Rapids Beats: Heart Disease News and Updates for December

December 2016

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Blood Glucose Control after Heart Surgery Decreases Risk of Infection

One of the main causes of post-cardiac surgery infection is high blood glucose, or hyperglycemia. A study led by the diabetes team of the Ottawa Heart Institute analyzed the aftermath of all cardiac surgeries to examine the effect of blood glucose levels on the occurrence of post-surgical infection. 

Heart Institute patients have significantly higher rates of diabetes and prediabetes. The study looked specifically at surgical patients who had high blood glucose levels, indicated by a hemoglobin A1C (HbA1C) of 6% or higher. About 80% of these patients’ glucose levels were regulated by IV-administered insulin during the immediate post-operative period, but only 50% were prescribed insulin upon transition to the ward and subsequently for their return home post-surgery. 

The researchers found a correlation between controlling insulin levels before and after surgery and a decreased risk of infection. Unexpectedly, infection without IV insulin administration was seen mostly in patients with an HbA1C of less than 7%—those with lower blood glucose. However, all in all, more than 25% of patients developed a post-operative infection and hyperglycemia remains the cause of complications.

The authors concluded that IV insulin control before and after cardiac surgery needs to be standardized, and should always be transitioned to subcutaneous insulin injections immediately. Such an approach will be piloted at the Heart Institute. 

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Level of Physical Fitness Can Predict Atrial Fibrillation and Flutter

Regular exercise and physical fitness are factors that are well known to promote cardiovascular health. At the 2016 American Heart Association conference, researchers from the Mayo Clinic presented findings on how they relate to the development of atrial fibrillation and flutter. 

Atrial fibrillation is a type of arrhythmia where the heart beats irregularly and too quickly as its electrical signals are disrupted. Atrial flutter is a similar condition in which these signals are coordinated but happen too fast. The study looked at around 3,000 patients who completed two treadmill exercise tests from 1993 to 2010 to evaluate their physical fitness. The researchers followed these patients’ medical histories to see which of them would later develop atrial fibrillation or flutter. 

They found a correlation between better fitness during the initial test and a smaller risk of acquiring these conditions. Ten per cent better fitness at baseline was found to decrease risk by 16%. By comparing the results between the two treadmill tests, they also found that improving aerobic health later in life significantly reduced this risk as well. The study concluded that physical fitness is an accurate way of predicting the future development of atrial fibrillation and flutter, and working to improve one’s fitness is an effective method of prevention.

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Blood Pressure Linked to Survival Following Cardiac Arrest

Comatose survivors of cardiac arrest have high rates of death and neurological damage. Juan Russo, MD, a cardiology resident at the Ottawa Heart Institute, is studying whether the prognosis of these patients can be assessed using a non-invasive estimate of how much blood is reaching the brain. 

In a presentation at AHA 2016—one of three he gave at the event—Dr. Russo showed that a blood pressure measurement called mean arterial pressure (MAP) was associated with survival after cardiac arrest. For the study, he and his colleagues looked at medical records from 122 patients who underwent therapeutic hypothermia following out-of-hospital cardiac arrest caused by an arrhythmia.

They adjusted for age, whether or not the patient received CPR from a bystander, and the use of drugs that cause blood vessels to tighten (and therefore blood pressure to rise). After these adjustments, they found that patients with higher average MAP during their first four days in hospital were more likely to survive. MAP did not help predict which patients would suffer severe neurological damage.

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