Long-Term Recording of Cardiac Arrhythmias With an Implantable Cardiac Monitor in Patients With Reduced Ejection Fraction After Acute Myocardial Infarction

Is heart rate important for patients with heart failure in atrial fibrillation?

OBJECTIVES

This study sought to investigate the relationship between resting ventricular rate and mortality in patients with chronic heart failure (CHF) and reduced left ventricular ejection fraction (LVEF) who were in sinus rhythm (SR) or atrial fibrillation (AF).

BACKGROUND

Slower heart rates are associated with better survival in patients with CHF in SR, but it is not clear whether this is true for those in AF.

METHODS

We assessed 2,039 outpatients with CHF and LVEF ≤50% undergoing baseline assessment, of whom 24% (n = 488) were in AF; and 841 outpatients reassessed after attempted treatment optimization at 1 year, of whom 22% (n = 184) were in AF. Cox proportional hazards models were used to assess the relationships between heart rate and survival in patients with CHF and AF or sinus rhythm. We analyzed heart rate and rhythm data recorded at the baseline review and after 1-year follow-up. Proportional hazards assumptions were checked by Schoenfeld and Martingale residuals.

RESULTS

The median survival for those in AF was 6.1 years (interquartile range [IQR]: 5.3 to 6.9 years) and 7.3 years (IQR: 6.5 to 8.1 years) for those in SR. In univariable analysis, patients with AF had a worse survival (hazard ratio [HR]: 1.26, 95% confidence interval [CI]: 1.08 to 1.47; p = 0.003) but after covariate adjustment, survival rates were similar. After adjusting Cox regression models, there was no association between heart rate (per 10 beats/min increments) and survival in patients with AF before (HR: 0.94, 95% CI: 0.88 to 1.00, p = 0.07) or after (HR: 1.00, 95% CI: 0.99 to 1.00, p = 0.84) therapy optimization. For patients in SR, higher heart rates were associated with worse survival, both before (HR: 1.10, 95% CI: 1.05 to 1.15, p <0.0001) and after (HR: 1.13, 95% CI: 1.03 to 1.24, p = 0.008) therapy optimization.

CONCLUSIONS

In patients with CHF and a reduced LVEF, slower resting ventricular rate is associated with better survival for patients in SR but not for those with AF.

Clinical utility of implantable loop recorders

Implantable loop recorders provide the highest sensitivity and accuracy of diagnosing cardiac arrhythmia that results in cardiac syncope. When bradyarrhythmia or tachyarrhythmia, including atrial fibrillation, is detected, appropriate secondary prevention therapy will be implemented, which will impact the long-term clinical outcome. An implantable loop recorder enables the clinician to record for a longer period of time, which increases the likelihood of detecting cardiac arrhythmia. Currently, this technology is being evaluated to diagnose a cardiac etiology of ischemic stroke and to optimize atrial fibrillation management that will predict the success of rhythm control and prevent thromboembolic events. This article reviews implantable loop recorder technology, and discusses the current indications, the outcomes of clinical studies and ongoing current studies, and future technological improvements.

The predictive value of CHADS₂ risk score in post myocardial infarction arrhythmias - a Cardiac Arrhythmias and RIsk Stratification after Myocardial infArction (CARISMA) substudy

BACKGROUND

Previous studies have shown substantially increased risk of cardiac arrhythmias and sudden cardiac death in post-myocardial infarction (MI) patients. However it remains difficult to identify the patients who are at highest risk of arrhythmias in the post-MI setting. The purpose of this study was to investigate if CHADS₂ score (congestive heart failure, hypertension, age ≥75 years, diabetes and previous stroke/TCI [doubled]) can be used as a risk tool for predicting cardiac arrhythmias after MI.

