Circadian variation of total ischaemic burden and its alteration with anti-anginal agents

The morning surge in blood pressure and heart rate is dependent on levels of physical activity after waking

OBJECTIVE

To define the influence of morning physical activity levels on the magnitude of the morning surge in blood pressure and heart rate.

DESIGN AND METHODS

Blood pressure and physical activity were simultaneously recorded in 420 patients by 24-h monitor and actigraphy. The morning surge was defined as the difference between mean blood pressure and heart rate values in the 4-h periods before and after waking; the trough-to-peak surge in blood pressure was also calculated. These values were regressed on the difference in mean (log transformed) physical activity for the same two periods. The analysis was adjusted for covariates, including age, sex, clinic blood pressure and use of antihypertensive medication, in a multiple linear regression.

RESULTS

The mean morning surges in blood pressure and heart rate were 23/15(+/- 13/10) mmHg and 17(+/- 10) beats/min, respectively. The geometric mean increase in physical activity after waking was 33(+/- 1.5) units. The magnitudes of the morning surge in systolic blood pressure, diastolic blood pressure and heart rate were all significantly and positively correlated with the difference in mean physical activity before and after waking (P < 0.005). Greater clinic blood pressure was significantly associated with a greater morning surge in blood pressure on physical activity (P < 0.0005).

CONCLUSIONS

The magnitude of the morning surge is significantly associated with the level of physical activity in the hours after waking. Physical activity should be taken into account when the results of ambulatory blood pressure monitoring are interpreted.

Insufficient duration of action of antihypertensive drugs mediates high blood pressure in the morning in hypertensive population: the Ohasama study

Blood pressure (BP) usually peaks in the morning. The circadian variation of the onset of cardiovascular disease mimics this circadian BP variation. To examine the determinants of the BP difference between the self-recorded BP in the morning (home BP) and daytime average ambulatory BP a cross sectional study was done in the general population of Ohasama, Japan. 1207 subjects > or = 20 years measured both home (more than 14 times) and ambulatory BPs (326 treated for hypertension and 881 untreated subjects), The prevalence of subjects with the systolic BP difference (home BP in the morning - daytime ambulatory BP) of > or = 10 mmHg (high morning BP) was 5.6% in untreated normotensives, 2.9% in untreated hypertensives, and 25.8% in treated hypertensives. This trend was also observed for diastolic pressure. Multiple regression analysis demonstrated that age, male sex, and use of antihypertensive drugs were positively associated and day-night difference of BP was negatively associated with the high morning BP, respectively. These results suggest an insufficient duration of antihypertensive action of widely used antihypertensive drugs in Japan from the 1980s to 1990s. The amplitude of the day-night difference of ambulatory BP in subjects with a high morning BP was lower (non-dipping) than that without high morning BP. The high morning BP is not necessarily accompanied by hypertension but might be mediated, at least in part, by an insufficient duration of action of antihypertensive drugs. The high morning BP accompanies so-called non-dipper pattern of circadian BP variation. An insufficient duration of action of drugs may partly mediate non-dipping in subjects with antihypertensive medication.

Uncontrolled early morning blood pressure in medicated patients: the ACAMPA study. Analysis of the Control of Blood Pressure using Abulatory Blood Pressure Monitoring

BACKGROUND

A blood pressure surge during the early morning may help to precipitate cardiovascular events. The objective of this study was thus to assess the blood pressure behaviour profile of early morning blood pressure in patients receiving antihypertensive treatment.

DESIGN

The ACAMPA study is a multi-center, open, prospective, observational study that was carried out by 24 investigators in Spain.

METHODS

Two hundred and ninety patients with essential hypertension who had been receiving the same antihypertensive treatment for at least 2 months were included in the study. Office blood pressure was measured before taking medication in the morning, and 24-h ambulatory blood pressure monitoring was performed. In addition to the automatic measurements, patients were instructed to take a blood pressure measurement after waking.

RESULTS

The group analysis used 240 patients (mean age 54 years, including 101 males). Good clinical control (a blood pressure of less than 140/90 mmHg) was found in 53 cases (22%). The differences between the clinical and ambulatory readings during the period of activity were minimal in the group with good control (127 +/- 9/81 +/- 7 versus 127 +/- 10/81 +/- 7 mmHg; non-significant) but were significant in the group with poor control (155 +/- 16/93 +/- 10 versus 138 +/- 14/86 +/- 11 mmHg; P < 0.001). The blood pressure values were synchronized according to the moment of awakening. In almost half of the patients with good control, systolic and diastolic blood pressure values were higher than normal (135/85 mmHg); in those patients with poor control, this fraction rose to over 70%. The proportion of patients presenting high blood pressure values became even greater during the second hour after waking (62% in patients with good blood pressure control and 82% in those with poor control).

CONCLUSIONS

In a large number of antihypertensive patients receiving treatment, blood pressure values remain high during the early-morning hours. At least half of those patients with an apparently well-controlled office blood pressure do not have their blood pressure under control for the period shortly after waking.

The 24-hour blood pressure pattern: does it have implications for morbidity and mortality?

The onset of adverse cardiovascular events demonstrates a circadian pattern that reaches a peak in the morning shortly after awakening and arising. A parallel, 24-hour cyclical pattern has also been observed in the activities of various physiologic measurements, including blood pressure, heart rate, sympathetic nervous system activity, and platelet adhesiveness. Although a direct link has not yet been established, it can be postulated that the early morning surge in blood pressure may be a factor in precipitating acute cardiovascular episodes. Similar to the early morning blood pressure surge, blood pressure variability throughout the day appears to be a further independent risk factor for hypertensive target organ damage. Thus, it is reasonable to select an antihypertensive agent that offers smooth and well-sustained blood pressure control for the full 24-hour dosing interval, including the vulnerable early morning period. The results of clinical trials using ambulatory blood pressure monitoring have shown that telmisartan, an angiotensin II receptor antagonist, possesses such properties. Whether or not these attributes of telmisartan might translate into improvements in cardiovascular morbidity and mortality will be explored in the Ongoing Telmisartan Alone and in Combination with Ramipril Global Endpoint Trial (ONTARGET). This study will compare the effects of telmisartan 80-mg monotherapy, ramipril 10-mg monotherapy, or a combination of telmisartan 80 mg plus ramipril 10 mg, on cardiovascular endpoints in patients at high risk of cardiovascular events, several of whom are likely to be hypertensive at baseline. Inclusion of the telmisartan plus ramipril treatment arm will allow investigation of the potential advantages presented by combining an angiotensin-converting enzyme inhibitor with an angiotensin II receptor antagonist.

