Hammill, Stephen C.

Introduction: Cardiac veins serve as substrate for arrhythmogenesis, and are especially involved as foci in atrial fibrillation. Understanding cardiac vein anatomy along with myocardial extension into these structures can improve electrophysiological mapping and electrical isolation of arrhythmogenic substrate. Accurately defining cardiac vein anatomy is critical in improving success of ablation therapy for atrial fibrillation. Methods: We performed measurements on 620 formalin-fixed autopsy hearts explanted from October 1998 to July 2003. The integrity of the thoracic veins and their cardiac connections were examined and systematic measurements of the superior and inferior vena cavae, azygous vein, vein of Marshall, coronary sinus, and pulmonary veins were performed and data were analyzed using univariate statistics. Results: We found that muscular extensions into the pulmonary veins were visible in 99% of the examined hearts, and were circumferential around the vein ostia (99.6%). Muscle extension into the SVC was found in 78% of examined hearts. These extensions were largely circumferential around the ostium (39%), but were also found to be asymmetric in a majority of hearts. Asymmetry was found in hearts with longer muscle extensions; no symmetry was observed in extensions greater than 0.8cm. Muscle extensions into the IVC were not seen. Occasionally, macroscopic muscle extensions into the azygous vein were visible (6%). The vein of Marshall was found to be patent to probing in the majority of hearts examined (72%) and was almost always overlying the lateral left atrial endocardial ridge. Conclusions: Our data suggest that all pulmonary veins need to be electrically isolated during atrial fibrillation ablation because of the almost universal presence of myocardial tissue extending into the veins. Mapping of the SVC should be done circumferentially and if potentials are noted isolation should also be performed. The IVC did not have muscle extensions and is unlikely to be a site of arrhythmogenesis. The azygous vein occasionally had muscle extensions and thus requires mapping and possible isolation. The vein of Marshall can be a substrate for arrhythmogenesis and is accessible for ablation by targeting the lateral left atrial endocardial ridge.

Introduction: Primary prevention implantable cardioverter defibrillators (ICDs) reduce mortality in select patients with left ventricular systolic dysfunction (LVSD). The occurrence of device therapies after ICD implantation in contemporary clinical practice is not well described, especially in patient subgroups designated in the Centers for Medicare and Medicaid Services (CMS) 2005 Coverage with Evidence Development (CED). Methods: The Longitudinal Study of ICDs assessed rates and correlates of device therapies (overall and those requiring shock) up to 3 years post-implant among 2540 patients with LVSD receiving first-time primary prevention ICDs in 7 US health care systems from 2006-2009. Implant data from the National Cardiovascular Data Registry ICD Registry were linked to electronic longitudinal health care system data and a novel centrally adjudicated repository of device therapies abstracted from medical records. Proportional hazard models evaluated associations with device therapies by appropriateness, adjusted for demographic and clinical factors. Results: Subjects were 26% women, 35% <65 years old, and 59% non-Hispanic white. Over a mean 26 months, 738 (29.1%) received at least 1 therapy (median 2). Estimated 3-year risk of any device therapy was 36% (24% appropriate, 12% inappropriate); for therapy requiring shock, corresponding values were 24%, 14%, 9%. The rate of appropriate therapy was higher in men than women (adjusted hazard ratio 1.84, 95% confidence interval 1.43-2.35). The rate of inappropriate therapy was higher for subjects <65 than for those >=65 years (1.40, 1.04-1.88), and lower among 2009 implants compared to 2006 (0.66, 0.46-0.95). Regarding the 3 CMS CED patient subgroups, neither ejection fraction nor heart failure symptom severity was associated with device therapy; for LVSD etiology, the rate of inappropriate therapy was nominally but not significantly higher among subjects with non-ischemic cardiomyopathy of < 9 months duration (1.38, 0.88-2.18). Conclusions: In a representative cohort of primary prevention ICD patients in usual care, rates of device therapies were somewhat lower than in landmark trials, differed by some patient characteristics, but did not differ meaningfully for CMS CED subgroups.

