Biventricular pacing attenuates T-wave alternans and T-wave amplitude compared to other pacing modes

Background: The impact of altered ventricular activation, including biventricular (BV) pacing, on T-wave alternans (TWA) and arrhythmic substrates is unclear. We studied how differing ventricular activation sequence alters TWA; the interval from peak-to-end of the T-wave (TpTe) and T-wave amplitude during right (RV), left (LV), and biventricular (BV) pacing; and right atrial (RA) pacing in patients with preexisting conduction delay.
Methods and Results: We measured TWA during RA, RV, LV, and BV pacing in 33 patients receiving cardiac-resynchronization-therapy-defibrillators. TWA magnitude (V_alt) was lower during BV than RV (P < 0.01), RA (P < 0.01), or LV pacing. As a result, BV-TWA was more often negative than RV-TWA (P < 0.01), LV-TWA, and RA-TWA, particularly when discordant between pacing modes (P < 0.01). Overall, 83% of TWA recordings were abnormal (25% indeterminate), and 17% negative. BV pacing reduced T-wave amplitude (P < 0.05) and TpTe (P < 0.005) compared to RV pacing and LV pacing (P < 0.05; P < 0.005 respectively). Notably, TWA magnitude varied linearly with T-wave amplitude for all pacing modes (P < 0.001). Over 410 ± 252 days' follow-up, RV-TWA predicted the combined endpoint of death and ICD therapy with 86% negative predictive value (P < 0.05). BV-TWA, RA-TWA, and other repolarization indices were not predictive.
Conclusions: BV pacing attenuates TWA in tandem with reduced T-wave magnitude. In these patients with baseline QRS prolongation, RV-TWA predicted events more effectively than BV-TWA and RA-TWA. Further studies are required to understand how altered ventricular activation influences repolarization dynamics and arrhythmic tendency.     

Comparison of microvolt T-wave alternans measurements using atrial pacing compared to atropine administration

Background: Microvolt T-wave alternans (MTWA) has been associated with malignant ventricular arrhythmias in patients (pts) with structural heart disease. MTWA has been shown to be a strong heart rate-dependent arrhythmia marker. However, in clinical practice some pts in which MTWA should be assessed are unable to perform physical exercise to increase heart rate due to various reasons.
Methods: In this study, we investigated the feasibility of noninvasive MTWA measurement by using intravenous atropine to increase heart rate and compared the results to MTWA measurement by right atrial (RA) pacing during electrophysiologic (EP) study in 27 consecutive pts (53 ± 14 years; nine women). Determining the arrhythmia event-rate, a follow-up of 18 months was performed in all pts.
Results: Using atropine, five pts (18%) did not reach the target heart rate (105 bpm). In the remaining group of pts, concordant results for MTWA assessment could be found in 21 pts (96%). Comparing MTWA positive tests there were slightly higher amplitudes using right atrial (RA) pacing than atropine (7.0 ± 2.3μV vs 6.3 ± 2.2μV, P = 0.03; r = 0.97). During follow-up all pts with a positive MTWA test had documented ventricular arrhythmias. There were no arrhythmic events in the MTWA negative group.
Conclusion: Whenever target heart rate for MTWA evaluation is obtained by intravenous atropine, the results are comparable to RA pacing. In using atropine there has been observed no pharmacologically influenced increase of MTWA voltage leading to false positive MTWA results. Therefore the use of atropine can be recommended as a safe, non-invasive, and reliable method for MTWA assessment.     

Microvolt T-wave alternans testing for ventricular arrhythmia risk stratification

Extensive research and clinical interest has focused recently on use of microvolt T-wave alternans (MTWA) as a means for sudden death risk stratification in patients with cardiomyopathy. Emphasis has been placed on determining whether MTWA testing can more accurately identify high-risk patients from the broad population who are potentially eligible for prophylactic implantable cardioverter defibrillators. More recent studies seek to determine if additional patients not currently covered by primary prevention implantable cardioverter defibrillator guidelines could be defined using MTWA. Unfortunately, accumulation of clinical data has not necessarily led to clarity in the minds of the end-users as to the role of MTWA in clinical practice. This article serves to provide background information, selective review of relevant studies, and a perspective on where the field stands today. A general framework for incorporating MTWA into clinical practice is presented.     

