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

Circadian variation of in-hospital cardiac arrest

BACKGROUND

Out of hospital cardiac arrests, especially those due to ventricular tachyarrhythmias, have higher incidence in the morning. It is unknown whether in-hospital cardiac arrests follow a similar pattern.

AIM OF THE STUDY

The purpose of this study was to analyze the circadian variation of in-hospital cardiac arrest incidence.

METHODS

This retrospective review of data from the multicenter Get With The Guidelines-Resuscitation registry between 2000 and 2014 used multivariable hierarchical logistic regression analysis to examine circadian rhythm of in-hospital cardiac arrest over a 24-h cycle, stratified by initial shockable versus non-shockable rhythm.

RESULTS

Among 154,038 patients, initial rhythm was recorded as asystole or pulseless electrical activity (non-shockable) in 124,918 (81%), and ventricular fibrillation or ventricular tachycardia (shockable) in 29,120 (19%). Among non-shockable events, the highest relative proportion occurred during 0400-0759 (17.9%), followed by 0000-0359 (17.1%). For shockable rhythms the greatest relative proportion occurred between 2000-2359 (17.0%), followed by 1200-1559 (16.9%). Multivariable analysis showed that the relative risk of non-shockable compared to shockable arrest was slightly higher from midnight through 0359 (aOR 1.13; 95% CI 1.06-1.20, p < 0.001) and from 0400 through 0759 h (aOR 1.14; 95% CI 1.07-1.22, p < 0.001). Although statistically significant, the magnitude of difference in incidence by time of day was small in both groups.

CONCLUSIONS

Although small differences in the relative frequency of in-hospital cardiac arrest (both shockable and non-shockable rhythms) were noted during different time intervals, in-hospital cardiac arrest occurs with nearly equal frequency throughout the day. Our findings have important implications for hospital staffing models to ensure that quality of resuscitation care is consistent regardless of 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.

Influence of the Circadian System on Disease Severity

The severity of many diseases varies across the day and night. For example, adverse cardiovascular incidents peak in the morning, asthma is often worse at night and temporal lobe epileptic seizures are most prevalent in the afternoon. These patterns may be due to the day/night rhythm in environment and behavior, and/or endogenous circadian rhythms in physiology. Furthermore, chronic misalignment between the endogenous circadian timing system and the behavioral cycles could be a cause of increased risk of diabetes, obesity, cardiovascular disease and certain cancers in shift workers. Here we describe the magnitude, relevance and potential biological basis of such daily changes in disease severity and of circadian/behavioral misalignment, and present how these insights may help in the development of appropriate chronotherapy.

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.

Effect of atenolol on symptomatic ventricular arrhythmia without structural heart disease: a randomized placebo-controlled study

BACKGROUND

Ventricular arrhythmia (VA) from the right ventricular outflow tract (RVOT) is a common problem. Symptomatic patients are usually treated with beta-blockers. There is little data on the systematic evaluation of the efficacy of beta-blocker. We determine the efficacy of atenolol in the treatment of symtomatic VA from RVOT compared with placebo.

METHODS AND RESULTS

This was a randomized, double-blinded, placebo-controlled study. We prospectively studied 52 consecutive patients with symptomatic VA. Severity of symptoms, 24-hour ambulatory monitoring (AECG) and quality of life (QOL) were assessed at baseline and 1 month after atenolol. Exercise testing was performed at baseline. Average premature ventricular complex (PVC) count at baseline was 21,407 +/- 1740 beats per 24 hours, and 19% had ventricular tachycardia as measured by AECG. Results of this study showed that atenolol significantly decreased symptom frequency (P =.03), PVC count (P =.001) and average heart rate (P <.001) measured by AECG, whereas placebo significantly decreased symptom frequency (P =.002) but had no effect on PVC count (P =.78) or average heart rate (P =.44). Neither atenolol nor placebo had an effect on QOL.

CONCLUSIONS

Atenolol improves symptoms and decreases PVC count from ambulatory monitoring. Placebo improved symptoms to the same extent as atenolol but had no effect on severity of VA. This might be the so-called placebo effect, which is a concern when treating patients or doing research on the effects of a drug.

[Circadian alterations of the cardiovascular system]

Circadian variations have been known for a long time for the influence they have on the physiological systems, including the cardiovascular system. The study of the mechanisms with circadian variation that change the function of the cardiovascular system and its diseases has increased greatly in recent years due to its clinical prominence. Through these studies, physiopathology, epidemiology and factors involved in cardiovascular diseases are more understandable. Thus, the incidence of cardiac events has been clearly associated with the morning hours, as well as the possible mechanisms involved in this variation during the daytime hours. The arterial blood pressure, plasma catecholamine levels and cortisol, platelet aggregation, and fibrinolytic system action are the most implicated mechanisms. From this knowledge, it is possible to design new therapeutic strategies that should consider the time of the day of higher risk for the onset of cardiovascular events.

Circadian variation of idiopathic ventricular tachycardia originating from right ventricular outflow tract

We determined circadian variation of isolated ventricular premature complexes (VPCs), 2 to 4 consecutive VPCs, and ventricular tachycardia (5 consecutive VPCs) originating from the right ventricular outflow tract in patients without apparent structural heart diseases. There was apparent circadian variation with 2 prominent peaks for these ventricular arrhythmias, and blockade abolished ventricular tachycardia and attenuated the circadian variation of consecutive VPCs.