Long-term temporal patterns of ventricular tachyarrhythmias

Management of patients with an electrical storm or clustered ventricular arrhythmias: a clinical consensus statement of the European Heart Rhythm Association of the ESC-endorsed by the Asia-Pacific Heart Rhythm Society, Heart Rhythm Society, and Latin-American Heart Rhythm Society

Electrical storm (ES) is a state of electrical instability, manifesting as recurrent ventricular arrhythmias (VAs) over a short period of time (three or more episodes of sustained VA within 24 h, separated by at least 5 min, requiring termination by an intervention). The clinical presentation can vary, but ES is usually a cardiac emergency. Electrical storm mainly affects patients with structural or primary electrical heart disease, often with an implantable cardioverter-defibrillator (ICD). Management of ES requires a multi-faceted approach and the involvement of multi-disciplinary teams, but despite advanced treatment and often invasive procedures, it is associated with high morbidity and mortality. With an ageing population, longer survival of heart failure patients, and an increasing number of patients with ICD, the incidence of ES is expected to increase. This European Heart Rhythm Association clinical consensus statement focuses on pathophysiology, clinical presentation, diagnostic evaluation, and acute and long-term management of patients presenting with ES or clustered VA.

Skin sympathetic nerve activity and the temporal clustering of cardiac arrhythmias

BACKGROUND

Simultaneous noninvasively recorded skin sympathetic nerve activity (SKNA) and electrocardiogram (neuECG) can be used to estimate cardiac sympathetic tone. We tested the hypothesis that large and prolonged SKNA bursts are associated with temporal clustering arrhythmias.

METHODS

We recorded neuECG in 10 patients (69 ± 10 years old) with atrial fibrillation (AF) episodes and in 6 patients (50 ± 13 years old) with ventricular tachycardia (VT) or fibrillation (VF) episodes. Clustering was defined by an arrhythmic episode followed within 1 minute by spontaneous recurrences of the same arrhythmia. The neuECG signals were bandpass filtered between 500-1000 Hz to display SKNA.

RESULTS

There were 22 AF clusters, including 231 AF episodes from 6 patients, and 9 VT/VF clusters, including 99 VT/VF episodes from 3 patients. A total duration of SKNA bursts associated with AF was longer than that during sinus rhythm (78.9 min/hour [interquartile range (IQR) 17.5-201.3] vs. 16.3 min/hour [IQR 14.5-18.5], P = 0.022). The burst amplitude associated with AF in clustering patients was significantly higher than that in nonclustering patients (1.54 μV [IQR 1.35-1.89], n = 114, vs. 1.20 μV [IQR 1.05-1.42], n = 21, P < 0.001). The SKNA bursts associated with VT/VF clusters lasted 9.3 ± 3.1 minutes, with peaks that averaged 1.13 ± 0.38 μV as compared with 0.79 ± 0.11 μV at baseline (P = 0.041).

CONCLUSION

Large and sustained sympathetic nerve activities are associated with the temporal clustering of AF and VT/VF.

FUNDING

This study was supported in part by NIH grants R42DA043391 (THE), R56 HL71140, TR002208-01, R01 HL139829 (PSC), a Charles Fisch Cardiovascular Research Award endowed by Suzanne B. Knoebel of the Krannert Institute of Cardiology (TK and THE), a Medtronic-Zipes Endowment, and the Indiana University Health-Indiana University School of Medicine Strategic Research Initiative (PSC).

Prognostic significance of ventricular tachycardia clustering after catheter ablation in non-ischemic dilated cardiomyopathy

BACKGROUND

Ventricular tachycardia clustering (VTc) is associated with a worse clinical outcome in patients with non-ischemic dilated cardiomyopathy (NI-DCM) and implantable cardioverter defibrillator (ICD); however, its role after catheter ablation (CA) has still not been investigated. Aim of this study was to evaluate the prognostic significance of VTc after CA.

METHODS

96 consecutive patients (59 ± 13 years, 82% males) with NI-DCM underwent CA for drug-refractory VT. After CA, patients with VT recurrence were divided into two groups: (1) patients that presented with VTc defined as the occurrence of three or more appropriate ICD interventions within 2 weeks, and (2) patients without VTc.

