricular epicardial lead in 1, subxiphoid ICD coil in 2, and subcutaneous ICD coil placement in 3. Mean hospitalization was 4.6 days. Postoperative hypotension and pulmonary edema occurred in 27% of patients. No patients died. CONCLUSIONS Conventional transvenous lead implantation may be difficult or impossible in some patients with aberrant or occluded venous access. Novel surgical approaches with the use of minimally invasive procedures can establish optimally functional pacing and ICD systems without sternotomy and low associated morbidity.

Atrioventricular Nodal Reentrant Tachycardia Requiring Ablation on the Mitral Annulus

Mitral Ablation for AV Nodal Reentry. We report a case of initial transient success during ablation for typical AV nodal reentrant tachycardia utilizing traditional right‐sided approaches, followed by recurrence of the same tachycardia and an ultimately successful ablation on the posteromedial mitral annulus.

Radiotherapy-induced pacemaker and implantable cardioverter defibrillator malfunction.

It is well known that ionizing radiation can interfere with circuits in permanent pacemakers and implantable cardioverter defibrillators. Contemporary implantable cardiac devices use complementary metal-oxide silicon in combination with other very sensitive transistors. These sensitive components are especially susceptible to electromagnetic and ionizing radiation, which can potentially cause permanent damage. Electromagnetic interference is, in general, a transient phenomenon. Radiologic imaging tests have been implicated in rare cases of implantable device dysfunction and these events have been mostly transient. The American Association of Physicists in Medicine last published recommendations regarding irradiation of pacemakers in 1994. This publication is outdated and may not be pertinent for the current technology used both in the field of artificial cardiac pacing and defibrillation and in the field of radiation oncology. Updated guidelines are definitely needed.

T-wave oversensing and inappropriate shocks: a case report

A 27-year-old male with congenital long QT syndrome, SCN5A mutation experienced recurrent inappropriate exercise-related implantable cardioverter defibrillator (ICD) shocks. This device showed T-wave oversensing with double, which lead to these device discharges. Dynamic T-wave oversensing was reproducibly provoked at exercise treadmill testing and was confirmed as the mechanism leading to double counting. The insertion of a new pacing and sensing lead with increased R-wave amplitude did not solve the problem. Exchanging the existing ICD generator with one capable of automatic sensitivity control (Biotronik, Lexos DR, Biotronik, Berlin, Germany) completely eliminated T-wave oversensing and inappropriate shocks.

Use of an Insertable Loop Recorder in a Myotonic Dystrophy Patient

Loop Recorder Use in Myotonic Dystrophy. The case of a 66‐year‐old woman with myotonic dystrophy is presented. This patient underwent implantation of an insertable loop recorder as a participant in a clinical trial. At 1‐month follow‐up, interrogation of the insertable loop recorder revealed multiple episodes of wide complex tachycardia. She underwent electrophysiologic study, which revealed moderate His‐Purkinje disease, focal atrial tachycardia, monomorphic ventricular tachycardia, and ventricular fibrillation. Successful radiofrequency ablation of the focal atrial tachycardia and implantation of a dual‐chamber implantable cardioverter defibrillator was performed.

Focal mechanism of ventricular tachycardia in coronary artery disease

BACKGROUND Re-entry is the most common mechanism of sustained monomorphic ventricular tachycardia (VT) in patients with coronary artery disease and prior myocardial infarction (MI). OBJECTIVE This study sought to report the electrophysiological properties of a series of patients with prior MI who underwent radiofrequency ablation (RFA) for VT originating instead from a focal source. METHODS The electrophysiological properties of 46 patients with prior MI (male 89%, age 64.8 +/- 10.2 years) who underwent RFA for sustained VT were studied. A total of 101 VTs were induced (92 [91%] macro-re-entrant VT and 9 [9%] focal VT). RESULTS One patient had adenosine-sensitive idiopathic focal VT. The focal VT group had a significantly shorter pre-systolic interval (electrogram to QRS) during VT compared with the macro-re-entrant VT group (36 +/- 17 ms vs. 117 +/- 67 ms, P = .001). The successful ablation sites in the focal VT group also had a significantly lower ratio (in percentage) of electrogram-QRS interval to diastolic interval (VT cycle length - QRS duration) during VT (14 +/- 8%) as compared with macro-re-entrant VTs (48 +/- 30%, P <.001). Focal VTs demonstrated an apparent point source of endocardial activation and could not be entrained, whereas 77% of macro-re-entrant VTs were entrained. Successful ablation sites for focal VT (success rate 100%) were predominantly in the basal half of the left ventricle (75%), whereas only 60% of macro-re-entrant VTs (success rate 90.7%) were basal (P = .01). However, the procedure time, VT cycle length, number of RFA applications required for success, and acute success results were not significantly different in these 2 groups. CONCLUSION A focal mechanism is present in up to 9% of VTs in patients with CAD and prior MI that are induced during electrophysiology study for RF ablation. Mechanistic distinction from more typical macro-re-entrant VT in this population is important because ablation site characteristics are very different.

Pneumopericardium and pneumothorax contralateral to venous access site after permanent pacemaker implantation

A 77-year-old female underwent implantation of a left-sided dual chamber permanent pacemaker for symptomatic bradycardia with active fixation leads. Eight hours after the procedure, the patient complained of shortness of breath and was found to have a 30% right pneumothorax on chest X-ray. Immediately, a chest tube was inserted, promptly relieving the symptoms. A CT scan of the chest revealed extrusion of the helix of the screw-in atrial lead, through the wall of the right atrial appendage. The helix was abutting a bulla in the right lung, the likely cause for pneumothorax and pneumopericardium. The atrial lead was explanted without incident.

Typical Atrial Flutter as a Risk Factor for the Development of Atrial Fibrillation in Patients Without Otherwise Demonstrable Atrial Tachyarrhythmias

OBJECTIVE To investigate the incidence of atrial fibrillation after successful radiofrequency ablation for typical atrial flutter (AFL) and to compare its incidence with that of a reference population from the Framingham Heart Study to determine whether atrial flutter is an independent predictor for development of atrial fibrillation. PATIENTS AND METHODS Medical records of 234 patients who underwent radiofrequency ablation for AFL between January 1, 2002, and June 30, 2006, were reviewed. Patients were excluded if they had a history of atrial fibrillation or sustained atrial arrhythmia other than AFL or if they had atrial tachyarrhythmias other than AFL that could be induced during electrophysiology study (133 total patients excluded). The remaining 101 patients who underwent successful radiofrequency ablation for AFL were monitored for new-onset atrial fibrillation. RESULTS During the mean+/-SD follow-up period of 574+/-315 days, atrial fibrillation developed in 13 (12.9%) of 101 patients. Atrial fibrillation developed in 12 of these patients within 6 months of ablation. The cumulative event-free rates (95% confidence intervals) were 97% (94%-100%) at 1 month, 91% (87%-97%) at 3 months, and 86% (81%-94%) at 6 months. Compared with the general population, patients aged 50 to 79 years who had ablation had a significantly higher incidence of atrial fibrillation (50-59 years, P=.01; 60-69 years, P=.001; 70-79 years, P=.007). CONCLUSION Our finding of atrial fibrillation in 12.9% of patients whose atrial flutter was successfully eradicated suggests that patients with atrial flutter are at increased risk of developing atrial fibrillation, especially within the first 6 months after ablation.