Background : Lipid lowering therapy reduces mortality in patients with both ischemic and nonischemic cardiomyopathies and recently has been shown to decrease ICD shocks. Radiofrequency ablation (RFA) of recurrent VT in patients with an ICD also reduces shocks following intervention. It is unclear if statin therapy after VT RFA will further impact ICD shock rates. Methods : All patients from 1993–2005 who underwent a RFA procedure for recurrent VT at the Mayo Clinic with an ICD were included. Patient records were extracted for medical and procedural details and all ICD interrogations were reviewed for VT recurrence and therapies. Results: 63 patients (age 62±15 years) were followed over 3.9±3.6 years. Comorbid diseases included: coronary artery disease 37(58%, 34 prior myocardial infarction), ARVD/C 6(10%), nonischemic dilated cardiomyopathy 7(11%), moderate-severe valve disease 14(22%), hypertension 34(54%), and hyperlipidemia 35(56%). Ejection fraction was <0.35 in 34(56%). VT was induced in all patients (LV 55 (LVOT 1), RV 8 (RVOT 3) with multiple inducible VTs in 21(33%). VT was noninducible after RFA in 39(62%) patients. Dismissal medications included: statins 19(30%), beta blockers 40(66%), ACE/ARB 37(61%), diuretics 34(55%), and digoxin 23(37%). 5-year overall survival was 63%(95% CI 55–71). Age, diabetes, and renal insufficiency were associated with increased post ablation mortality, with no medication improving survival. 5-year survival free of ICD shocks was 31%(95% CI 24–38). Only statin therapy at discharge was associated with a decreased risk of ICD shocks [5(26%) versus 26(59%), p=0.020]. 7 additional patients received statins during follow-up, but not at discharge, of these 5(71%) had shocks. Conclusion : Statin use at discharge in patients with an ICD undergoing RFA for refractory VT significantly reduced recurrent ventricular arrhythmias and ICD shocks. Although the mechanism underlying the effects of statins on arrhythmic recurrence early after RFA requires further study, these data support aggressive therapy of the underlying substrate responsible for the VT.

Current guidelines recommend cardiac resynchronization therapy (CRT-D) in appropriate patients undergoing ICD implantation. However, not all physicians who implant ICDs are trained to perform CRT-D. We examined the ICD Registry to assess whether use of CRT-D implantation varied by physician certification. We determined the certification of 2128 physicians who had submitted >=10 cases between April 2006 and June 2007. We excluded patients with a prior ICD, an epicardial lead, or aged ≤18 years, leaving 111,293 patients. Physicians were grouped into mutually exclusive categories reflecting highest current certification- Electrophysiology (EP), Cardiovascular Disease (CVD), Thoracic Surgery (TS), Internal Medicine (IM), Heart Rhythm Society alternative pathway (HRS), and Other. Patients were considered eligible for CRT-D if they met the following criteria: QRS duration >=120ms, LVEF ≪26>35%, and NYHA Class III-IV. We examined crude rates of CRT-D across physician categories and developed a logistic regression model to assess the association of physician certification and CRT-D implantation. Candidate variables included demographics, cardiac status, comorbidities, and physician volume. Odds ratios were converted to relative risks. 35,851 patients met all three eligibility criteria for CRT-D, and 28,932 (80.7%) had a CRT-D implanted. EP physicians implanted the majority of CRT-D (73.6%), with fewer CRT-D placed by CVD (20.6%), TS (0.9%), IM (0.8%), HRS (1.1%), or Other (3.1%). The crude rate of CRT-D implantation was highest among EP physicians and lower in all other categories: EP- 83.1%, CVD-75.8%, TS- 57.9%, IM- 76.5%, HRS- 77.1%, Other- 73.5% (p<0.001). In multivariable analysis, CVD and TS physicians were less likely to implant CRT-D in eligible patients compared with EP physicians (EP: Ref; CVD: RR 0.92 (0.90 – 0.94); TS: RR 0.76 (0.71– 0.85)). CRT-D rates were comparable for other physician groups (IM RR 0.95 (0.87–1.01); HRS: RR 0.97 (0.90 –1.02); Other RR 0.97 (0.93–1.00)). Among eligible patients, use of CRT-D varies by physician certification. Given the benefits of CRT-D, clinicians should consider referring eligible patients to physicians with familiarity and expertise in CRT-D implantation.

