Long-term outcome of intraventricular conduction delays in the general population.

BACKGROUND: Previous population studies have presented conflicting results regarding the prognostic impact of intraventricular conduction delays (IVCD). METHODS: We studied long-term prognostic impact and the association with comorbidities of eight IVCDs in a random sample of 6,299 Finnish subjects (2,857 men and 3,442 women, mean age 52.8, SD 14.9 years) aged 30 or over who participated in the health examination including 12-lead ECG. For left bundle branch block (LBBB) and non-specific IVCD (NSIVCD), two different definitions were used. RESULTS: During 16.5 years' follow-up, 1,309 of the 6,299 subjects (20.8%) died and of these 655 (10.4%) were cardiovascular (CV) deaths. After controlling for known clinical risk factors, the hazard ratio for CV death, compared with individuals without IVCD, was 1.55 for the Minnesota definition of LBBB (95% confidence interval 1.04-2.31, p = .032) and 1.27 (95% confidence interval 0.80-2.02, p = .308) for the Strauss' definition of LBBB. Subjects with NSIVCD were associated with twofold to threefold increase in CV mortality depending on the definition. While right bundle branch block, left anterior fascicular block and incomplete bundle branch blocks were associated with seemingly higher mortality, this was no longer the case after adjustment for age and sex. The presence of R-R' pattern was not associated with any adverse outcome. CONCLUSIONS: In a population study with long-term follow-up, NSIVCD and Minnesota definition of LBBB were independently associated with CV mortality. Other IVCDs had no significant impact on prognosis. The prognostic impact of LBBB and NSIVCD was affected by the definition of the conduction disorder.

The long-term therapeutic effects of His-Purkinje system pacing on bradycardia and cardiac conduction dysfunction compared with right ventricular pacing: A systematic review and meta-analysis.

AIMS: His-Purkinje system pacing has been demonstrated as a synchronized ventricular pacing strategy via pacing His-Purkinje system directly, which can decrease the incidence of adverse cardiac structure alteration compared with right ventricular pacing (RVP). The purpose of this meta-analysis was to compare the effects of His-Purkinje system pacing and RVP in patients with bradycardia and cardiac conduction dysfunction. METHODS: PubMed, Embase, Cochrane Library, and Web of Science were systematically searched from the establishment of databases up to 15 December 2019. Studies on long-term clinical outcomes of His-Purkinje system pacing and RVP were included. Chronic paced QRS duration, chronic pacing threshold, left ventricular ejection fraction (LVEF), left ventricular end-diastolic volume (LVEDV), left ventricular end-systolic volume (LVESV), all-cause mortality, and heart failure hospitalization were collected for meta-analysis. RESULTS: A total of 13 studies comprising 2348 patients were included in this meta-analysis. Compared with RVP group, patients receiving His-Purkinje system pacing showed improvement of LVEF (mean difference [MD], 5.65; 95% confidence interval [CI], 4.38-6.92), shorter chronic paced QRS duration (MD, - 39.29; 95% CI, - 41.90 to - 36.68), higher pacing threshold (MD, 0.8; 95% CI, 0.71-0.89) and lower risk of heart failure hospitalization (odds ratio [OR], 0.65; 95% CI, 0.44-0.96) during the follow-up. However, no statistical difference existed in LVEDV, LVESV and all-cause mortality between the two groups. CONCLUSION: Our meta-analysis suggests that His-bundle pacing is more suitable for the treatment of patients with bradycardia and cardiac conduction dysfunction.

Effect of Left Ventricular Conduction Delay on All-Cause and Cardiovascular Mortality (from the PRECISION Trial).

