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

The 24 h pattern of arterial pressure in mice is determined mainly by heart rate-driven variation in cardiac output

Few studies have systematically investigated whether daily patterns of arterial blood pressure over 24 h are mediated by changes in cardiac output, peripheral resistance, or both. Understanding the hemodynamic mechanisms that determine the 24 h patterns of blood pressure may lead to a better understanding of how such patterns become disturbed in hypertension and influence risk for cardiovascular events. In conscious, unrestrained C57BL/6J mice, we investigated whether the 24 h pattern of arterial blood pressure is determined by variation in cardiac output, systemic vascular resistance, or both and also whether variations in cardiac output are mediated by variations in heart rate and or stroke volume. As expected, arterial pressure and locomotor activity were significantly (P < 0.05) higher during the nighttime period compared with the daytime period when mice are typically sleeping (+12.5 ± 1.0 mmHg, [13%] and +7.7 ± 1.3 activity counts, [254%], respectively). The higher arterial pressure during the nighttime period was mediated by higher cardiac output (+2.6 ± 0.3 mL/min, [26%], P < 0.05) in association with lower peripheral resistance (-1.5 ± 0.3 mmHg/mL/min, [-13%] P < 0.05). The increased cardiac output during the nighttime was mainly mediated by increased heart rate (+80.0 ± 16.5 beats/min, [18%] P < 0.05), as stroke volume increased minimally at night (+1.6 ± 0.5 μL per beat, [6%] P < 0.05). These results indicate that in C57BL/6J mice, the 24 h pattern of blood pressure is hemodynamically mediated primarily by the 24 h pattern of cardiac output which is almost entirely determined by the 24 h pattern of heart rate. These findings suggest that the differences in blood pressure between nighttime and daytime are mainly driven by differences in heart rate which are strongly correlated with differences in locomotor activity.

Repeated Phase Shifts in the Lighting Regimen Change the Blood Pressure Response to Norepinephrine Stimulation in Rats

Disturbed circadian activity of the sympathetic system may be involved in negative consequences of chronodisruption on the cardiovascular system. We studied daily changes in pressure response to adrenergic stimulation in rats exposed to repeated phase advance shifts (PAS) of light/dark (LD) regimen. Blood pressure (BP), heart rate (HR) and locomotor activity was measured by radiotelemetry in normotensive Wistar rats exposed to repeated PAS (three 8-h shifts per week) lasting for 12 weeks. Norepinephrine was administered subcutaneously in the middle of L and D during week 12 of PAS exposure. In the control LD cycle, cardiovascular parameters exhibited significant daily rhythms with expected higher values during D than L phase. Rats exposed to PAS showed disturbed rhythms without a BP and HR increase. Administration of norepinephrine to control rats revealed daily variability in the cardiovascular response with higher stimulation of BP during L than D. This daily pattern of BP response to norepinephrine was diminished in the PAS group. The damped daily variability in pressure response to norepinephrine and augmented response during the light phase of the day suggest that the increased and desynchronized activity of the sympathetic system may worsen responses of the cardiovascular system to load in individuals exposed to irregular LD conditions.

Circadian variation in vascular function and regenerative capacity in healthy humans

Background

Progenitor cells (PCs) are mobilized in response to vascular injury to effect regeneration and repair. Recruitment of PCs requires intact nitric oxide (NO) synthesis by endothelial cells, and their number and activity correlate with cardiovascular disease risk burden and future outcomes. Whereas cardiovascular vulnerability exhibits a robust circadian rhythm, the 24‐hour variation of PCs and their inter‐relation with vascular function remain unknown. We investigated the circadian variation of PCs and vascular function with the hypothesis that this will parallel the pattern observed for cardiovascular events (CVEs).

Methods and Results

In 15 healthy subjects (9 men, 37±16 years), circulating PCs and vascular function were measured at 8 am, noon, 4 pm, 8 pm, midnight, 4 am (only PCs counts), and 8 am the following day. Circulating PCs were enumerated as mononuclear cells (MNCs; CD45^med) that express CD34 as well as CD133, and their activity was assessed as the number of colonies formed by culturing MNCs. Vascular function was evaluated by measurement of endothelium‐dependent, flow‐mediated vasodilation (FMD) of the brachial artery and tonometry‐derived indices of arterial stiffness. Higher CD34⁺ and CD34⁺/CD133⁺ cell counts were observed at 8 pm than any other time of the day (P‐ANOVA=0.038 and <0.001; respectively) and were lowest at 8 am. PC colony formation was highest at midnight (P‐ANOVA=0.045) and lowest in the morning hours. FMD was highest at midnight and lowest at 8 am and 8 pm, and systemic arterial stiffness was greatest at 8 am and lowest at 4 pm and midnight (P‐ANOVA=0.03 and 0.01; respectively).

Conclusion

A robust circadian variation in PC counts and vascular function occurs in healthy humans and both exhibit an unfavorable profile in the morning hours that parallels the preponderance of CVEs at these times. Whether these changes are precipitated by awakening and time‐dependent physical activity or governed by the endogenous circadian clock needs to be further investigated.

Circadian rhythms in leukocyte trafficking

A broad range of immunological processes oscillates over the course of a day. Recent findings have identified a molecular basis for the circadian clock in the regulation of the immune system. These rhythms manifest themselves in oscillatory behavior of immune cells and proinflammatory mediators, which causes a time-dependent sensitivity in the reaction to pathogens. This rhythmicity impacts disease manifestations and severity and provides an option for therapy that incorporates chronopharmacological considerations. This review will focus on the current knowledge and relevance of rhythmic immune cell trafficking. It will provide an overview of the molecular clock machinery and its interrelations with leukocyte migration and the immune response.

