Subramaniam C. Krishnan

Low energy conversion of atrial fibrillation in the sheep

OBJECTIVES In this study, the feasibility, efficacy and safety of low energy internal atrial cardioversion were investigated in a sheep model. The relation between the level of energy used for atrial defibrillation and the probability of successful cardioversion was examined. BACKGROUND Atrial fibrillation is a common clinical arrhythmia that frequently recurs after termination with high energy external cardioversion. In some patients with drug-refractory and poorly tolerated atrial fibrillation, an automatic implantable cardioverter may prove useful by providing rapid restoration of sinus rhythm. METHODS In 16 pentobarbital-anesthetized sheep, a right atrial spring electrode was implanted percutaneously and a left thoracic cutaneous patch electrode was placed on the thorax. Sustained atrial fibrillation was induced by rapid atrial pacing and terminated by biphasic cathodal shocks synchronized to the R wave of the surface electrocardiogram (ECG). RESULTS During 768 defibrillation attempts in 16 sheep, the percent of successful cardioversion attempts increased in a dose-response manner, reaching a plateau at the average energy level of 5 J. With greater than or equal to 1.5 and greater than or equal to 2.5 J energy levels, cardioversion was achieved, respectively, in greater than 50% and greater than 80% of attempts. Ventricular fibrillation occurred in 18 (2.4%) of 768 cardioversion attempts; in all 18 cases, the shock was poorly synchronized with the ECG R wave. CONCLUSIONS Low energy cardioversion of atrial fibrillation to sinus rhythm is feasible with use of a right atrial spring/cutaneous patch electrode configuration. The percent of successful cardioversion attempts depends on the level of energy output, and there is a risk of ventricular fibrillation if cardioversion is poorly synchronized with ventricular depolarization.

Septal Pouch in the Left Atrium: A New Anatomical Entity With Potential for Embolic Complications

OBJECTIVES The purpose of this study was to develop a better understanding of the pathophysiology of the condition, we studied the patterns by which the septum primum (SP) and septum secundum (SS) fuse. BACKGROUND A patent foramen ovale (PFO) is a communication across the interatrial septum between a nonadherent SP and SS and is considered to be a risk factor for serious clinical syndromes. METHODS We examined the interatrial septum in 94 randomly selected autopsied hearts, with a focus on the SP and SS and the patterns by which the 2 structures fuse. RESULTS Of the 94 specimens that were suitable for analysis, 26 (27.66%) had a PFO. Of the remaining 68 hearts, complete fusion of the SP and SS along the entire zone of overlap was seen in 27 (28.7%) hearts. In the remaining 41 hearts (60.29%), a PFO was absent, but incomplete fusion of the SP and SS was seen. Of 41 hearts, 37 (90%) had a septal pouch that opened into the left atrial (LA) cavity. Four hearts (10%) had a pouch accessible from the right atrium. Hearts with left-sided pouches tended to be younger (50 +/- 18 years of age) than hearts where there was complete fusion (age 63 +/- 23 years) (p = 0.06). CONCLUSIONS Our data suggest that when a foramen ovale closes spontaneously, the SP and SS fuse initially at the caudal limit of the zone of overlap of the 2 structures. This incomplete fusion results in a pouch that, in the majority of instances, communicates with the LA cavity.

Right Atrial Cavotricuspid Isthmus: Anatomic Characterization with Multi–Detector Row CT

PURPOSE To retrospectively evaluate the anatomic characteristics of the right atrial cavotricuspid isthmus (CTI) by using 64-section multi-detector row computed tomography (CT). MATERIALS AND METHODS Institutional review board approval and waiver of informed consent were obtained for this HIPAA-compliant study. The anatomic region of the CTI was evaluated in 201 patients (116 men and 85 women; mean age, 58 years +/- 11 [standard deviation]) who underwent coronary multi-detector row CT. CTI length was assessed along three parallel isthmic levels (paraseptal, central, and inferolateral). Central isthmus depth was classified as straight (3 mm), concave (>3 to </=5 mm), or pouchlike (>5 mm). Measurements were obtained during three cardiac phases: midsystole, middiastole, and atrial contraction. Subthebesian recess dimensions and eustachian ridge width were measured. Distances from the atrioventricular node artery to the coronary sinus, from the right coronary artery (RCA) to the inferior vena cava, and from the RCA to the tricuspid valve annulus were measured. Software was used for statistical analysis. RESULTS At middiastole, the paraseptal isthmus (mean length, 20 mm +/- 3.5; range, 11-34 mm) was significantly shorter than the central isthmus (24 mm +/- 4.3; range, 12-43 mm) and the central isthmus was shorter than the inferolateral isthmus (27 mm +/- 4.8; range, 13-45 mm) (P < .001). The longest CTI measurements were obtained during midsystole, and the shortest were obtained during atrial contraction (40% variation per cardiac cycle). Isthmus contraction occurred primarily in the posterior segment of the central isthmus (RCA to inferior vena cava distance). At middiastole, the central isthmus was straight in 8% of patients, concave in 47% of patients, and pouchlike (>5 mm) in 45% of patients. The mean depth was greater during atrial contraction (6.3 mm +/- 2.1) than in midsystole (4.3 mm +/- 1.5) and middiastole (5.1 mm +/- 1.8) (32% variation during cardiac cycle). A subthebesian recess greater than 5 mm deep was identified in 45% of patients. In 24% of patients, a thick eustachian ridge greater than 4 mm was seen. The atrioventricular node artery passed close to the coronary sinus wall (mean distance, 2.1 mm +/- 0.7; range, 1-6 mm). CONCLUSION Cardiac multi-detector row CT provides extensive information regarding the size and morphology of the CTI and its related structures.