RESULTS

At 56-months follow-up after ablation 52/96 (54%) patients had recurrent VT, 28/52 (54%) patients experienced VTc and 24/52 (46%) no VTc. When comparing patients with VTc after CA with those without, no differences in terms of age, sex, ejection fraction and cardiovascular risk factors were found. However, patients with VTc showed higher mortality rates at follow-up (54% vs 21% p = 0.04; log-rank p ≤ 0.01). No survival differences were found between patients without VT recurrence and those with VT recurrence but without VTc (29% vs 21% p = 0.77). Predictors of VTc were LVEF < 30% at follow-up and endo-epicardial scar at 3D voltage mapping. At stepwise multivariate analysis VTc and NHYA class were the only independent predictors of death (respectively, RR 3.4, CI 95% 1.16-10.3, p = 0.02; RR 4.18, CI 95% 1.3-12.6, p = 0.01).

CONCLUSIONS

VTc after CA is an independent predictor of survival and is associated with reduced LVEF at follow-up and endo-epicardial scar at 3D voltage mapping.

Electrical Storm: Incidence, Prognosis and Therapy

The term "electrical storm" indicates a life-threatening clinical condition characterized by the recurrence of hemodynamically unstable ventricular tachycardia and/or ventricular fibrillation, in particular in patients with ICD implanted for primary or secondary prevention. Although there isn't a shared definition of electrical storm, nowadays the most accepted definition refers to three or more separate arrhythmia episodes leading to ICD therapies including antitachycardia pacing or shock occurring over a single 24 hours' time period. Clinical presentation can be dramatic and triggering mechanism are not clear at all yet, but electrical storm is associated with high mortality rates and low patients quality of life, both in the acute phase and in the long term. The first line therapy is based on antiarrhythmic drugs to suppress electrical storm, but in refractory patients, interventions such as catheter ablation or in some cases surgical cardiac sympathetic denervation might be helpful. Anyhow, earlier interventional management can lead to better outcomes than persisting with antiarrhythmic pharmacologic therapy and, when available, an early interventional approach should be preferred.

Increased variability of the coupling interval of premature ventricular contractions as a predictor of cardiac mortality in patients with left ventricular dysfunction

BACKGROUND

The characteristics and prognostic value of the variability of premature ventricular contraction (PVC) coupling intervals (CIs) for cardiac mortality are not yet decisive.

METHODS AND RESULTS

In 133 consecutive patients (58±14 years old, 53 women) who had left ventricular dysfunction (LVD: ejection fraction <50%) and frequent PVCs (≥10/h) who underwent 24-h ambulatory electrocardiography (AECG) recording and (123)I-metaiodobenzylguanidine myocardial single-photon emission computed tomography simultaneously, the heart rate turbulence onset, slope, and T-wave alternans were analyzed from the 24-h AECG. The CI of the PVCs (MEANNV), standard deviation of the CI of the PVCs (SDNV) as an index of the variability of the PVC CI, and their ratio to the preceding N-N intervals (SDNV/SDNN) were calculated from constructed Poincaré plots using the annotated 24-h AECG QRS data. The primary endpoint was cardiac mortality. The mean follow-up period was 63 months. Among 133 patients, 114 survived (group 1) and 19 (14%, group 2) died during the follow-up. The MEANNVand SDNVwere higher in group 2 (539±104 vs. 599±114 ms, P=0.021; 64±34 vs. 83±37 ms, P=0.022, respectively). The SDNV, PVC count, and delayed heart/mediastinum ratio remained as significant predictors of cardiac mortality in the binary logistic regression analysis.

CONCLUSIONS

These results suggest that the SDNVcould be another adjunctive parameter for predicting cardiac mortality in LVD.

Optimal antiarrhythmic drug therapy for electrical storm

Electrical storm, defined as 3 or more separate episodes of ventricular tachycardia or ventricular fibrillation within 24 hours, carries significant morbidity and mortality. These unstable ventricular arrhythmias have been described with a variety of conditions including ischemic heart disease, structural heart disease, and genetic conditions. While implantable cardioverter defibrillator implantation and ablation may be indicated and required, antiarrhythmic medication remains an important adjunctive therapy for these persons.

