The pathophysiology of the onset of morning cardiovascular events

Gut microbiome and metabolites, the future direction of diagnosis and treatment of atherosclerosis?

Over the past few decades, the treatment of atherosclerotic cardiovascular disease has mainly been through an LDL lowering strategy and treatments targeting other traditional risk factors for atherosclerosis, which has significantly reduced cardiovascular mortality. However, the overall benefit of targeting these risk factors has stagnated, and the discovery of new therapeutic targets for atherosclerosis remains a challenge. Accumulating evidence from clinical and animal experiments has revealed that the gut microbiome play a significant role in human health and disease, including cardiovascular diseases. The gut microbiome contribute to host health and disease through microbial composition and function. The gut microbiome function like an endocrine organ by generating bioactive metabolites that can impact atherosclerosis. In this review, we describe two gut microbial metabolites/pathways by which the gut affects atherosclerotic cardiovascular disease. On the one hand, we discuss the effects of trimethylamine oxide (TMAO), bile acids and aromatic amino acid metabolites on the development of atherosclerosis, and the protective effects of beneficial metabolites short chain amino acids and polyamines on atherosclerosis. On the other hand, we discuss novel therapeutic strategies for directly targeting gut microbial metabolites to improve cardiovascular outcomes. Reducing gut-derived TMAO levels and interfering with the bile acid receptor farnesoid X receptor (FXR) are new therapeutic strategies for atherosclerotic disease. Enzymes and receptors in gut microbiota metabolic pathways are potential new drug targets. We need solid insight into these underlying mechanisms to pave the way for therapeutic strategies targeting gut microbial metabolites/pathways for atherosclerotic cardiovascular disease.

Rescue Operations Lead to Increased Cardiovascular Stress in HEMS Crew Members: A Prospective Pilot Study of a German HEMS Cohort

Helicopter emergency medical service (HEMS) is an essential part of prehospital emergency medicine. The working conditions lead to high physical stress, especially in rescue operations. The study aimed to determine the cardiovascular stress profile during rescue situations in HEMS crew members. Twenty-one HEMS crew members (male n = 20) participated in the prospective study. Heart rate, blood pressure and long-term ECG measurements were recorded during the whole operation day. The changes of measurements during rescue operation (52 operations in total) were compared to these of standby time. Rescue operations lead to increased load on the cardiovascular system, as expressed by significantly higher blood pressure, heart rate values and rate of cardiac events compared to standby time. Of special note, the difference in systolic blood pressure mean was 7.4 ± 9.0 mmHg (CI [5.1; 9.7], p < 0.001). Maximal heart rate was on average 33.7 bpm higher during rescue operation than in the standby time (CI [26.2; 40.8], p < 0.001). Cardiac events occurred significantly more frequently during the period of rescue operation than in standby time hours (p = 0.02). The results reported a significant load on the cardiovascular system during rescue operations in HEMS crew members. Therefore, it is necessary to carry out a risk stratification of the HEMS crew members to prevent cardiovascular risk and events.

Relationship between Sleep Duration and Risk Factors for Stroke

Stroke is a leading cause of death and disability worldwide. While various risk factors have been identified, sleep has only been considered a risk factor more recently. Various epidemiologic studies have associated stroke with sleep such as sleep duration, and laboratory and clinical studies have proposed various underlying mechanisms. The pathophysiology is multifactorial, especially considering sleep affects many common risk factors for stroke. This review aims to provide an outline of the effect of sleep duration on common stroke risk factors. Appropriate sleep duration, especially in patients who have stroke risk factors, and increasing awareness and screening for sleep quality may contribute to primary prevention of stroke.

Heart rate and blood pressure variability in children with chronic kidney disease: a report from the CKiD study

BACKGROUND

Autonomic nervous system dysfunction and sympathetic nervous system over-activity play important roles in the development of hypertension associated with chronic kidney disease (CKD). In adults, increased blood pressure variability (BPV) appears to be directly related to sympathetic over-activity with increased risk of end-organ damage and cardiovascular events. Decreased heart rate variability (HRV) has been observed in adults with CKD, and is an independent predictor of mortality.

METHODS

The purpose of this study was to evaluate BPV and HRV in pediatric patients enrolled in the Chronic Kidney Disease in Children Study. Ambulatory blood pressure monitoring data were available for analysis of 215 person-visits from 144 children that were not receiving antihypertensive medications.