Pivotal role of Rho-associated kinase 2 in generating the intrinsic circadian rhythm of vascular contractility

BACKGROUND

The circadian variation in the incidence of cardiovascular events may be attributable to the circadian changes in vascular contractility. The circadian rhythm of vascular contractility is determined by the interplay between the central and peripheral clocks. However, the molecular mechanism of the vascular intrinsic clock that generates the circadian rhythm of vascular contractility still remains largely unknown.

METHODS AND RESULTS

The agonist-induced phosphorylation of myosin light chain in cultured smooth muscle cells synchronized by dexamethasone pulse treatment exhibited an apparent circadian oscillation, with a 25.4-hour cycle length. The pharmacological inhibition and knockdown of Rho-associated kinase 2 (ROCK2) abolished the circadian rhythm of myosin light chain phosphorylation. The expression and activity of ROCK2 exhibited a circadian rhythm in phase with that of myosin light chain phosphorylation. A clock gene, RORα, activated the promoter of the ROCK2 gene, whereas its knockdown abolished the rhythmic expression of ROCK2. In the mouse aorta, ROCK2 expression exhibited the circadian oscillation, with a peak at Zeitgeber time 0/24 and a nadir at Zeitgeber time 12. The myofilament Ca(2+) sensitization induced by GTPγS and U46619, a thromboxane A2 analog, at Zeitgeber time 0/24 was greater than that seen at Zeitgeber time 12. The circadian rhythm of ROCK2 expression and myofilament Ca(2+) sensitivity was abolished in staggerer mutant mice, which lack a functional RORα.

CONCLUSIONS

ROCK2 plays a pivotal role in generating the intrinsic circadian rhythm of vascular contractility by receiving a cue from RORα. The ROCK2-mediated intrinsic rhythm of vascular contractility may underlie the diurnal variation of the incidence of cardiovascular diseases.

[Relation between myocardial infarction and circadian rhythm in patients attended in a prehospital emergency service]

BACKGROUND AND OBJECTIVES

The aim of this study is to analyze the presence of circadian rhythm in the time of onset of symptoms of acute myocardial infarction treated by a prehospital emergency system and the influence of modifiable cardiovascular risk factors and non-modifiable as modulators of that circadian rhythm.

PATIENTS AND METHODS

Retrospective analysis of 709 patients clinically diagnosed with acute myocardial infarction on-site in the prehospital setting. The variables were time to onset of symptoms, age, sex, previous ischemic heart disease, hypertension, diabetes mellitus, hyperlipidemia and smoking. We analyzed the rhythm with cosinor multiple sinusoid method, with 3 harmonics (24, 12 and 8h) for the adjustment.

RESULTS

The time of onset of pain showed circadian rhythm (P <,001), peaking at 10.39 and a valley at 4.28, showing a sinusoidal curve fitting bimodal aspect with a predominant morning peak and another evening one of lower amplitude. All subgroups categorized by the study variables showed circadian rhythm, with a cosine curve similar to the global infarction. Smokers had a predominantly evening peak.

CONCLUSIONS

Acute myocardial infarction shows a circadian rhythm. Smoking and diabetes mellitus can modify the standard incidence rate of occurrence of myocardial infarction.

Twenty-four-hour patterns in occurrence and pathophysiology of acute cardiovascular events and ischemic heart disease

The scientific literature clearly establishes the occurrence of cardiovascular (CV) accidents and myocardial ischemic episodes is unevenly distributed during the 24 h. Such temporal patterns result from corresponding temporal variation in pathophysiologic mechanisms and cyclic environmental triggers that elicit the onset of clinical events. Moreover, both the pharmacokinetics and pharmacodynamics of many, though not all, CV medications have been shown to be influenced by the circadian time of their administration, even though further studies are necessary to better clarify the mechanisms of such influence on different drug classes, drug molecules, and pharmaceutical preparations. Twenty-four-hour rhythmic organization of CV functions is such that defense mechanisms against acute events are incapable of providing the same degree of protection during the day and night. Instead, temporal gates of excessive susceptibility exist, particularly in the morning and to a lesser extent evening (in diurnally active persons), to aggressive mechanisms through which overt clinical manifestations may be triggered. When peak levels of critical physiologic variables, such as blood pressure (BP), heart rate (HR), rate pressure product (systolic BP × HR, surrogate measure of myocardial oxygen demand), sympathetic activation, and plasma levels of endogenous vasoconstricting substances, are aligned together at the same circadian time, the risk of acute events becomes significantly elevated such that even relatively minor and usually harmless physical and mental stress and environmental phenomena can precipitate dramatic life-threatening clinical manifestations. Hence, the delivery of CV medications needs to be synchronized in time, i.e., circadian time, in proportion to need as determined by established temporal patterns in risk of CV events, and in a manner that averts or minimizes undesired side effects.

Sudden cardiac death: epidemiology, circadian variation, and triggers

Sudden cardiac death (SCD) remains a major health issue accounting for over 5% of annual mortality in the Western world. There are several causes of SCD, most commonly, coronary artery disease. Although identifying the prodrome of SCD has attracted considerable interest, a large proportion of patients die before any medical contact is established. SCD onset seems to follow a circadian pattern, most likely because of exposure to endogenous and exogenous triggers. The aim of the present report is to review the current knowledge of epidemiology, patterns of onset, and triggers of SCD and present directions for future research with a focus on coronary artery disease.