Diurnal variation of QT dispersion in patients with and without coronary artery disease

QT dispersion defined as interlead QT variability in a 12-lead electrocardiogram was proposed by Day and associates as a simple method to evaluate the repolarization heterogenicity of the ventricular myocardium. The frequency of onset of myocardial infarction and sudden death has been reported to have a circadian variation, with a peak incidence in the early morning hours. The authors investigated whether there is diurnal variation of QT interval and QT interval dispersion in healthy subjects and in patients with coronary artery disease. The study population consisted of two groups. Group I consisted of 62 subjects without coronary artery disease and group II consisted of 82 patients with coronary artery disease. Twelve-lead ECG was recorded for each patient in the morning (between 7 AM and 8 AM), afternoon (between 3 PM and 5 PM) and at night (between 11 PM and 1 AM), on the day after performance of coronary angiography. QTc dispersion was significantly higher in patients with coronary artery disease than in healthy subjects in the morning hours and afternoon (p<0.001). Although the differences were much prominent in group I than group II, both QTc dispersion of morning and afternoon were significantly greater than those at night. There were no statistically significant differences between group I and group II at nighttime with respect to maximum QTc, minimum QTc intervals, and QTc dispersion (p>0.05). In conclusion, QT dispersion shows diurnal variation with an increase in the morning hours in both patients with coronary artery disease and subjects without coronary artery disease. The mechanism of diurnal variation of QT dispersion in patients with coronary artery disease is quite different from that of healthy subjects.

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 of paroxysmal atrial fibrillation. PA3 Investigators. Atrial Pacing Peri-ablation for Prevention of Atrial Fibrillation Trial

The circadian variation of paroxysmal atrial fibrillation (AF) was studied in 67 patients who received a dual-chamber pacemaker 3 months before a planned atrioventricular node ablation. A distinct circadian variation of AF was observed with 2 time peaks in initiation (1 in the early morning and 1 in the early evening hours), which was modulated by atrial pacing, the duration of AF, and the use of beta-adrenergic blocking agents.

Acute inhibitory effect of alcohol on fibrinolysis

In contrast to a reduced risk of coronary heart disease (CHD) with light to moderate alcohol consumption, heavy alcohol intake and binge drinking are associated with increased cardiovascular mortality. Alcohol has an acute and profound effect on fibrinolysis that may be relevant to the pathogenesis of CHD. The short-term effects of a low (two glasses, 250 mL, 20 g ethanol) and a high (six glasses, 750 mL, 60 g ethanol) intake of red wine were studied in male volunteers and compared to the intake of mineral water. To find a threshold for inhibition of fibrinolysis and to study a binge effect, a second experiment was performed comparing the intake of four (500 mL, 40 g ethanol) and eight (1000 mL, 80 g ethanol) glasses of red wine with mineral water. Plasminogen activator inhibitor-1 (PAI-1), tissue-type plasminogen activator (t-PA), plasmin-antiplasmin (PAP) complexes and clot lysis time were measured. In contrast to the circadian rhythm with an enhanced fibrinolysis in the evening that was found in the mineral water group, an intake above four glasses of wine inhibited fibrinolysis significantly. After the intake of two glasses no significant disturbance of the circadian rhythm was observed. Five hours after the consumption of six glasses of wine, a dramatic increase occurred of PAI-1 antigen (77 +/- 42 microg L-1 vs. - 5 +/- 10 microg L-1 in the mineral water controls; P < 0.001) and PAI-1 activity (27 +/- 15 U mL-1 vs. - 2 +/- 3 U mL-1 in mineral water controls; P < 0.001). Despite a rise in t-PA antigen, t-PA activity dropped (- 0.5 +/- 0.2 U mL-1 vs. - 0.1 +/- 0.2 in controls; P < 0.001) as did PAP complexes (- 103 +/- 55 microg L-1 vs. - 26 +/- 57 microg L-1 in controls; P < 0.01). After the consumption of eight glasses of wine, the clot lysis assay indicated continued inhibition of fibrinolysis the following morning. Drinking a large amount of alcohol in the evening results in an acute inhibition of fibrinolysis, persisting the following morning. This may predispose to accelerated atherosclerosis and set the stage for thrombotic coronary events, explaining the higher cardiovascular mortality risk in binge drinkers.

Silent ischaemia and hypertension

For many years now, silent ischaemia has been recognized as a distinct clinical entity, and its relevance in different patient groups has been established. However, a number of basic questions have not been answered. In explaining the pathophysiology of silent ischaemia, factors affecting both the demand and the supply side are now being recognized. With the exception of certain well-defined groups, it is not clear why some patients are mostly symptomatic, while other patients are predominantly asymptomatic. There appear to be many factors influencing the ischaemic pain threshold. Studies investigating the prevalence of silent ischaemia show a remarkably high prevalence of silent ischaemia in different patient groups. Patients with hypertension but without coronary artery disease form a specific and vulnerable high-risk population that is particularly prone to silent ischaemia. Since changes at the macrovascular level are not responsible, various factors negatively influencing either cardiac supply or demand have been investigated. A reduced coronary reserve is central in explaining the increased prevalence of silent ischaemia in hypertensives. Left ventricular hypertrophy renders meaningful detection of ST segment changes difficult, but a possible solution dealing with this problem is offered by applying more stringent criteria in terms of minimal ST depression in the definition of ischaemia. The treatment of silent ischaemia is largely the same as for angina pectoris, but whether therapy should be directed at elimination of all ischaemic episodes or only of symptomatic episodes depends on further prospective work addressing this question.

