Verapamil and circadian variation of sudden cardiac death

Circadian Rhythms in Sudden Cardiac Arrest: A Review

BACKGROUND

Sudden cardiac arrest (SCA) is a serious public health issue caused by the cessation of cardiac electrical and mechanical activity. Despite advances in pedestrian lifesaving technologies like defibrillators, the SCA mortality rate remains high, and survivors are at risk of suffering ischemic injury to various organs. Understanding the contributing factors for SCA is essential for improving morbidity and mortality. One factor capable of influencing SCA incidence and survival is the time of day at which SCA occurs.

OBJECTIVES

This review focused on the effect of time of day on SCA incidence, survival rate, and survival to discharge over the past 30 years and the role of age, sex, and SCA location in modulating the timing of SCA.

METHODS

The Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews criteria guided this review. Four databases (PubMed, Cochrane Libraries, Scopus, and Cumulative Index to Nursing and Allied Health Literature) were queried for research reports or articles addressing time of day and cardiac arrest, which were subsequently screened by the authors for inclusion in this analysis.

RESULTS

A total of 48 articles were included in the final analysis. This analysis showed a bimodal SCA distribution with a primary peak in the morning and a secondary peak in the afternoon; these peaks were dependent on age (older persons), sex (more frequent in males), and the location of occurrence (out-of-hospital cardiac arrest vs. in-hospital cardiac rest). Survival following SCA was lowest between midnight and 06:00 a.m.

DISCUSSION

The circadian rhythm likely plays an important role in the time-of-day-dependent pattern that is evident in both the incidence of and survival following SCA. There is a renewed call for nursing research to examine or address circadian rhythm as an element in studies involving older adults and activities affecting cardiovascular or respiratory parameters.

Elevated heart rate in cardiovascular diseases: a target for treatment?

Heart rate is a major determinant of myocardial oxygen consumption and of cardiac work, and thus reduction of heart rate may represent an important strategy for the treatment of patients with a wide range of cardiac disorders. In addition, several experimental lines of research point to high heart rate as an important risk factor for atherosclerosis and, thus, pharmacologic heart rate reduction could prevent or retard the development of atherosclerotic plaques and increase survival. Today, in patients with acute or chronic coronary syndromes or with congestive heart failure, reducing heart rate is a generally accepted treatment modality. Up to now, no human study has been performed to demonstrate the efficacy and the risk-benefit ratio of cardiac slowing in patients without cardiac disorders. However, recent retrospective analyses of the INternational VErapamil-SR/trandolapril STudy and the Paris Prospective Study 1 provided promising results. Treatment of high heart rate in healthy subjects appears to be premature, but in clinical conditions such as hypertension or diabetes, the reduction of elevated heart rate appears a desirable additional goal of therapy.

Clinical benefits versus shortcomings of diltiazem once-daily in the chronotherapy of cardiovascular diseases

BACKGROUND

The introduction of chronotherapy (that is improving a drugs therapeutic efficacy by paralleling the drugs plasma levels to circadian rhythms) has recently become a focus of interest.

OBJECTIVE

This article addresses the efficacy and potential shortcomings of chronotherapy, and focuses on one specific type of chronotherapy: a novel long-acting diltiazem formulation, DTZ-LA.

METHODS

We reviewed the literature to assess the clinical benefits and shortcomings associated with DTZ-LA in the management of hypertension and angina.

RESULTS/CONCLUSIONS

The clinical benefits of DTZ-LA outweigh its disadvantages when surrogate outcomes are evaluated, but it still remains to be determined whether chronotherapy benefits hard clinical outcomes. Nonetheless, chronotherapy has the potential to address the cardiovascular triggers that peak in the early morning hours when the preponderance of cardiovascular events occur, as well as providing better target organ protection compared with non-chronotherapeutic therapy.

Failure of magnesium to protect isolated cardiomyocytes from effects of hypoxia or metabolic poisoning

BACKGROUND

MgSO4 appears to reduce infarct size in animal models of myocardial infarction-reperfusion, but only if given before reperfusion. The mechanisms underlying this effect have not been established, nor has the discrepancy between these results and the lack of efficacy in the Fourth International Study of Infarct Survival (ISIS-4) been explained.

HYPOTHESIS

The study was undertaken to examine the hypothesis that Mg2+ protects myocardium threatened by ischemia.

METHODS

We studied the effects of extracellular magnesium [Mg2+](e) at 0.6 and 1.8 mmol/l on isolated myocytes exposed to 2.5 mmol/l NaCN + 5 mmol/l 2-deoxyglucose or to profound hypoxia.

RESULTS

Nonpaced cells shortened at a mean of 8.8 min after onset of metabolic inhibition in [Mg2+](e) = 1.8 mmol/l, 9.6 min in [Mg2+](e) = 0.6 mmol/l (not significant). Paced cells shortened after 9.5 min in [Mg2+](e) = 1.8 mmol/l, 10.2 min at [Mg2+](e) = 0.6 mmol/l. On washout of inhibitors, 93% of cells underwent hypercontracture at [Mg2+](e) = 1.8 mmol/l, 94.8% at [Mg2+](e) = 0.6 mmol/l. During hypoxia, nonpaced cells in [Mg2+](e) = 1.8 mmol/l shortened after 67 +/- 11 min compared with 62.5 +/- 28 min at [Mg2+](e) = 0.6 mmol/l. Paced cells shortened after 25.8 +/- 12.9 min at [Mg2+](e) = 1.8 mmol/l and after 28.7 +/- 13.6 min at [Mg2+]e = 0.6 mmol/l. Although there was a trend toward longer survival at higher [Mg2+](e), the difference was small and not significant (p > 0.05, Student's paired t-test).

CONCLUSION

We find no evidence to support the hypothesis that [Mg2+] protects myocardium threatened by ischemia. This is consistent with clinical data but contradicts data from animal experiments.

Meta-analysis of the morning excess of acute myocardial infarction and sudden cardiac death

To evaluate the impact of elimination of the morning peak of cardiovascular events, we performed a meta-analysis of studies of circadian variation of myocardial infarction and sudden cardiac death. The impact would be significant because approximately 1 of every 11 acute myocardial infarctions and 1 of every 15 sudden cardiac deaths are attributable to the morning excess incidence.

Effect of sustained-release Verapamil on the morning systemic arterial pressure surge during daily activity in patients with systemic hypertension

In a placebo-controlled study of 13 subjects with systemic hypertension, sustained-release verapamil reduced the morning surge in systolic pressure by 10.2 mm Hg (p = 0.04), diastolic pressure by 11.1 mm Hg (p = 0.008), and heart rate by 3.3 beats/min (p = 0.17). Blunting of the morning hemodynamic surge may be a mechanism by which verapamil could reduce the risk of plaque disruption and acute coronary events in the morning.