[Electrical storm: definition, prevalence, causes and prognostic implications]

BACKGROUND

Electrical storm (ES) represents a state of cardiac electrical instability which manifests by multiple episodes of ventricular tachyarrhythmia (VT) within a short time. In patients with an implantable cardioverter-defibrillator (ICD), ES is best defined as ≥ 3 appropriate VT detections in 24 h, treated by antitachycardia pacing or shock. The number of shocks and inappropriate detections are irrelevant for the definition. Within a period of 3 years ES occurred in approximately 25 % of ICD patients with secondary prophylaxis indications of sudden cardiac death. Although the definition includes minor arrhythmic events, ES frequently consists of up to 50 VTs. Potential triggers found in 20-65 % of patients include new/deteriorated heart failure, diarrhea/hypokalemia, changes in antiarrhythmic medication, association with other illnesses, and psychological stress. In most patients ES consists of monomorphic VT indicating the presence of reentry while ventricular fibrillation indicating acute ischemia is rare.

MATERIAL AND METHODS

ES seems to have a low immediate mortality (1 %) but frequently (50-80 %) leads to hospitalization. Long-term prognostic implications of ES are unclear. The key intervention in ES is a reduction of the elevated sympathetic tone by beta blockers and also frequently sedation. Amiodarone i.v. is highly efficient in ES while class I antiarrhythmic drugs are usually unsuccessful. Substrate mapping and VT ablation may be useful in treatment and prevention of ES. Prevention of ES requires ICD programming systematically avoiding unnecessary shocks by long VT detection and numerous attempts of antitachycardia pacing before shock therapy which can fuel the sympathetic tone and prolong ES.

Electrical storms in patients with an implantable cardioverter defibrillator

PURPOSE

In some patients with an implantable cardioverter defibrillator (ICD), multiple episodes of electrical storm (ES) can occur. We assessed the prevalence, features, and predictors of ES in patients with ICD.

MATERIALS AND METHODS

Eighty-five patients with an ICD were analyzed. ES was defined as the occurrence of two or more ventricular tachyarrhythmias within 24 hours.

RESULTS

Twenty-six patients experienced at least one ES episode, and 16 patients experienced two or more ES episodes. The first ES occurred 209 ± 277 days after ICD implantation. In most ES cases, the index arrhythmia was ventricular tachycardia (65%). There were no obvious etiologic factors at the onset of most ES episodes (57%). More patients with a structurally normal heart (p = 0.043) or ventricular fibrillation (VF) as the index arrhythmia (p = 0.017) were in the ES-free group. Kaplan-Meier estimates and a log-rank test showed that patients with nonischemic dilated cardiomyopathy (DCMP) (log-rank test, p = 0.016) or with left ventricular ejection fraction < 35% (p = 0.032) were more likely to experience ES, and that patients with VF (p = 0.047) were less affected by ES. Cox proportional hazard regression analysis showed that nonischemic DCMP correlated with a greater probability of ES (hazard ratio, 3.71; 95% confidence interval, 1.16-11.85; p = 0.027).

CONCLUSION

ES is a common and recurrent event in patients with an ICD. Nonischemic DCMP is an independent predictor of ES. Patients with VF or with a structurally normal heart are less likely to experience ES.

Predictors of electrical storm recurrences in patients with implantable cardioverter-defibrillators

AIMS

To determine prevalence and predictors of electrical storm recurrences (ES-Rs) in patients with implantable cardioverter-defibrillators (ICDs) as electrical storms (ESs) represent serious clinical events carrying a high risk of mortality.

METHODS AND RESULTS

Single-centre study analysing data of consecutive patients receiving an ICD between 1993 and 2008. Electrical storm was defined as ≥ 3 separate ventricular tachyarrhythmic (VT/VF) episodes ≤ 24 h. Nine hundred and fifty-five patients [mean left ventricular ejection fraction (LVEF) 35.7 ± 15.6%] were prospectively followed for 54.2 ± 35.5 months. In 274 of 955 patients (28.7%), 2871 VT/VF episodes were observed. One hundred and fifty-three ES episodes occurred in 63 of 955 patients (6.6%). Thirty-two of 63 patients (50.8%) experienced ≥ 2 ES episodes. Twenty-six of 32 patients (81.2%) with ES-Rs experienced the second ES episode within 1 year after the initial event. Cox regression analysis identified an LVEF ≤ 30% (OR 2.2; 95% CI 1.021-4.856; P = 0.044) and a patient's age >65 years (OR 3.5; 95% CI 1.207-10.176; P = 0.021) to be predictive for ES-Rs. Patients with angiotensin-converting enzyme (ACE) inhibitor therapy were less likely to experience ES-Rs (OR 0.39; 95% CI 0.187-0.817; P = 0.013).