RESULTS

BPV and HRV were determined by standard deviation and coefficient of variation for heart rate and systolic and diastolic blood pressure for each patient averaged for wake/sleep periods during 24-h monitoring. Uniformly lower values were displayed during sleep versus wake periods: BPV was 20 % lower during sleep (p < 0.001) and HRV was 30 % lower during sleep (p < 0.001). A significant increase in systolic BPV was observed in hypertensive children compared to children with normal blood pressure (6.9 %, p = 0.009). Increased diastolic BPV was detected among hypertensive children during sleep period compared to children with normal blood pressure (11.5 %, p = 0.008). There was a significant decrease in HRV in hypertensive compared to normotensive children (-8.2 %, p = 0.006).

CONCLUSIONS

These findings are similar to those in adult patients and may underscore childhood origin and natural progression of adverse cardiovascular outcomes in adults with CKD.

Circadian variation in the circulatory responses to exercise: relevance to the morning peaks in strokes and cardiac events

Sudden cardiac and cerebral events are most common in the morning. A fundamental question is whether these events are triggered by the increase in physical activity after waking, and/or a result of circadian variation in the responses of circulatory function to exercise. Although signaling pathways from the master circadian clock in the suprachiasmatic nuclei to sites of circulatory control are not yet understood, it is known that cerebral blood flow, autoregulation and cerebrovascular reactivity to changes in CO(2) are impaired in the morning and, therefore, could explain the increased risk of cerebrovascular events. Blood pressure (BP) and the rate pressure product (RPP) show marked 'morning surges' when people are studied in free-living conditions, making the rupture of a fragile atherosclerotic plaque and sudden cardiac event more likely. Since cerebral autoregulation is reduced in the morning, this surge in BP may also exacerbate the risk of hemorrhagic and ischemic strokes in the presence of other acute and chronic risk factors. Increased sympathetic activity, decreased endothelial function, and increased platelet aggregability could also be important in explaining the morning peak in cardiac and cerebral events but how these factors respond to exercise at different times of day is unclear. Evidence is emerging that the exercise-related responses of BP and RPP are increased in the morning when prior sleep is controlled. We recommend that such 'semi-constant routine' protocols are employed to examine the relative influence of the body clock and exogenous factors on the 24-h variation in other circulatory factors.

Emergency duties and deaths from heart disease among firefighters in the United States

BACKGROUND

Heart disease causes 45% of the deaths that occur among U.S. firefighters while they are on duty. We examined duty-specific risks of death from coronary heart disease among on-duty U.S. firefighters from 1994 to 2004.

METHODS

We reviewed summaries provided by the Federal Emergency Management Agency of the deaths of all on-duty firefighters between 1994 and 2004, except for deaths associated with the September 11, 2001, terrorist attacks. Estimates of the proportions of time spent by firefighters each year performing various duties were obtained from a municipal fire department, from 17 large metropolitan fire departments, and from a national database. Odds ratios and 95% confidence intervals for death from coronary heart disease during specific duties were calculated from the ratios of the observed odds to the expected odds, with nonemergency duties as the reference category.

RESULTS

Deaths from coronary heart disease were associated with suppressing a fire (32.1% of all such deaths), responding to an alarm (13.4%), returning from an alarm (17.4%), engaging in physical training (12.5%), responding to nonfire emergencies (9.4%), and performing nonemergency duties (15.4%). As compared with the odds of death from coronary heart disease during nonemergency duties, the odds were 12.1 to 136 times as high during fire suppression, 2.8 to 14.1 times as high during alarm response, 2.2 to 10.5 times as high during alarm return, and 2.9 to 6.6 times as high during physical training. These odds were based on three estimates of the time that firefighters spend on their duties.

CONCLUSIONS

Certain emergency firefighting duties were associated with a risk of death from coronary heart disease that was markedly higher than the risk associated with nonemergency duties. Fire suppression was associated with the highest risk, which was approximately 10 to 100 times as high as that for nonemergency duties.

Hemodialysis timing, survival, and cardiovascular outcomes in the Hemodialysis (HEMO) Study

BACKGROUND

The timing of medical therapies has been shown to influence the outcomes and side effects of treatments for disease. This report examines the extent to which hemodialysis treatment time of day was associated with cardiovascular mortality and morbidity and all-cause mortality in a secondary analysis of the Hemodialysis Study.

METHODS

Dialysis start time defined dialysis shift: morning beginning between 0400 and 0930 hours (n = 822); midday, between 0930 and 1530 hours (n = 851); and evening, between 1530 and 2200 hours (n = 172). Outcome measures included all-cause mortality, cardiac death, composite end point of all-cause mortality or first cardiac hospitalization, and composite end point of first cardiac hospitalization or cardiac death.