Bachmann Bundle and Its Arterial Supply: Imaging with Multidetector CT—Implications for Interatrial Conduction Abnormalities and Arrhythmias

PURPOSE To retrospectively investigate anatomy of Bachmann Bundle (BB) and its vascular supply at 64-section multidetector computed tomography (CT) in healthy patients and patients with abnormalities. MATERIALS AND METHODS The institutional review board approved this HIPAA-compliant study and waived informed consent. Clinical histories, electrocardiograms (ECGs), and coronary 64-section multidetector CT angiograms in 317 patients were reviewed (healthy group, 164; group with abnormalities, 153). Among patients with abnormalities, 68 had atrial fibrillation (AF) or interatrial conduction block (IAB) (P wave duration, >or=120 msec), 46 had severe coronary artery disease (CAD) (>or=70% stenosis of coronary artery giving rise to sinuatrial node [SAN] artery), and 39 had severe CAD and an abnormal ECG (AF or IAB). Length, anteroposterior and superoinferior diameters, attenuation, and vascular supply of BB were studied. Student t test for continuous variables and contingency tables for categorical variables were used. RESULTS BB was visualized, to greater degree, in the healthy group (90.2% vs 73.9% for group with abnormalities, P < .001). Visualization of BB was similar among subgroups with abnormalities: 71.7% in patients with severe CAD, 73.5% in patients with abnormal ECG, and 76.9% in patients with severe CAD and abnormal ECG. BB measurements were similar for both groups. Patients with nonvisualized BB displayed lower overall mean attenuation in the region, with -30.6 HU +/- 33.4 (standard deviation), but mean attenuation in healthy patients was 51.3 HU +/- 59.9 (P < .001). This finding suggests fatty infiltration. BB and BB region were mainly supplied by the right SAN artery (55.5%), followed by the left SAN artery (39.6%) and both SAN arteries (4.9%). In the group with abnormalities, there was a significant difference for SAN artery nonvisualization between those with and without identifiable BB (P = .001). CONCLUSION BB and its vascular supply can easily be demarcated on cardiac CT images. BB was visualized less in patients with severe CAD and abnormal ECG, a finding that suggests that disease of BB fibers may play a role in development of atrial arrhythmias.

Noncoronary applications of cardiac multidetector row computed tomography.

Multidetector row computed tomography (MDCT) has a high diagnostic accuracy to evaluate coronary artery stenoses. Additionally, the 4-dimensional aspect of cardiac MDCT allows a comprehensive evaluation of cardiac structure and function. Left ventricular volumes and systolic function can be accurately assessed with MDCT, and imaging of myocardial infarction is a promising application of cardiac MDCT. In addition, MDCT may provide anatomical visualization of heart valves. Also, evaluation of anatomy of the pulmonary veins and cardiac venous system render MDCT a valuable tool for the cardiologist performing electrophysiological procedures. In this article, the role of MDCT in the noninvasive evaluation of cardiac structure and function is discussed. An overview of the wide range of noncoronary applications of cardiac MDCT is provided, focusing on the assessment of left ventricular function, valvular heart disease, and cardiac venous anatomy.