Circadian variation of acute st segment elevation myocardial infarction by anatomic location in a Turkish cohort

Background

To evaluate the relationship between site of infarction (anterior vs. inferior) and circadian variation in patients with ST segment elevation myocardial infarction (STEMI) in a Turkish cohort.

Material/Methods

This restrospective study enrolled 465 patients (407 male, mean age 65±7 years) with STEMI. Patients were then categorised into 4 6-hour increments according to the time of day during which the symptoms began (12:00 AM–06:00 AM, 06:00 AM–12:00 PM; 12:00 PM–06:00 PM and 06:00 PM–12:00 AM hours). Characteristics of patients by site of infarction (anterior vs. inferior) were compared.

Results

The frequency of onset of acute anterior MI as determined by onset of pain demonstrated significant circadian variation among the 4 time periods, demonstrating bimodal peaks (afternoon and morning) and a trough between 06:00 PM to 06:00 AM. The incidence of occurrence of MI between 06:00 AM to 06:00 PM was 4.50 times that of the average frequency of the remaining 12 hours of the day. The frequency of onset of acute inferior MI as determined by onset of pain exhibited significant circadian variation among the 4 time periods, demonstrating bimodal peaks (midnight to 06:00 AM and 06:00 AM to noon) and a trough between noon to midnight. The incidence of occurrence of MI between midnight to noon was 4.25 times that of the average frequency of the remaining 12 hours of the day.

Conclusions

Different circadian periodicity in the time of onset of STEMI was found regarding infarction site in a Turkish cohort. This may be related to genetic and/or demographic characteristics of the Turkish population.

Circadian distribution of paroxysmal atrial fibrillation in patients with and without structural heart disease in untreated state

BACKGROUND

This study aimed to compare the circadian distribution of the onset, maintenance and termination of paroxysmal atrial fibrillation (PAF) between structural and non-structural heart diseases (SHD and NSHD, respectively) in the untreated state.

SUBJECTS AND METHODS

We included 217 patients with 338 PAF (79 SHD patients with 131 episodes; 138 NSHD patients with 207 episodes). The probabilities for the onset, maintenance and termination of PAF for each hour were analyzed using Holter monitoring data and harmonic models being fitted into a cosinusoidal function.

RESULTS

The SHD group had a triphasic circadian pattern at the onset with higher peaks at midnight, in the early morning and in the late afternoon (p < 0.05), whereas the NSHD group showed a single peak at midnight (p < 0.01). The probability of maintenance revealed a single peak during midnight (SHD, p < 0.0001; NHD, p < 0.01). The termination showed a peak at noon in the SHD group (p < 0.05), whereas there was a double peak at 10:00 am and 8:00 pm in the NSHD group (p=0.06). RR intervals just after the PAF onset showed marked shortening in the daytime initiation PAF as compared to the nighttime initiation PAF in both SHD and NSHD groups (p < 0.01).

CONCLUSION

These observations suggest that the SHD group has very complex onset hours, whereas the NSHD group shows complex termination hours. Reflexly accelerated sympathetic tone just after the PAF onset is suggested in the daytime initiation PAF.

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.

Circadian patterns in the onset of cardiogenic acute pulmonary edema

BACKGROUND

Circadian patterns of onset favoring the morning hours have been demonstrated for many cardiovascular disorders. Although much is known about cardiogenic acute pulmonary edema (CAPE), the relationship between time of day and CAPE episode onset has not been previously studied.

METHODS

We examined 154 consecutive episodes of CAPE treated at an urban community hospital to determine whether circadian patterns existed in the time these episodes began.

RESULTS

For all episodes, a significant circadian pattern existed, with peak onset between 6:00 and 11:59 A.M. (p < 0.01). When CAPE episodes were analyzed by the most probable precipitant of pulmonary edema, only the pattern for patients with progressive symptoms, showing a peak in the 6:00 and 11:59 A.M. interval, was statistically significant (p < 0.01). Although a similar trend existed for CAPE occurring in association with acute myocardial infarction, the pattern fell short of statistical significance (p = 0.09).

CONCLUSIONS

These data suggest that circadian patterns favoring the morning hours exist for episodes of CAPE, and that patterns may vary depending on the precipitant of the episode.

Importance of alpha 1-sympathetic activity for diurnal change in ischemic threshold in patients with stable angina

BACKGROUND

Although ischemic threshold reportedly is lower in the early morning than in the afternoon, the mechanisms that account for the diurnal change in minimal coronary vascular resistance in the potentially ischemic area are unknown.

HYPOTHESIS

We hypothesized that calcium-channel blockers and alpha 1 blockers may affect the ischemic threshold in the early morning and afternoon in patients with stable angina.

METHODS

Before and after the administration of the calcium antagonist amlodipine (5 mg) alone and combined with the alpha 1 blocker prazosin (1 mg), a treadmill exercise test using the Balke-Ware protocol was undertaken in the morning (8:00 A.M.) and repeated in the afternoon (1:00 P.M.) with 15 stable angina patients. The ischemic threshold was defined as a reciprocal of minimal coronary vascular resistance in the presence of comparable levels of myocardial ischemia indicated by 0.1 mV ST depression. Minimal coronary vascular resistance was calculated as mean blood pressure divided by coronary blood flow. Since the coronary blood flow is closely related to myocardial oxygen consumption, which can be replaced by the double product of heart rate and systolic blood pressure, minimal coronary vascular resistance was approximated to 1/heart rate.