A cross-sectional and diurnal study of thrombogenesis among patients with chronic atrial fibrillation

OBJECTIVES

First, we sought to determine whether there is diurnal variation in hemostatic factors related to thrombogenesis and hypercoagulability among patients with chronic atrial fibrillation (AF). Second, we sought to determine whether levels of soluble thrombomodulin (sTM), a marker of endothelial function, or soluble P-selectin (sP-sel), an index of platelet activation, are altered in patients with AF as compared with subjects in sinus rhythm.

BACKGROUND

Atrial fibrillation is associated with an increased risk of stroke and thromboembolism and is known to confer a hypercoagulable state, with abnormalities of thrombosis, platelet activation and endothelial cell function. Many cardiovascular events, such as acute myocardial infarction, have thrombosis as an underlying process, and they undergo diurnal variation.

METHODS

Fifty-two patients (45 men, mean [+/- SD] age 66 +/- 6 years) with chronic AF, none of whom received antithrombotic therapy, were studied. Baseline levels of fibrinogen, sP-sel, sTM and von Willebrand factor (vWF) were compared to those levels in matched healthy control subjects in sinus rhythm. In a subgroup of 20 patients, five venous blood samples were collected through an indwelling cannula at 6-h intervals from 12 PM to 12 PM the following day and were analyzed for the same markers.

RESULTS

Patients with chronic AF had higher plasma sP-sel, sTM, vWF and fibrinogen levels as compared with control subjects in sinus rhythm. Significant correlations were found between fibrinogen and sP-sel in patients with AF (r = 0.567 [Spearman], p < 0.001) and in control subjects (r = 0.334, p = 0.016). There was no significant diurnal variation in plasma levels of sP-sel, sTM, vWF or fibrinogen over the 24-h study period (repeated measures analysis of variance, p = NS).

CONCLUSIONS

There is no circadian or diurnal variation in the hypercoagulable state seen in AF, as assessed by plasma fibrinogen and markers of platelet (sP-sel) and endothelial function (vWF and sTM). The persistent hypercoagulable state, together with the loss of diurnal variation in various hemostatic markers, in chronic AF may contribute to the high risk of stroke and thromboembolic complications in these patients.

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.

The safety and effectiveness of esmolol in the perioperative period in patients undergoing abdominal aortic surgery

OBJECTIVES

To determine (1) if perioperative use of esmolol in major vascular surgery patients provides strict heart rate (HR) control, (2) what doses of esmolol are required to do this, and (3) does this control influence myocardial ischemia or result in adverse consequences.

DESIGN

Prospective study of 40 patients randomized to two groups: The HR was controlled to either less than 80 beats/min (group 80) or less than 110 beats/min (group 110) using esmolol. Patients were monitored continuously for electrocardiographic changes perioperatively. HR control began after induction of anesthesia and continued for 48 hours thereafter.

SETTING

Operating room and intensive care unit.

PATIENTS

Patients undergoing abdominal vascular surgery involving aortic cross-clamping.

INTERVENTIONS

Esmolol was titrated until the target HR was met.

MEASUREMENTS AND RESULTS

Only one patient demonstrated an adverse effect. The median infusion rates were 100 and 12.5 microg/kg/min for groups 80 and 110. Target HR was met less in group 80 than in group 110, primarily in the postoperative period. Ischemia patterns were not significantly different between groups.

CONCLUSION

Using esmolol for HR control in the intraoperative period for abdominal vascular surgery patients is effective and safe. HR control was much less effective in the postoperative period, but esmolol is safe when used at recommended doses. Further study with a larger number of patients is necessary to determine whether strict HR control with esmolol affects the incidence of myocardial ischemia or infarction in this patient population.

Thoracic epidural anesthesia reduces infarct size in a canine model of myocardial ischemia and reperfusion injury

OBJECTIVE

To determine the effects of thoracic epidural anesthesia on myocardial infarct size, regional myocardial blood flow (RMBF), and plasma norepinephrine in an anesthetized canine model of ischemia reperfusion injury with infarction.

DESIGN

Blinded, randomized, placebo-controlled animal study.

SETTING

Experiments were performed in the cardiothoracic research laboratory at Wake Forest University Baptist Medical Center.

PARTICIPANTS

Anesthetized, open-chest mongrel dogs were used in these studies.

METHODS

Dogs were instrumented for measurement of aortic pressure (AP) and left ventricular systolic pressure (LVSP), dP/dt, and RMBF Epidural catheters were inserted at thoracic segment T5. Three groups received epidural 0.5% bupivacaine: low-dose (n = 7; 0.3 mg/kg bolus, 0.15 mg/kg/ h), mid-dose (n = 7; 0.6 mg/kg bolus, 0.3 mg/kg/h), high-dose (n = 7; 1.2 mg/kg bolus, 0.6 mg/kg/h). The vehicle (VEH) group received epidural saline. Bolus followed by maintenance infusions began 30 minutes before the onset of ischemia (60 min) and continued through reperfusion (180 min).

RESULTS

Myocardial infarct size was significantly reduced in the high-dose group versus the VEH and low-dose groups (p < 0.05). After initiation of the mid and high dose, AP, LVSP, and dP/dt decreased 7% to 16% (high vVEH; p < 0.05). VEH dogs showed a 130% increase from control in early postischemic RMBF. There was a dose-dependent attenuation in this reflow response: 72%, 31%, and 6% increase in RMBF in the low, mid, and high groups, relative to controls (p < 0.05 high v VEH). Although there was no significant difference in plasma norepinephrine, fewer surges occurred in the high-dose group.

CONCLUSIONS

Thoracic epidural anesthesia reduces infarct size and postischemic hyperemia in a model of ischemia reperfusion injury.

Chronotherapeutics: are there meaningful differences among antihypertensive drugs?