CONCLUSIONS

Electrical storm events are not rare in a 'real-world' patient population with ICDs (6.6% in 4.5 years). The risk for ES-Rs, especially within the first year after the initial event, is high. Left ventricular ejection fraction ≤ 30%, age >65 years, and a lack of ACE inhibitor therapy are independent predictors of ES-R.

Modification of the circadian pattern of ventricular tachyarrhythmias by beta-blocker therapy

BACKGROUND

Sudden cardiac death exhibits a circadian variation and predominantly occurs during morning hours, Beta-adrenergic antagonists have shown to blunt this morning peak. However, previous reports studying the effects of beta blockers on the circadian variation did not analyze the underlying cause of sudden cardiac death. It thus remains unclear whether ventricular tachyarrhythmias are influenced by beta-blocker therapy.

HYPOTHESIS

This study tested the hypothesis that beta-blocking agents blunt the morning peak of life-threatening ventricular tachyarrhythmias.

METHODS

In 87 patients who were treated and monitored with an implantable cardioverter defibrillator, the circadian distribution of ventricular tachyarrhythmias terminated by appropriate shocks was analyzed and compared in those receiving beta blockers versus those not receiving beta-blocker therapy.

RESULTS

Tachyarrhythmic episodes in the absence of beta-blocker therapy (n = 344) exhibited a circadian variation with a distinct morning peak (16, 38, 28, and 18% of episodes at 0-6, 6-12, 12-18, and 18-24 h, respectively, p < 0.001). In contrast, tachyarrhythmic episodes during beta-blocker therapy (n = 104) were equally distributed over time (22, 27, 24, and 27% of episodes at 0-6, 6-12, 12-18, and 18-24 h, respectively, p = 0.95). The circadian distribution of episodes was significantly different in patients with and those without beta blockade (p < 0.05).

CONCLUSION

Beta-adrenergic antagonists influence the circadian distribution of malignant ventricular tachyarrhythmias in patients with an implantable cardioverter defibrillator. The blunted morning peak of tachyarrhythmic events during beta blockade supports the hypothesis that a sympathetic surge is involved in the circadian pattern of malignant arrhythmias.

Recurrent ventricular arrhythmia storms in the age of implantable cardioverter defibrillator therapy: a comprehensive review

Rapidly recurrent ventricular arrhythmia is not an infrequent clinical entity in the era of implantable cardioverter defibrillator therapy. Clinical presentation can vary dramatically, from multiple defibrillator shocks with hemodynamic instability, to asymptomatic delivery of anti-tachycardia pacing. Although some investigators have reported disparate prognostic implications with electrical storm, in larger trials of both primary and secondary defibrillator populations, electrical storm appears to be a harbinger of cardiac death with a notably high mortality early post event. While acute cessation of electrical storm is generally achievable with medical therapy, it is critical to recognize that the causes for subsequent mortality are often not arrhythmic in nature. Thus, the challenge for cardiovascular practitioners is to maximize substrate based therapy and modification to not only prevent further episodes of electrical storm and possibly curtail the considerable risk of subsequent cardiac mortality.

Complex temporal patterns of spontaneous initiation and termination of reentry in a loop of cardiac tissue

A two-component model is developed consisting of a discrete loop of cardiac cells that circulates action potentials as well as a pacing mechanism. Physiological properties of cells such as restitutions of refractoriness and of conduction velocity are given via experimentally measured functions. The dynamics of circulating pulses and the pacer's action are regulated by two threshold relations. Patterns of spontaneous initiations and terminations of reentry (SITR) generated by this system are studied through numerical simulations and analytical observations. These patterns can be regular or irregular; causes of irregularities are identified as the threshold bistability (T-bistability) of reentrant circulation and in some cases, also phase-resetting interactions with the pacer.

Electrical storm in patients with an implanted defibrillator: a matter of definition