The prognosis associated with prolonged intraventricular conduction on electrocardiogram (ECG) remains uncertain. We aimed to compare clinical outcomes of narrow versus prolonged intraventricular conduction on ECG stratified by QRS morphology and cardiovascular disease (CVD) status. A post-hoc analysis was performed of the randomized-control PRECISION trial. Patients with centrally adjudicated, nonpaced baseline ECGs were included. QRS duration was classified narrow (≤100 ms) versus prolonged (>100 ms) with additional categorization into left (LBBB) or right (RBBB) bundle branch block or nonspecific intraventricular conduction delay (IVCD). IVCD was subclassified if left ventricular conduction delay (LVCD) was present (L-IVCD) or absent (O-IVCD). The primary outcome was adjudicated all-cause and cardiovascular (CV) mortality. Of 24,081 patients randomized, 22,067 (92%) were included with follow-up 34 ± 13 months. Study patients were 63 ± 9 years, 64% female, 75% Caucasian, 23% with established CVD. The prevalence of QRS prolongation was 5.6% (1,240): 760 right bundle branch block (3.4%), 313 LBBB (1.4%), and 161 IVCD (0.7%), 95 subclassified L-IVCD (0.4%). After adjustment, LBBB and L-IVCD were similarly associated with increased all-cause (LBBB: 2.3 [1.4 to 3.8], p = 0.001; L-IVCD: 4.0 [2.1 to 7.9], p <0.001) and CV (LBBB: 3.6 [2.0 to 6.5], p <0.001; L-IVCD 3.6 [1.3 to 9.7], p = 0.001) mortality. The presence of LVCD (LBBB or L-IVCD) was associated with all-cause (2.8 [1.8 to 4.2], p <0.001) and CV (3.6 [2.2 to 6.1], p <0.001) mortality exceeding the observed risks of coronary artery disease, left ventricular hypertrophy, or diabetes. The LVCD hazard persisted across QRS durations (100 to 120 vs >120 ms) and CVD status. In conclusion, LVCD, whether LBBB or L-IVCD, was strongly associated with increased mortality in patients with and at-risk for CVD.

Mortality among autoworkers manufacturing electronics in Huntsville, Alabama.

BACKGROUND: Workers raised concerns over suspected excesses of mortality at automotive electronics manufacturing facilities in Huntsville, Alabama. METHODS: A study of 4396 UAW members ever-employed at Huntsville facilities between 1972 and 1993 was conducted with mortality follow-up through 2016. Standardized Mortality Ratios (SMRs) were estimated using U.S. and Alabama reference rates. RESULTS: Relative to U.S. rates, there was a modest excess of all-cause mortality among White female workers (SMR 1.08, 95%CI: 0.99-1.18) and among all workers hired <1977 at the original plant building (SMR 1.10, 95%CI: 0.99-1.22). There was excess nervous system disorder (SMR 1.24, 95%CI: 0.91-1.65) and brain and nervous system cancer (SMR 1.31, 95%CI: 0.67-2.28) mortality. Estimates for several causes of interest were imprecise. CONCLUSIONS: All-cause mortality estimates were greater than anticipated based on results from other UAW cohorts. The excess of nervous system disease mortality is consistent with other studies of electronics workers exposed to lead-solder and chlorinated solvents.

Intra- and interatrial conduction abnormalities: hemodynamic and arrhythmic significance.

Alterations of normal intra- and interatrial conduction are a common outcome of multiple cardiovascular conditions. They arise most commonly in the context of advanced age, cardiovascular risk factors, organic heart disease, atrial fibrosis, and left atrial enlargement. Interatrial block (IAB), the most frequent and extensively studied atrial conduction disorder, affects up to 20% of the general primary care population. IAB can be partial (P wave duration ≥ 120 ms on any of the 12 ECG leads) or advanced (P wave ≥ 120 ms and biphasic morphology (positive-negative) in inferior leads). Advanced IAB is an independent risk factor for supraventricular tachyarrhythmias and embolic stroke in a variety of clinical settings. Advanced IAB is a cause of left atrial electromechanical dysfunction and left atrioventricular dyssynchrony and has been associated with left ventricular diastolic dysfunction. P wave duration is associated with cardiovascular and all-cause mortality in the general population. Atrial conduction abnormalities should be identified as markers of atrial remodeling, prognostic indicators, and, in the case of advanced IAB, a true arrhythmologic syndrome. IAB and other P wave abnormalities should prompt the search for associated conditions, the treatment of which may partially reverse atrial remodeling or prevent it if administered upstream. Future studies will help define the role of preventive therapeutic interventions in high-risk patients, including antiarrhythmic drug therapy and oral anticoagulation. Implications for the treatment of heart failure and for pacing should also be further investigated.

The effects of septal myectomy and alcohol septal ablation for hypertrophic cardiomyopathy on the cardiac conduction system.