RESULTS

Morning hemodialysis was associated with a lower likelihood of cardiovascular events compared with the evening shift in all-cause mortality or first cardiac hospitalization (evening versus morning, relative risk [RR], 1.29; 95% confidence interval [CI], 1.01 to 1.65; P = 0.043), as well as first cardiac hospitalization or cardiac death (evening versus morning, RR, 1.44; 95% CI, 1.11 to 1.89; P = 0.007). No differences were noted in the other 2 outcomes, and there was no statistically significant difference between the morning and midday shifts. Although crude mortality rates were greater in the midday compared with morning (RR, 1.21; 95% CI, 1.05 to 1.39; P = 0.008), this association was attenuated after adjustment (RR, 1.04; 95% CI, 0.89 to 1.22; P = 0.64).

CONCLUSION

Making extensive adjustment for patient characteristics, this report does not support the association of lower all-cause mortality with morning hemodialysis or a particular benefit for older patients.

Circadian variation in stroke - a prospective hospital-based study

A particular pattern of circadian variation of cardiovascular and cerebrovascular diseases has been reported in the literature. The circadian periodicity of ischaemic stroke with peak onset in the morning hours may not be a random event and could depend on some underlying precipitating and associated cardiovascular risk factors. In a prospective observational study, we observed that ischaemic stroke onset was significantly higher in late morning hours between 6.00 and 12.00 hours. Ischaemic heart disease and hypertension were significantly associated with the occurrence of late morning ischaemic strokes. Further studies in the future are needed to understand the significance of this association and whether these risk factors are implicated in the pathogenesis of stroke.

The 1999 Ji-Ji (Taiwan) earthquake as a trigger for acute myocardial infarction

The authors evaluated the effect of stress due to the Ji-Ji, Taiwan, earthquake, which occurred at 1:47 a.m. on September 21, 1999, on the onset of acute myocardial infarction in six counties near the earthquake epicenter. The rate of hospitalization due to acute myocardial infarction increased during the 6 weeks after the earthquake, and a significantly higher number of patients were hospitalized with acute myocardial infarction during that period, compared with the same 6-week period in the previous year (99 and 65 patients, respectively). The findings suggest that extreme emotional stress due to the natural disaster, superimposed on the stress of awakening, increased the incidence of acute myocardial infarction in this population.

Linear dynamic features of ambulatory blood pressure in a population-based study

BACKGROUND

The objective of the present study was to characterize inter-individual variation in traits that measure linear dynamic features of ambulatory blood pressure (BP) measurements that may be used in future population studies to investigate the relationships between variation in genetic and environmental factors that influence BP regulation and risk of hypertension, and among hypertensives, provide new insights into variation in risk of target organ damage.

DESIGN

We obtained ambulatory BP measurements every 10 min over a 24-h period in 199 healthy non-Hispanic Whites (84 females, 115 males) from Rochester, Minnesota, USA.

METHODS

We then used the autocorrelation function (ACF) to measure linear dynamic features of the daytime and night-time observations in females and males separately. Re-sampling procedures were used to test whether these individuals had significant linear dependencies.

RESULTS

We found that systolic and diastolic ambulatory BP measurements in our sample have statistically significant linear dependencies and that the ACFs are approximately normally distributed among individuals. In addition, we found that the distributions of the ACF traits among individuals are not significantly correlated with the mean of the ambulatory BP measurements, are different in men and women, and are different during the daytime versus the night-time.

CONCLUSIONS

We conclude that ACF traits are different measures of BP than the mean that capture information about the biology of BP regulation reflected in the dynamics of a person's minute-to-minute and hour-to-hour BP phenotype. Studies of measures of linear dynamic features of BP are likely to offer new insights into the genetic and environmental factors that contribute to inter-individual variation in BP regulation and risk of future hypertension as well as new insights into the causes of variation in risk of target organ damage in individuals with established hypertension.

Firefighters and on-duty deaths from coronary heart disease: a case control study

BACKGROUND

Coronary heart disease (CHD) is responsible for 45% of on-duty deaths among United States firefighters. We sought to identify occupational and personal risk factors associated with on-duty CHD death.

METHODS

We performed a case-control study, selecting 52 male firefighters whose CHD deaths were investigated by the National Institute for Occupational Safety and Health. We selected two control populations: 51 male firefighters who died of on-duty trauma; and 310 male firefighters examined in 1996/1997, whose vital status and continued professional activity were re-documented in 1998.