The term "electrical storm" (ES) indicates a state of cardiac electrical instability manifested by several episodes of ventricular tachyarrhythmias (VTs) within a short time. In patients with an implantable cardioverter defibrillator (ICD), ES is best defined as 3 appropriate VT detections in 24 h, treated by antitachycardia pacing, shock or eventually untreated but sustained in a VT monitoring zone. The number of shocks and inappropriate detections are irrelevant for the definition. ES occurs in approximately 25% of ICD patients within 3 years, with typically 5-55 individual VTs within one storm. Potential triggers can be found in approximately 66% of patients and include new/worsened heart failure, changes in antiarrhythmic medication, context with other illness, psychological stress, diarrhea, and hypokalemia. In most patients, ES consists of monomorphic VT indicating the presence of reentry while ventricular fibrillation indicating acute ischemia is rare. ES seems to have a low immediate mortality (1%) but frequently (50-80%) leads to hospitalization. Long-term prognostic implications of ES are unclear. The key intervention in ES is reduction of the elevated sympathetic tone by beta blockers and frequently benzodiazepines. Amiodarone i.v. has also been successful and azimilide seems promising while class I antiarrhythmic drugs are usually unsuccessful. Substrate mapping and VT ablation may be useful in treatment and prevention of ES. Prevention of ES requires ICD programming systematically avoiding unnecessary shocks (long VT detection, antitachycardia pacing where ever possible) which otherwise can fuel the sympathetic tone and prolong ES.

Seasonal variations of ventricular arrhythmia clusters in defibrillator recipients

BACKGROUND

Clustering ventricular arrhythmias are the consequence of acute ventricular electrical instability and represent a challenge in the management of the growing number of patients with an implantable cardioverter-defibrillator (ICD). Triggering factors can rarely be identified.

OBJECTIVES

Several studies have revealed seasonal variations in the frequency of cardiovascular events and life-threatening arrhythmias, and we sought to establish whether seasonal factors may exacerbate ventricular electrical instability leading to arrhythmia clusters and electrical storm.

METHODS

Two hundred and fourteen consecutive defibrillator recipients were followed-up during 3.3 +/- 2.2 years. Arrhythmia cluster was defined as the occurrence of three or more arrhythmic events triggering appropriate defibrillator therapies within 2 weeks. Time intervals between two clusters were calculated for each month and each season, and were compared using Kruskal-Wallis test and Wilcoxon-Mann-Whitney test with Bonferroni adjustment.

RESULTS

During a follow-up of 698 patient years, 98 arrhythmia clusters were observed in 51 patients; clustering ventricular arrhythmias were associated with temporal variables; they occurred more frequently in the winter and spring months than during the summer and fall. Accordingly, the time intervals between two clusters were significantly shorter during winter and spring (median and 95% CI): winter 16 (5-19), spring 11.5 (7-25), summer 34.5 (15-55), fall 50.5 (19-65), P = 0.0041.

CONCLUSION

There are important seasonal variations in the incidence of arrhythmia clusters in ICD recipients. Whether these variations are related to environmental factors, change in physical activity, or psychological factors requires further study.

Clustering of Ventricular Tachyarrhythmias in Heart Failure Patients Implanted with a Biventricular Cardioverter Defibrillator

BACKGROUND

Temporal patterns of ventricular tachyarrhythmia (VT/VF) have been studied only in patients who have received implantable cardioverter defibrillators (ICD) for secondary prevention of sudden death, and mainly in ischemic patients. The aim of this study was to evaluate VT/VF recurrence patterns in heart failure (HF) patients with biventricular ICD and to stratify results according to HF etiology and ICD indication.

METHODS AND RESULTS

We studied 421 patients (91% male, 66 +/- 9 years). HF etiology was ischemic in 292 patients and nonischemic in 129. ICD indication was for primary prevention in 227 patients and secondary prevention in 194. Baseline left ventricular ejection fraction (LVEF) was 26 +/- 7%, QRS duration 168 +/- 32 msec, and NYHA class 2.9 +/- 0.6. In a follow-up of 19 +/- 11 months, 1,838 VT/VF in 110 patients were appropriately detected. In 59 patients who had > or = 4 episodes, we tried to determine whether VT/VF occurred randomly or rather tended to cluster by fitting the frequency distribution of tachycardia interdetection intervals with exponential functions: VT/VF clusters were observed in 46 patients (78% of the subgroup of patients with > or = 4 episodes and 11% of the overall population). On multivariate logistic analysis, VT/VF clusters were significantly (P < 0.01) associated with ICD indication for secondary prevention (odds ratio [OR] = 3.12; confidence interval [CI] = 1.56-6.92), nonischemic HF etiology (OR = 4.34; CI = 2.02-9.32), monomorphic VT (OR = 4.96; CI = 2.28-10.8), and LVEF < 25% (OR = 3.34; CI = 1.54-7.23). Cardiovascular hospitalizations and deaths occurred more frequently in cluster (21/46 [46%]) than in noncluster patients (63/375 (17%), P < 0.0001).

