Circadian pattern of ventricular tachyarrhythmias in patients with implantable cardioverter-defibrillators

Circadian Regulation of Cardiac Arrhythmias and Electrophysiology

Circadian rhythms in physiology and behavior are ≈24-hour biological cycles regulated by internal biological clocks (ie, circadian clocks) that optimize organismal homeostasis in response to predictable environmental changes. These clocks are present in virtually all cells in the body, including cardiomyocytes. Many decades ago, clinicians and researchers became interested in studying daily patterns of triggers for sudden cardiac death, the incidence of sudden cardiac death, and cardiac arrhythmias. This review highlights historical and contemporary studies examining the role of day/night rhythms in the timing of cardiovascular events, delves into changes in the timing of these events over the last few decades, and discusses cardiovascular disease-specific differences in the timing of cardiovascular events. The current understanding of the environmental, behavioral, and circadian mechanisms that regulate cardiac electrophysiology is examined with a focus on the circadian regulation of cardiac ion channels and ion channel regulatory genes. Understanding the contribution of environmental, behavioral, and circadian rhythms on arrhythmia susceptibility and the incidence of sudden cardiac death will be essential in developing future chronotherapies.

[Circadian and septadian variation in sudden cardiac death : Autopsy registry of the Tunisian North]

INTRODUCTION

Several studies have suggested a circadian and septadian pattern of incidence of sudden cardiac death with a morning peak and a Monday peak.

OBJECTIVE

To analyze the circadian and septadian pattern of occurrence of sudden cardiac death in the eight northern Tunisian governorates.

METHODS

We prospectively collected epidemiological and autopsy data of sudden cardiac death victims occurring in the northern region of Tunisia between January 2013 and December 2019.

RESULTS

The population included 1834 men (79.6%) and 468 women (20.4%) with a mean age of 56.5 ± 14 years. Smoking (53.9%) was the most prevalent cardiovascular risk factor. One-fifth (20.9%) of victims had known heart disease, and 3% had a family history of sudden death. ischemic heart disease was the leading cause of sudden death (46.8% of cases). One- fourth (25.7%) of autopsies were negative. Analysis of the circadian pattern of occurrence of sudden cardiac death identified a peak (36.1%, p < 0.001) between midnight and 6 am. This nocturnal excess mortality was significant (p < 0.001) and independent of sex (34.1 % in men and 43.8 % in women) and cause of death (39.3 % of cases of sudden ischemic death and 33.3 % of cases of nonischemic death). Moreover, there was a significant septadian variability in the occurrence of sudden death (p: 0.0015), with a peak on Friday (15.8 %, p: 0.042).

CONCLUSION

This study showed a peak of sudden death between midnight and 6 am, and on Fridays, confirming the modification of the classic circadian and septadian pattern of sudden death occurrence. These results may help optimize the deployment of emergency mobile teams and structures during the most vulnerable periods.

Circadian Pattern of Ion Channel Gene Expression in Failing Human Hearts

BACKGROUND

Ventricular tachyarrhythmias and sudden cardiac death show a circadian pattern of occurrence in patients with heart failure. In the rodent ventricle, a significant portion of genes, including some ion channels, shows a circadian pattern of expression. However, genes that define electrophysiological properties in failing human heart ventricles have not been examined for a circadian expression pattern.

METHODS

Ventricular tissue samples were collected from patients at the time of cardiac transplantation. Two sets of samples (n=37 and 46, one set with a greater arrhythmic history) were selected to generate pseudo-time series according to their collection time. A third set (n=27) of samples was acquired from the nonfailing ventricles of brain-dead donors. The expression of 5 known circadian clock genes and 19 additional ion channel genes plausibly important to electrophysiological properties were analyzed by real-time polymerase chain reaction and then analyzed for the percentage of expression variation attributed to a 24-hour circadian pattern.

RESULTS

The 5 known circadian clock gene transcripts showed a strong circadian expression pattern. Compared with rodent hearts, the human circadian clock gene transcripts showed a similar temporal order of acrophases but with a ≈7.6 hours phase shift. Five of the ion channel genes also showed strong circadian expression. Comparable studies of circadian clock gene expression in samples recovered from nonheart failure brain-dead donors showed acrophase shifts, or weak or complete loss of circadian rhythmicity, suggesting alterations in circadian gene expression.