In the past decade, many publications have dealt with the possible relationship between biological rhythms and the incidence of cardiovascular events. A high proportion of treated hypertensive patients have cardiovascular complications, and chronotherapy, which permits the use of drugs that are maximally effective at different points in the circadian cycle, may be an interesting and valuable approach to decreasing morbidity and mortality in these patients. This article summarizes current knowledge on the new science of chronopharmacology, as demonstrated in several clinical studies that have used conventional agents administered at various points in the circadian cycle as well as new chronotherapeutic agents, such as controlled onset extended release (COER)-verapamil. In addition, emphasis is given to a rigorous evaluation of antihypertensive agents in terms of efficacy and duration of effect to obtain adequate and sustained lowering of blood pressure over the 24-hour period.

"Circadian" variation in cardiovascular events and implications for therapy?

For many years, it was thought that acute cardiovascular events occurred in a random fashion. However, over the past 13 years or so, a significant amount of research, both retrospective and prospective, has shown that there is an excess of ischaemic activity, arrhythmic activity and acute cardiovascular events in the first few hours after waking and commencing activity. This excess may well be at least partly linked to the known physiological changes which occur after waking, including a surge in heart rate, blood pressure and catecholamine release, activation of the renin-angiotensin system, an increase in platelet aggregability on assuming the upright posture, and the final trough in the fibrinolytic system. Because of the relatively short half-life and duration of the therapeutic effect (<24 h) of many anti-ischaemic and anti-arrhythmic agents, it is likely that single day agents taken in the morning will have reached subtherapeutic levels at the time of waking and commencing activity the following morning. As many patients do not take their daily (morning) medication immediately on rising, and allowing for time for adsorption, it is likely that, despite our knowledge of "circadian variations" in both physiological responses and pathophysiological events in the morning waking hours, patients are in fact at least protection at this particular high-risk time of the 24 h day. With our knowledge about when events are more likely to happen, we should consider carefully the timing of administration of medications, having factored in the likely length of therapeutic effect in each instance. It is likely that the almost universal inability to demonstrate prognostic benefit with many anti-ischaemic and anti-arrhythmic agents to date relates at least in part to a lack of appropriate "protection" at the time of apparent greatest risk in the patient with cardiovascular disease. Intelligent prescribing might indeed improve outcome, and even in the absence of proof on this regard, it would seem appropriate that we at least strive to achieve such an outcome.

European survey on circadian variation of angina pectoris (ESCVA): design and preliminary results

A circadian variation has been observed for acute coronary syndromes (myocardial infarction, sudden cardiac death, angina pectoris) with a peak during the morning and a trough during the night. The previous reports, however, were based primarily on selected patients in clinical studies. The present study has been designed to determine the timing of attacks of angina pectoris in ambulatory patients, the association of wake time and possible external triggers with angina attacks, and the influence of cardiac medication. The European Survey on Circadian Variation of Angina Pectoris is a multicenter international cross-sectional survey of outpatients treated in general medical practice of seven European countries. Inclusion criteria are stable angina pectoris for at least 3 months, average frequency of two or more attacks per week, and treatment with on-demand nitrates. Standardised self-administered questionnaires are provided to all consecutive patients and their physicians. From January to July 1998, 1087 patients (61% male, 64 +/- 9 years; 39% female, 67 +/- 10 years) were enrolled in 196 centers. A total of 3453 angina pectoris attacks were reported, on average 3.2 per patient per week (range 0-48). The occurrence of angina pectoris attacks demonstrates a significant circadian variation (p < 0.001) with a primary morning peak from 9:00 to 12:00 (relative risk 3.0 compared with other times of day) and a secondary afternoon peak from 15:00 to 18:00. Of all attacks, 50% occured within 6 h after awakening. Seventy-four percent of all patients reported possible external triggers of angina such as physical activity or anger. The present multicenter survey in general medical practice demonstrates a marked wake time related circadian variation in angina pectoris attacks. To improve preventive strategies, therefore, type, dosage and particularly timing of cardiac medication appear of importance, as may be behavior modification approaches.

Chronopharmacokinetics: implications for drug treatment

Nearly all functions of the human body are organized across the 24 hours of the day. This is also true for functions involved in the regulation of pharmacokinetics such as gastric absorption and emptying, gastro-intestinal perfusion, and liver and kidney functions. Several clinical studies, performed in a cross-over design, have provided evidence that the pharmacokinetics of mainly lipophilic drugs can be circadian phase-dependent. These studies show that after oral dosing, peak drug concentration (Cmax) is, in general, higher or time-to-peak (tmax) shorter after morning, compared with evening application. A few studies performed with both immediate-release and sustained-release preparations (isosorbide-5-mononitrate, nifedipine) gave evidence that only the immediate-release formulation displayed circadian time-dependent pharmacokinetics, but not the sustained-release form. Most importantly, pharmacodynamic studies performed in parallel revealed that the effects, as well as the dose-response relationship, can be circadian phase-dependent, an observation which has an impact on pharmacokinetic/pharmacodynamic modelling. Moreover, this can be of relevance because the onset of certain diseases (e.g., bronchial asthma, coronary infarction, angina pectoris, rheumatic complaints) is not randomly distributed across the 24-h scale. In conclusion, there is now convincing evidence that the time-of-day has to be taken into account both in clinical pharmacokinetic and pharmacodynamic studies.

Optimal nitrate therapy with a once-daily sustained-release formulation of isosorbide mononitrate

