J. Michael Mangrum

Electrical, Morphological, and Ultrastructural Remodeling and Reverse Remodeling in a Canine Model of Chronic Atrial Fibrillation

BackgroundIn patients with recurrent persistent atrial fibrillation (AF), vulnerability to AF persists indefinitely despite presumed completion of reverse electrical remodeling within days of return to normal sinus rhythm. Atrial electrical and anatomic remodeling and reverse remodeling were studied in a canine model of chronic AF. Methods and ResultsChronic AF was induced in 8 dogs by creating moderate mitral regurgitation and rapidly pacing the right atrium at 640 bpm for >8 weeks. Measurements performed at baseline, after establishment of chronic AF, and then at 4 hours and again at 7 to 14 days after cardioversion to sinus rhythm included atrial effective refractory periods, AF cycle lengths, left atrial dimensions, premature atrial contraction (PAC) frequency, and atrial vulnerability to atrial extrastimuli. After establishing chronic AF, atrial effective refractory period shortening, increases in spontaneous PAC frequency, increases in left atrial size with loss of contractility, and multiple ultrastructural abnormalities were demonstrated. Complete reverse electrical remodeling and decreases in PACs were observed after 7 to 14 days of sinus rhythm, but there was no resolution of anatomic and ultrastructural abnormalities. Occurrence of spontaneous AF paralleled PAC frequency, but vulnerability to AF induction persisted (75% immediately after conversion versus 63% at 4 hours and 50% at 7 to 14 days) despite reverse electrical remodeling. ConclusionsAfter conversion from chronic AF to sinus rhythm in this canine model, electrical remodeling occurs rapidly. However, gross and ultrastructural anatomic changes persist, as does vulnerability to induced AF. Vulnerability to AF initiation 7 to 14 days after cardioversion is more dependent on persisting structural abnormalities than on electrophysiological abnormalities.

Impact of Mechanical Activation, Scar, and Electrical Timing on Cardiac Resynchronization Therapy Response and Clinical Outcomes

OBJECTIVESnUsing cardiac magnetic resonance (CMR), we sought to evaluate the relative influences of mechanical, electrical, and scar properties at the left ventricular lead position (LVLP) on cardiac resynchronization therapy (CRT) response and clinical events.nnnBACKGROUNDnCMR cine displacement encoding with stimulated echoes (DENSE) provides high-quality strain for overall dyssynchrony (circumferential uniformity ratio estimate [CURE] 0 to 1) and timing of onset of circumferential contraction at the LVLP. CMR DENSE, late gadolinium enhancement, and electrical timing together could improve upon other imaging modalities for evaluating the optimal LVLP.nnnMETHODSnPatients had complete CMR studies and echocardiography before CRT. CRT response was defined as a 15% reduction in left ventricular end-systolic volume. Electrical activation was assessed as the time from QRS onset to LVLP electrogram (QLV). Patients were then followed for clinical events.nnnRESULTSnIn 75 patients, multivariable logistic modeling accurately identified the 40 patients (53%) with CRT response (area under the curve: 0.95 [p < 0.0001]) based on CURE (odds ratio [OR]: 2.59/0.1 decrease), delayed circumferential contraction onset at LVLP (OR: 6.55), absent LVLP scar (OR: 14.9), and QLV (OR: 1.31/10 ms increase). The 33% of patients with CURE <0.70, absence of LVLP scar, and delayed LVLP contraction onset had a 100% response rate, whereas those with CURE ≥0.70 had a 0% CRT response rate and a 12-fold increased risk of death; the remaining patients had a mixed response profile.nnnCONCLUSIONSnMechanical, electrical, and scar properties at the LVLP together with CMR mechanical dyssynchrony are strongly associated with echocardiographic CRT response and clinical events after CRT. Modeling these findings holds promise for improving CRT outcomes.

Impact of the CHA2DS2-VASc score on anticoagulation recommendations for atrial fibrillation.