Relationship between abnormal microvolt T-wave alternans and poor glycemic control in type 2 diabetic patients

BACKGROUND: Abnormal microvolt T-wave alternans (TWA) predicts the risk of ventricular arrhythmias and sudden cardiac death. Although type 2 diabetes is associated with an increased risk of these events, there is a dearth of available data on microvolt TWA measurements in type 2 diabetic populations. METHODS: We studied 59 consecutive type 2 diabetic outpatients without manifest cardiovascular disease (CVD) and 35 non-diabetic controls who were matched for age, sex, and blood pressure values. Microvolt TWA analysis was performed non-invasively using the CH-2000 system during a sub-maximal exercise with the patient sitting on a bicycle ergometer. RESULTS: The frequency of abnormal TWA was significantly higher in diabetic patients than in controls (25.4 vs 5.7%; P < 0.01). Among diabetic patients, those with abnormal TWA (n = 15) had remarkably higher hemoglobin A1c (HbA1c) (8.1 +/- 0.9 vs 7.1 +/- 0.8%, P < 0.001) and slightly smaller time-domain heart rate variability parameters (i.e., RMSSD, root mean square of difference of successive R-R intervals) than those with normal TWA (n = 44). Gender, age, body mass index, lipids, blood pressure values, cigarette smoking, diabetes duration, microvascular complication status, QTc interval, and current use of medications did not significantly differ between the groups. In multivariate regression logistic analysis, HbA1c (OR 13.6, 95% CI 2.0-89.1; P = 0.0076) predicted abnormal TWA independent of RMSSD values and other potential confounders. CONCLUSIONS: Our findings suggest that abnormal TWA is a very common condition (approximately 25%) among people with type 2 diabetes without manifest CVD and is closely correlated to glycemic control.     

The immediate reproducibility of T wave alternans during bicycle exercise

A number of recent studies have demonstrated that the microvolt level T wave alternans measured during bicycle exercise can identify patients at high risk for developing malignant ventricular arrhythmias. However, little is known about the reproducibility of T wave alternans measured during bicycle exercise. The purpose of this study was to prospectively evaluate the immediate reproducibility of T wave alternans measured during bicycle exercise testing. Thirty-five patients with congestive heart failure underwent two sequential bicycle exercise tests with the measurement of T wave alternans. The T wave alternans tests were randomly sorted and then classified by two readers who were blinded to the patient and the sequence of the two tests. Tests were classified as determinate (positive or negative) or indeterminate according to previously published criteria. Of the 22 patients that had two determinate T wave alternans tests, 18 (82%) of 22 patients had concordant test results (kappa 0.58). Of the four patients who had discordant test results on the two tests, three patients had one test that was borderline and difficult to interpret. One patient had two sequential tests that were clearly different. Of the ten patients whose initial test was indeterminate, five became determinate on the second test. T wave alternans measured during bicycle exercise has an acceptable reproducibility when measurements are madefrom two sequential exercise tests performed within a short period. This data suggests that the measurement of T wave alternans during exercise is reliable. Repeating the exercise test with a second measure of T wave alternans during the same session can significantly reduce the proportion of patients with indeterminate test results.     

