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Author Interview: Dr. Shea: Endogenous Circadian Blood Pressure Rhythm
Author Interview: Dr. Steven Shea
Existence of an Endogenous Circadian Blood Pressure Rhythm in Humans That Peaks in the Evening.
Shea SA, Hilton MF, Hu K, Scheer FA.
Circ Res. 2011 Apr 7
Brigham and Women's Hospital and Harvard Medical School, Boston, MA.
1. What are the main findings of the study?
In humans there is a well documented increase in blood pressure (BP) during the waking hours and decrease in BP during sleep. This day/night pattern may be mostly attributable to the different behaviors that occur across the day and night.
However, this day/night pattern could also be influenced by the internal body clock (circadian pacemaker), irrespective of the ongoing behaviors.
This study supports the hypothesis that an endogenous circadian rhythm of BP exists in humans. The data reveal robust circadian rhythms in systolic and diastolic BP in healthy adults.
The peak in BP caused by the circadian system occurred at the circadian time corresponding to roughly 9:00 pm.
This internal rhythm is quite robust as there were almost identical rhythm amplitudes and phase relationships for BP among three different protocols in three groups of study participants.
2. Were any of the findings unexpected?
The endogenous circadian rhythm of BP did not appear to be caused by endogenous circadian rhythms in other variables that are often related to blood pressure, such as cortisol, heart rate and sympathetic activity.
We also note that there is a well-documented peak in adverse cardiovascular events, such as myocardial infarction and stroke, in the mornings around 9 am.
Since elevated blood pressure is a cardiovascular risk factor, our results are unexpected as the lowest circadian BP occurred around the most vulnerable time for adverse cardiovascular events.
Thus, the peak in cardiovascular events in the mornings is unlikely to be caused by circadian rhythm-related increases in BP at that time.
3. What should clinicians and patients take away from this study?
If such results are similar in more vulnerable individuals with underlying cardiovascular risk factors, then we would likely conclude that ongoing behaviors are more likely to be the triggers for adverse cardiovascular events compared to the circadian rhythm of BP.
However, both clinicians and patients should also be aware that an elevation in cardiovascular events in the mornings could still be caused by internal circadian rhythms in other cardiovascular variables such as platelet function, endothelial function, and plasma cortisol, among others.
4. What recommendations do you have for cardiology health care providers as a result of your study?
It is too early to make any firm recommendations based on these initial studies of healthy people. Further studies in more vulnerable individuals need to be performed.
ABSTRACT
Existence of an Endogenous Circadian Blood Pressure Rhythm in Humans That Peaks in the Evening.
Shea SA, Hilton MF, Hu K, Scheer FA.
Circ Res. 2011 Apr 7
Brigham and Women's Hospital and Harvard Medical School, Boston, MA.
Rationale: Blood pressure (BP) usually decreases during nocturnal sleep and increases during daytime activities. Whether the endogenous circadian control system contributes to this daily BP variation has not been determined under appropriately controlled conditions.
Objective: To determine whether there exists an endogenous circadian rhythm of BP in humans.
Methods and Results: In 28 normotensive adults (16 men), we assessed BP across 3 complementary, multiday, in-laboratory protocols performed in dim light, throughout which behavioral and environmental influences were controlled and/or uniformly distributed across the circadian cycle via:
(1) a 38-hour "constant routine," including continuous wakefulness;
(2) a 196-hour "forced desynchrony" with 7 recurring 28-hour sleep/wake cycles; and
(3) a 240-hour forced desynchrony with 12 recurring 20-hour sleep/wake cycles.
Circadian phases were derived from core body temperature. Each protocol revealed significant circadian rhythms in systolic and diastolic BP, with almost identical rhythm profiles among protocols.
The peak-to-trough amplitudes were 3 to 6 mm Hg for systolic BP and 2 to 3 mm Hg for diastolic BP (always P<0.05). All 6 peaks (systolic and diastolic BP in 3 protocols) occurred at a circadian phase corresponding to ≈9:00 pm (ie, the biological evening).
Based on substantial phase differences among circadian rhythms of BP and other variables, the rhythm in BP appeared to be unrelated to circadian rhythms in cortisol, catecholamines, cardiac vagal modulation, heart rate, or urine flow.
Conclusions: There exists a robust endogenous circadian rhythm in BP.
The highest BP occurred at the circadian time corresponding to ≈9:00 pm, suggesting that the endogenous BP rhythm is unlikely to underlie the well-documented morning peak in adverse cardiovascular events.
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Highlights of Article by Dr. Erik Hess et of Mayo Clinic ;CIRCOUTCOMES 2012
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Chest pain is the 2nd most common reason patients come to EDs across the United States
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Initial testing – including information obtained from the history, physical exam, electrocardiogram, and cardiac troponin – identifies > 98% of heart attacks
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To avoid missing a diagnosis of heart attack or pre-heart attack symptoms, emergency physicians often admit patients to observation units or to the hospital for extensive diagnostic testing, including stress testing
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This results in false positive test results, unnecessary exposure to radiation, and unnecessary downstream procedures such as stent placement in arteries of the heart
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Decision aids are evidence-based tools designed to educate and engage patients in decisions regarding their care
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We hypothesized that patients who were educated regarding their future risk for a heart attack and engaged in the decision of whether to be admitted to the observation unit for stress testing or to follow-up with a Mayo Clinic heart doctor in the next 72 hours would have greater knowledge about their short-term risk for heart attack, be more aware of the management options, and choose less intensive approaches to evaluation
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We randomly assigned 204 patients who came to the ED with chest pain and were being considered for observation unit admission to the decision aid or to usual care
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Decision aid patients:
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Had greater knowledge regarding their short-term risk for a heart attack
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Less frequently decided to be admitted to the observation unit for stress testing
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Had 4 times greater engagement in the decision making process
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Had no adverse events within 30 days of the ED visit
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Take home points
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Patients want to be educated and engaged in decisions regarding their care
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Once properly informed and engaged in treatment decisions, patients often choose less intensive treatment options
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Integrated health systems like the Mayo Clinic in which physicians collaboratively work together to provide ER patients ready access to outpatient follow-up have potential to improve the value of Emergency care
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Glucose, Insulin and Potassium (“GIK”) TO MINIMIZE IMPACT OF HEART ATTACKS BEFORE PATIENTS GET TO THE HOSPITAL
Study puts life-saving drugs in the hands of paramedics, decreasing rate of cardiac arrest and death from heart attacks
CHICAGO (March 27, 2012) — Paramedics can potentially reduce someone’s chances of having a cardiac arrest or dying by 50 percent by immediately administering a mixture of glucose, insulin and potassium (“GIK”) to people having a heart attack, according to research presented today at the American College of Cardiology’s 61st Annual Scientific Session. The Scientific Session, the premier cardiovascular medical meeting, brings cardiovascular professionals together to further advances in the field.