METHODS

The study included 297 post-MI patients from the CARISMA study with left ventricular ejection fraction (LVEF) ≤40%. All patients were implanted with an implantable cardiac monitor (ICM) within 5 to 21 days post-MI and followed every three months for two years. Atrial fibrillation, bradyarrhythmias and ventricular tachycardias were diagnosed using the ICM, pacemaker or ICD. Patients were stratified according to CHADS₂ score at enrollment. Congestive heart failure was defined as LVEF ≤40% and NYHA class II, III or IV.

RESULTS

We found significantly increased risk of an arrhythmic event with increasing CHADS₂ score (CHADS₂ score=1-2: HR=2.1 [1.1-3.9], p=0.021, CHADS₂ score ≥ 3: HR=3.7 [1.9-7.1], p<0.001). This pattern was identical when dividing the arrhythmias into subgroups of atrial fibrillation, ventricular tachycardias and bradyarrhythmias. CHADS₂ score was similarly associated with the development of major cardiovascular events defined as reinfarction, stroke, and hospitalization for heart failure or cardiovascular death.

CONCLUSION

In the post-MI setting, CHADS₂ score efficiently identifies populations at high risk for cardiac arrhythmias.

Cardiac imaging in evaluating patients prone to sudden death

Identifying subjects who are at risk for SCD and stratifying them correctly into low or high-risk groups is the holy grail of Cardiology. While imaging shows a lot of promise, it is plagued by the fact that most SCD occurs in relatively healthy subjects, a massive group who would not ordinarily be subjected to imaging. Left ventricular ejection fraction (LVEF) currently is our primary parameter for risk stratification for sudden cardiac death but is a poor marker with low sensitivity and specificity. Current data shows that sophisticated imaging with techniques, mainly Cardiac magnetic resonance Imaging (CMR), have the potential to identify novel high-risk markers underlying SCD, beyond ejection fraction. Imaging seems to further refine risk in patients with low LVEF as well as in those with normal EF; this is a major strength of advanced imaging. Clinical application has been slow and not fully prime time. It is important to remember that while promising, imaging techniques including CMR, have not been tested in rigorous prospective studies and thus have not as yet replaced EF as the gatekeeper to ICD implantation.

Association between the quality of life and asymptomatic episodes of paroxysmal atrial fibrillation in the J-RHYTHM II study

BACKGROUND

Paroxysmal atrial fibrillation (AF) patients have a reduced quality-of-life (QoL) despite the fact that the majority of AF episodes are asymptomatic. Asymptomatic AF is likely to be associated with substantial morbidity and mortality rates similar to those with symptomatic AF, whereas its effect on the QoL has not yet been clarified.

PURPOSE

We studied the specific contribution of asymptomatic AF episodes to reducing the QoL.

METHODS

We assessed the QoL in 233 patients with paroxysmal AF and hypertension (age 64.9 ± 9.7 years, 71% male) enrolled in the Japanese Rhythm Management Trial II for Atrial Fibrillation (J-RHYTHM II study) using an AF-specific QoL questionnaire (AFQLQ). The AFQLQ comprised 3 components: AFQLQ1, the frequency and duration of symptoms; AFQLQ2, severity of symptoms; and AFQLQ3, limitations in daily activities and mental anxiety. Higher scores indicated a better QoL. Each patient transmitted electrocardiograms for 30s daily at a predetermined time as well as whenever arrhythmia-related symptoms were experienced. We examined the relationship between the 3 AFQLQ components and frequency of symptomatic and asymptomatic AF episodes (days/month) during 12 months of follow-up.

RESULTS

The symptomatic and asymptomatic AF frequencies were 0.9 ± 3.1 days/month and 1.5 ± 3.5 days/month, respectively. AFQLQ1 negatively correlated with the symptomatic AF frequency (Spearman's correlation coefficient: r = -0.332, p < 0.001). AFQLQ2 and AFQLQ3 correlated with both the symptomatic AF frequency (r = -0.27, p < 0.001 and r = -0.265, p < 0.001, respectively) and asymptomatic AF frequency (r = -0.197, p < 0.01 and r = -0.229, p < 0.005, respectively).