T-wave alternans testing in pacemaker patients: comparison of pacing modes and long-term prognostic relevance

Background: T‐wave alternans (TWA) is a useful method for identifying patients who are at risk for sudden cardiac death. We aimed to determine the effects of different pacing modes on test results and long‐term prognostic relevance of TWA in patients following a dual‐chamber (DDD) pacemaker implantation. Methods: Sixty‐three patients (mean age 68 ± 13 years) with structural heart disease and recently implanted DDD pacemakers were enrolled. Left ventricular (LV) function was normal or moderately impaired (mean LV ejection fraction 61 ± 13%). All patients underwent sequential TWA testing using atrial and ventricular pacing. Results: During atrial pacing requiring physiologic conduction to the ventricles, 21% of TWA tests were positive, 43% negative, and 36% indeterminate. When using right ventricular (RV) pacing in the same patients, 19% of tests were positive, 40% negative, and 41% indeterminate. When positive and indeterminate tests were grouped as nonnegative, the concordance between atrial and ventricular pacing was 62% (κ= 0.22). After a mean follow‐up of 5.9 ± 1.9 years, 18 (29%) patients had died. Improved survival was predicted by a negative TWA test using atrial pacing (P = 0.028), but not with ventricular pacing (P = 0.722). Conclusions: In patients with dual‐chamber pacemakers, there is a low concordance of TWA test results between atrial pacing with intrinsic conduction to the ventricles and apical RV pacing via pacemaker electrode. However, TWA during atrial pacing clearly exerts long‐term prognostic relevance in a patient group with preserved LV function and structural heart disease. (PACE 2011; 34:1054–1062)     

Abnormal heart rate turbulence predicts the initiation of ventricular arrhythmias

BACKGROUND: Abnormal heart rate turbulence (HRT) reflects autonomic derangements predicting all-cause mortality, yet has not been shown to predict ventricular arrhythmias in at-risk patients. We hypothesized that HRT at programmed ventricular stimulation (PVS) would predict arrhythmia initiation in patients with left ventricular dysfunction. METHODS: We studied 27 patients with coronary disease, left ventricular ejection fraction (LVEF) 26.7 +/- 9.1%, and plasma B-type natriuretic peptide (BNP) 461 +/- 561 pg/mL. Prior to arrhythmia induction at PVS, we measured sinus cycles after spontaneous or paced premature ventricular contractions (PVCs) for turbulence onset (TO; % cycle length change following PVC) and slope (TS; greatest slope of return to baseline cycle). T-wave alternans (TWA) was also measured during atrial pacing. RESULTS: At PVS, abnormal TO (> or =0%) predicted inducible ventricular tachycardia (VT; n = 10 patients; P < 0.05). TO was greater in inducible than in noninducible patients (2.3 +/- 3.1% vs -0.02 +/- 2.8%, P < 0.05) and correlated with LVEF (P < 0.05) but not with BNP. TS did not differ between groups. Conversely, ambulatory HRT differed significantly from HRT at PVS (TO -0.55 +/- 1.08% vs 0.85 +/- 3.02%, P < 0.05; TS 2.63 +/- 2.09 ms/RR vs 8.70 +/- 6.56 ms/RR, P < 0.01), and did not predict inducible VT but trended (P = 0.05) to predict sustained VT on 739 +/- 179 days follow-up. TWA predicted inducible (P < 0.05) and spontaneous (P = 0.0001) VT but did not co-migrate with HRT. CONCLUSIONS: Abnormal HRT measured at PVS predicted the induction of sustained ventricular arrhythmias in patients with ischemic cardiomyopathy. However, HRT at PVS did not correlate with ambulatory HRT, nor with TWA, both of which predicted spontaneous ventricular arrhythmias. Thus, HRT may reflect the influence of autonomic milieu on arrhythmic susceptibility and is likely complementary to traditional arrhythmic indices.     