RESULTS

At baseline, minimal coronary vascular resistance was significantly higher in the early morning than in the afternoon (8.5 +/- 0.3 x 10(-3) min/beats vs. 7.8 +/- 0.4 x 10(-3) min/beats, p < 0.01). Although treatment with amlodipine alone did not abolish the circadian pattern of minimal coronary vascular resistance (8.0 +/- 0.6 x 10(-3) min/beats vs. 7.7 +/- 0.6 x 10(-3) min/ beats, p < 0.05), the addition of prazosin virtually eliminated the diurnal difference in minimal coronary vascular resistance (7.4 +/- 0.5 x 10(-3) min/beats vs. 7.5 +/- 0.5 x 10(-3) min/beats, p = NS).

CONCLUSIONS

These findings indicate that alpha 1-sympathetic activity may play a role in the pathogenesis of the diurnal change of ischemic threshold in patients with stable angina.

Magnitude of the early morning blood pressure surge in untreated hypertensive patients: a pooled analysis

OBJECTIVES

A post hoc analysis was performed to assess the magnitude of the early morning blood pressure surge (EMBPS), which is associated with peak cardiovascular risk, in untreated hypertensive patients enrolled in two sister studies (Prospective, Randomised Investigation of the Safety and efficacy of MICARDIS vs. ramipril using ambulatory blood pressure monitoring I and II) with identical design.

METHODS

In adults with a mild-to-moderate primary hypertension and no significant comorbidities, 24-h ambulatory blood pressure monitoring was conducted after a 2- to 4-week placebo run-in period and before treatment initiation. Individual blood pressure measurements at 20-min intervals were analysed.

RESULTS

In 1419 hypertensive patients with normal sleeping times, blood pressure displayed a typical circadian rhythm, with a mean EMBPS of 29/24 mmHg. An EMBPS of >or= 25 mmHg was observed in around 60% of patients. The surge was significantly increased with smoking, alcohol consumption, longer sleep, later waking times, and increased blood pressure variability during waking and sleeping. The magnitude of the EMBPS was significantly reduced in Black vs. White patients. The surge was not affected by gender, body mass index or duration of hypertension. Further analysis showed that ethnicity, alcohol consumption and smoking were all found to have a significant impact on surge around waking and age, sleep duration and sleep blood pressure variability were all found to have an effect on the prewake surge.

CONCLUSIONS

In untreated hypertensive patients, the magnitude of the EMBPS is significant when compared with the 24-h mean and is affected by individual patient characteristics. In light of these findings, physicians should understand the importance of 24-h blood pressure control and the modification of certain lifestyle factors as ways of reducing the EMBPS.

Chronobiology and chronotherapy of ischemic heart disease

The occurrence of the clinical manifestations of ischemic heart disease (IHD)--myocardial ischemia and angina pectoris, acute myocardial infarction, and sudden cardiac death--is unevenly distributed during the 24 h with greater than expected events during the initial hours of the daily activity span and in the late afternoon or early evening. Such temporal patterns result from circadian rhythms in pathophysiological mechanisms plus cyclic environmental stressors that trigger ischemic events. Both the pharmacokinetics (PK) and pharmacodynamics (PD) of many, though not all, anti-ischemic oral nitrate, calcium channel blocker, and beta-adrenoceptor antagonist medications have been shown to be influenced by the circadian time of their administration. The requirement for preventive and therapeutic interventions varies predictably during the 24 h, and thus therapeutic strategies should also be tailored accordingly to optimize outcomes. During the past decade, two first generation calcium channel blocker chronotherapies have been developed, trialed, and marketed in North America for the improved treatment of IHD. Nonetheless, there has been relatively little investigation of the administration-time (circadian rhythm) dependencies of the PK and PD of conventional anti-ischemic medications, and there has been little progress in the development of new generation IHD chronotherapies. Available epidemiologic, pharmacologic, and clinico-therapeutic evidence demonstrates how the chronobiologic approach to IHD can contribute new insight and opportunities to improve drug design and drug delivery to enhance therapeutic outcomes.

Importance of aggressive blood pressure lowering when it may matter most

Variation in blood pressure levels follows a reproducible circadian pattern, characterized by low levels during sleep and a rapid increase during the early-morning period. The incidence of cardiovascular events displays a similar circadian variation, with peak occurrence coinciding with the early-morning blood pressure surge. Numerous prospective studies have shown that blood pressure measured over a 24-hour period is superior to clinic blood pressure in predicting future cardiovascular events. Thus, the use of ambulatory blood pressure monitoring (ABPM) to identify patients at risk of cardiovascular events could improve the management of the patient with hypertension. ABPM has also become widely adopted to evaluate antihypertensive therapeutic options that might provide blood pressure reduction throughout the 24-hour dosing interval. Recently, community-based trials have shown that it is feasible to perform ABPM-oriented research in nonresearch environments. This allows us to better understand the efficacy of antihypertensive therapies in a "real-world" setting. Studies of this nature can even assess blood pressure control in the early-morning period by sequestering data before and after awakening.

Early Morning Blood Pressure Surge

Alterations in the circadian rhythm of blood pressure, whether a loss of the nighttime dip or an exaggeration of the early morning increase that occurs upon rising, indicate increased cardiovascular risk. Estimates of the magnitude of the blood pressure surge on rising vary depending on technique and population, but it is usually around 10-30 mm Hg systolic and 7-23 mm Hg diastolic. The magnitude of the surge increases with age, alcohol consumption, and smoking and is greater in whites. Blood pressure variations and morning plasma aldosterone are closely correlated. A high morning surge is linked to increased target organ damage as well as strokes and other cardiovascular complications. Therapeutic options exist to reduce the magnitude of the morning blood pressure surge-notably, the use of drugs with a long duration of action, the use of medications that specifically antagonize the morning surge (such as alpha blockers), and the administration of drugs upon awakening but before rising.