CONCLUSION

The asymptomatic AF episode frequency correlates with a reduced QoL in patients with paroxysmal AF, suggesting that there would be psychological benefits to its reduction.

New-onset atrial fibrillation predicts malignant arrhythmias in post-myocardial infarction patients--a Cardiac Arrhythmias and RIsk Stratification after acute Myocardial infarction (CARISMA) substudy

BACKGROUND

After myocardial infarction (MI) the risk of sudden cardiac death due to arrhythmias is substantial.

OBJECTIVE

The purpose of this study was to investigate if new-onset atrial fibrillation (AF) is associated with development of potential malignant brady- and tachyarrhythmias after an acute MI.

METHODS

The study included 277 post-MI patients from the CARISMA study with left ventricular ejection fraction ≤ 40%, New York Heart Association class I, II, or III and no history of AF. All patients were implanted with an implantable cardiac monitor within 4 to 27 days after an acute MI and followed every 3 months for 2 years. Time-dependent association between new-onset AF > 30 s and the development of bradyarrhythmias and/or ventricular tachyarrhythmias were investigated using Cox proportional hazard regressions.

RESULTS

New-onset AF was associated with an increased risk of bradyarrhythmias when adjusting for male gender and baseline age, left ventricular ejection fraction and QRS width (HR = 2.8 [1.3-5.8], P = .006). Similarly, new-onset AF predicted ventricular tachyarrhythmias when adjusting for New York Heart Association class ≥ II and baseline QRS width (HR = 2.3 [1.2-4.4], P = .019). After dividing ventricular tachyarrhythmias into subgroups of non-sustained ventricular tachycardia (VT), sustained VT and ventricular fibrillation (VF), new-onset AF was significantly associated with an increased risk of non-sustained- and sustained VT but not VF (non-sustained VT: HR = 3.5 [1.7-7.2], P < .001, sustained VT: HR = 4.2 [1.1-15.7], P = .035, VF: HR = 1.1 [0.2-5.8], P = .877).

CONCLUSION

In patients surviving a MI with reduced left ventricular systolic function, new-onset AF is associated with a significantly increased risk of developing ventricular brady- and tachyarrhythmias.

Mechanisms of altered Ca²⁺ handling in heart failure

Ca²⁺ plays a crucial role in connecting membrane excitability with contraction in myocardium. The hallmark features of heart failure are mechanical dysfunction and arrhythmias; defective intracellular Ca²⁺ homeostasis is a central cause of contractile dysfunction and arrhythmias in failing myocardium. Defective Ca²⁺ homeostasis in heart failure can result from pathological alteration in the expression and activity of an increasingly understood collection of Ca²⁺ homeostatic and structural proteins, ion channels, and enzymes. This review focuses on the molecular mechanisms of defective Ca²⁺ cycling in heart failure and considers how fundamental understanding of these pathways may translate into novel and innovative therapies.

Role of extended external loop recorders for the diagnosis of unexplained syncope, pre-syncope, and sustained palpitations

AIMS

To assess the diagnostic yield of new external loop recorders (ELRs) in patients with history of syncope, pre-syncope, and sustained palpitations.

METHODS AND RESULTS

Since 2005, we have established a registry including patients who consecutively received ELR monitoring for unexplained syncope or pre-syncope/palpitations. The registry included 307 patients (61% females, age 58 ± 19 years, range 8-94 years) monitored by high-capacity memory ELR of two subsequent generations: SpiderFlash-A(®) (SFA(®), Sorin CRM), storing two-lead electrocardiogram (ECG) patient-activated recordings by loop-recording technique (191 patients, 54 patients with syncope, years 2005-09), and SpiderFlash-T(®) (SFT(®)), adding auto-trigger detection for pauses, bradycardia, and supraventricular/ventricular arrhythmias (116 patients, 38 patients with syncope, years 2009-12). All the patients previously underwent routine workup for syncope or palpitation, including one or more 24 h Holter, not conclusive for diagnosis. Mean monitoring duration was 24.1 ± 8.9 days. Among 215 patients with palpitations, a conclusive diagnosis was obtained in 184 patients (86% diagnostic yield for palpitation). Among 92 patients with syncope, a conclusive diagnosis was obtained in 16 patients (17% clinical diagnostic yield for syncope), with recording during syncope of significant arrhythmias in 9 patients, and sinus rhythm in 7 patients. Furthermore, asymptomatic arrhythmias were de novo detected in 12 patients (13%), mainly by auto-trigger detection, suggesting an arrhythmic origin of the syncope.