Socioeconomic Status and Survival from Out-of-hospital Cardiac Arrest

Background: Socioeconomic status (SES) has been linked to heart disease, but its influence on outcome from out‐of‐hospital cardiac arrest (OHCA) is not well understood. Objectives: The authors hypothesized that higher levels of SES would be associated with better survival, potentially through demographic, circumstance, or care factors. Methods: A cohort investigation of OHCA due to heart disease treated by emergency medical services between January 1, 1999, and December 31, 2003, was conducted in the study county. Socioeconomic status was assessed using two different measures: an individual‐level measure, tax‐assessed property value per unit, and a geography‐based measure, median household income from the 2000 Census. The authors used logistic regression to evaluate the association between survival to hospital discharge and quartile of SES. Models systematically adjusted for demographic, circumstance, and care factors that could potentially confound the association. Results: Socioeconomic status as measured by value per unit was associated with survival in unadjusted models (odds ratio [OR] = 1.21; 95% confidence interval [95% CI] = 1.05 to 1.36, for each successive increase in value‐per‐unit quartile). Adjustment for demographic, circumstance, and care factors altered the association only slightly (fully adjusted OR = 1.23; 95% CI = 1.08 to 1.39). In contrast, SES as measured by median household income was not associated with survival. The study could not investigate all potentially explanatory factors. The findings may not be generalizable to persons or communities that differ from the current investigation. Conclusions: An individual‐level, but not an area‐level, measure of SES predicted survival following OHCA independent of demographic, circumstance, or care factors. Future research should continue to investigate mechanisms through which SES is associated with OHCA survival.     

急性心肌梗死患者T波电交替及窦性心率震荡的特征及临床意义

目的研究心肌梗死及心肌梗死合并糖尿病患者T波电交替(TWA)和窦性心率震荡(HRT)的特征及其临床意义。方法选取149例患者,其中心肌梗死(MI)57例,心肌梗死合并糖尿病(MI+DM)52例,对照组40例。给予动态心电图检查,应用时域分析法和渐量修正技术分析TWA值,以及HRT的两个参数:震荡初始(TO)、震荡斜率(TS)。分析:1三组患者TWA、TO及TS均值的比较;TWA阳性率的比较;2心肌梗死患者复合心脏事件(室速/室颤、心脏性死亡)的发生率。结果 1MI组和MI+DM组患者TWA均值及TWA的阳性率明显高于对照组(P0.01),MI+DM组患者TWA的阳性率高于MI组,但TWA均值差异无统计学意义;2MI+DM组室速/室颤发生率高于MI组(P0.05),MI+DM组心脏性死亡患者2例;3心肌梗死患者的震荡初始(TO)较对照组增加(P0.05),而震荡斜率(TS)则减低(P0.01)。结论心肌梗死患者TWA值增加,HRT的两个参数-TS减弱而TO增加。TWA和HRT可能为评价心肌梗死患者发生恶性心律失常及心脏性猝死的有用指标。     

Effect of known history of heart disease on survival outcomes after out‐of‐hospital cardiac arrests

Objective

We aimed to investigate the effect of known heart disease on post‐out‐of‐hospital cardiac arrest (OHCA) survival outcomes, and its association with factors influencing survival.

Methods

This was an observational, retrospective study involving an OHCA database from seven Asian countries in 2009–2012. Heart disease was defined as a documented diagnosis of coronary artery disease or congenital heart disease. Patients with non‐traumatic arrests for whom resuscitation was attempted and with known medical histories were included. Differences in demographics, arrest characteristics and survival between patients with and without known heart disease were analysed. Multivariate logistic regression was performed to identify factors influencing survival to discharge.

Results

Of 19 044 eligible patients, 5687 had known heart disease. They were older (77 vs 72 years) and had more comorbidities like diabetes (40.9 vs 21.8%), hypertension (60.6 vs 36.0%) and previous stroke (15.2 vs 10.1%). However, they were not more likely to receive bystander cardiopulmonary resuscitation (P = 0.205) or automated external defibrillation (P = 0.980). On univariate analysis, known heart disease was associated with increased survival (unadjusted odds ratio 1.16, 95% confidence interval 1.03–1.30). However, on multivariate analysis, heart disease predicted poorer survival (adjusted odds ratio 0.76, 95% confidence interval 0.58–1.00). Other factors influencing survival corresponded with previous reports.

Conclusions

Known heart disease independently predicted poorer post‐OHCA survival. This study may provide information to guide future prospective studies specifically looking at family education for patients with heart disease and the effect on OHCA outcomes.     