CONCLUSIONS

In HF patients with biventricular ICDs, VT/VF clusters may be regarded as the epiphenomenon of HF deterioration or as a marker of suboptimal response to cardiac resynchronization therapy.

Characteristics and Relevance of Clustering Ventricular Arrhythmias in Defibrillator Recipients

INTRODUCTION

Studies of recurrent ventricular tachycardia and ventricular fibrillation (VT/VF) have been limited to "electrical storms," where recurrent arrhythmias necessitate repeated external cardioversions or defibrillations. Patients with an implantable cardioverter-defibrillator (ICD) may also suffer frequently recurrent arrhythmias. The aim of this study was to analyze the temporal pattern and the clinical relevance of clustering ventricular arrhythmias in ICD recipients.

METHODS

The incidence and the type of arrhythmias were determined by reviewing stored electrograms. VT/VF clusters were defined as the occurrence of three or more adequate and successful ICD interventions within 2 weeks. Two hundred and fourteen consecutive ICD recipients were followed during an average of 3.3 +/- 2.2 years (698 patient-years).

RESULTS

Fifty-one patients (24%) suffered 98 VT/VF clusters 21 +/- 22 months after ICD implantation, 93% of these clusters consisting of recurrent regular VT. Monomorphic VT as index event leading to ICD implantation was the only factor predicting VT/VF clusters. Kaplan-Meier estimates of the combined end-point of death or heart transplantation showed a 5-year event-free survival of 67% versus 87% in patients with and without clusters, respectively (P = 0.026). Adjusted hazard ratios for death or heart transplantation in the group with arrhythmia clusters was 3.5 (95% confidence interval 1.5-7.9 P = 0.003).

CONCLUSIONS

VT/VF clusters are frequent late after ICD implantation particularly in patients who had VT as index-event. As arrhythmias and recurrent ICD interventions are responsible for an important morbidity, there is a possible role for a prophylactic intervention. Furthermore, VT/VF clusters are an independent marker of increased risk of death or need for heart transplantation.

Temporal patterns of ventricular tachyarrhythmia recurrences follow a Weibull distribution

Temporal patterns of ventricular tachyarrhythmias.

INTRODUCTION

The objective of this study was to test whether the temporal patterns of ventricular tachyarrhythmia recurrences in patients with implantable cardioverter-defibrillator (ICD) follow a random or a clustered distribution.

METHODS

Data analysis was conducted using the Medtronic (Minneapolis, MN) Gem DR database of 521 ICD patients. Patients with >or=3 sustained ventricular tachyarrhythmia detections that resulted in shock or antitachycardia pacing therapies were studied. The times between consecutively treated ICD detections for each patient were compared to an exponential model of random recurrences and a Weibull model for clustered recurrences.

RESULTS

Seventy-one patients had >or=3VT episodes during follow-up of 131+/-86 days. A total of 2347 VT episodes were recorded (33+/-65 episodes/patient, median 10 episodes/patient). Patient age was 66+/-13 years, 78% male, 83% coronary artery disease, ejection fraction 31+/-11%, and 63% were taking antiarrhythmic drugs. By the Kolmogorov-Smirnov goodness-of-fit test, 38 of 71 patients (53.5%) showed that the pattern of detections differed from an exponential model (P<0.01 for each patient and the proportion of patients was similar to chance at P=0.65). In contrast, only 11 out of 71 patients (15.5%) showed that the pattern differed from the Weibull model (P<0.01 for each patient). The proportion of patients fitting the Weibull model was significantly greater than chance and was greater that the proportion fitting the exponential model (both P<0.001). The time interval between consecutive detections was less than 1 hour for 78% of all 2347 detections. The proportion of all 521 patients with >or=2, >or=3, >or= 4, >or=6, >or=8, and >or=10 ICD detections in a 24-hour period was 10.5%, 9.5%, 8.1%, 7.0%, 6.3%, and 5.2%, respectively.

CONCLUSION

In most patients with >or=3 ICD detections, the recurrence pattern of treated ventricular tachyarrhythmia detections are clustered and can be described by a Weibull distribution. The proportion of patients with multiple detections in a 24-hour period declines in a linear fashion as the number of events in 24 hours increases from 2 to 10 events.

Increased variability of the coupling interval of premature ventricular beats may help to identify high-risk patients with coronary artery disease

OBJECTIVE

The purpose of this study was to determine the characteristics and predictive value of the variability of coupling interval of ventricular premature beats (VPBs) for cardiac mortality in patients with coronary artery disease (CAD).