Circadian variation in endothelial function is attenuated in postmenopausal women

OBJECTIVE

The present study was undertaken to investigate the possible existence of an endogenously generated circadian rhythm in endothelial function in women and whether this rhythm is altered after the menopause.

METHODS

Healthy non smoking women (11 pre-menopausal and 13 postmenopausal women) were studied during a 22 h period under constant routine conditions; endothelium-dependent (flow-mediated dilation (%FMD)) and -independent (glyceryl-trintrate (GTN)-mediated) function was assessed every 2 and 4 h, respectively, by high-resolution ultrasound of the brachial artery.

RESULTS

%FMD and %GTN was significantly higher in pre-menopausal women (9.9+/-1.0%FMD (mean+/-S.E.M.); 18.2+/-1.8%GTN; P<0.01) compared with postmenopausal women (6.5+/-0.5%FMD; 11.5+/-1.6%GTN). A significant day-night variation in %FMD was observed pre-menopausal women (day 9.2+/-0.8%; night 10.4+/-1%; P<0.05) with an attenuated rhythm in postmenopausal women (day 6.8+/-0.6%; night 6.0+/-0.4%).

CONCLUSIONS

The findings show a circadian rhythm in %FMD in pre-menopausal women, which disappears after the menopause. The reduction in %FMD and an absence of a day-night variation in %FMD in postmenopausal women may have important implications for the incidence of coronary heart disease in women after the menopause.

Prognostic Significance for Stroke of a Morning Pressor Surge and a Nocturnal Blood Pressure Decline

There is continuing controversy over whether the pattern of circadian blood pressure (BP) variation that includes a nocturnal decline in BP and a morning pressor surge has prognostic significance for stroke risk. In this study, we followed the incidence of stroke in 1430 subjects aged > or =40 years in Ohasama, Japan, for an average of 10.4 years. The association between stroke risk and the pattern of circadian BP variation was analyzed with a Cox proportional hazards model after adjustment for possible confounding factors. There was no significant association between total stroke risk and the nocturnal decline in BP (percentage decline from diurnal level) or between total stroke risk and the morning pressor surge. The cerebral infarction risk was significantly higher in subjects with a <10% nocturnal decline in BP as compared with subjects who had a > or =10% nocturnal decline in BP (P=0.04). The morning pressor surge was not associated with a risk of cerebral infarction. On the other hand, an increased risk of cerebral hemorrhage was observed in subjects with a large morning pressor surge (> or =25 mm Hg; P=0.04). Intracerebral hemorrhage was also observed more frequently in extreme dippers (those with a > or =20% nocturnal decline in BP) than dippers (those with a 10% to 19% decline; P=0.02). A disturbed nocturnal decline in BP is associated with cerebral infarction, whereas a large morning pressor surge and a large nocturnal decline in BP, which are analogous to a large diurnal increase in BP, are both associated with cerebral hemorrhage.

Telmisartan/Hydrochlorothiazide in comparison with losartan/hydrochlorothiazide in managing patients with mild-to-moderate hypertension

Hypertension is risk factor for cardiovascular morbidity and mortality, and stroke. A critical surge in blood pressure occurs during the early morning hours coincident with increased incidences of myocardial infarction, unstable angina, stroke and sudden cardiac death. This suggests that, in patients with hypertension, it may be important to maintain the efficacy of antihypertensive medication over the 24-h dosing interval, especially in the risky early morning hours. In order to evaluate the antihypertensive efficacies of fixed-dose combinations of angiotensin II receptor blockers with hydrochlorothiazide (HCTZ) 12.5 mg, a multicenter, randomized, prospective, open-label, blinded-endpoint study was performed in 805 patients with mild-to-moderate hypertension randomized to once-daily treatment with telmisartan 40 mg plus HCTZ (T40/H12.5), losartan 50 mg plus HCTZ (L50/H12.5), or telmisartan 80 mg plus HCTZ (T80/H12.5), with the primary objective of comparing T40/H12.5 with L50/H12.5 and evaluating the additional response of T80/H12.5. Efficacy was assessed by ambulatory blood pressure monitoring (ABPM), clinic seated cuff sphygmomanometry and calculated responder rates after 6 weeks' active treatment. The primary endpoint was reduction from baseline in the last 6-h mean (relative to dosing) diastolic blood pressure (DBP) measured using 24-h ABPM. Compared with the L50/H12.5 group, the mean reductions in the last 6-h mean DBP for the T40/H12.5 and T80/H12.5 groups were significantly greater: -2.0 mmHg (p=0.0031) and -2.8 mmHg (p=0.0003), respectively. We conclude that T40/H12.5 provided clinically and statistically significantly superior blood pressure reductions compared with L50/H12.5 during the last 6 h of the 24-h dosing interval, which corresponds to the high-risk early-morning hours, and that T80/H12.5 provided additional blood pressure reductions.

Temporal variation in inhospital mortality with percutaneous coronary intervention: a report from the National Heart, Lung and Blood Institute Dynamic Registry

BACKGROUND

Cardiovascular morbidity and mortality display a distinct time dependence also known as circadian variation. Whether such time dependence extends to the risk of procedural-related mortality after percutaneous coronary intervention (PCI) is presently unknown.

METHODS

Inhospital mortality was analyzed in 6,347 patients with PCI start times from 8:00 am to 6:59 pm ("usual" workday). The sample was divided into 3 evenly populated groups (morning start 8:00-10:59 AM, midday start 11:00 AM-1:59 PM, afternoon start 2:00-6:59 PM). The association between procedural start time and mortality was assessed using multivariable analysis including a propensity score accounting for factors associated with procedural start time.