Epidemiology of Ventricular Tachycardia/Ventricular Fibrillation and Sudden Cardiac Death

Despite the difficulties correlating pathological data with acute clinical events in the field of sudden cardiac death, information useful to both the clinician and the epidemiologist has developed. Sudden cardiac death may be defined broadly. These definitions have varied, but it is now generally recognized that sudden cardiac death should reflect a time span of less than one hour. The epidemiology of sudden cardiac death incorporates many factors, including age, heredity, gender, and race. Coronary risk factors and the history of prior coronary heart disease constitute additional points of importance. Finally, clinical characteristics of the cardiac arrest patient are variable. Improving outcome in prehospital cardiac arrest victims involves a multifactorial approach involving rescue personnel, resuscitation technology, and the participation of the public.     

The effect of skin incision followed by alfentanil on catecholamine levels and on the T-wave amplitude of ECG during isoflurance anaesthesia

Haemodynamic, ECG T-wave amplitude and plasma potassium changes and plasma catecholamine responses to skin incision followed by alfentanil were studied in 24 ASA I patients. Propofol and vecuronium were used without anticholinergics for induction of anaesthesia followed by isoflurane in O₂/air. End-tidal isoflurane concentration was kept constant (0.7%) for 30 min before the skin incision. Five min after the skin incision alfentanil 30 g kg^–1 was given. Blood samples for catecholamines and plasma potassium concentrations were drawn from right ventricle of the heart one minute before and after the skin incision and two minutes after alfentanil.Heart rate, systolic and diastolic arterial pressures increased after the skin incision (P<0.001), and decreased after alfentanil (P<0.001). Plasma adrenaline and noradrenaline concentrations increased slightly after the skin incision (P<0.05 andP<0.01, respectively). Noradrenaline levels continued to increase after alfentanil (P<0.001) despite totally abolished haemodynamic responses to the skin incision.ECG T-wave amplitude changes, measured as R/T ratio, did not correlate to the changes in plasma catecholamine levels: both rapid increases and decreases in R/T ratio were seen. No plasma potassium changes were seen during the trial. T-wave changes, occurring in seconds after the skin incision, are probably produced by a direct catecholamine release from cardiac sympathetic nerve endings.     

A Critical Appraisal of Quantitative Spectro-Temporal Analysis of the Signal-Averaged ECG: Predicting Arrhythmic Events After Myocardial Infarction

The objective of this study was to determine if spectra-temporal analysis of the signal-averaged ECG (SAECG) predicts spontaneous sustained ventricular tachyarrhythmias and sudden death in patients prospectively followed after myocardial infarction (MI). A SAECG was recorded in 177 patients 9 ± 5 days after MI. Spectro-temporal analysis of the SAECG involved incrementing a Hanning window every 3 ms beginning 20 ms before the end of the QRS complex and extending into the ST segment. Quantitative analysis was performed using a cross-correlation function to create a normality factor. A normality factor < 0.3 was deemed abnormal. The SAECG was abnormal in 41 % of patients using time-domain analysis and 44% of patients using spectra-temporal analysis. There was no correlation between an abnormal SAECG in the time domain and the frequency domain. Patients with inferior wall MI were more likely to have an abnormal spectra-temporal map (odds ratio 2.26, P < 0.05). Time-domain analysis of the SAECG (relative risk (RE) 2.6) was a statistically significant univariate predictor of arrhythmic events. Spectra-temporal analysis of the SAECG was only weakly (RR 1.8) and not significantly (P = 0.15) associated with the spontaneous occurrence of these arrhythmias. When both time-domain analysis and spectra-temporal analysis of the SAECG were abnormal, the relative risk for an arrhythmic event was increased by 3.3-fold. Quantitative spectra-temporal analysis of high frequency signals within the SAECG cannot by itself predict the occurrence of spontaneous ventricular arrhythmias in patients after MI.     