BACKGROUND

Frequent VPBs have been linked to an increased risk for cardiac death in patients with coronary artery disease. It is unknown whether analysis of coupling interval of VPBs from ambulatory ECG recordings can be used for risk statification in these patients.

METHODS

In 78 consecutive symptomatic patients with documented CAD who presented with frequent VPBs (>720/24 h), the analysis of VPBs' coupling interval (SDNV) was performed. Left ventricular function, ventricular arrhythmias and simple measures of heart rate variability were assessed. Mean follow-up was 702+/-329 days. Cardiac mortality was the primary end-point of the study.

RESULTS

During follow-up, 14 patients died-11 deaths were cardiac. Left ventricular ejection fraction (LVEF)<40%; no beta-blocker treatment and digoxin use were clinical variables showing a significant association with cardiac mortality. The presence of non-sustained ventricular tachycardia (nsVT), especially if more than five episodes were present; short mean sinus cycle (<750 ms) and SDNV were associated with cardiac deaths. Mean SDNV was 79+/-29 in victims and 63+/-29 in survivors (p<0.05). Univariate Cox regression analysis revealed that the presence of SDNV>80 ms carried a relative risk of 6.7 for cardiac mortality. The adjusted relative risk was 13.3 for nsVT and 4.4 for SDNV>80 ms. Among patients with nsVT, mortality rate was significantly higher with SDNV>80 ms (58%), compared to lower SDNV (14%, p<0.01). Sixty-four percent mortality rate was observed in patients with LVEF<40%, presence of nsVT and SDNV>80 ms, compared to 17% in similar patients with lower SDNV (p<0.05).

CONCLUSION

The analysis of coupling interval of ventricular premature beats form the same 24-h ECG recordings may complement the standard Holter analysis for risk stratification. This seems especially promising in the subgroups of patients at highest risk-those with LV systolic dysfunction, non-sustained VT or both.

High rate atrial tachyarrhythmia detections in implantable pulse generators: low incidence of false-positive detections. The PA Clinical Trial Investigators

Some newer pulse generators have enhanced diagnostic features that provide information on the frequency, date, time of onset, and duration of atrial and/or ventricular tachyarrhythmias. However, the sensitivity and specificity of device-based atrial tachyarrhythmia detections may vary and depend, in part, on lead position and selected programming parameters. The prevalence of inappropriate detections of paroxysmal atrial fibrillation (PAF) was investigated in 97 patients who received a Thera DR pacemaker 3 months prior to a planned AV node ablation. Patients were randomized to no atrial or to rate adaptive atrial pacing therapy and followed for 3 months. Following a total AV node ablation, patients were randomized to DDDR versus VDD pacing and followed for 1 year. The high rate atrial episode diagnostic feature was used for detection of PAF and the diagnostic data were retrieved during follow-up visits. Criteria were developed to identify oversensing due to near-field P wave detections, far-field R wave detections, or competitive atrial pacing as causes of false-positive atrial tachyarrhythmia detections. A total of 1,636 detections of PAF were recorded in patients preablation. Only 48 episodes (2.9%) were characterized as false-positive detections; 25 episodes (1.5%) were classified as oversensing, and 23 episodes (1.4%) were classified as competitive atrial pacing. A total of 3,061 detections of PAF were recorded postablation. Only four episodes (0.1%) were classified as oversensing. Thus, the diagnostic atrial tachyarrhythmia detection feature in newer pacemakers is an effective method for evaluating the time course of PAF in patients with implantable pulse generators.

Temporal patterns of paroxysmal atrial fibrillation following DDDR pacemaker implantation