Septal thrombus in the left atrium: is the left atrial septal pouch the culprit?

cardioembolic strokes are responsible for more than 20% of all ischemic strokes. The examination of atrial sources of cardioembolic strokes has focused almost exclusively on the left atrial appendage (LAA) and the pathophysiology of thrombus formation at this site is well understood. However,

Posterior Interatrial Muscular Connection between the Coronary Sinus and Left Atrium: Anatomic and Functional Study of the Coronary Sinus with Multidetector CT

PURPOSE To demonstrate coronary sinus-left atrium connections and evaluate coronary sinus function and anatomy in detail by using multidetector computed tomography (CT). MATERIALS AND METHODS In this institutional review board-approved retrospective study, the authors evaluated coronary CT angiograms obtained in 65 patients with normal sinus rhythm (normal group) and seven with atrial fibrillation at CT (atrial fibrillation group). Coronary sinus-right atrium muscle continuity was indirectly evaluated by measuring the length of the coronary sinus contraction during atrial systole. The length, number, and extent of coronary sinus-left atrium connections were recorded. The accuracy of CT was validated by comparing microscopic images of autopsied hearts with corresponding CT images. Comparisons were performed by using Student t tests for continuous variables. P ≤ .05 was considered indicative of a statistically significant difference. RESULTS In the normal group, coronary sinus contraction was seen in 60 of the 65 patients (92%, mean length ± standard deviation, 25.7 mm ± 8.0). The coronary sinus narrowed 26% from middiastole to atrial systole (P < .0001). Coronary sinus-left atrium muscle connections were seen in 58 of the 65 patients (89%). A single connection was seen in 43 of the 65 patients (66%), with a mean length of 21.0 mm ± 14.0 within 12.0 mm ± 11.0 of the coronary sinus ostium. In 10 of the 43 patients (26%) with single connections, the connection extended to the coronary sinus ostium. In 10 of the 65 patients (15%), the entire coronary sinus was attached to the left atrial wall. Fifteen patients (23%) had two connections; distal connections measured 9 mm ± 2.4 in length within 2.2 mm ± 3.8 of the coronary sinus ostium, and proximal connections measured 15.4 mm ± 10.0 in length within 24.0 mm ± 8.0 of the coronary sinus ostium. In seven patients (11%), no coronary sinus-left atrium connection was seen; however, all showed a coronary sinus constriction during atrial systole, indicating that coronary sinus-right atrium muscle continuity is likely the primary cause for coronary sinus contractions. In the atrial fibrillation group, no coronary sinus contraction was seen. All images in the atrial fibrillation group showed a coronary sinus-left atrium connection, which was single in five patients and double in two. The area of the coronary sinus during diastole was larger in the atrial fibrillation group than in the normal group (114 mm(2) ± 37 vs 77 mm(2) ± 40, respectively; P = .02). CONCLUSION CT can provide excellent information about coronary sinus function and coronary sinus-left atrium muscle connections.

Reproducible Induction of "Atypical" Torsades de Pointes by Programmed Electrical Stimulation:.: A Novel Form of Sotalol-Induced Proarrhythmia?

Sotalol‐Induced Polymorphic VT. We present a patient with sotalol‐induced polymorphic ventricular tachycardia that was seen only with programmed ventricular stimulation. Electrophysiologic studies performed prior to initiation of sotalol therapy revealed inducible monomorphic ventricular tachycardia. Possible underlying electrophysiologic mechanisms are discussed.

Avoiding oesophageal injury during cardiac ablation: insights gained from mediastinal anatomy

Aims This study investigates the lateral displacement of the oesophagus at the level of the left atrium (LA) in 11 cadavers. Methods and results The study was conducted using human cadavers. An endotracheal stylet probe was inserted into the eosphagus. The pericardium overlying the posterior LA was fixed in place. The lateral movement of the oesophagus from side to side was recorded. The initial study method had the stylet probe extending to the gastroesophageal (GE) junction. A revised protocol had the distal end of the endotracheal stylet probe ∼4 cm cranial to the GE junction. In six cadavers using the initial study method, the oesophagus was displaced a mean of 1.8 ± 0.35 cm to the right and 2 ± 0.48 cm to the left. In five cadavers, using the revised method, the oesophagus was displaced by a mean of 2.26 ± 0.27 cm to the right and 2.3 ± 0.66 cm to the left. Conclusion Mediastinal anatomy, specifically the presence of a loose connective tissue that attaches the oesophagus to the parietal pericardium overlying the posterior LA wall will allow for a lateral displacement of the oesophagus. This should decrease or eliminate the likelihood of thermal injury of the oesophagus. Using an endotracheal stylet, we investigated the lateral displacement of the oesophagus in 11 human cadavers. In six with the stylet extending to the GE junction, the oesophagus was displaced a mean of 3.8 cm. In five, with stylet 4 cm cranial to the junction, the displacement was 4.56 cm.

Cardiac Resynchronization Therapy Devices Guided by Imaging Technology

IN PATIENTS WITH CONGESTIVE HEART FAILURE DUE TO SYSTOLIC DYSFUNCTION WHERE ELECTRICAL AND MECHANICAL DYSSYNCHRONY IS PRESENT, cardiac resynchronization therapy has been shown to make patients “feel better” and “live longer” ([1][1]). In these procedures, left ventricular pacing is