People with lower levels of calcium in the blood are more likely to experience sudden cardiac arrest than those with higher calcium levels, new research from the Mayo Clinic has found. Sudden cardiac arrest (SCA) results in death for over 90% of patients.

Over 50% of men and nearly 70% of women who die of SCA do not have a history of heart disease prior to this cardiac event. It is one of the leading causes of death in the United States and kills more people than any single cancer.

Many patients who suffer SCA would not be considered high risk under current guidelines. Furthermore, blood levels of calcium are easily monitored.

Lower Serum Calcium Levels

Lead investigator Sumeet S. Chugh, MD, Pauline and Harold Price Chair in Cardiac Electrophysiology, Cedars-Sinai Heart Institute, Los Angeles, explained,

“Our study found that serum calcium levels were lower in individuals who had a sudden cardiac arrest than in a control group. Patients with serum calcium in the lowest quartile (<8.95 mg/dL) had twice the odds of sudden cardiac arrest compared to those in the highest quartile (>9.55 mg/dL), even after controlling for multiple patient characteristics including demographics, cardiovascular risk factors and comorbidities, and medication use."

Data from 2002 until 2015 were gathered from the Oregon Sudden Unexpected Death Study (Oregon SUDS). The goal of the Oregon SUDS is to improve understanding of who is at risk for out-of-hospital sudden cardiac arrest.

This study included 267 SCA cases and 445 control subjects whose serum calcium levels were measured during routine medical care. All sudden cardiac arrest cases had had serum calcium levels measured in the 90 days prior to their cardiac arrest.

The Oregon SUDS collaborates with emergency responders and hospitals in the Portland, OR metro area to identify all cases of sudden cardiac arrest. This enabled researchers to collect comprehensive patient medical history from the time prior to their cardiac arrest.

Each patient’s total serum calcium was corrected by their serum albumin level to estimate a more physiologically relevant corrected calcium level.

Sudden Cardiac Arrest

Cardiac arrest is a sudden stop in effective blood flow due to the failure of the heart to contract effectively. Symptoms include loss of consciousness and abnormal or absent breathing.

Some people may have chest pain, shortness of breath, or nausea before this occurs. If not treated within minutes, death usually occurs.

[caption id=“attachment_92484” align=“aligncenter” width=“680”]Sudden cardiac arrest Sudden cardiac arrest cases had lower corrected calcium levels than control subjects did (9.18 mg/dL vs. 9.27 mg/dL).
Credit: Mayo Clinic Proceedings[/caption]

The most common cause of cardiac arrest is coronary artery disease. Less common causes include major blood loss, lack of oxygen, very low potassium, heart failure, and intense physical exercise. A number of inherited disorders may also increase the risk including long QT syndrome.

The initial heart rhythm is most often ventricular fibrillation. The diagnosis is confirmed by finding no pulse. While a cardiac arrest may be caused by heart attack or heart failure, these are not the same.

Singer Tom Petty, aged 66 and comedian Ralphie May, 45, both recently died due to SCA.

Other Risk Factors

SCA cases had a significantly higher percentage of African Americans and patients with diabetes mellitus, chronic obstructive pulmonary disease, and chronic kidney disease compared to the control group. Cases were also more likely than controls to be on hemodialysis.

In addition, diuretics, especially loop diuretics, were prescribed more for cases than for controls with no differences in the rate of utilization of beta blockers.

“Overall, it seems that further study is required to elucidate the mechanisms underlying the adverse associations with lower calcium levels and to determine whether controlling calcium levels improves the prognosis in the general population or in high-risk patients,"

commented Dr. Chugh.

First author Hirad Yarmohammadi, MD, MPH, Brigham and Women’s Hospital, said:

“Our study showed that lower serum calcium levels, even within the normal range of values, may increase risk for sudden cardiac death. Although our findings may not be ready for routine clinical use in patients at this time, they are a step towards the goal of improving patient care by better prediction of risk."

In an accompanying editorial, Hon-Chi Lee, MD, PhD, of the Department of Cardiovascular Medicine, Mayo Clinic, Rochester, MN, noted that although results should be interpreted with caution, he recommends that

  • serum calcium levels should be examined and followed longitudinally more carefully

  • low serum calcium levels may be considered a potential risk factor for SCA in the community

  • more research is necessary to determine whether patients in the lowest quartile of serum calcium would benefit from higher dietary calcium intake or calcium supplementation.

With the main driver of cardiac arrest being ischemic heart disease, efforts to promote a healthy diet, exercise, and smoking cessation are important. For people at risk of heart disease, measures such as blood pressure control, cholesterol lowering, and other medico-therapeutic interventions are used.

One review published in 2016 found moderate-quality evidence to show that blood pressure-lowering drugs do not appear to reduce sudden cardiac death.

Yarmohammadi, Hirad et al. Serum Calcium and Risk of Sudden Cardiac Arrest in the General Population Mayo Clinic Proceedings , Volume 92 , Issue 10 , 1479 - 1485

Lee, Hon-Chi Serum Calcium Mayo Clinic Proceedings , Volume 92 , Issue 10 , 1466 - 1468

Top image: Wellcome Images

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