CONCLUSIONS

Ventricular tissue from failing human hearts display a circadian pattern of circadian clock gene expression but phase-shifted relative to rodent hearts. At least 5 ion channels show a circadian expression pattern in the ventricles of failing human hearts, which may underlie a circadian pattern of ventricular tachyarrhythmia/sudden cardiac death. Nonfailing hearts from brain-dead donors show marked differences in circadian clock gene expression patterns, suggesting fundamental deviations from circadian expression.

Do peak times exist for sudden cardiac arrest?

Sudden cardiac arrest remains an unexpected and dynamic cardiovascular disease process that continues to present challenges for accurate risk prediction and prevention. The notion of a circadian pattern in the occurrence of sudden cardiac arrest had long been supported by the presence of an early morning peak; however, more recent studies are calling this observation into question. This likely paradigm shift in the presentation and mechanisms of sudden cardiac arrest has major implications and needs to be carefully considered. In this review, we present the current state of the science of circadian and septadian trends in sudden cardiac arrest through an in-depth analysis of the published literature.

Characteristics and periodicity of sustained ventricular tachyarrhythmia events in a population of military veterans with implantable cardioverter defibrillator

PURPOSE

Circadian patterns of ventricular tachyarrhythmias (VTAs) in ICD patients from SCD-HeFT and MADIT-CRT have yielded differing results. The aim was to investigate VTA patterns in a large population of military veterans with ICD.

METHODS

This retrospective study analyzed biorhythm periodicity of sustained VTAs (≤ 300 ms). Findings were derived from the Veterans Affairs (VA) National Cardiac Device Surveillance database encompassing January 1, 2005, to December 31, 2017.

RESULTS

The patient population comprised 1559 consecutive patients with 17,039 VTAs. There were 763 patients with clinical information with the mean age of 67.8 ± 9 years old and 99% male. An hourly non-uniform VTA distribution with a bimodal pattern and a predominant afternoon peak was seen (χ² = 5057, P < 0.0001). VTAs treated successfully by anti-tachycardia pacing (ATP) showed a bimodal pattern with even distributions. VTAs treated by ICD shocks showed a bimodal pattern with a predominant afternoon peak. The duration of VTA peaks was increased from 13.5 to 17 h with increasing daylight time from 9.9 to 14.5 h. The weekly VTA distribution showed a significant septadian pattern with lowest frequency on weekend and highest on weekdays (χ² = 4840, P < 0.0001). No annual periodicity and monthly periodicity were seen.

CONCLUSIONS

Sustained VTA events exhibited a circadian rhythm in a large population of military veterans with ICD/CRT-D; specifically, a bimodal pattern with a predominant afternoon peak was observed. Further, the majority of VTA episodes treated by ICD shock occurred in the afternoon, and the duration of VTA peak lengthened with increased duration of daylight time.

Unexpected deviation in circadian variation of ventricular arrhythmias: the SCD-HeFT (Sudden Cardiac Death in Heart Failure Trial)

OBJECTIVES

This study sought to determine whether circadian patterns in ventricular arrhythmias (VAs) occur in a current primary prevention defibrillator (implantable cardioverter-defibrillator [ICD]) population.

BACKGROUND

Cardiovascular events, including VAs, demonstrate biorhythmic periodicity.

METHODS

We tested for deviation from the previously described occurrences of a morning peak, early morning nadir, and peak on Mondays in ICD therapies using generalized estimating equations and Student t tests. All hypothesis tests were performed in the entire cohort of patients with VAs as well as pre-specified subgroups.

RESULTS

Of 811 patients with an ICD, 186 subjects experienced 714 ICD therapy episodes for life-threatening VA. There was no morning (6 am to 12 pm) peak in therapies for the entire cohort or any subgroups. The overall cohort and several subgroups had a typical early morning (12 am to 6 am) nadir in therapies, with significantly less than 25% of therapies occurring during this 6-h block (all p < 0.05). A significant peak in therapies on Mondays occurred only in patients not on beta-blocker therapy (22% of events for the week, p = 0.029).

CONCLUSIONS

In the SCD-HeFT (Sudden Cardiac Death in Heart Failure Trial) population, the distribution of life-threatening VA failed to show a typical early morning peak or increased VA events on Mondays. A typical early morning nadir was seen in the entire cohort. An increased rate of events on Mondays was found in the subgroup of subjects not on beta-blocker therapy. These findings may indicate suppression of the neurohormonal triggers for VA by current heart failure therapy, particularly the use of beta-blockers in heart failure.