The study showed that patients who received GIK immediately after being diagnosed with acute coronary syndrome — which indicates a possible heart attack is either in progress or on the way — were 50 percent less likely to have cardiac arrest (a condition in which the heart suddenly stops beating) or die than those who received a placebo, although the treatment did not prevent the heart attack from occurring. The reduction in in-hospital cardiac arrest or death was a “secondary endpoint”, so statistically was not definitive, but was consistent with how GIK seems to work in experimental models of heart attack.
The effect was also present for patients with ST-elevation heart attacks, which require immediate treatment. For those patients, immediate GIK was associated with a 60 percent reduction in in-hospital cardiac arrest or death.
“When started immediately in the home or on the way to the hospital — even before the diagnosis is completely established — GIK appears not completely prevent any heart attack from occurring, but appeared in this trial to reduce the size of heart attacks and to reduce by half the risk of having a cardiac arrest or dying,” said Harry P. Selker, MD, MSPH, executive director of the Institute for Clinical Research and Health Policy Studies at Tufts Medical Center, who led the study with Joni Beshansky, RN, MPH, co-principal investigator and project director. “Acute coronary syndromes represent the largest cause of death in this country. GIK is a very inexpensive treatment that appears to have promise in reducing those deaths and morbidity.”
The cost of the treatment is about $50.
“Because the trial is the first to show GIK could be effective when used by paramedics in real-world community settings, it could have important implications for the treatment of heart attacks,” Dr. Selker said. Previous clinical trials have shown no consistent effect, likely because the GIK was given too late to help. This study, the “IMMEDIATE Trial,” was the first to test the effectiveness of administering GIK at the very first signs of a threatening heart attack, in the community, rather than waiting hours until the diagnosis was well-established at a hospital, as done in previous clinical trials.
“We wanted to do something that is effective and can be used anywhere,” said Dr. Selker. “We’ve done a lot of studies of acute cardiac care in emergency departments and hospitals, but more people die of heart attacks outside the hospital than inside the hospital. Hundreds of thousands of people per year are dying out in the community; we wanted to direct our attention to those patients.”
The researchers trained paramedics in 36 Emergency Medical Services systems in 13 cities across the country to administer GIK after determining that a patient was likely having a threatened or already established heart attack using electrocardiograph-based ACI-TIPI (acute cardiac ischemia time-insensitive predictive instrument) and thrombolytic predictive instrument decision support that prints patient-specific predictions on the top of an electrocardiogram. The paramedics used these predictions to decide if a patient would likely benefit from treatment. There were 911 patients randomized to receive either the GIK treatment or a placebo.
Administering GIK immediately also reduced the severity of the damage to the heart tissue from the heart attack. On average, 2 percent of the heart tissue was destroyed by the heart attack in people receiving GIK, compared with 10 percent in those who received the placebo. Although a significant proportion of suspected heart attacks are later determined to be false alarms (23 percent in this study), administering GIK does not appear to cause any harmful effects in such patients.
The research team will follow up with study participants at six and 12 months to evaluate the longer-term benefit of the GIK treatment.
This study was funded by the NIH’s National Heart, Lung and Blood Institute.
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Amazon.com 's Editorial Reviews
Angina: New Ways to Treat
Chronic Chest Pain
Part of the award winning public television series Healthy head
/Healthy Mind. It's one of the scariest medical symptoms for people who are generally healthy: a tightening, painful feeling in the chest known as Angina. In some cases this chest pain can be a serious warning that requires immediate treatment. But for the millions of people with chronic, stable angina the discomfort is something that can be readily managed with a variety of treatments. In this program we take a look at what generally causes angina, what can be done to prevent it and how it can be effectively treated with lifestyle changes, innovative drug therapies and medical procedures.
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Amazon.com Editorial Review:
Philips HeartStart Home Defibrillator (AED)
Be prepared for the unexpected.
When sudden cardiac arrest (SCA) strikes, the electrical system of the heart short circuits, causing the heart to quiver rather than pump in a normal rhythm. It typically results in the abnormal heart rhythm know as ventricular fibrillation (VF). It usually happens without warning and the majority of people have no previously recognized symptoms of heart disease. And it most often happens at home. For the best chance of survival from SCA caused by VF, a defibrillator should be used within 5 minutes. Yet, less than 1 in 20 people survive largely because a defibrillator does not arrive in time.
Just as seat belts or airbags do not save every life in a traffic accident, a defibrillator will not save every person who suffers a sudden cardiac arrest. Yet many lives could be saved if more people could be reached more quickly.
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