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Author Interview: Abhinav Goyal, MD, MHS, FACC
Physician Quality Lead for Cardiology, Emory University Hospital and Emory University Hospital Midtown
Assistant Professor of Medicine (Cardiology), Emory School of Medicine
Assistant Professor of Epidemiology, Emory Rollins School of Public Health
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Publication:
Serum Potassium Levels and Mortality in Acute Myocardial Infarction
Abhinav Goyal, John A. Spertus, Kensey Gosch
Lakshmi Venkitachalam, Philip G. Jones,
Greet Van den Berghe, Mikhail Kosiborod
JAMA. 2012;307(2):157-164.doi:10.1001/jama.2011.1967
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What are the main findings of the study? |
Generally, the normal range for serum (blood) potassium is considered to be 3.5-5.0 mEq/L. However, in patients with acute myocardial infarction (AMI) or acute heart attacks, clinical practice guidelines recommend maintaining a potassium value > 4.0 mEq/L (usually 4.0-5.0 mEq/L) in order to avoid ventricular arrhythmias.
These guidelines are based on studies from the 1980’s and early 1990’s, a period in which beta-blockers and early reperfusion therapy were not yet standard of care. In the current treatment era, ventricular arrhythmias in AMI patients are much less common than they were 20 years ago, and therefore, we thought it would be important to take a fresh look at the relationship between potassium levels and more relevant outcomes (particularly mortality, which prior investigations were too underpowered to study) in AMI patients.
Our study uses data from the current treatment era for AMI and suggests that hospital mortality rates are twice as high in AMI patients with potassium levels of 4.5-5.0 mEq/L (the “upper third” of what is considered a “normal” potassium range of 3.5-5.0 mEq/L), compared with patients with potassium levels of 3.5 to <4.5 mEq/L (“lower and middle thirds” of the “normal” potassium range).
At the same time, ventricular fibrillation / cardiac arrest rates did not increase significantly until potassium levels decreased below 3.0 mEq/L.
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Were any of the findings unexpected?
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We found a U-shaped relationship between potassium levels and mortality in AMI patients. This in itself was not a surprise. What was a surprise was that the lowest mortality rates were observed for potassium levels between 3.5-4.5 mEq/L, and not 4.0-5.0 mEq/L as suggested by current AMI guidelines. Another surprise was that the relationship between ventricular fibrillation / cardiac arrest and potassium levels was flatter compared with the mortality curve, and only extreme potassium levels (either very high or very low) predicted somewhat higher rates of ventricular fibrillation or cardiac arrest.
This may be due to misclassification bias (failure to code nonshockable rhythms as cardiac arrest, which occurs more commonly in hyperkalemic than in hypokalemic patients), or to reverse causation (hyperkalemia or hypokalemia could be a marker of illness severity, and not a cause of mortality observed in this study).
Nevertheless, the discrepancy between the mortality curve and the ventricular fibrillation / cardiac arrest curve underscore the importance of not relying on ventricular fibrillation as an endpoint in potassium studies, given the much lower rate of ventricular fibrillation events in the current AMI treatment era (with routine use of beta-blockers and invasive therapies) compared with 20 years ago, when the initial potassium studies were published.
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What should clinicians and patients take away from this study?
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Although our findings are observational, they suggest that it might be reasonable to amend the guidelines to recommend maintaining a potassium range between 3.5-4.5 mEq/L in most AMI patients.
Even though our study did not look at potassium treatment per se, perhaps we also might also need to rethink the common practice (supported by existing guidelines) of routinely giving potassium supplementation to AMI patients with potassium levels between 3.5 and <4.0 mEq/L, with the intent of increasing their potassium levels to ≥ 4.0 mEq/L.
Our data suggest that this may not be sound practice, because of the potential risk of “overcorrecting” potassium levels and increasing them to ≥ 4.5 mEq/L, a range that was associated with harm in our study.
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What recommendations do you have for future studies as a result of your study?
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Our study is observational, and not a randomized controlled trial. The gold standard approach to determining the optimal potassium range in AMI patients would be to conduct a randomized controlled trial in which AMI patients are allocated to one arm receiving potassium supplementation if their potassium levels fall below 3.5 mEq/L, or to another arm in which patients receive potassium supplementation only if their potassium levels fall below 4.0 mEq/L, and then compare relevant outcomes (including hospital mortality) between the two groups. Having said that, such a trial is unlikely to be undertaken in the foreseeable future due to the high cost and regulatory burden associated with conducting trials in today’s environment, and the low likelihood of finding a sponsor to fund a trial that studies a generic treatment such as potassium supplementation.
Furthermore, according to another recent publication in JAMA (Tricoci et al, JAMA 2009;301(8):831-841), most recommendations in cardiology clinical practice guidelines are based on observational studies (like ours), or expert consensus or case studies.
In addition, the existing potassium guidelines are already based on outdated observational studies, and our observational study is substantially larger (well-powered to look at mortality as an endpoint) and more relevant to current clinical practice.
Therefore, in our opinion, it would be reasonable to consider the findings of our study when the AMI guidelines undergo their next revision.
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| More Author Interviews from Angina.com |
| More on Potassium and Kidney Disease from Hemodialysis.com |
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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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