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.

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.

Circadian variations of stellate ganglion nerve activity in ambulatory dogs

BACKGROUND

The presence of circadian variations in sympathetic outflow from the stellate ganglia is unclear.

OBJECTIVES

The purpose of this study was to continuously record stellate ganglion nerve activity (SGNA) in ambulatory dogs.

METHODS

We performed continuous 24-hour left (N = 3) or bilateral (N = 3) SGNA recordings in normal ambulatory dogs using implanted Data Sciences International transmitters. We also performed simultaneous ECG recording (n = 5) or simultaneous ECG and blood pressure recordings (n = 1).

RESULTS

The total duration of continuous ambulatory recording averaged 41.5 +/- 16.6 days. Five dogs had persistent stable recording, and one dog developed hardware malfunction in week 3. SGNA was followed immediately (<1 second) by heart rate and blood pressure elevation and a reduced standard deviation of consecutive activation cycle length (SDNN) from 236 +/- 93 ms to 121 +/- 51 ms (P = 0.007). Heart rate correlated significantly with SGNA. When there was a sudden increase of SGNA, the sudden increase occurred bilaterally in 90% of the episodes. Both heart rate and SGNA showed statistically significant (P <.01) circadian variation. Nadolol (20 mg/day for 5 days) reduced average heart rate from 99 +/- 8 bpm at baseline to 88 +/- 9 bpm (N = 6, P = .001) but did not significantly alter SGNA. Immunohistochemical staining of the stellate ganglia showed tyrosine hydroxylase-positive ganglion cells and nerves at the recording site.

CONCLUSION

There is a circadian variation in sympathetic outflow from canine stellate ganglia. Circadian variation of SGNA is an important cause of circadian variations of cardiac sympathetic tone.

The normal circadian pattern of blood pressure: implications for treatment

Blood pressure fluctuates over 24 h following a circadian rhythm that reaches a peak in the morning shortly after awakening. The onset of many acute cardiovascular and cerebrovascular events shows a synchronous cyclical pattern, with the highest incidence of morbidity and mortality in the early morning hours. Strong, although circumstantial, evidence suggests that the early morning surge in blood pressure may contribute to the onset of acute cardiovascular episodes. Sustained blood pressure control that blunts the early morning blood pressure surge may help to reduce the incidence of these events. Antihypertensive agents are needed that provide smooth and sustained blood pressure control for the full 24 h, including the risky early morning hours. The angiotensin II receptor blocker telmisartan given once daily, because of its long half-life and mechanism of action, is likely to confer benefit in terms of 24-h blood pressure control and may reduce cardiovascular risk at the time of greatest patient vulnerability.

Factors affecting diurnal variability of ventricular tachyarrhythmias detected by multiprogrammable implantable cardioverter-defibrillators

Many cardiovascular events, including ventricular arrhythmias, display diurnal variability with a morning peak, and a less pronounced afternoon peak. Since the advent of multiprogrammable implantable cardioverter-defibrillators (ICDs), it has been possible to analyse ventricular tachyarrhythmic events. This study aims to evaluate the circadian pattern of ventricular tachycardias in patients treated with ICDs and examines whether antiarrhythmic medications affect this pattern. Data recorded from 83 patients' ICDs were manually analysed and events other than ventricular arrhythmias were excluded. There was a morning peak of ventricular arrhythmias at around 9.00 a.m. This peak was maintained in patients with ejection fractions of less than 40% and those whose arrhythmias had cycle lengths of less than 230ms. Beta blockers appeared to have no effect on this morning peak but the peak appeared later with amiodarone.

Circadian variation in ventricular tachycardia and atrial fibrillation in a medical-cardiological ICU

OBJECTIVE

To assess the diurnal distribution of ventricular tachycardia (VT) and atrial fibrillation (AF) in critically ill patients.

DESIGN AND SETTING

Prospective observational study (episode-based design) in an eight-bed medical/cardiological ICU at a university hospital that also admits postoperative patients.

PATIENTS

98 consecutive patients with AF ( n=55) or ventricular tachycardia ( n=43).

MEASUREMENTS AND RESULTS

There were a total of 218 arrhythmia episodes (83 AF, 136 VT). The time of arrhythmia onset was not evenly distributed. Circadian variation in VT but not AF onset was well represented by a sine wave function. Both VT and AF fibrillation showed a trough during the night. The distribution of VT and AF episodes did not differ significantly with or without analgosedation.