RESULTS

The circadian pattern of CHD deaths was associated with emergency response calls: 77% of CHD deaths and 61% of emergency dispatches occurred between noon and midnight. Compared to non-emergency duties, fire suppression (OR = 64.1, 95% CI 7.4-556); training (OR = 7.6, 95% CI 1.8-31.3) and alarm response (OR = 5.6, 95% CI 1.1-28.8) carried significantly higher relative risks of CHD death. Compared to the active firefighters, the CHD victims had a significantly higher prevalence of cardiovascular risk factors in multivariate regression models: age >or= 45 years (OR 6.5, 95% CI 2.6-15.9), current smoking (OR 7.0, 95% CI 2.8-17.4), hypertension (OR 4.7, 95% CI 2.0-11.1), and a prior diagnosis of arterial-occlusive disease (OR 15.6, 95% CI 3.5-68.6).

CONCLUSIONS

Our findings strongly support that most on-duty CHD fatalities are work-precipitated and occur in firefighters with underlying CHD. Improved fitness promotion, medical screening and medical management could prevent many of these premature deaths.

Circadian pattern of emergency calls: implications for ED organization

A circadian variation has been shown in the onset of acute medical diseases and we postulate that there is a circadian variation in emergency calls. We reviewed the 20,858 emergency calls addressed to the Emergency Coordinating Unit of the Hospital of Ferrara, Italy, from January 1 to December 31, 1998. Precise determination of the time of calls was available from the recordings. Total calls and subgroups by different diseases were categorized into 24 one-hour increments and analyzed for circadian rhythmicity by applying a partial Fourier series. A circadian variation was found for all subgroups, except for alcoholic intoxication. There was a peak frequency of calls in the morning hours for cardiologic, respiratory, and neurologic disease. There was a peak frequency of calls in the afternoon for trauma, neoplastic diseases, and acute poisoning. Organization of quantity and quality of Emergency Department (ED) staff should take into account the increased demand of specific facilities during certain hours of the day.

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.

Is fitness training always good for your health?

This case report illustrates the significance of biomechanical forces, such as static exercise as a precipitating factor for plaque rupture resulting in coronary dissection and secondary thrombus formation, as documented by angiography in this particular patient.

Atherosclerotic plaque rupture: a fatigue process?

The mechanism of atherosclerotic plaque rupture is not known. Current theories focus on the acute triggers of plaque rupture and myocardial infarction such as increased shear or circumferential stress, rupture of the vasa vasorum and vasospasm. We hypothesize that a critical mechanism causing plaque rupture is fatigue failure, the catastrophic rupture of a material following exposure to high-cycle, low-amplitude repetitive stress. Comparisons between material fatigue and plaque rupture demonstrate that this hypothesis is consistent with known physiologic and epidemiologic data on plaque rupture.

Biological time and in vivo research: a field guide to pitfalls

Biological rhythmicity is a fundamental characteristic of all life forms, from primitive bacteria to man. The molecular biology, genetics, and the neurobiology of the biological clock(s) are being elucidated. Daily (circadian) statistically significant fluctuations occur in all of the normal biological variables studied in the experimental animal and the human. Many researchers, however, are not aware of the negative impact biological rhythmicity can have on experimental design and/or data interpretation. This article serves not as a review, but as a "field guide" to the pitfalls that can occur when research is performed in the absence of an understanding of biological rhythmicity. The major topics discussed are: 1) data transfer from the diurnally in-active/resting/sleeping lab animal to the diurnally active human, 2) frequency of sampling, 3) free-running vs. synchronization, 4) alternating periods of resistance and susceptibility, 5) phase shifting of a rhythm, 6) the assumption that one mean +/- S.E. from control animals can be "stretched" across an experimental time span, and 7) plotting data on an "hours after treatment" format vs. a "time of day" format. The hope is that by avoiding the pitfalls, biological time will become an ally in the endeavor to understand human biology.

Are there any unique epidemiological and vascular risk factors for ischaemic strokes that occur in the morning hours?

It is now accepted that the incidence of ischaemic stroke is significantly increased in the morning. Any attempts to prevent its occurrence must be based on determining the mechanisms, special risk factors and appropriate protective measures needed during this vulnerable period. We studied the epidemiological features of morning stroke and reviewed the records of 2312 consecutive patients recorded prospectively in the Tel Aviv Stroke Register. Information about time of stroke onset was obtained from the patient, family members or other observers. The study parameters of age, sex, vascular distribution (carotid versus vertebrobasilar), ischaemic heart disease, myocardial infarction, diabetes mellitus, arterial hypertension, smoking, hyperlipidaemia, stroke severity and recurrence were compared between patients with morning stroke and those with stroke occurring at other times. In 599 patients (34%) stroke occurred between 06:00 and 10:00 h. No evaluated parameter was found to be statistically different among the morning stroke patients compared with stroke occurring at other times (P < 0.2). Patients with arterial hypertension and ischaemic heart disease and male patients had a greater likelihood of stroke occurrence between 22:00 and 02:00 h (P < 0.05). Our data suggest that none of the common vascular risk factors could explain the morning peak of stroke occurrence. The next step in the quest for understanding the phenomenon of circadian variation is to identify other physiological factors and the effects of pharmacological agents in morning stroke protection.