Determining whether retrograde ventriculoatrial (VA) conduction is through the AV node (AVN) or an accessory pathway (AP) is critical for successful ablation of supraventricular tachycardia (SVT). With introduction of ventricular extrastimuli (VEST), retrograde right bundle branch block (retro RBBB) may occur and result in abrupt VH interval prolongation. We hypothesized when retrograde conduction is via an AP, VA interval change is less than VH interval change, whereas with retrograde AVN conduction, VA interval change is equal to or greater than VH interval change. We retrospectively reviewed the electrophysiology (EP) studies of patients undergoing ablation for AVNRT (n=55) or AVRT (n=50). The intracardiac electrograms were reviewed for induction of retro RBBB and change in VH and VA intervals during VEST. Parahisian pacing, decremental pacing, arrhythmia diagnosis and ablation outcomes were reviewed. All results were found to be reproducible between two independent observers with inter and intra observer reliability scores of 1.00 for identification of retro RBBB and greater than 0.85 for measurement of VH and VA intervals. Of 105 patients, 84 (80%) had evidence of induced retro RBBB during VEST. The average VH interval increase with induction of retro RBBB was 53.7 ms for patients with retrograde AP conduction and 54.4 ms for patients with AVN conduction (p=ns). The average VA interval increase with induction of retro RBBB was 13.6 ms with AP conduction and 70.1 ms with AVN conduction (P < 0.001). All patients with a greater VH than VA interval change had a final diagnosis of AVRT and those with a VH change less than VA change had AVNRT, yielding sensitivity and specificity of 100%. Using a cutoff of 50 ms for change in VA interval with onset of retro RBBB to diagnose AVNRT accurately identified AVNRT in 100% and AVRT in 95%. Induction of retro RBBB during VEST is common during EP studies for SVT. The relative change in the VH and VA intervals during retro RBBB accurately differentiates retrograde AVN from retrograde AP conduction with strong predictive accuracy. The use of retro RBBB based intervals is a useful technique facilitating the diagnosis of SVT in the EP laboratory, even in the absence of inducible tachycardia.

OBJECTIVE To determine whether burden of multiple chronic conditions (MCCs) influences the risk of receiving inappropriate vs appropriate device therapies. DESIGN Retrospective cohort study. SETTING Seven US healthcare delivery systems. PARTICIPANTS Adults with left ventricular systolic dysfunction receiving an implantable cardioverter‐defibrillator (ICD) for primary prevention. MEASUREMENTS Data on 24 comorbid conditions were captured from electronic health records and categorized into quartiles of comorbidity burden (0‐3, 4‐5, 6‐7 and 8‐16). Incidence of ICD therapies (shock and antitachycardia pacing [ATP] therapies), including appropriateness, was collected for 3 years after implantation. Outcomes included time to first ICD therapy, total ICD therapy burden, and risk of inappropriate vs appropriate ICD therapy. RESULTS Among 2235 patients (mean age = 69 ± 11 years, 75% men), the median number of comorbidities was 6 (interquartile range = 4‐8), with 98% having at least two comorbidities. During a mean 2.2 years of follow‐up, 18.3% of patients experienced at least one appropriate therapy and 9.9% experienced at least one inappropriate therapy. Higher comorbidity burden was associated with an increased risk of first inappropriate therapy (adjusted hazard ratio [HR] = 1.94 [95% confidence interval {CI} = 1.14‐3.31] for 4‐5 comorbidities; HR = 2.25 [95% CI = 1.25‐4.05] for 6‐7 comorbidities; and HR = 2.91 [95% CI = 1.54‐5.50] for 8‐16 comorbidities). Participants with 8‐16 comorbidities had a higher total burden of ICD therapy (adjusted relative risk [RR] = 2.12 [95% CI = 1.43‐3.16]), a higher burden of inappropriate therapy (RR = 3.39 [95% CI = 1.67‐6.86]), and a higher risk of receiving inappropriate vs appropriate therapy (RR = 1.74 [95% CI = 1.07‐2.82]). Comorbidity burden was not significantly associated with receipt of appropriate ICD therapies. Patterns were similar when separately examining shock or ATP therapies. CONCLUSIONS In primary prevention ICD recipients, MCC burden was independently associated with an increased risk of inappropriate but not appropriate device therapies. Comorbidity burden should be considered when engaging patients in shared decision making about ICD implantation.

Background Primary prevention implantable cardioverter‐defibrillators (ICDs) reduce mortality in selected patients with left ventricular systolic dysfunction by delivering therapies (antitachycardia pacing or shocks) to terminate potentially lethal arrhythmias; inappropriate therapies also occur. We assessed device therapies among adults receiving primary prevention ICDs in 7 healthcare systems. Methods and Results We linked medical record data, adjudicated device therapies, and the National Cardiovascular Data Registry ICD Registry. Survival analysis evaluated therapy probability and predictors after ICD implant from 2006 to 2009, with attention to Centers for Medicare and Medicaid Services Coverage With Evidence Development subgroups: left ventricular ejection fraction, 31% to 35%; nonischemic cardiomyopathy <9 months’ duration; and New York Heart Association class IV heart failure with cardiac resynchronization therapy defibrillator. Among 2540 patients, 35% were <65 years old, 26% were women, and 59% were white. During 27 (median) months, 738 (29%) received ≥1 therapy. Three‐year therapy risk was 36% (appropriate, 24%; inappropriate, 12%). Appropriate therapy was more common in men (adjusted hazard ratio [HR], 1.84; 95% confidence interval [CI], 1.43–2.35). Inappropriate therapy was more common in patients with atrial fibrillation (adjusted HR, 2.20; 95% CI, 1.68–2.87), but less common among patients ≥65 years old versus younger (adjusted HR, 0.72; 95% CI, 0.54–0.95) and in recent implants (eg, in 2009 versus 2006; adjusted HR, 0.66; 95% CI, 0.46–0.95). In Centers for Medicare and Medicaid Services Coverage With Evidence Development analysis, inappropriate therapy was less common with cardiac resynchronization therapy defibrillator versus single chamber (adjusted HR, 0.55; 95% CI, 0.36–0.84); therapy risk did not otherwise differ for Centers for Medicare and Medicaid Services Coverage With Evidence Development subgroups. Conclusions In this community cohort of primary prevention patients receiving ICD, therapy delivery varied across demographic and clinical characteristics, but did not differ meaningfully for Centers for Medicare and Medicaid Services Coverage With Evidence Development subgroups.