CONCLUSIONS

The diagnostic yield of ELR in patients with syncope, pre-syncope, or palpitation of unknown origin after routine workup was similar to implantable loop recorder (ILR) within the same timeframe, therefore, ELR could be considered for patients candidate for long-term ECG monitoring, stepwise before ILR.

The evolution of ambulatory ECG monitoring

Ambulatory Holter electrocardiographic (ECG) monitoring has undergone continuous technological evolution since its invention and development in the 1950s era. With commercial introduction in 1963, there has been an evolution of Holter recorders from 1 channel to 12 channel recorders with increasingly smaller storage media, and there has evolved Holter analysis systems employing increasingly technologically advanced electronics providing a myriad of data displays. This evolution of smaller physical instruments with increasing technological capacity has characterized the development of electronics over the past 50 years. Currently the technology has been focused upon the conventional continuous 24 to 48 hour ambulatory ECG examination, and conventional extended ambulatory monitoring strategies for infrequent to rare arrhythmic events. However, the emergence of the Internet, Wi-Fi, cellular networks, and broad-band transmission has positioned these modalities at the doorway of the digital world. This has led to an adoption of more cost-effective strategies to these conventional methods of performing the examination. As a result, the emergence of the mobile smartphone coupled with this digital capacity is leading to the recent development of Holter smartphone applications. The potential of point-of-care applications utilizing the Holter smartphone and a vast array of new non-invasive sensors is evident in the not too distant future. The Holter smartphone is anticipated to contribute significantly in the future to the field of global health.

Early echocardiographic deformation analysis for the prediction of sudden cardiac death and life-threatening arrhythmias after myocardial infarction

OBJECTIVES

This study sought to hypothesize that global longitudinal strain (GLS) as a measure of infarct size, and mechanical dispersion (MD) as a measure of myocardial deformation heterogeneity, would be of incremental importance for the prediction of sudden cardiac death (SCD) or malignant ventricular arrhythmias (VA) after acute myocardial infarction (MI).

BACKGROUND

SCD after acute MI is a rare but potentially preventable late complication predominantly caused by malignant VA. Novel echocardiographic parameters such as GLS and MD have previously been shown to identify patients with chronic ischemic heart failure at increased risk for arrhythmic events. Risk prediction during admission for acute MI is important because a majority of SCD events occur in the early period after hospital discharge.

METHODS

We prospectively included patients with acute MI and performed echocardiography, with measurements of GLS and MD defined as the standard deviation of time to peak negative strain in all myocardial segments. The primary composite endpoint (SCD, admission with VA, or appropriate therapy from a primary prophylactic implantable cardioverter-defibrillator [ICD]) was analyzed with Cox models.

RESULTS

A total of 988 patients (mean age: 62.6 ± 12.1 years; 72% male) were included, of whom 34 (3.4%) experienced the primary composite outcome (median follow-up: 29.7 months). GLS (hazard ratio [HR]: 1.38; 95% confidence interval [CI]: 1.25 to 1.53; p < 0.0001) and MD (HR/10 ms: 1.38; 95% CI: 1.24 to 1.55; p < 0.0001) were significantly related to the primary endpoint.

