Managing risk

Researchers examine implantable cardiac devices in the fight against sudden cardiac death

Author

Dawn Smith

It isn’t uncommon to hear that someone has collapsed suddenly, become unresponsive and died from something related to the heart. Many chock these deaths up to heart attacks, but sudden cardiac death (SCD) is often the culprit. SCD is the largest cause of natural death in North America, taking  the lives of 360,000 adults annually.  
SCD is usually caused by a very rapid heart rhythm originating in the left ventricle – the heart’s main pumping chamber. 


The rapid heart rhythm causes the blood pressure to drop, which in turn means that not enough blood is pumped to the vital organs including the brain, kidneys and liver. Although these deaths may seem random, there are certain patient groups who are at a higher risk of SCD, such as those who have suffered a heart attack (myocardial infarction). 


The risk is higher for these patients because of scarring on the ventricular muscle of the heart caused by blockages in one or more arteries in the heart. The scarring can reduce the heart’s ability to pump and is also the site where an arrhythmia can originate. 


According to the REFINE-ICD website, heart attack survivors are four times more likely to die of SCD, especially those with reduced heart pumping function, but there are options for improving the odds. 
Implantable cardioverter defibrillators (ICD), devices made to restore normal rhythm to heart, have revolutionized treatment for those at risk of SCD. 


But there are limitations to who is eligible to receive an ICD. Patients with severe loss of heart function (measured by left-ventricular ejection fraction [LVEF] of 35 per cent or lower) are given an option to have the device implanted, while patients with mild to moderately reduced LVEFs (36-50 per cent) aren’t. 


Instead, patients in the mildly to moderately impacted group are generally treated with medication and lifestyle changes. This cutoff poses a problem, according to the Libin’s Dr. Katherine Kavanagh, MD, a cardiologist with a specialty in treating heart rhythm problems.


 “We know a certain number of patients in this [mild to moderate] group will have an elevated risk of SCD following a heart attack, but we don’t know who,” she says. 


Fortunately, researchers within the Libin Institute are working to address this question. 


Kavanagh is the local principle investigator for the REFINE-ICD study, a multi-centre trial led by her colleague Dr. Derek Exner, MD, a heart-rhythm specialist. The project studies the risk of SCD in individuals who have suffered a heart attack within the past five years and who fall within the mild to moderately affected group.

 
Participants are asked to wear a Holter monitor, which records their heart rhythm, for 24 hours. The results are screened for specific electrical signals as studies suggest that the presence of certain abnormalities in electrical signals may increase the risk of SCD by up to nine times. 


Patients are then randomized into two groups: those who receive ICDs and those who receive standard care following a heart attack. 


According to Kavanagh, ICDs aren’t necessary or beneficial for all heart attack patients. The goal of REFINE-ICD is to determine if there are patients in this mild to moderate risk group who would benefit from an ICD so that we can provide more precise care for future patients with similar characteristics and/or cardiac abnormalities.
REFINE-ICD is funded by CIHR and CANN-NET. Recruitment for the study is still underway.