New Blood Test Helps Determine Who Benefits Most From Implantable Cardioverter Defibrillators

Some heart failure patients benefit from having an implantable cardioverter defibrillator (ICD) while others do not – a new blood test that predicts risk of death may help doctors determine who should get an ICD, Professor Samuel Dudley, from the University of Illinois at Chicago College of Medicine explained at the European Society of Cardiology Congress 2012, in Munich, Germany.

An estimated 5 million people in the USA suffer from heart failure, a condition where not enough blood is pumped around the body. According to the National Institutes of Health (USA), almost 550,000 Americans are diagnosed with heart failure annually. It is the single most common cause of hospitalizations in the country.

Implantable cardioverter defibrillators (ICDs) are surgically implanted in heart failure patients to prevent sudden death; they are similar to pacemakers in that they monitor and treat arrhythmias (abnormal heartbeats).

ICDs being used on wrong patients

Professor Dudley explained that over 50% of heart failure patients who have ICDs implanted do not need them, while nearly half of those who would really benefit do not get one.

In a clinical trial, Prof. Dudley demonstrated that a blood test – called PulsePredic – can predict who would benefit from an ICD during the next 12 months. The test can tell, with high accuracy, who will or will not require an ICD to prevent arrhythmia and its subsequent sudden death.

Described as a straightforward laboratory test, PulsePredic detects alterations in the gene message (mRNA) for the SCN5A gene, which previous studies have shown to be closely linked with sudden death. The increase in the altered gene message was found to be a good predictor of which patients were most likely to have a sudden death episode requiring defibrillation.

Professor Dudley explained:

“The test predicts whether you will have sudden death from heart failure and whether you will need a defibrillator in the next year.”

Certain proteins, called voltage-gated sodium channels, are responsible for generating the main current for the electrical signals in the heart. The SCN5A gene encodes for these proteins. Arrhythmias occur when there are rises or falls in the sodium current.

The team tried out PulsePredic on 180 adults participants – 135 of them had heart failure, and 45 were healthy individuals (the control group). They excluded people with inflammatory conditions, infections and congenital heart disease.

The researchers measured the SCN5A gene in white blood cells and heart muscle cells. By analyzing the alterations in the gene message, they could predict who would have a sudden death episode where defibrillation would be required. The patients with heart failure who had arrhythmias that would cause sudden death were found to have considerably higher levels of these genetic mutations, compared to those with normal heartbeats.

By measuring variant levels in the blood, they were able to predict surprisingly accurately who had arrhythmic risk, suggesting that it is possible to have a blood test for sudden death risk and the need for an implantable cardioverter defibrillator.

Professor Dudley said:

“This is the first test of its kind, It is amazing stuff, with promise to change dramatically the way we direct treatments to patients at risk for sudden death.”

The team plan to carry out a much larger trial, and to work with the FDA to receive approval for the PulsePredic to be used clinically.

What is an implantable cardioverter defibrillator (ICD)?

An implantable cardioverter defibrillator is a small device which is implanted into patients at high risk of sudden cardiac death caused by ventricular fibrillation and ventricular tachycardia. It is a small battery-powered electrical impulse generator.

The ICD detects irregular heartbeats and corrects them by sending a jolt of electricity in the heart. Put simply, it is a device that “shocks” an irregular heartbeat back to normal.

The ICD is implanted in the same way a pacemaker is. Electrode wires pass through a vein to the right chambers of the heart. Unlike a pacemaker, which is usually a temporary device and corrects a slow heartbeat (bradycardia), the ICD is usually permanent and is programmed to correct sudden abnormalities.