Survivors of out-of-hospital cardiac arrest: Morbidity and long-term survival

Sudden cardiac death accounts for two thirds of death due to coronary artery disease. Advanced cardiac life support can now be brought directly to patients with out-of-hospital cardiac arrest, and in this country, as many as 30% of such patients can be discharged from the hospital annually. Certain clinical and resuscitation-related factors are predictive of mortality and morbidity. The best clinical predictors of long-term survival are absence of previous history of myocardial infarction, lack of congestive heart failure during hospitalization, and age less than 60 years. Resuscitation-related predictors of long-term survival are a short time from collapse to cardiopulmonary resuscitation (CPR), and a short time from collapse to CPR combined with a short time to provision of definitive care. The majority of cardiac arrest survivors are able to resume previous levels of function.     

Reproducibility of Time and Frequency Domain Analysis of Heart Rate Variability in Patients with Chronic Stable Angina

Before heart rate variability (HRV) can be used to investigate the effects of drugs or other clinical interventions in chronic stable angina, it is important to establish the stability and reproducibility of HRV indices over time. HRV analysis was performed on two consecutive 24-hour ambulatory ECG recordings in 19 patients with chronic stable angina. Time-domain analysis included average heart rate, variance, SDNN, SDANN5, ASDNN5, and PNN50. The power spectral analysis was computed using fast Fourier transformation for the total power (0.003 and 0.40 Hz), low frequency (0.04–0.15 Hz), and high frequency (0.15–0.40 Hz) bands. No statistically significant differences in the time or frequency domains were found between the two ambulatory ECG recordings. HRV indices in the time and frequency domains are consistent and reproducible in patients with chronic stable angina. Thus, cardiac autonomic tone can be evaluated using HRV analyses, and any significant changes that occur after medical therapy or other clinical interventions can be ascribed to the intervention rather than the lability of cardiac autonomic tone.     

肺动脉高压与心律失常

心律失常是影响肺动脉高压患者病死率的重要因素.目前认为肺动脉高压患者发生心律失常的因素包括心脏自律性改变、心脏复极化延迟导致QT间期延长、右心室心肌缺血等.室上性心动过速直接导致肺动脉高压患者预后不良.肺动脉高压患者室性心律失常少见,心动过缓是其强烈的死亡预测因子.本文对肺动脉高压患者出现不同心律失常的研究进展作一综述,旨在阐明肺动脉高压与心律失常的关系.     

Low‐Risk Profile for Malignant Ventricular Arrhythmias and Sudden Cardiac Death after Surgical Ventricular Reconstruction

Background: Although it has been recently demonstrated that there was no significant difference in total survival and clinical outcomes between patients who underwent coronary artery bypass grafting (CABG) with or without surgical ventricular reconstruction (SVR), the question of whether or not SVR decreases the arrhythmic risk profile in this population has not been clarified yet. Objective: To determine the real incidence of sudden cardiac death (SCD) and sustained ventricular tachycardia/ventricular fibrillation (sustained VT/VF) in patients following CABG added to SVR and to define their clinical and echocardiographic parameters predicting in‐hospital and long‐term arrhythmic events (SCD + sustained VT/VF). Methods: Pre‐ and postoperative clinical and echocardiographic values as well as postoperative electrocardiogram Holter data of 65 patients (21 female, 63 ± 11 years) who underwent SVR + CABG were retrospectively evaluated. Results: Mean follow‐up was 1,105 ± 940 days. At 3 years, the SCD‐free rate was 98% and the rate free from arrhythmic events was 88%. Multivariate logistic analysis identified a preoperative left ventricular end‐systolic volume index (LVESVI) > 102 mL/m² (odds ratio [OR] 1.4, confidence interval [CI] 1.073–1.864, P = 0.02; sensitivity 100%, specificity 94%) and a postoperative pulmonary artery systolic pressure (PASP) > 27 mmHg (OR 2.3, CI 1.887–4.487, P = 0.01; sensitivity 100%, specificity 71%) as independent predictors of arrhythmic events. Conclusions: Our and previous studies report a low incidence of arrhythmic events in patients following SVR added to CABG, considering the high‐risk profile of the study population. A preoperative LVESVI > 102 mL/m² and a postoperative PASP > 27 mmHg had a good sensitivity and specificity in predicting arrhythmic events. (PACE 2010; 33:1054–1062)