During long-term prophylaxis of angina with oral nitrates, sustained high plasma nitrate concentrations produce partial or complete tolerance to both the haemodynamic and the clinical effects of the drug. There is substantial evidence that this can be prevented by an adequate nitrate-free or nitrate-low period during each 24 h dosing interval. However, a nitrate-free interval carries the risk of a rebound increase in myocardial ischaemia. Once-daily formulations of isosorbide mononitrate deliver high plasma nitrate concentrations that improve exercise tolerance in patients with angina for at least 12 h after dosing. During the remainder of the dosage interval, plasma nitrate concentrations fall but are sufficient to protect against coronary artery spasm overnight. Myocardial ischaemia has a marked circadian rhythm. All ischaemic events (total ischaemic burden, myocardial infarction and sudden cardiac death) are most frequent in the hours immediately after waking. Oral anti-ischaemic prophylaxis should ideally provide protection during this critical period, in order to minimize symptoms, maximize exercise capacity and perhaps also to reduce the risk of clinical events. The ideal long-acting nitrate formulation should therefore provide a rapid rise in plasma nitrate concentration as well as maintaining prolonged efficacy throughout the dosing interval. Elantan LA is a sustained-release capsule formulation of isosorbide mononitrate for once-daily dosing. This capsule contains pellets which release 30% of the dose immediately, while 70% is released slowly to maintain the therapeutic response. The pharmacokinetic profile of this formulation prevents the development of tolerance, while also conferring long-term anti-anginal efficacy. Patients reported an improvement in both severity of angina and quality of life indices when their therapy was changed from multiple daily dosing with isosorbide dinitrate to once-daily dosing with Elantan LA (50 mg). The anti-anginal effect of Elantan LA is attained rapidly after dosing. Within 30 min of ingestion, there are clinically significant improvements in exercise tolerance, comparable with the speed of onset after an immediate-release formulation of isosorbide mononitrate. Elantan LA is an effective once-daily prophylaxis for angina which also produces a rapid onset of therapeutic effect. The release profile of this formulation maximizes protection against the morning surge in myocardial ischaemia.

Circadian variation of paroxysmal supraventricular tachycardia

BACKGROUND

Various clinical manifestations of cardiovascular diseases have a pattern of circadian variation. In this study, we investigated whether the onset and duration of paroxysmal supraventricular tachycardia (PSVT) has a circadian variation.

METHODS AND RESULTS

In our analysis, we included 105 patients with 498 PSVT episodes. In this study, the onset of PSVT did not have a uniform distribution throughout the 24-h period. There were nearly equal peaks in the time periods from 8:00 to 9:00 AM, 12:00 to 1:00 PM, and 5:00 to 6:00 PM, with a trough at night. The duration of PSVT also did not show a uniform distribution throughout the 24-h period; it increased significantly during the daytime, with a peak between 1:00 and 2:00 PM, another peak between 6:00 and 7:00 PM, and a significant reduction at night.

CONCLUSIONS

The onset and duration of PSVT showed a circadian variation. However, the time-oriented antiarrhythmic therapy for preventing PSVT needs further study.

Circadian variations of QTc dispersion: is it a clue to morning increase of sudden cardiac death?

BACKGROUND

Several studies related to cardiac events including sudden death have shown a peak incidence in the early morning hours. It has also been known that acute ischemia is a potent stimulus to increased dispersion of repolarization and development of malignant arrhythmias.

HYPOTHESIS

The purpose of the present study was to investigate diurnal variations of corrected QT dispersion (QTcD) in patients with coronary artery disease (CAD) (Group 1) compared with controls with normal coronary angiograms (Group 2).

METHODS

We investigated a total of 110 patients who had been referred for coronary angiography, of whom 62 (42 men, 20 women; age 55 +/- 7 years) had double- or triple-vessel disease, and of whom 48 (31 men, 17 women; age 54 +/- 9 years) had normal coronary angiograms. QTcD measurements were calculated from a 12-lead resting electrocardiogram (ECG) during sinus rhythm. These ECGs were obtained for each patient in the morning, at noon, in the evening, and at night on the day after performance of coronary angiography. QTcD was significantly greater in patients with abnormal coronary angiograms (Group 1) than in patients with angiographically documented normal coronary arteries (Group 2). This difference appeared to be more prominent in the morning hours (p < 0.001) than at other times. QTcD in the evening and night hours was not statistically different (p > 0.05) between both groups. We also compared intragroup QTcD values: QTcD values were significantly increased in the morning hours and were more prominent in Group 1 than in Group 2.

CONCLUSIONS

Our data suggest that QTcD has a circadian variation with an increase in the morning hours, especially in patients with coronary artery disease. This finding was thought to be an explanation for the role played by sympathetic nervous system in the occurrence of acute cardiac events and sudden death during these hours.

From a static to a dynamic concept of risk: the circadian epidemiology of cardiovascular events

A growing body of evidence substantiates that the occurrence of cardiovascular events in unevenly distributed in time, especially during the 24 h. These temporal patterns are indicative of temporal variation in the (1) pathophysiological mechanisms that trigger cardiovascular events and (2) physiological status of the cardiovascular system, which combine to give rise to 24 h and other periodicities in the susceptibility to disease. The classic assumption of epidemiologic studies is constancy (or homeostasis) in one's risk to disease during the 24 h, as well as other, time domains. However, we propose a new concept, that of chronorisk since it takes into account the temporal variability in the pathophysiological mechanisms and their reciprocal temporal interactions that lead to day-night and other time-dependent patterns in cardiovascular events. This chronobiological approach, which is expected to contribute new insight into the prognostic and therapeutic assessment of cardiovascular events, is worthy of broader application in cardiovascular and other fields of medicine and warrants further investigation.

Analysis of arrhythmias in the Circadian Antiischemia Program in Europe (CAPE) study

The aim of this study was to analyze whether, in patients with long-standing (>4 years) coronary artery disease (CAD), the addition of the long-acting calcium channel blocker (CCB) amlodipine to conventional treatment [beta-blockers (BBLs) and nitrates] during anginal attacks would have a proarrhythmic effect. This was tested by analyzing data from patients who had taken part in the Circadian Anti-ischemia Program in Europe (CAPE) trial. After a 2-week, single-blind, run-in period (Phase 1), patients were randomized to amlodipine, 5 mg/day (first 4 weeks) and 10 mg/day (second 4 weeks), or placebo for 8 weeks (Phase 2). The 48-h Holter data were analyzed for 167 amlodipine-treated patients and 83 placebo patients based on a 2:1 randomization scheme. Sixty-three per cent of amlodipine patients and 67% of placebo patients were receiving concomitant BBLs, and >90% had taken sublingual nitrates during anginal attacks, as basic antiischemic therapy. After 7 weeks of therapy, when 48-h Holter monitoring was repeated, there were no significant changes in the frequency of ventricular arrhythmias in the placebo or amlodipine groups for all patients or subgroups of patients with or without BBLs. Also, between-group comparisons showed no significant differences in arrhythmias between amlodipine and placebo patients. In summary, amlodipine (5-10 mg/day) given to patients with severe, chronic CAD receiving conventional antiischemic therapy, did not produce any proarrhythmic effects.