Paroxysmal atrial fibrillation (AF) episodes have been reported to be randomly distributed. However, because patients are not always symptomatic, it has been difficult to study temporal patterns of AF. Newer implantable pulse generators have data-logging capabilities that permit the detection and analysis of temporal patterns of AF. This study tested the hypothesis that AF episodes occur in clusters over time and that these episodes are not randomly distributed in individual patients. The date and time of 582 episodes of AF were recorded from the data logs of 16 patients with a Medtronic Thera DR followed 6 weeks and 6 and 12 months after pulse generator implant. The probability of AF recurrence and the interevent intervals between successive episodes of AF were fitted to monoexponential and Weibull distributions. A Weibull distribution best described the nonrandom distribution of AF for 67% of follow-up visits. Temporal clustering of AF (interevent intervals <24 hours) declined during follow-up (95 +/- 10%, 90 +/- 11%, and 74 +/- 28% at the 6-week and 6- and 12-month visits, respectively; p <0.05). The average duration of an episode of AF tended to increase over time (0.31 hour, 95% confidence intervals [CI] 0.17 to 0.58 hours; 0.36 hours, 95% CI 0. 17 to 0.78 hours; 0.65 hours, 95% CI 0.29 to 1.45 hours [p = 0.07] at the 6-week and 6- and 12-month visits, respectively). Paroxysmal AF recurrence is nonrandomly distributed over the long term in many patients. The temporal patterns of AF change over time after pacemaker implantation. This has implications for the selection of study end points in AF clinical trials.

Evaluation of the bias in using the time to the first event when the inter-event intervals have a Weibull distribution

Currently the analysis of clinical trials for treatment of paroxysmal atrial fibrillation (PAF) relies on the assumption that the events are distributed according to a Poisson distribution. We contend that the occurrence of PAF events are clearly not Poisson and tend to occur in clusters. A candidate parametric model of the inter-event interval, the Weibull distribution, is presented. When the events are distributed according to a Poisson distribution, the time to the first event (TFE) has the same distribution as the inter-event intervals (IEI) due to the 'memoryless' property of the Poisson distribution, hence the TFE can be used instead of the IEI. When the events do not form a Poisson distribution, the TFE does not have the same distribution as the IEI. We show that for the Weibull distribution, when the TFE is used to model the IEI, both the mean and the survivor distribution are biased. The bias in the survivor function is a function both of time and the parameters of the distribution. Therefore when two groups have different parameters for their distributions (as in the case of different treatment effects), the discrepancy between the survivor distribution of the IEI and the survivor distribution of the TFE is affected differentially. We demonstrate the low coverage probabilities of the mean and the survivor function which result when the underlying distribution is Weibull with shape parameter kappa < 1.0. It is likely that this problem will arise for other clustered event processes. This suggests that careful empirical investigation of the distribution of IEI for recurrent events is necessary before choosing to analyse the data using the TFE.

Influence of beta-blockers on the frequency of arrhythmia recurrences in patients with implantable cardioverter-defibrillator: an intraindividual comparison

We studied retrospectively 60 consecutive recipients of an implantable cardioverter-defibrillator and identified 16 patients who were temporarily on and off beta-blockers (further medication unchanged). An intraindividual analysis revealed that 56% of the patients experienced more arrhythmic episodes during follow-up off beta-blockers compared to 44% while being on beta-blockers. Also, the mean episode frequency during follow-up time on and off beta-blockers was comparable (0.4+/-0.6 vs. 0.5+/-0.5, ns).

Implantable cardioverter defibrillators

Implantable cardioverter defibrillators have proven to be an effective therapy for life-threatening ventricular arrhythmias. Given the ever-increasing number of patients who have these devices, increasing numbers of patients are likely to present to emergency departments with defibrillator-related problems. This article discusses normal device function, indications for implantation, and technique of implantation. It also focuses on the evaluation and management of patients with these devices presenting to the emergency department.

Rewards in practice from chrono-meta-analyses 'recycling' heart rate, ectopy, ischemia and blood pressure information

Previously published average curves of heart rate and duration of ischemia in patients with coronary artery disease, studied while on placebo or on treatment with either atenolol or diltiazem, are re-analysed for the assessment of about-daily (circadian) and about-weekly (circaseptan) changes in these variables and of any treatment effect on rhythm characteristics. In addition to circadians, a circaseptan pattern characterizes the duration of ischemia in all three aforementioned study stages. Both drugs decrease the duration of ischemia, atenolol, but not diltiazem, also affects the circadian amplitude and acrophase of this variable. A circaseptan pattern is also found for heart rate on placebo and on treatment with atenolol, but not with diltiazem. Both drugs lower heart rate and the circadian amplitude and 24-h standard deviation of heart rate, atenolol much more markedly than diltiazem. Circadian and circaseptan rhythm characteristics and their alterations with treatment serve to optimize treatment by timing its administration. Chronobiologic surveillance of variables that are being readily monitored as-one-goes by modern implantable devices can also serve for the validation of the effectiveness of drug and electrical therapy. Rhythm alterations, in turn, can provide the earliest warnings of an elevated disease risk and lead to an improved diagnosis.