RESULTS

There was a significant, nonlinear relationship between procedural-related mortality and start time (P = .03). Afternoon start patients were at higher adjusted risk of mortality compared with midday start patients (OR 2.03, 95% CI 1.07-3.83, P = .03 ). Morning start patients were also at higher risk compared with midday start patients although the association was not statistically significant (OR 1.73, 95% CI 0.89-3.39, P = .11).

CONCLUSIONS

There is a significant time-dependent variation in the risk of inhospital PCI-related mortality during usual working hours. The highest risk period, taking into account numerous factors that confound this association, is the latter part of the workday. A second period of apparent greater risk occurs during the early part of the workday and is consistent with our present understanding of circadian variation in cardiovascular disease processes.

Are there ethnic differences in the circadian variation in onset of acute myocardial infarction?

We hypothesised that ethnicity may influence the circadian pattern in acute myocardial infarction (MI), in view of the potential differences in genetic background, cardiovascular risk factors and cultural habits. To test our hypothesis, we studied 340 consecutive acute MI patients (268 males; mean age 61.6+/-12.3 years) from two different city-centre teaching hospitals in Birmingham (United Kingdom) and Alicante (Spain). A different circadian rhythm in MI onset was observed between the ethnic groups (p=0.001), with a significantly higher number of acute MI onset occurring between midnight and noon in British Caucasians and Indo-Asians. In contrast, Mediterranean Caucasians showed the converse circadian pattern, with most of the acute MI events happened between noon and midnight. Indo-Asian patients were the youngest patient group and showed the highest prevalence of diabetes and increased body mass index. Mediterranean patients had the highest prevalence of smokers but their mean serum cholesterol was the lowest. No differences in sex, blood pressure, height and weight were observed. In conclusion, this study has shown a different circadian rhythm in acute MI onset between 3 ethnic groups from two different city-centre teaching hospitals in Birmingham (United Kingdom) and Alicante (Spain) and, for the first time, provide data in the Indo-Asian population. Further studies are required to determine the pathophysiological mechanism(s) underlying these differences.

Blood pressure variability: its measurement and significance in hypertension

The occurrence of blood pressure fluctuations over time has been documented since the 18th century, but the clinical importance of this phenomenon is only now being recognized. The introduction of ambulatory blood pressure monitoring in the late 1960s represented a major step forward in the study of blood pressure behaviour and helped to characterize the relationship between blood pressure variability and cardiovascular disease. In hypertension, blood pressure variability increases with increasing blood pressure and correlates closely with target-organ damage, independently of absolute blood pressure values. This has important consequences for treatment, which in the past has focused on reducing mean blood pressure values as the main goal. Experimental evidence suggests that drugs capable of buffering or reducing blood pressure variability may confer additional benefits on target-organ protection. Effective target-organ protection could best be afforded by antihypertensive agents that provide efficient 24-h blood pressure control and also stabilize blood pressure variability. Mathematical indices, such as the trough:peak ratio and the smoothness index, provide useful measures of the homogeneity of the antihypertensive effect over 24 h; optimum control is provided by drugs with a trough:peak ratio close to 1 and a smoothness index > 1, as is observed with long-acting drugs such as telmisartan or amlodipine. Recently, a direct relationship was demonstrated between homogeneous blood pressure control and treatment-induced regression of left ventricular hypertrophy, emphasizing the importance of smooth 24-h blood pressure control. In conclusion, the goals of antihypertensive treatment should consider the reduction of both 24-h mean blood pressure and its variability. Long-lasting drugs or drug combinations are preferable to ensure a homogeneous and smooth 24-h blood pressure profile.

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.

Circadian variations in blood pressure : implications for chronotherapeutics

The management of hypertensive patients usually ignores or gives little credit to the biologic rhythms inherent to the disease process and their potential clinical implications. The development of ambulatory blood pressure monitoring and the rapidly growing popularity of home blood pressure measurements by patients have now generated a series of new clinical questions that are directly linked to the chronobiology of the cardiovascular system, such as the clinical interpretation of a blunted nocturnal fall in blood pressure or the difficulty of achieving adequate blood pressure control in the morning. Today, there is growing evidence that night-time blood pressure, and particularly the absence of a decrease in sleep blood pressure, contributes to the occurrence of target organ damages, and that the early morning rise in blood pressure increases the risk of developing cardiovascular events, including stroke, perhaps independently of 24-hour blood pressure levels. On the basis of these observations, it may be necessary to reconsider the way antihypertensive drugs are prescribed in order to obtain smooth, 24-hour blood pressure control, respecting the circadian pattern of blood pressure. Several approaches exist, including the use of drugs that lower blood pressure around the clock and respect the diurnal rhythm. Preliminary studies performed with such agents have provided interesting results. However, there is a clear need for large clinical trials demonstrating the clinical superiority of this approach. In any case, a better understanding of the importance of the circadian variations of blood pressure could certainly have a major impact on our view of the therapeutic management of hypertensive patients.