ST segment changes following retinal surgery

STUDY OBJECTIVE

To describe the perioperative cardiac morbidity in adult patients undergoing retinal surgery using continuous Holter monitoring.

DESIGN

Prospective study.

SETTING

University hospital.

PATIENTS

56 patients scheduled for elective retinal surgery with local anesthesia.

INTERVENTIONS

Patients were monitored continuously for 24 hours using a Holter recorder. Blood samples for creatine phosphokinase (CPK) and serum myocardial creatine phosphokinase (CPK-MB) were taken preoperatively and 24 hours postoperatively. The characteristics of myocardial ischemia were compared according to the number of risk factors for ischemic heart disease.

MEASUREMENTS AND MAIN RESULTS

The overall incidence of perioperative myocardial ischemia was high: 26.7% (n = 15). These patients exhibited 41 episodes of ischemia with mean ST segment change from baseline of 2.2+/-0.7 mm. However, almost all (93.3%) ischemic episodes were silent. Patients with two risk factors or more had 77% more episodes of ischemia than patients with one risk factor (p < 0.005), and the duration of ischemia was 47+/-22.5 minutes compared with 34.8+/-27.5 minutes (p = NS). The first episode of ischemia occurred an average of 10 hours after surgery. No patient had intraoperative evidence of ischemia. Half of the ischemic episodes were associated with an increase in heart rate. No patient had evidence of acute myocardial infarction.

CONCLUSION

Retinal surgery with local anesthesia is accompanied by a high incidence of postoperative myocardial ischemia. No negative outcome was correlated to the occurrence of postoperative myocardial ischemia. The significance of these findings has yet to be evaluated.

Circadian variation of paroxysmal atrial fibrillation

BACKGROUND

Circadian variation in the incidence of acute cardiovascular events is well known but has not been extensively investigated in paroxysmal atrial fibrillation, although the significance of this arrhythmia is growing in our society with the increasing number of aged people.

METHODS AND RESULTS

We detected 150 patients with paroxysmal atrial fibrillation in a drug-free state from among 25,500 consecutive Holter recordings. To determine whether the onset, maintenance, and termination of paroxysmal atrial fibrillation were random events, we analyzed the total recorded duration of arrhythmia and the incidence of and number of patients with the onset, maintenance, and termination of this arrhythmia as hourly data and as hourly probabilities. A prominent circadian rhythm of the total duration of atrial fibrillation, approximately 90% of which was well explained by a single cosinusoidal function, was detected with a nadir around 11 AM. Because the onset of the arrhythmia had little or no circadian rhythm, this finding was due to a diurnal pattern of maintenance and termination, both of which were well expressed by a double-harmonic density function. Maintenance showed a trough at 11 AM, and termination showed a peak at the same time, leading to the nonuniform duration of single episodes of atrial fibrillation throughout the 24-hour day.

CONCLUSIONS

Paroxysmal atrial fibrillation showed a unique circadian variation that differed from the well-known pattern for acute cardiovascular events, a point that should be kept in mind when antiarrhythmic therapy is evaluated. Identification of factors that regulate the circadian pattern of the maintenance and termination of paroxysmal atrial fibrillation may lead to better chronotherapy for preventing perpetuation of this arrhythmia.

Circadian variation in the onset of unstable angina and non-Q-wave acute myocardial infarction (the TIMI III Registry and TIMI IIIB)

Circadian variation has been demonstrated in several types of acute cardiovascular disease, including acute myocardial infarction (AMI), sudden cardiac death, silent ambulatory ischemia, and thrombotic stroke. In contrast, no diurnal variation was observed in 1 study of non-Q-wave AMI, and limited data are available for unstable angina. To assess whether circadian variation is present in unstable angina and non-Q-wave AMI, we examined the time of onset of ischemic pain in 7,731 patients who were prospectively identified in the Thrombolysis in Myocardial Ischemia (TIMI) III Registry, 3,318 of whom were enrolled in the prospective study, and in 1,473 patients enrolled in the TIMI IIIB trial. A circadian variation in the onset of pain was observed, with an increase in the number of patients experiencing the onset of pain in the morning hours between 6 A.M. and 12 noon (p <0.001). This circadian variation was observed both in patients with unstable angina and in those with evolving non-Q-wave AMI. A similar circadian pattern was observed in all subgroups tested. These findings were confirmed in the TIMI IIIB trial and complement previous studies suggesting that circadian variation exists in the onset of the full spectrum of myocardial ischemic syndromes.

Novel delivery system for verapamil designed to achieve maximal blood pressure control during the early morning

Because the risk of cardiovascular events appears to be greatest in the early morning, this period is a time during which adequate blood pressure (BP) control appears to be most desirable. In this study, a controlled-onset extended-release system (COER-24) that delivers verapamil in a manner designed to achieve maximal levels of drug during the early morning surge in BP was compared with placebo. Ninety-five patients with mild to moderate hypertension were studied. Of this group, 49 patients (mean age 57.6 +/- 1.4 years; 35 men and 14 women) were randomized to take verapamil COER-24 240 mg at 10 PM, and 46 subjects (mean age 55.8 +/- 1.5 years; 29 men and 17 women) were randomized to take placebo. Ambulatory BP monitoring was performed after a 4-week initial placebo period and was repeated after 4 weeks of treatment with verapamil or placebo. Verapamil COER-24 resulted in significant (p < 0.001) decreases in mean whole-day systolic and diastolic BP (-8.2/-6.3 mm Hg; baseline 152/93.0 mm Hg) when compared with placebo (+0.3/-0.9 mm Hg; baseline 150.3/93.2 mm Hg). From 6 AM to noon, verapamil COER-24 resulted in a change in systolic and diastolic BP of -11.6/-9.0 mm Hg, which was significantly (p < 0.001) greater than the change that occurred with placebo (-0.5/-1.0 mm Hg) during the same period. In the last 4 hours of the dosing interval (6 PM to 10 PM), verapamil COER-24 caused significantly greater (p < 0.001) decreases in BP (-7.4/-4.8 mm Hg) than did placebo (+2.7/+1.0 mm Hg). These data demonstrate that the COER-24 system, when administered in the late evening, achieves maximal BP reduction during the early morning hours. Moreover, BP reductions were sustained throughout the 24-hour period.