GLS (HR

1.24; 95% CI: 1.10 to 1.40; p = 0.0004) and MD (HR/10 ms: 1.15; 95% CI: 1.01 to 1.31; p = 0.0320) remained independently prognostic after multivariate adjustment. Integrated diagnostic improvement (IDI) and net reclassification index (NRI) were significant for the addition of GLS (IDI: 4.4% [p < 0.05]; NRI: 29.6% [p < 0.05]), whereas MD did not improve risk reclassification when GLS was known.

CONCLUSIONS

Both GLS and MD were significantly and independently related to SCD/VA in these patients with acute MI and, in particular, GLS improved risk stratification above and beyond existing risk factors.

A translational approach in using cell sheet fragments of autologous bone marrow-derived mesenchymal stem cells for cellular cardiomyoplasty in a porcine model

Based on a porcine model with surgically created myocardial infarction (MI) as a pre-clinical scheme, this study investigates the clinical translation of cell sheet fragments of autologous mesenchymal stem cells (MSCs) for cellular cardiomyoplasty. MSC sheet fragments retaining endogenous extracellular matrices are fabricated using a thermo-responsive methylcellulose hydrogel system. Echocardiographic observations indicate that transplantation of MSC sheet fragments in infarcted hearts can markedly attenuate the adverse ventricular dilation and preserve the cardiac function post MI, which is in contrast to the controlled groups receiving saline or dissociated MSCs. Additionally, histological analyses suggest that administering MSC sheet fragments significantly prevents the scar expansion and left ventricle remodeling after MI. Immunohistochemistry results demonstrate that the engrafted MSCs can differentiate into endothelial cells and smooth muscle cells, implying that angiogenesis and the subsequent regional perfusion improvement is a promising mechanism for ameliorating post-infarcted cardiac function. However, according to the data recorded by an implantable loop recorder, the transplanted MSCs may provoke arrhythmia. Nevertheless, the proposed approach may potentially lead to the eventual translation of MSC-based therapy into practical and effective clinical treatments.

Stepwise screening of atrial fibrillation in a 75-year-old population: implications for stroke prevention

BACKGROUND

Atrial fibrillation (AF) is a frequent source of cardiac emboli in patients with ischemic stroke. AF may be asymptomatic and therefore undiagnosed. Screening for silent AF seems suitable in risk populations, however little is known on the yield and cost-effectiveness of such screening.

METHODS AND RESULTS

All inhabitants in the municipality of Halmstad, Sweden aged 75 to 76 years were invited to a stepwise screening program for AF. As a first step, participants recorded a 12-lead ECG and reported their relevant medical history. Those with sinus rhythm on 12-lead ECG, no history of AF, and ≥2 risk factors according to CHADS(2) were invited to a 2-week recording period using a hand-held ECG and asked to record 20 or 30 seconds twice daily and if palpitations occurred. One thousand, three hundred thirty inhabitants were invited, of whom 848 (64%) participated. Previously undiagnosed silent AF was found in 10 (1%) among 848 individuals who recorded 12-lead ECG. Among 81 patients with known AF, 35 (43%) were not on oral anticoagulation treatment. Among 403 persons with ≥2 risk factors for stroke, who completed the hand-held ECG event recording, 30 (7.4%) were diagnosed with paroxysmal AF. Thus 75/848 (9%) of the screened population were candidates for new oral anticoagulation treatment, of those 57 actually started oral anticoagulation treatment.

CONCLUSIONS

Stepwise risk factor-stratified AF screening in a 75-year-old population yields a large share of candidates for oral anticoagulation treatment on AF indication.

Patient selection for ambulatory cardiac monitoring in the Indian healthcare environment

Cardiovascular disease (CVD) in India comprises the bulk of non-communicable diseases, resulting in 2 million deaths per year. The incidence of CVD in India is estimated to be up to four times higher than in other countries. Though the quantification of the prevalence of rhythm disorders in India is not available, it can be inferred to be proportionately high. Identification and treatment of arrhythmia is limited by several socioeconomic factors including low health insurance penetration, limited reimbursement and high out-of-pocket expenditures. Thus, there exists a need in India to (1) select an appropriate tool that is both high yielding and cost effective and (2) employ a suitable patient selection method. This paper focuses on these two aspects for cardiac arrhythmia diagnosis using ambulatory monitoring technology, while keeping in mind the dynamics of the Indian healthcare setting.