Chronobiology of rupture and dissection of aortic aneurysms

A growing body of evidence suggests that the occurrence of cardiovascular events is not evenly distributed over time, but shows peculiar temporal patterns that vary with time of day, day of the week, and month (season) of the year. These patterns coincide with the temporal variation in the pathophysiologic mechanisms that trigger cardiovascular events and the physiologic changes in body rhythms. These two factors in combination contribute to the periodicity in susceptibility to acute cardiovascular events. The classic assumption of epidemiologic studies that there is a constancy in risk for disease during the various time domains has now been challenged by the emerging new concept of chronorisk. In the last two decades temporal patterns (circadian, weekly, seasonal) have been identified for several acute cardiovascular diseases, such as acute myocardial infarction, sudden death, pulmonary embolism, and stroke, with peak incidence for most in the morning and during winter. One of the most life-threatening cardiovascular emergencies, aortic aneurysm rupture or dissection, also demonstrates periodicity, characterized by a similar temporal distribution, which suggests a common pathophysiologic mechanism or triggers similar to other cardiovascular acute emergencies. We review the data on chronobiology of acute aortic rupture or dissection, and discuss various pathophysiologic mechanisms that account for this variability. It is likely that identification of consistent recurring patterns in the underlying risk mechanisms could provide potential new insights for more precise diagnosis and efficacious therapeutic intervention.

Circadian variation in myocardial ischemia: the possible mechanisms involving in this phenomenon

Circadian rhythms have long been recognized to occur in many biologic phenomena, including secretion of hormones as well as autonomic nervous system. There is increasing evidence that circadian rhythms have been also found in cardiovascular events, for example, myocardial infarction, sudden cardiac death as well as stroke have shown a circadian pattern of the distribution. Transient myocardial ischemia, detected by ambulatory ST segment monitoring, is also unevenly distributed during the day. The pathophysiology and the mechanism underlying these variations are the focus of much investigation, while it is not full understood up to date. Heart rate, blood pressure, neural and humoral vasoactive factors such as plasma norepinephrine levels and renin activity, and probably also contractility are increased in the morning hours, indicating that increase in myocardial oxygen demand contribute importantly to the increased prevalence of ischemia in the morning. Our recent study found that circadian rhythm of ischemic threshold detected by repetitive exercise treadmill tests in patients with chronic coronary artery disease is also apparently associated with levels of plasma ET-1. This information should enable better understanding as well as treatment on patients on circadian variation of cardiovascular events.

Relevance of blood pressure variation in the circadian onset of cardiovascular events

Ambulatory blood pressure monitoring (ABPM) is a highly useful diagnostic tool as it can detect non-dipping and can distinguish masked hypertension, white-coat hypertension and sustained hypertension. Furthermore, measurement of blood pressure using ABPM has greater prognostic strength than single clinic blood pressure measurements. The Systolic Hypertension in Europe study, for example, found that elevation of ambulatory systolic blood pressure, but not conventional single cuff systolic blood pressure, by 10 mmHg was associated with adverse cardiovascular outcomes. Blood pressure follows a circadian rhythm, with peak levels during the morning hours. The morning period has also been associated with a greater risk for cardiovascular events compared with the rest of the 24 h. The morning surge in blood pressure, along with haemostatic changes that promote thrombosis, is believed to contribute to this heightened risk. Long-acting antihypertensive agents that provide blood pressure control throughout the 24-h dosing interval, including the morning hours, are the most appropriate therapeutic approach to hypertension. Direct comparative studies with telmisartan and other angiotensin-II receptor blockers and with amlodipine have shown that telmisartan has a long duration of action and controls blood pressure over the 24-h dosing period.

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.

[Control of arterial hypertension based on self-measurement of blood pressure: APACHE study]

BACKGROUND AND OBJECTIVE

The objective was to analyze the control rates of hypertension in a large group of hypertensives on antihypertensive treatment by means of blood pressure (BP) self-measurements, and to assess if the degree of control at early morning hours differs from that at the rest of the day.

PATIENTS AND METHOD

9,227 subjects [4,398 men, mean age 61.0 (11.4) yr, body mass index 28.4 (4.1) kg/m2] who had hypertension and were on antihypertensive treatment at least during one month before were included. Patients were recruited from primary care physicians. After receiving training, six BP measurements over one day were performed by means of a Braun Precision Sensor BP 2550 monitor, which measures BP at wrist level.

RESULTS

Whole day SBP and DBP averages were 138.4 (16.5) mmHg and 85.4 (8.7) mmHg, respectively. Both SBP and DBP in early morning hours were significantly higher than those observed before lunch or before dinner. The percentage of subjects with BP < 130/80 mmHg was 15.5%; 15.4% had SBP < 130 mmHg but DBP > 80 mmHg, and 2.0% had DBP < 80 mmHg and SBP > 130 mmHg). Control rates were lower at early morning hours and in men.

CONCLUSIONS

By using BP self-measurement, control rates of hypertension are low, especially in early morning hours as compared to the rest of the day. New strategies are needed to further increase the control of hypertension.

The importance of von Willebrand factor level and heart rate changes in acute coronary syndromes: a comparison with chronic ischemic conditions