Assessment of time domain and spectral components of heart rate variability immediately before ischemic ST segment depression episodes

In an attempt to study autonomic function during the 5-minute period preceding ischemic ST segment depression (decreases ST) episodes, we selected 138 decreases ST episodes, without preceding decreases ST during the last 15 minutes before each episode, from the Holter tapes of 35 patients with multivessel coronary artery disease. For the 5-minute period preceding each decreases ST episode, we calculated the following heart rate variability (HRV) indices; the mean RR interval (RR5), the standard deviation of all RR intervals (SD Index5), the corresponding coefficient of variation (CV5), and the natural log (Ln) of the spectral components, total power at 0.000 to 0.400 Hz (TP5), low frequency power at 0.040 to 0.150 Hz (LF5), high frequency power at 0.150 to 0.400 Hz (HF5), and the ratio of the low to high frequency power (LF5/HF5). As HRV indices of the 24-hour period, we calculated the respective RR, SD Index, CV, LnTP, LnLF, LnHF, and Ln LF/HF. RR5, SD Index5, CV5, and Ln TP5 were all significantly lower than RR (t = -5.343, p = 3.7 x 10(-7)), SD Index (t = -19.091, p = 1.99 x 10(-40)), CV (t = -15.780, p = 1.28 x 10(-32)), and LnTP (t = -3.210, p = 0.0016), respectively. LnHF5 was inversely correlated with the magnitude of the decreases ST; r = -0.174, P < 0.05, and CV5 was inversely correlated with the natural log (Ln) of the ischemic event duration; r = -0.183, P < 0.05. Analogous results were obtained for both the painful and silent decreases ST episodes. It is concluded that HRV is decreased during the 5-minute period preceding decreases ST episodes, and is inversely related with the magnitude and the duration of the *ST.

Signal transduction in animal models of normotension and hypertension

Experiments in inbred strains of normotensive and hypertensive rats have clearly demonstrated circadian rhythms in blood pressure and heart rate. Pre- and postsynaptic signal transduction processes in vitro can, but need not, vary with circadian time, greatly depending on the strain of rats investigated. These data highlight the notion of a strain-dependent, and thus genetic, regulation of the cardiovascular system. Obviously, circadian rhythms in blood pressure cannot be explained by single biochemical parameters, but results from both in vitro and in vivo studies give first evidence that the vascular nitric oxide-cGMP system may be involved in the circadian regulation of blood pressure in WKY and SHR rats. In secondary hypertensive TGR and in their normotensive controls, SPRD, the guanylyl cyclase system does not seem to play a role in circadian blood pressure regulation. In neither of the four strains studied did aortic adenylyl cyclase show any time-dependent variation. Because vascular tissue was taken from the thoracic aorta of the rats, a contribution of adenylyl cyclase to circadian blood pressure regulation in small resistance arteries cannot be ruled out. Further studies in different parts of the vascular tree are needed to definitely answer that question. No data are available on time-dependent variation in the activity of phospholipase C, the second messenger pathway of vascular alpha-adrenoceptors and angiotensin II AT1-receptors, both of which mediate vasoconstriction. Future research into this system will be helpful in identifying mechanisms involved in blood pressure regulation in SPRD and TGR.

Relationships of the circadian rhythms of thrombotic, ischemic, hemorrhagic, and arrhythmic events to blood pressure rhythms

Convincing evidence has recently accumulated that several unfavorable cardiovascular events show a well defined pattern in their occurrence throughout the day. Myocardial angina and infarction, sudden cardiac death, arrhythmias, fatal pulmonary thromboembolism, and ischemic and hemorrhagic cerebrovascular accidents occur more frequently in the morning, after awaking, until noon. Diurnal variations in multiple biologic functions, such as assumption of an upright posture associated with increased platelet aggregability, changes in blood clotting, fibrinolysis, and vascular tone and resistance, may be potentially active triggering factors. Moreover, variations in sympathetic tone, catecholamine secretion, and blood pressure have to be considered. The role of triggering factors and their relationships with blood pressure patterns is discussed in view of an optimized pharmacologic treatment.

Patterns and behavior of transient myocardial ischemia in stable coronary disease are the same in both men and women: a comparative study

OBJECTIVES

This study sought to compare the circadian variations in transient ischemic activity, mean heart rate and ischemic threshold between women and men with coronary artery disease.

BACKGROUND

There is a circadian variation in ischemic activity, onset of myocardial infarction and sudden cardiac death in patients with coronary artery disease, but studies assessing ischemia have incorporated predominantly male subjects.

METHODS

Thirty-one women and 45 men underwent at least 48 h of ambulatory ST segment monitoring.

RESULTS

There was a similar and significant circadian variation in ischemic activity in both women and men (p < 0.0001 and p < 0.0001, respectively), with a trough at night, a surge in the morning and a peak between 1 and 2 PM, corresponding to a similar circadian variation in mean hourly heart rate (p < 0.0001) that was not different between men and women (p = 0.28, power to detect a shift 99.9%). Mean heart rate at onset of ischemia (ischemic threshold) had similar variability in women and men (p = 0.96), and harmonic regression analysis confirmed a significant circadian variation (p < 0.0001), with a trough at night and a peak during activity hours. Heart rate increased significantly in the 5 min before ischemia throughout the 24 h (p < 0.0001), with no gender differences in the pattern of preonset to onset heart rate changes over time (p = 0.52); the smallest differences were recorded in the middle of the night. The majority of ischemic episodes (80%) had a heart rate increase > 5 beats/min in the 5 min before ischemia, but there were no gender differences.