CONCLUSIONS

In critically ill patients the onset of VT and AF over 24-h is nonuniformly distributed. In VT this circadian pattern of occurrence is well modeled by a sine wave function peaking between noon and 2 p.m. The circadian pattern is less clear for AF. The circadian variation is seen irrespective of the presence of absence of analgosedation for both arrhythmias.

Analysis of the corrected QT before the onset of nonsustained ventricular tachycardia in patients with hypertrophic cardiomyopathy

This study examined ventricular repolarization before the onset of 37 episodes of nonsustained ventricular tachycardia (NSVT) in 26 untreated patients with hypertrophic cardiomyopathy (HCM). Fourteen episodes were recorded in patients with a history of cardiac arrest or patients who died suddenly during follow-up. The QT interval was measured beat-by-beat on 24-hour ambulatory electrocardiograms. Mean 24-hour, hourly QTc and QTc of the last 10 beats prior to NSVT, consisted of 4-50 cycles (mean 9 +/- 10), at the fastest rates of 100-175 beats/min (mean 122 +/- 22) were analyzed. NSVT was more prevalent during nighttime (23 episodes), than during daytime (14 episodes, P < 0.05). No significant differences were observed between mean 24-hour, mean hourly QTc during the hour with NSVT, and QTc of the last 10 cycles prior to onset of NSVT. QTc was significantly longer in patients with a history of sudden cardiac death (SCD) or who died suddenly during follow-up than in survivors. The 24-hour QT variability was higher in nonsurvivors than in survivors (-39 +/- 6 vs 33 +/- 6 ms, P = 0.03). Episodes of NSVT in untreated patients with hypertrophic cardiomyopathy were more frequent during the nighttime. The 24-hour QT variability was higher in nonsurvivors than in survivors.

Cardiovascular risk and therapeutic intervention for the early morning surge in blood pressure and heart rate

The incidence of most adverse cardiovascular events appears to follow a circadian pattern, reaching a peak in the morning shortly after wakening and arising. The activities of many physiologic parameters, including hemodynamic, hematologic and humoral factors, also fluctuate in a cyclical manner over the 24h. It has been suggested that, during the post-awakening hours, the phases of these cycles synchronize to create an environment that predisposes to atherosclerotic plaque rupture and thrombosis in susceptible individuals, thereby accounting for the heightened cardiovascular risk at this time of day. Blood pressure and heart rate are part of this physiologic process, following a clear circadian rhythm characterized by a fall during sleep and a sharp rise upon awakening. This so-called 'morning surge' in blood pressure may act as a trigger for cardiovascular events, including myocardial infarction and stroke. The clinical implication of these observations is that antihypertensive therapy should provide blood pressure control over the entire interval between doses. For agents taken once daily in the morning, the time of trough plasma drug level (and lowest pharmacodynamic effect) will often coincide with the early morning surge in blood pressure and heart rate. For these reasons, chronotherapeutic formulations of drugs and intrinsically long-acting antihypertensive agents provide the most logical approach to the treatment of hypertensive patients since they provide 24 h blood pressure control from a single daily dose as well as attenuating the early morning rise in blood pressure (and in some instances heart rate).

Circadian variation and onset mechanisms of ventricular tachyarrhythmias in patients with coronary disease versus idiopathic dilated cardiomyopathy

To determine the circadian variations and the onset mechanisms of ventricular tachyarrhythmias (VT) in patients with implantable cardioverter defibrillators, stored electrograms of 364 VT episodes occurring in 40 patients with coronary artery disease (CAD) and in 29 patients with idiopathic dilated cardiomyopathy (DCM) were analyzed. A similar circadian distribution of VT episodes was observed in both groups, with a morning peak and less pronounced evening peak. After exclusion of patients with atrial fibrillation, VT onset was classified as (1) sudden if preceded by > or = 8 regular cycles without ventricular premature beats, (2) onset with a short-long-short interval, and (3) a more complex onset with variable patterns of ventricular premature beats before initiation of VT. Sudden onset was found in 26% and 21% of VTs in CAD and DCM respectively. A short-long-short interval preceded 29% of VTs in CAD compared to 14% of VTs in DCM (P < 0.05). A more complex onset was observed in the remaining 45% of VTs in CAD and 65% of VTs in DCM (P < 0.05). In conclusion, patients with DCM and CAD had similar circadian distributions of VT episodes. The majority of episodes were preceded by complex occurrence of ventricular premature beats rather than by the classic short-long-short sequence. These findings have important implications for the development of preventive pacing methods.