BACKGROUNDnThe Congestive heart failure, Hypertension, Age ≥ 75 years, Diabetes mellitus, Stroke (CHADS(2)) score is used to predict the need for oral anticoagulation for stroke prophylaxis in patients with atrial fibrillation. The Congestive heart failure, Hypertension, Age ≥ 75 years, Diabetes mellitus, Stroke, Vascular disease, Age 65-74 years, Sex category (CHA(2)DS(2)-VASc) schema has been proposed as an improvement. Our objective is to determine how adoption of the CHA(2)DS(2)-VASc score alters anticoagulation recommendations.nnnMETHODSnBetween 2004 and 2008, 1664 patients were seen at the University of Virginia Atrial Fibrillation Center. We calculated the CHADS(2) and CHA(2)DS(2)-VASc scores for each patient. The 2006 American College of Cardiology/American Heart Association/Heart Rhythm Society guidelines for atrial fibrillation management were used to determine anticoagulation recommendations based on the CHADS(2) score, and the 2010 European Society of Cardiology guidelines were used to determine anticoagulation recommendations based on the CHA(2)DS(2)-VASc score.nnnRESULTSnThe average age was 62±13 years, and 34% were women. Average CHADS(2) and CHA(2)DS(2)-VASc scores were 1.1±1.1 and 1.8±1.5, respectively (P<.0001). The CHADS(2) score classified 33% as requiring oral anticoagulation. The CHA(2)DS(2)-VASc score classified 53% as requiring oral anticoagulation. For women, 31% had a CHADS(2) score ≥ 2, but 81% had a CHA(2)DS(2)-VASc score ≥ 2 (P = .0001). Also, 32% of women with a CHADS(2) score of zero had a CHA(2)DS(2)-VASc score ≥ 2. For men, 25% had a CHADS(2) score ≥ 2, but 39% had a CHA(2)DS(2)-VASc score ≥ 2 (P<.0001).nnnCONCLUSIONnCompared with the CHADS(2) score, the CHA(2)DS(2)-VASc score more clearly defines anticoagulation recommendations. Many patients, particularly older women, are redistributed from the low- to high-risk categories.

Placement of transvenous pacemaker and ICD leads across total chronic occlusions

Objective: To establish a method of implantation for device leads across total venous occlusions.

Sonication of Explanted Cardiac Rhythm Management Devices for the Diagnosis of Pocket Infections and Asymptomatic Bacterial Colonization

Background: Correct diagnosis of the causative organism is critical for the treatment of pacemaker and defibrillator pocket infections. No gold standard for this exists, although swab and tissue cultures are frequently used. The purpose of this study was to determine the value of ultrasonication of explanted generators in the diagnosis of pocket infections and asymptomatic bacterial colonization.

Femoral vascular complications following catheter ablation of atrial fibrillation.

BackgroundFemoral vascular complications remain a significant complication of catheter ablation of atrial fibrillation as a result of peri-procedural anticoagulation protocols.ObjectiveWe investigated the effect of three different anti-coagulation regimens on the incidence of femoral vascular complications following AF ablation over a 4xa0year period.MethodsWe performed 603 catheter ablations in 539 patients from January 2004 to January 2008. All patients were started on coumadin immediately after procedure and received enoxaparin at 1xa0mg/kg 4xa0h post procedure and again 12xa0h later. Three protocols for enoxaparin, administered 12 hourly, were used post-procedure: Protocol A—1xa0mg/kg × ten doses; Protocol B—1xa0mg/kg × six doses, and Protocol C—0.5xa0mg/kg × six doses. We documented occurrence of femoral vascular complications prior to discharge and at the 1xa0month post-op visit using a prospective database. A femoral vascular complication was defined as hematoma requiring prolonged hospitalization, blood transfusion or surgical intervention.ResultsThere were 21 femoral vascular complications during the study period. The rate of complication fell from 5.7% (protocol A) to 1.6% (protocol C) (pu2009<u20090.03). We attribute the decrease in complication rate to the shorter anticoagulation protocol, as the reduction remained significant regardless of variation in catheter sizes. There were no new cerebral vascular events with the lower enoxaparin protocols.ConclusionA shorter course of post procedure anticoagulation protocol can reduce femoral complications without contributing to increased risk of thromboembolic events.

Patterns of Late Gadolinium Enhancement in Chronic Hemodialysis Patients

OBJECTIVESnThe aim of this work was to characterize patterns of late gadolinium enhancement (LGE) by cardiovascular magnetic resonance imaging in a hemodialysis population at high risk for cardiovascular events.nnnBACKGROUNDnThe prevalence and distribution of LGE and its relationship to left ventricular mass (LVM) and function in this population is unknown.nnnMETHODSnChronic hemodialysis patients at high risk for cardiovascular events-age >50 years, diabetes, or known cardiovascular disease-were enrolled prior to concerns regarding nephrogenic systemic fibrosis. Cardiovascular magnetic resonance imaging was performed in 24 patients (age, 59 +/- 11 years; dialysis, 45 +/- 38 months) and included steady-state free precession cine imaging and late gadolinium-enhanced, phase-sensitive, inversion-recovery gradient echo images. Left ventricular mass, volumes, and function were calculated and indexed to body surface area. A 16-segment analysis was performed to calculate percentage of LGE, LV wall thickness, and percentage of wall thickening.nnnRESULTSnLeft ventricular ejection fraction was 48 +/- 15%, and the LV mass index was 100 +/- 52 g/m(2). Late gadolinium enhancement was observed in 79% (19 of 24) of patients in 3 distinct patterns: infarct-related (32%, 6 of 19), diffuse (37%, 7 of 19), and focal noninfarct (37%, 7 of 19). Late gadolinium enhancement constituted 15 +/- 18% of the LVM and correlated with LVM (r = 0.44, p = 0.03). A significant, inverse relationship existed between segmental LGE and the percentage of wall thickening (p > 0.0001). Excluding infarct-related segments, as end-diastolic wall thickness increased, so did LGE (p < 0.0001), and as LGE increased, the percentage of wall thickening decreased (p = 0.0012). After 23 +/- 3 months of follow-up, 1 patient had developed nephrogenic systemic fibrosis. Seven of the patients (29%) had developed a hard cardiovascular event, 5 of 19 (26%) with LGE and 2 of 5 (40%) without.nnnCONCLUSIONSnLate gadolinium enhancement is prevalent in the hemodialysis population and its extent is related to LVM. Most cases of LGE are not infarct-related and are associated with hypertrophied, dysfunctional LV segments. Non-infarct-related LGE may signify fibrosis from LV hypertrophy and/or an infiltrative process. Further studies in this patient population will not be possible due to the risk of nephrogenic systemic fibrosis.