Background In US clinical practice, many patients who undergo placement of an implantable cardioverter‐defibrillator ( ICD ) for primary prevention of sudden cardiac death receive dual‐chamber devices. The superiority of dual‐chamber over single‐chamber devices in reducing the risk of inappropriate ICD shocks in clinical practice has not been established. The objective of this study was to compare risk of adverse outcomes, including inappropriate shocks, between single‐ and dual‐chamber ICD s for primary prevention. Methods and Results We identified patients receiving a single‐ or dual‐chamber ICD for primary prevention who did not have an indication for pacing from 15 hospitals within 7 integrated health delivery systems in the Longitudinal Study of Implantable Cardioverter‐Defibrillators from 2006 to 2009. The primary outcome was time to first inappropriate shock. ICD shocks were adjudicated for appropriateness. Other outcomes included all‐cause hospitalization, heart failure hospitalization, and death. Patient, clinician, and hospital‐level factors were accounted for using propensity score weighting methods. Among 1042 patients without pacing indications, 54.0% (n=563) received a single‐chamber device and 46.0% (n=479) received a dual‐chamber device. In a propensity‐weighted analysis, device type was not significantly associated with inappropriate shock (hazard ratio, 0.91; 95% confidence interval, 0.59–1.38 [ P =0.65]), all‐cause hospitalization (hazard ratio, 1.03; 95% confidence interval, 0.87–1.21 [ P =0.76]), heart failure hospitalization (hazard ratio, 0.93; 95% confidence interval, 0.72–1.21 [ P =0.59]), or death (hazard ratio, 1.19; 95% confidence interval, 0.93–1.53 [ P =0.17]). Conclusions Among patients who received an ICD for primary prevention without indications for pacing, dual‐chamber devices were not associated with lower risk of inappropriate shock or differences in hospitalization or death compared with single‐chamber devices. This study does not justify the use of dual‐chamber devices to minimize inappropriate shocks.

Objective Patients with chronic kidney disease (CKD) have higher risk of sudden cardiac death; however, they may not receive implantable cardioverter defibrillators (ICDs), in part due to higher risk of complications. We evaluated whether CKD is associated with greater risk of device-delivered shocks/antitachycardia pacing (ATP) therapies among patients receiving a primary prevention ICD. Methods We studied participants in the observational Cardiovascular Research Network Longitudinal Study of Implantable Cardioverter Defibrillators. CKD was defined as estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m2. Outcomes included all delivered shocks/ATPs therapies and type of shock/ATP therapies (inappropriate or appropriate, determined by physician adjudication) within the 3 years. We evaluated the associations between CKD and time to first device therapy, burden of device therapy, and inappropriate versus appropriate device therapy, adjusting for demographics, comorbidity, laboratory values and medication use. Results Among 2161 participants, 1066 (49.3%) had CKD (eGFR 44±11 mL/min/1.73 m2) at ICD implantation. During mean of 2.26±0.89 years, 9.8% and 18.5% of participants had at least one inappropriate and appropriate shock/ATP therapies, respectively. CKD was not associated with time to first shock/ATP therapies (adjusted HR 0.87, 95% CI 0.73 to 1.05), overall burden of shock/ATP therapies (adjusted relative rate 0.93, 95% CI 0.74 to 1.17) or inappropriate versus appropriate shock/ATP therapies (adjusted relative risk 0.88, 95% CI 0.68 to 1.14) compared with not having CKD. Conclusions In adults receiving a primary prevention ICD, mild-to-moderate CKD was not associated with the timing, burden or appropriateness of subsequent device therapy. Potential concern for inappropriate ICD-delivered therapies should not preclude ICDs among eligible patients with CKD.