Circadian variation of malignant ventricular arrhythmias in patients with ischemic and nonischemic heart disease after cardioverter defibrillator implantation. European 7219 Jewel Investigators

OBJECTIVES

The purpose of this study was to examine the circadian variation of ventricular arrhythmias detected by an implantable cardioverter defibrillator in patients with and without ischemic heart disease.

BACKGROUND

Previous studies have shown a circadian variation of ventricular arrhythmias, sudden death and myocardial infarction with a peak occurrence in the morning hours. The circadian pattern, which is similar for both arrhythmic and ischemic events, suggests that ischemia may play a critical role in the genesis of ventricular arrhythmias and sudden death. We hypothesized that, if ischemia plays an important role in the triggering of ventricular arrhythmias, the circadian pattern should be different in patients with ischemic heart disease compared with patients with nonischemic heart disease.

METHODS

The circadian variation of ventricular arrhythmias recorded by an implantable cardioverter defibrillator was studied in 310 patients during a mean follow-up of 181 +/- 163 days. Two hundred four patients had a history of ischemic heart disease and 106 patients had nonischemic heart disease. The times of the episodes of ventricular arrhythmias were retrieved from the data log of each device during follow-up, and the circadian pattern was compared between the two groups.

RESULTS

During follow-up, 1,061 episodes of ventricular arrhythmias were recorded by the device in the 310 patients. Six hundred eighty-two episodes occurred in the group of patients with ischemic heart disease and 379 occurred in the nonischemic heart disease group. The circadian variation of the episodes showed a typical pattern with a morning and afternoon peak in both groups of patients with ischemic and nonischemic heart disease, but there was no significant difference between the two groups.

CONCLUSIONS

The circadian rhythm of ventricular arrhythmias in patients with ischemic heart disease is similar to patients with nonischemic heart disease, suggesting that the trigger mechanisms of the initiation of ventricular tachyarrhythmias may be similar, irrespective of the underlying heart disease.

Implantable defibrillator diagnostic storage capabilities: evolution, current status, and future utilization

There has been a rapid and significant evolution in the stored diagnostic information available from implantable cardioverter defibrillators (ICDs). The diagnostic information available in current generation ICDs has greatly enhanced the clinicians' ability to determine the rhythm triggering device therapy as well as to identify potential problems with the ICD system. Furthermore, this information may be useful in identifying triggers of ventricular arrhythmias in patients at high risk for sudden death. The history, evolution, value, and limitations of the stored diagnostic capabilities of implantable defibrillators are discussed.

Circadian rhythm of the signal averaged electrocardiogram and its relation to heart rate variability in healthy subjects

OBJECTIVE

To examine the circadian variation in the signal averaged electrocardiogram (saECG) and heart rate variability and investigate their relations in healthy subjects.

METHODS

24 hour ECGs were obtained with a three channel recorder using bipolar X, Y, and Z leads in 20 healthy subjects. The following variables were determined hourly: heart rate, filtered QRS (f-QRS) duration, low and high frequency components of heart rate variability (LF and HF), and the LF/HF ratio.

RESULTS

Heart rate, f-QRS duration, HF, and the LF/HF ratio showed significant circadian rhythms, as determined by the single cosinor method. Heart rate and the LF/HF ratio increased during daytime, and f-QRS duration and HF increased at night. f-QRS duration was negatively correlated with heart rate (r = 0.95, p < 0.001) and the LF/HF ratio (r = 0.94, p < 0.001) and positively with HF (r = 0.93, p < 0.001).

CONCLUSIONS

f-QRS duration has a significant circadian rhythm in healthy subjects and is closely related to the circadian rhythm of autonomic tone.

Nonuniform nighttime distribution of acute cardiac events: a possible effect of sleep states

BACKGROUND

Although 250,000 myocardial infarctions and 38,000 sudden cardiac deaths occur at night annually, this public health problem is underappreciated and poorly understood. We examined whether the incidence of myocardial infarction, sudden cardiac death, and automatic implantable cardioverter-defibrillator (AICD) discharge was nonuniform, a result that may implicate physiological triggers such as sleep-state dependent changes in autonomic nervous system activity.