Systems biology and cardiac arrhythmias

During the past few years, the development of effective, empirical technologies for treatment of cardiac arrhythmias has exceeded the pace at which detailed knowledge of the underlying biology has accumulated. As a result, although some clinical arrhythmias can be cured with techniques such as catheter ablation, drug treatment and prediction of the risk of sudden death remain fairly primitive. The identification of key candidate genes for monogenic arrhythmia syndromes shows that to bring basic biology to the clinic is a powerful approach. Increasingly sophisticated experimental models and methods of measurement, including stem cell-based models of human cardiac arrhythmias, are being deployed to study how perturbations in several biologic pathways can result in an arrhythmia-prone heart. The biology of arrhythmia is largely quantifiable, which allows for systematic analysis that could transform treatment strategies that are often still empirical into management based on molecular evidence.

Nonsustained ventricular tachycardia

Nonsustained ventricular tachycardia (NSVT) has been recorded in a wide range of conditions, from apparently healthy individuals to patients with significant heart disease. In the absence of heart disease, the prognostic significance of NSVT is debatable. When detected during exercise, and especially at recovery, NSVT indicates increased cardiovascular mortality within the next decades. In trained athletes, NSVT is considered benign when suppressed by exercise. In patients with non-ST-segment elevation acute coronary syndrome, NSVT occurring beyond 48 h after admission indicates an increased risk of cardiac and sudden death, especially when associated with myocardial ischemia. In acute myocardial infarction, in-hospital NSVT has an adverse prognostic significance when detected beyond the first 13 to 24 h. In patients with prior myocardial infarction treated with reperfusion and beta-blockers, NSVT is not an independent predictor of long-term mortality when other covariates such as left ventricular ejection fraction are taken into account. In patients with hypertrophic cardiomyopathy, and most probably genetic channelopathies, NSVT carries prognostic significance, whereas its independent prognostic ability in ischemic heart failure and dilated cardiomyopathy has not been established. The management of patients with NSVT is aimed at treating the underlying heart disease.

Heart rate achieved or beta-blocker dose in patients with chronic heart failure: which is the better target?

AIMS

To investigate whether the mortality of patients with chronic heart failure (CHF) due to left ventricular systolic dysfunction (LVSD) is more strongly related to beta-blocker dose or to heart rate. It is known that beta-blockers reduce mortality in patients with CHF and LVSD, but the primary mechanism of action is uncertain.

METHODS AND RESULTS

Patients with an ejection fraction ≤40%, who were in sinus rhythm both at an initial (visit 1) and at a 4-month clinic review (visit 2), were followed for a maximum of 36 months. The relationships between heart rate, beta-blocker dose, and survival in a multivariable model were examined. Of 654 eligible patients, 381 (58%) were started on beta-blockers prior to the initial visit, increasing to 537 (82%) by visit 2. During follow-up, 142 (22%) patients died. Neither resting heart rate nor beta-blocker dose at visit 1 predicted mortality (P = 0.09 and P = 0.99), but resting heart rate at visit 2 did (P = 0.02). Beta-blocker use at visit 2 was associated with better outcome (P = 0.03) but with little variation in outcome according to dose. Patients with a heart rate of 58-64 b.p.m. at visit 2 had the best prognosis.

CONCLUSIONS

The use of beta-blockers and resting heart rate at visit 2 both independently indicated prognosis, but beta-blocker dose did not. Beta-blockers may reduce mortality by several mechanisms; one that may be specific to blockade of adrenergic receptors and another related to heart rate reduction. Achieving a target heart rate range may be an appropriate therapeutic goal for patients with CHF.