Chronopharmacology and chronotherapy of cardiovascular medications: relevance to prevention and treatment of coronary heart disease

Biological functions and processes, including cardiovascular ones, exhibit significant circadian (24-hour) and other period rhythms. Ambulatory blood pressure assessment reveals marked circadian rhythms in blood pressure both in normotensive persons and hypertensive patients, whereas Holter monitoring substantiates day-night patterns in electrocardiographic events of patients with ischemic heart disease. The concept of homeostasis, that is, constancy of the milieu interne, which has dominated the teaching, research, and practice of medicine during the 20th century,is now being challenged by emerging concepts from the field of chronobiology-the science of biological rhythms. Epidemiologic studies document the heightened morning-time risk of angina, myocardial infarction, and stroke. Circadian rhythms in coronary tone and reactivity, plasma volume, blood pressure, heart rate, myocardial oxygen demand, blood coagulation, and neuroendocrine function plus day-night patterns in the nature and strength of environmental triggers all contribute to this morning vulnerability. Homeostatically devised pharmacotherapies, that is, medications formulated to ensure a near-constant drug concentration, may not be optimal to adequately control diseases that vary in risk and severity during the 24 hours. Moreover, circadian rhythms in the physiology of the gastrointestinal tract, vital organs, and body tissues may give rise to administration-time differences in the pharmacokinetics and effects of therapies. Thus the same medication consumed in the same dose under identical conditions in the evening and morning may not exhibit comparable pharmacokinetics and dynamics. New technology makes possible chronotherapy, that is, increase of the efficiency and safety of medications by proportioning their concentrations during the 24 hours in synchrony with biological rhythm determinants of disease. The chronotherapy of peptic ulcer disease achieved by the evening dosing of H 2-receptor antagonists and of asthma by the evening dosing of special drug delivery forms of theophylline and morning methylprednisolone administration has proven to be beneficial. Controlled-onset extended-release verapamil constitutes the first chronotherapy of essential hypertension and ischemic heart disease; once-a-day bedtime dosing results in a high drug concentration in the morning and afternoon and a reduced one overnight. Studies demonstrate effective 24-hour control of blood pressure, including the attenuation of its rapid rise in the morning, without induction of nighttime hypotension. Moreover, this formulation effectively controls angina, especially in the morning when the risk of ischemia is greatest. Determination of the role of verapamil chronotherapy in the primary prevention of cardiovascular morbidity and mortality awaits the results of the CONVINCE trial now in progress.

Effects of controlled-onset extended-release verapamil on nocturnal blood pressure (dippers versus nondippers). COER-Verapamil Study Group

Approximately 1 in 4 patients with systemic hypertension have a 24-hour blood pressure (BP) profile characterized by a blunted or absent nocturnal decline in pressure. We evaluated the effects of a chronotherapeutic delivery system of controlled-onset extended-release (COER) verapamil hydrochloride and placebo in 257 hypertensive patients according to their circadian BP pattern in an 8-week prospective, multicenter, randomized, and double-blind clinical trial. Patients were stratified into 193 dippers (>10% decline in BP during the period of 10 P.M. to 5 A.M. compared with the hours of 5 A.M. to 10 P.M.) and 64 nondippers (<10% decline in BP during nighttime). During daytime, placebo-subtracted BP was similarly decreased in dippers and nondippers by COER verapamil. During nighttime, the placebo increased nocturnal BP in dippers (baseline nocturnal BP, 133/78 mm Hg) by 3/3 +/- 2/2 mm Hg and reduced BP by -5/-3 +/- 2/2 mm Hg in nondippers (baseline nocturnal BP, 152/94 mm Hg) (p = NS between groups). After controlling for age, gender, ethnicity, and the regression to the mean observed on placebo for all doses, COER verapamil reduced nocturnal BP more in nondippers than dippers -5.8/-2.4 mm Hg, p <0.0001 for systolic BP and p = 0.09 for diastolic BP). Additionally, a significant dose-related reduction in systolic and diastolic nocturnal BP (r = 0.56, p <0.0001 for systolic BP and r = 0.62, p <0.0001 for diastolic BP) was observed with COER verapamil after controlling for baseline covariates. These data demonstrate that nocturnal BP is decreased by a greater extent in nondipper hypertensives than in dipper hypertensives following treatment with COER verapamil HCL.