METHODS AND RESULTS

We conducted a review of the circadian pattern of the onset of myocardial infarction (n=19), sudden cardiac death (n=12), and AICD discharge (n=7). The nighttime period was chosen a priori as midnight to 5:59 AM. These reports documented 11,633 nocturnal myocardial infarctions (20% of the total myocardial infarctions), 1981 nocturnal sudden cardiac deaths (14.6% of the total sudden cardiac deaths), and 1200 nocturnal AICD discharges (15.0% of the total discharges). The distributions of myocardial infarction, sudden cardiac death, and AICD discharge were each significantly nonuniform (P<.001). The peak incidence of myocardial infarction and AICD discharge occurred between midnight and 0:59 AM, whereas the peak incidence of sudden cardiac death was between 1:00 and 1:59 AM. The trough in incidence occurred between 4:00 and 4:59 AM for sudden cardiac death and between 3:00 and 3:59 AM for myocardial infarction and AICD discharge.

CONCLUSIONS

Nocturnal myocardial infarction, sudden cardiac death, and AICD discharge exhibit nonuniform distributions. This finding is consistent with the hypothesis that sleep-state dependent fluctuations in autonomic nervous system activity may trigger the onset of major cardiovascular events and provides further impetus for more directly testing this hypothesis at population, individual, and mechanistic levels. A better understanding of nocturnal triggers may make it possible to reduce the incidence of myocardial infarction, ventricular tachyarrhythmias, and sudden cardiac death during the nocturnal period.

Circadian variation of sustained ventricular tachycardia in patients subject to standard adrenergic blockade

Morning peaks in the circadian variation of sustained ventricular tachycardia (VT) may reflect the contribution of sympathetic activation to onset of VT. We hypothesized that adrenergic blockade would eliminate this morning peak. Fifty-four patients using a defibrillator had 1114 time-stamped episodes of VT requiring therapy with a device: 1012 episodes with and 102 episodes without antiadrenergic medications. Nine patients had episodes both with and without antiadrenergic medication and were examined separately. In patients taking antiadrenergic agents, data fitted to a harmonic regression model revealed a morning peak at 9:00 AM (R2= 0.542; p < 0.05), with a secondary peak at 4 PM. Those not receiving antiadrenergic therapy had a similar morning peak. Antiadrenergic agents as used in standard clinical practice do not prevent circadian variation in onset of VT. This variation may be mediated by systems other than adrenergic receptor-linked activation or may reflect inadequacy of adrenergic blockade in standard clinical dosing.

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.

[Circadian variation of ventricular tachyarrhythmias in patients with an implantable cardioverter-defibrillator]

For the acute myocardial infarction and sudden cardiac death a circadian variation can be observed. There are several, mostly epidemiological studies that demonstrate this non-uniform distribution of events in different day-time periods. These studies are in the vast majority based on eye-witness reports, medical documents and retrospective evaluation of the timing of the event. Moreover, they represent only singular observations in a heterogeneous population. With the introduction of implantable cardioverter-defibrillators which provide extensive diagnostic features such as stored RR-intervals, endocardial electrograms of each episode and internal time storage, an exact analysis of the circadian variation of malignant ventricular tachyarrhythmias became feasible. Ventricular tachyarrhythmias follow a different circadian distribution with increased number of events at certain day-time periods. For patients with a coronary artery disease a significantly higher risk to experience a potentially fatal arrhythmia could be shown for the mid-morning hours and a secondary peak occurrence for the late afternoon and the early evening. Patients with idiopathic dilated cardiomyopathy tend to have a higher probability of events in the evening hours. With respect to beta-blockers and other antiarrhythmic drugs most of the studies failed to confirm a blunting influence on the degree of variability for fast arrhythmias. Others showed similar patterns for fast and slow tachycardias. Another clinical parameter, the degree of congestive heart failure was in some studies found to influence the pattern in the sense of causing a distinct difference in occurrence frequency. A higher vairation was determined for lower NYHA classes < III. Other studies were contrary to these findings. The activity level before the onset of arrhythmias has yet been only insufficiently analyzed regarding the day-time-variability. But first results make believe, that patients younger than 50 years and still involved in the working process seem to follow a more varying circadian distribution. More substudies will have to be performed to compare working and nonworking patients and patients with different structural heart diseases. Furthermore ther influence of antiarrhythmic agents on the day-time-variation of ventricular tachyarrhythmias should be assessed. Finally, there, should be systematic prospective studies that evaluate the influence of drug administration on triggers of ventricular tachyarrhythmias such as sympathoadrenergic activity, premature ventricular beats, reduction of heart rate variability and others with respect to their day-time-variability.