Circulation: Heart Failure Editors' Picks

The following are highlights from Circulation: Heart Failure Topic Review. This series will summarize the most important articles, as selected by the editors, that have published in the Circulation portfolio. The objective of this series is to provide our readership with a timely comprehensive selection of important papers that are relevant to the heart failure audience. The studies included in this article represent the most noteworthy research in the areas of heart failure and electrophysiology.

Current and emerging indications for implantable cardiac monitors

Implantable cardiac monitors (ICMs) continuously monitor the patient's electrocardiogram and perform real-time analysis of the heart rhythm, for up to 36 months. The current clinical use of ICMs involves the evaluation of transitory symptoms of possible arrhythmic origin, such as unexplained syncope and palpitations. Moreover, ICMs can also be used for the evaluation of difficult cases of epilepsy and unexplained falls, though current indications for their application in these sectors are less clearly defined. Finally, the ability of new-generation ICMs to automatically record arrhythmic episodes suggests that these devices could also be used to study asymptomatic arrhythmias, and thus could be proposed for the long-term evaluation of the total (symptomatic and asymptomatic) arrhythmic burden in patients at risk of arrhythmic events. In particular, ICMs may have an emerging role in the management of patients with atrial fibrillation and in those at risk of ventricular arrhythmias.

Circulation: Arrhythmia and Electrophysiology Editors' Picks

The following articles are being highlighted as part of Circulation: Arrhythmia and Electrophysiology's Topic Review series. This series will summarize the most important articles, as selected by the editors, published in Circulation: Arrhythmia and Electrophysiology, Circulation, and the other Circulation subspecialty journals. The studies included in this article represent the most read articles published on the topic of bradyarrhythmias in 2010 and 2011.

[Update on ischemic heart disease]

This article contains a review of the main developments reported in 2011 on the pathophysiology, prevention, prognosis and treatment of chronic coronary artery disease and acute coronary syndrome, with or without ST-segment elevation. It also discusses the recommendations of the latest clinical practice guidelines.

Circulation: Arrhythmia and Electrophysiology Editors' Picks

The following articles are being highlighted as part of Circulation: Arrhythmia and Electrophysiology's Topic Review series. This series will summarize the most important manuscripts, as selected by the editors, published in Circulation: Arrhythmia and Electrophysiology and the rest of the Circulation portfolio. The studies included in this article represent the most read manuscripts published on the topic of atrial fibrillation in 2009 and 2010.

Clinical significance of late high-degree atrioventricular block in patients with left ventricular dysfunction after an acute myocardial infarction--a Cardiac Arrhythmias and Risk Stratification After Acute Myocardial Infarction (CARISMA) substudy

BACKGROUND

High-degree atrioventricular block (HAVB) is a frequent complication in the acute stages of a myocardial infarction associated with an increased rate of mortality. However, the incidence and clinical significance of HAVB in late convalescent phases of an AMI is largely unknown. The aim of this study was to assess the incidence and prognostic value of late HAVB documented by continuous electrocardiogram (ECG) monitoring in post-AMI patients with reduced left ventricular function.

METHODS

The study included 286 patients from the CARISMA study with AMI and left ventricular ejection fraction of 40% or less. An insertable loop recorder was implanted 5 to 21 days after AMI for incessant arrhythmia surveillance. Furthermore, ECG documentation was supplemented by a 24-hour Holter monitoring conducted at week 6 post-AMI. The clinical significance of HAVB occurring more than 21 days after AMI was examined with respect to development of major heart failure events and major ventricular tachyarrhythmic events.

RESULTS

During a median follow-up of 1.9 years (interquartile range 0.9-2.0), late HAVB was documented in 30 patients. The risk of major heart failure events (hazard ratio [HR] 4.08 [1.38-12.09], P = .01) and major ventricular tachyarrhythmic events (HR = 5.41 [1.88-15.58], P = .002) were significantly increased in patients who developed late HAVB.