CONCLUSIONS

Women with coronary artery disease have a pattern of ischemic activity and underlying pathophysiologic mechanisms very similar to men. The importance of increase in myocardial oxygen demand in the genesis of ischemia in both men and women is reflected by similar magnitude of heart rate increases before ischemia. The lower ischemic threshold during the nocturnal hours, when blood pressure is also lower, is consistent with a circadian variation in underlying coronary vascular tone.

The circadian variation of cardiovascular stress levels and reactivity: relationship to individual differences in morningness/eveningness

Two studies assessed the circadian variation of cardiovascular responses to stress in healthy and coronary artery disease (CAD) populations. In within-subjects designs, stressors were administered to healthy male subjects and male CAD patients both in the morning and afternoon, and subjects were classified as either morning or evening types using the Morningness-Eveningness Questionnaire (Horne & Ostberg, 1976, International Journal of Chronobiology, 4, 97-110). No consistent circadian variation in blood pressure or heart rate responses was observed in the aggregate sample of either healthy subjects or CAD patients. However, there were significant interactions between circadian type and time of day. In both populations, morning subjects exhibited higher cardiovascular levels during the morning session, and evening subjects exhibited higher levels during the afternoon session. Analyses of cardiovascular reactivity revealed less consistent evidence for this interaction. Self-reports of stress revealed interactions between time of day and morningness/eveningness only in the CAD sample. In CAD patients, preliminary analysis of myocardial wall function, an index of myocardial ischemia, did not reveal a significant interaction between morningness/eveningness and time of day, perhaps due to small sample size. The presence of differing circadian patterns in stress response based on individual differences in morningness/eveningness is discussed in terms of its methodological implications for psychophysiological research and in terms of the role of stress as an acute trigger of CAD.

Prevention and practical aspects of triggering of cardiovascular events

The recognition of the peak morning incidence of cardiovascular events and the role of triggering mechanisms can lead to some practical suggestions. For instance, adequate pharmacologic coverage over the full 24-hour period, in particular during the morning period of increased risk, is desirable among individuals taking antihypertensive and anti-ischemic medication. Although the absolute risk of an event occurring following a single exposure to a potential trigger is in general too low to recommend avoidance of the stressor, further research in this area may result in the design of pharmacologic and nonpharmacologic means to prevent the trigger from precipitating disease onset.

Circadian variation of alpha 1-adrenoceptor-mediated pressor response to phenylephrine in man

The variability in the pressor effects of the alpha 1-adrenoceptor agonist phenylephrine was observed under placebo conditions in ten healthy subjects in a double blind randomized study. Phenylephrine infusions were administered before administration of placebo (baseline) and 2, 4, 8, 12, 24 and 48 h later. The doses of phenylephrine required to increase systolic blood pressure by 20 mmHg after 8 and 12 h (5.30 and 9.30 pm, 81.4 +/- 15.3 and 71.1 +/- 16.0 micrograms min-1, respectively) were significantly (P < 0.01) less than the baseline values (8.30 am, 108.0 +/- 27.6 g min-1). These results might indicate a circadian variation in the phenylephrine-induced alpha-adrenoceptor-mediated vascular response in healthy subjects. These observations lend further insight into circadian variations of vascular tone that might contribute to circadian rhythms in cardiovascular disease.

Circadian variation of ambulatory myocardial ischemia. Triggering by daily activities and evidence for an endogenous circadian component

BACKGROUND

The morning peak in myocardial ischemia has been related to diurnal variations in physical and mental activities and to postural changes upon awakening. This study assesses (1) the effects of exogenous activity triggers at different times of the day and (2) the contribution of an endogenous (ie, activity- and posture-independent) circadian vulnerability for ambulatory ischemia.

METHODS AND RESULTS

Sixty-three stable coronary artery disease patients underwent ambulatory ECG monitoring and completed a structured diary assessing physical and mental activities. During 2519 hours of observation, a morning increase in ischemia coincided with increases in physical and mental activities, and an evening decrease in ischemia coincided with a decline in activities. During the morning, ischemic versus ischemia-free periods were more likely to occur with high levels of physical activity (P < .001). High physical activity triggered ischemia to a lesser but still significant extent (P < .05) in the afternoon but not in the evening (P = NS). High levels of mental activity triggered ischemia significantly during the morning (P < .04) and evening (P < .04) but not in the afternoon. When a residualized score procedure was used to correct ischemic time for each patient's simultaneously measured activities, for hourly heart rates, or for activity-related heart rate fluctuations, the circadian variation in ischemia was still observed (P < .001), with a peak at 6 AM. A significant increase in ischemia occurred immediately after awakening (P < .05), but activity-adjusted increases in morning ischemia persisted (P < .05) for 2 hours after awakening.

CONCLUSIONS

Exogenous factors (physical and mental activities) are most potent as triggers of ischemia during the morning hours, and the postural change after awakening contributes to the morning increase in ischemia. There is also evidence for an endogenous, activity-independent circadian influence on ischemic susceptibility that is independent of exogenous factors and that sustains the increase in ischemia upon awakening.

Daily peaks in the incidence of sudden cardiac death and fatal stroke in Niigata Prefecture

To clarify the circadian variation in sudden death (SD) in Japan, where the causes of sudden death differ from those in the USA, we examined all of the death certificates from 1984 to 1986 in Niigata Prefecture, Japan. We defined SD as death which occurred within 1 h from the onset of the underlying cause. A significant circadian variation, with a high incidence between 6 and 8 am and a secondary peak between 6 and 8 pm, was found in the occurrence of sudden cardiac death (SCD, n = 2953). Although the proportion of SCD due to acute myocardial infarction (AMI) was as low as 28% of SCD cases, the circadian variation of SCD was similar to that previously reported in the USA. In SCD due to AMI in males (n = 487), a significant circadian variation with 3 peaks, including a primary peak between 4 and 6 am, was evident. There was also a marked increase in the incidence of fatal stroke between 6 and 8 pm (n = 529). We concluded that 1) a circadian variation with two peak incidences, one between 6 and 8 am, and one between 6 and 8 pm, was characteristic of SCD in general, 2) there was a primary peak between 4 and 6 am for SCD due to AMI in males, and 3) there was a peak between 6 and 8 pm in the incidence of fatal stroke for both men and women.