Circadian patterns and triggers of sudden cardiac death

Sudden cardiac death and other acute cardiovascular events have been demonstrated to occur in certain temporal patterns. The study of these patterns may yield important clues to the pathophysiology of the disease process. Most studies of the timing of onset of sudden cardiac death have revealed a prominent midmorning peak, thought to be related to a surge in catecholamines associated with arising and assuming the upright posture, that is blunted or eliminated by beta blockers. In addition, some studies have also shown a secondary peak in late afternoon or early evening of uncertain cause. The development of third-generation implantable cardioverter defibrillators with memory capabilities offers a unique opportunity to accurately define event chronology.

Circadian variation in sudden cardiac death: effects of age, sex, and initial cardiac rhythm

STUDY OBJECTIVE

Previous studies based on data obtained from vital statistics records have demonstrated circadian variation in the occurrence of sudden cardiac death. The purpose of this study was to examine the effects of age, sex, and initial cardiac rhythm on circadian variability in sudden cardiac death.

METHODS

This study employed a retrospective analysis of the records of adult patients with witnessed cardiac arrest who underwent resuscitation in an urban paramedic system during a 5-year period.

RESULTS

The records of 2,250 consecutive patients with witnessed cardiac arrest were reviewed. Spectral analysis was used to decompose the data into frequency components. A circadian variation in the occurrence of sudden cardiac death was demonstrated, with a low occurrence rate between midnight and 6 AM and a 2.4-fold increase between the rate at 6 AM and the rate at noon. The same circadian pattern was noted among both men and women, among both patients aged 18 to 70 and those older than 70 years, and among patients with various initial cardiac arrest rhythms (ventricular tachycardia or fibrillation, asystole, and electromechanical dissociation). However, the outcome of resuscitation in these patients (ie, the rate of successful resuscitation and the rate of survival) did not demonstrate circadian variation.

CONCLUSION

Witnessed out-of-hospital sudden cardiac death demonstrated circadian variation, and this variability was observed regardless of the patient's age, sex, or initial cardiac arrest rhythm. The outcome of resuscitation did not show circadian variability. These results suggest a common pathophysiologic mechanism leading to sudden cardiac death.

Long-term temporal patterns of ventricular tachyarrhythmias

BACKGROUND

Technological limitations have precluded investigation of long-term temporal patterns of ventricular tachyarrhythmia recurrences. Newer implantable cardioverter-defibrillators permit such analyses by accurately recording the time and date of tachycardia detections during long-term follow-up. This study tests the hypothesis that ventricular tachycardia occurrences are randomly distributed over time in individual patients.

METHODS AND RESULTS

The time and date of 727 episodes of ventricular tachyarrhythmias were recorded from the data logs of 31 patients with implantable cardioverter-defibrillators followed for a median of 177 days (range, 7 to 782 days). All patients had three or more ventricular tachycardia detections and no detections from causes other than ventricular arrhythmias. In 28 of 31 patients, the distribution of the interdetection time intervals during follow-up differed significantly (all P < .01) from an exponential model distribution of interdetection intervals that assumed that detections were equally likely to occur at any time during follow-up (random). The Kolmogorov-Smirnov goodness-of-fit test was used to compare sample and model distributions. In each patient, the nonrandom distributions resulted from a preponderance of interdetection time intervals that were shorter than predicted by the random model, resulting in a temporal clustering of arrhythmic events. The interdetection interval was < or = 1 hour and < or = 91 hours for 55% and 78% of all intervals, respectively. When only those episodes receiving shock or antitachycardia pacing therapy were analyzed, 25 of 29 patients still manifested nonrandom distributions (all P < .01). When only episodes with tachycardia rates > 240 beats per minute were analyzed, 11 of 13 patients manifested non-random distributions (all P < .01).

CONCLUSIONS

Ventricular tachycardia detections and delivered antitachycardia therapies by implantable cardioverter-defibrillators are nonrandomly distributed throughout long-term follow-up in the majority of patients. The temporal clustering of these arrhythmic events may allow preemptive antiarrhythmic therapy and should be considered in the design of therapy based on suppression of spontaneous ventricular arrhythmias to statistically derived end points.