CONCLUSION

High-degree atrioventricular block documented by continuous ECG monitoring occurring more than 3 weeks after AMI is a frequent complication in post-AMI patients with left ventricular dysfunction. Furthermore, HAVB is associated with ominous prognostic implications of both potentially lethal arrhythmias and heart failure.

Circulation Editors' Picks

The following articles are being highlighted as part of Circulation's Topic Review series. This series will summarize the most important manuscripts, as selected by the editors, published in Circulation and the Circulation subspecialty journals. The studies included in this article represent the most read manuscripts published on the topic of arrhythmia and electrophysiology in 2009 and 2010.

Oxidized CaMKII causes cardiac sinus node dysfunction in mice

Sinus node dysfunction (SND) is a major public health problem that is associated with sudden cardiac death and requires surgical implantation of artificial pacemakers. However, little is known about the molecular and cellular mechanisms that cause SND. Most SND occurs in the setting of heart failure and hypertension, conditions that are marked by elevated circulating angiotensin II (Ang II) and increased oxidant stress. Here, we show that oxidized calmodulin kinase II (ox-CaMKII) is a biomarker for SND in patients and dogs and a disease determinant in mice. In wild-type mice, Ang II infusion caused sinoatrial nodal (SAN) cell oxidation by activating NADPH oxidase, leading to increased ox-CaMKII, SAN cell apoptosis, and SND. p47-/- mice lacking functional NADPH oxidase and mice with myocardial or SAN-targeted CaMKII inhibition were highly resistant to SAN apoptosis and SND, suggesting that ox-CaMKII-triggered SAN cell death contributed to SND. We developed a computational model of the sinoatrial node that showed that a loss of SAN cells below a critical threshold caused SND by preventing normal impulse formation and propagation. These data provide novel molecular and mechanistic information to understand SND and suggest that targeted CaMKII inhibition may be useful for preventing SND in high-risk patients.

Prolonged QRS duration on the resting ECG is associated with sudden death risk in coronary disease, independent of prolonged ventricular repolarization

BACKGROUND

Abnormalities of ventricular repolarization as well as depolarization have been associated with increased risk of ventricular arrhythmias.

OBJECTIVE

To evaluate the relative contribution of these predictors to risk of sudden cardiac death (SCD) in patients with coronary artery disease (CAD).

METHODS

In the ongoing Oregon Sudden Unexpected Death Study, adult residents from the Portland, Oregon, metropolitan area (population ~1 million) who suffered SCD were identified prospectively (2002-2007). Of these, we analyzed the subgroup of SCDs that had a resting 12-lead ECG prior to SCD and also had associated CAD. Comparisons were conducted with a control group of subjects with known CAD but no history of SCD from the same geographic region. Corrected QT interval (QTc), JT interval (JTc), QRS duration (QRSd), and other parameters were measured from ECG prior and unrelated to SCD. Analysis of left ventricular function was limited to those subjects who had undergone echocardiography prior to and remote from SCD.

RESULTS

A total of 642 SCD cases (71 ± 13 years, 62% male) were compared to 450 controls (66 ± 12 years, 64% male). SCD cases had significantly longer QRSd (102 ± 25 ms vs 97 ± 20 ms, P = .0008) as well as JTc (348 ± 44 ms vs 339 ± 34 ms, P = .0006) vs controls. In cases with prolonged QRSd, 38% had severe left ventricular systolic dysfunction and 62% had normal, mild, or moderately decreased left ventricular systolic function. In a multivariable model, QRSd, JTc, age, and severe left ventricular systolic dysfunction were independent predictors. There was minimal overlap between prolonged QRSd and JTc in both case and control groups (3% and 4%, respectively).

CONCLUSION

Prolonged QRSd, JTc, and severe left ventricular systolic dysfunction had independent contributions to risk of SCD in coronary disease, in this community-based setting.