The prevalence of extracardiac findings by multidetector computed tomography before atrial fibrillation ablation

BACKGROUND AND OBJECTIVESnThe study was designed to determine the prevalence of extracardiac findings discovered during multidetector computed tomography (CT) (MDCT) examinations before atrial fibrillation ablation. Multidetector CT has become a valuable tool in detailing left atrial anatomy before catheter ablation. The incidence of extracardiac findings has been reported for electron beam CT calcium scoring and coronary MDCT, but no data exist for the prevalence of extracardiac findings discovered before atrial fibrillation ablation with MDCT.nnnMETHODS AND RESULTSnClinical reports from MDCT examinations before atrial fibrillation ablation and interpretations by 2 radiologists blinded to the clinical reports were reviewed for significant additional extracardiac findings and recommendations for follow-up. In 149 patients who underwent MDCT, the mean age was 55.9 +/- 11.0 years, 75% were men, and 47% had a history of smoking. Extracardiac findings were identified in 69% of patients with clinical, 90% of reader 1, and 97% of reader 2 interpretations (kappa = 0.086). Follow-up was recommended in 30% of clinical, 50% of reader 1, and 38% of reader 2 interpretations (kappa = 0.408). Pulmonary nodules were the most common additional finding and reason for suggested follow-up for all interpreters.nnnCONCLUSIONSnThe prevalence of extracardiac abnormalities detected by MDCT is considerable. Significant variability in their identification exists between interpreters, but there is good agreement about the need for further follow-up. It is important that those who interpret these examinations are adequately trained in the identification and interpretation of both cardiac and extracardiac findings.

Effectiveness of integrating delayed computed tomography angiography imaging for left atrial appendage thrombus exclusion into the care of patients undergoing ablation of atrial fibrillation

BACKGROUNDnComputed tomography angiography (CTA) can identify and rule out left atrial appendage (LAA) thrombus when delayed imaging is also performed.nnnOBJECTIVEnIn patients referred for CTA to evaluate pulmonary vein anatomy before the ablation of atrial fibrillation (AF) or left atrial flutter (LAFL), we sought to determine the effectiveness of a novel clinical protocol for integrating results of CTA delayed LAA imaging into preprocedure care.nnnMETHODSnAfter making delayed imaging of the LAA part of our routine preablation CTA protocol, we integrated early reporting of preablation CTA LAA imaging results into clinical practice as part of a formal protocol in June 2013. We then analyzed the effectiveness of this protocol by evaluating 320 AF/LAFL ablation patients with CTA imaging during the time period 2012-2014.nnnRESULTSnIn CTA patients with delayed LAA imaging, the sensitivity and negative predictive values for LAA thrombus using intracardiac echocardiography or transesophageal echocardiography (TEE) as the reference standard were both 100%. Intracardiac echocardiography during ablation confirmed the absence of thrombus in patients with negative CTA or negative TEE results. No patients with either negative CTA results or equivocal CTA results combined with negative TEE results had strokes or transient ischemic attacks. Overall, the need for TEE procedures decreased from 57.5% to 24.0% during the 3-year period because of the CTA protocol.nnnCONCLUSIONnClinical integration of CTA delayed LAA imaging into the care of patients having catheter ablation of AF or LAFL is feasible, safe, and effective. Such a protocol could be used broadly to improve patient care.

Elimination of focal atrial fibrillation with a single radiofrequency ablation: use of a basket catheter in a pulmonary vein for computerized activation sequence mapping.

Three‐Dimensional Mapping System. A focal source for atrial fibrillation (AF) may he found in the first few centimeters of the pulmonary veins. Radiofrequency (RF) ahiation may be directed at this source using activation mapping., but if the responsible atrial extrasystoles arc infrequent or difficult to map, elimination of the source may require complete electrical isolation of the vein with multiple RF lesions. A new three‐dimensional mapping system using a 64‐pole hasket catheter has been developed recently. We report the use of this system for abiation of focal AF in two patients. Mapping identified foci in the left and right superior pulmonary veins. Each focus was eliminated with a single RF ablation.