The pathogenesis of acute coronary syndrome (ACS) and transient myocardial ischemia (TMI) is not completely understood. Therefore, the authors studied the biological indicators of thrombogenesis and sympathetic activity. The study was conducted on 50 patients with acute coronary syndrome and 30 patients with stable angina pectoris. Treatment was standardized with low-molecular-weight heparin and 300 mg aspirin/day but with no IIb/IIIa inhibitors, an oral beta-blocker, diltiazem 60 mg tid, glyceryl trinitrate i.v. in patients with ACS but with mononitrates orally and low-molecular-weight heparin in patients with stable angina. Twenty-four-hour continuous ECG monitoring and ST segment analysis were performed on day 2 of admission and heart rate analysis was performed 10, 5, and 1 minute before and during the myocardial ischemia periods. Blood sampling for von Willebrand factor (vWf) determination was performed through a peripheral vein at 8 AM, noon, 6 PM and 10 PM and half an hour after the description of angina. The patients with ACS were grouped as transient myocardial ischemia positive (n = 20) and negative (n = 30). The patients with stable angina were designated as the control group (n = 30). The detected vWf levels at 4 different daytime periods in patients with ACS were significantly higher than those in patients with stable angina. At the 6 PM to 10 PM period, the vWf level increase was significantly higher in patients with TMI than in the patients without TMI. At the 8 AM to noon period, the detected vWf levels decreased significantly in both TMI groups. During the nocturnal ischemia periods, the increase in vWf levels immediately after angina was significantly more apparent than the detected changes during daytime ischemia. Analysis showed that heart rates before the ischemia during stable angina episodes were significantly higher than those in TMI (-) (silent) angina. The heart rate difference between 10 minutes before and during the ischemia in the angina group was significantly different from that during TMI (-) (silent) ischemia. The heart rates at the times related to ischemia in the nocturnal period were significantly lower than those in the daytime period. The heart rate differences between the ischemia-related times and during the ischemia were significantly higher in daytime ischemic attacks than in nocturnal ischemic attacks. The study confirms that the vWf level, which is an indicator of thrombogenesis, was significantly increased in patients with ACS. Nocturnal ischemia is associated with thrombogenesis. Daytime ischemia is associated with increased sympathetic activity, and symptomatic ischemia is usually associated with increased sympathetic activity.

Therapeutic effects of evening administration of guanabenz and clonidine on morning hypertension: evaluation using home-based blood pressure measurements

OBJECTIVE

To clarify the effects of bedtime administration of the centrally acting alpha(2)-agonists, guanabenz and clonidine, on morning hypertension.

METHODS

Patients with morning hypertension were assigned to receive once-daily evening administration of guanabenz (2 mg/day, n = 81; 4 mg/day, n = 2) or clonidine (75 microg/day, n = 40; 150 microg/day, n = 10) for 4 weeks, and the blood pressure (BP)-lowering effects of these drugs in the morning and evening were evaluated by assessing self-monitored BP in the home environment. The subjects were then subdivided into different groups according to their evening BP, and the effects of guanabenz and clonidine on evening BP were evaluated further for each group. In addition, as a substitute for the trough/peak ratio, the evening/morning (E/M) ratio was calculated to assess the duration of action of the two alpha(2)-agonists.

RESULTS

Evening dosing with guanabenz or clonidine lowered morning BP significantly. Both drugs decreased evening BP in the subgroup of subjects with a high evening BP, but not in those with a normal evening BP. The individual E/M ratios for guanabenz, but not for clonidine, were significantly greater in those with a high evening BP than in those with a normal evening BP. In the early treatment period, treatment with guanabenz resulted in a higher diastolic E/M ratio in those subjects with a high evening diastolic BP than did treatment with clonidine.

CONCLUSION

The results suggest that evening administration of the central alpha(2)-agonists guanabenz and clonidine effectively suppresses the morning BP elevation in treated hypertensive patients.

Medical treatment of myocardial ischemia in coronary artery disease: effect of drug regime and irregular dosing in the CAPE II trial

OBJECTIVES

The Circadian Anti-ischemia Program in Europe (CAPE II) compared the efficacy of amlodipine and diltiazem (Adizem XL) and the combination of amlodipine/atenolol and diltiazem (Adizem XL)/isosorbide 5-mononitrate on exercise and ambulatory myocardial ischemia during regular therapy and after omission of medication.

BACKGROUND

The optimal medical therapy for ischemia suppression and the impact of irregular dosing using agents with different pharmacologic properties has not been established in patients with coronary disease.

METHODS

Patients with > or = 4 ischemic episodes or > or = 20 min of ST segment depression on 72-h electrocardiogram were randomized to amlodipine 10 mg once daily or diltiazem (Adizem XL) 300 mg once daily in a 14-week double-blind randomized multicountry study. In the second phase, atenolol 100 mg was added to amlodipine and isosorbide 5-mononitrate 100 mg to diltiazem (Adizem XL). Ambulatory monitoring (72 h) and exercise testing were repeated after both phases, on treatment and after a 24-h drug-free interval.

RESULTS

Both monotherapy with amlodipine and diltiazem (Adizem XL) were effective on symptoms and ambulatory and exercise ischemia. Combination therapy reduced ischemia further, with amlodipine/atenolol superior to diltiazem (Adizem XL)/isosorbide 5-mononitrate. Amlodipine/atenolol was significantly superior during the drug-free interval with maintenance of ischemia reduction.

CONCLUSIONS

Amlodipine, with its intrinsically long half-life alone or together with beta-blocker, is likely to produce superior ischemia reduction in clinical practice when patients frequently forget to take medication or dose irregularly.

Restricted feeding induces daily expression of clock genes and Pai-1 mRNA in the heart of Clock mutant mice

Plasminogen activator inhibitor-1 (PAI-1) is a key factor of fibrinolytic activity. The activity and mRNA abundance show a daily rhythm. To elucidate the mechanism of daily Pai-1 gene expression, the expression of Pai-1 and several clock genes was examined in the heart of homozygous Clock mutant (Clock/Clock) mice. Damping of the daily oscillation of Pai-1 gene expression in Clock/Clock mice was accompanied with damped or attenuated oscillations of mPer1, mPer2, mBmal1, and mNpas2 mRNA. Daily restricted feeding induced a daily mRNA rhythm of all clock genes and Pai-1 mRNA in Clock/Clock mice as well as wild-type mice. The peaks of clock genes and Pai-1 mRNA were phase-advanced in the heart of both genotypes after 6 days of restricted feeding. The present results demonstrate that daily Pai-1 gene expression depends on clock gene expression in the heart and that a functional Clock gene is not required for restricted feeding-induced resetting of the peripheral clock.