AV conduction abnormalities are observed in 15-30% of patients with hypertrophic cardiomyopathy but are usually not severe enough to require permanent pacemaker implant. Both septal myectomy and alcohol septal ablation are effective options to relieve symptoms due to left ventricular outflow tract gradient in patients with hypertrophic cardiomyopathy but have procedure-specific effects on AV conduction and the His Purkinje system. Septal myectomy is associated with the development of LBBB in 50-100% of patients, while alcohol septal ablation is associated with RBBB in 37-70% of patients. Baseline abnormalities in the contralateral bundles and the presence of conduction disease have an important impact on the likelihood of the development of AV block for both of these therapies. AV block requiring permanent pacing occurs in approximately 2-3% of patients after septal myectomy and 10-15% of patients after alcohol septal ablation. Permanent pacemaker implant after alcohol septal ablation is more common in older patients (> 55 years old 13 vs. < 55 years old 5%; p = 0.06). Improved outcomes for septal myectomy and alcohol septal ablation are observed in experienced centers. Septal reduction therapies should be performed at medical centers with a dedicated hypertrophic cardiomyopathy program using a multidisciplinary approach.

Incidence and predictors of sudden death, major conduction defects and sustained ventricular tachyarrhythmias in 1388 patients with myotonic dystrophy type 1.

AIMS: To describe the incidence and identify predictors of sudden death (SD), major conduction defects and sustained ventricular tachyarrhythmias (VTA) in myotonic dystrophy type 1 (DM1). METHODS AND RESULTS: We retrospectively enrolled 1388 adults with DM1 referred to six French medical centres between January 2000 and October 2013. We confirmed their vital status, classified all deaths, and determined the incidence of major conduction defects requiring permanent pacing and sustained VTA. We searched for predictors of overall survival, SD, major conduction defects, and sustained VTA by Cox regression analysis. Over a median 10-year follow-up, 253 (18.2%) patients died, 39 (3.6%) suddenly. Analysis of the cardiac rhythm at the time of the 39 SD revealed sustained VTA in 9, asystole in 5, complete atrioventricular block in 1 and electromechanical dissociation in two patients. Non-cardiac causes were identified in the five patients with SD who underwent autopsies. Major conduction defects developed in 143 (19.3%) and sustained VTA in 26 (2.3%) patients. By Cox regression analysis, age, family history of SD and left bundle branch block were independent predictors of SD, while age, male sex, electrocardiographic conduction abnormalities, syncope, and atrial fibrillation were independent predictors of major conduction defects; non-sustained VTA was the only predictor of sustained VTA. CONCLUSIONS: SD was a frequent mode of death in DM1, with multiple mechanisms involved. Major conduction defects were by far more frequent than sustained VTA, whose only independent predictor was a personal history of non-sustained VTA. ClinicalTrials.gov no: NCT01136330.

Electrocardiographic predictors of mortality and sudden cardiac death in patients with end stage renal disease on hemodialysis.

Patients with end stage renal disease (ESRD) on hemodialysis experience a high incidence of cardiovascular mortality, and sudden cardiac death (SCD) accounts for approximately 25% of all deaths in this patient population. Despite this high risk of SCD, many non-invasive SCD risk stratification tools that are frequently applied to other patient populations (such as those with prior myocardial infarction and reduced left ventricular systolic function) may be less useful markers of increased SCD risk in ESRD. Improved SCD risk stratification tools for use specifically in patients on hemodialysis are therefore necessary to optimally target use of primary prevention interventions aimed at decreasing SCD incidence. Electrocardiography is an effective, non-invasive SCD risk stratification tool in hemodialysis patients. This article reviews data supporting the association between various ECG parameters (QT interval, spatial QRS-T angle, signal averaged ECG, heart rate variability, and T-wave alternans) and mortality/SCD in the dialysis population. Despite the association between abnormal ECG parameters and SCD, it remains unclear if these abnormal parameters (such as prolonged QT interval) are mechanistically related to SCD and/or ventricular arrhythmias, or if they are simply markers for more severe cardiac disease, such as left ventricular hypertrophy, that may independently predispose to SCD. Current obstacles that impair widespread implementation of ECG risk stratification in the hemodialysis population are also discussed.