Non-invasive test to determine risk of sudden cardiac arrest in heart bypass surgery patients

Nov 10 2009

Years after heart bypass surgery, Jim Miller was symptom free. Several measures of his heart’s functioning did not show that he was in danger of sudden cardiac arrest (SCA). But Miller’s doctor decided to make sure and the quick, non-invasive test he performed may have saved Miller’s life.

The test, called Microvolt T-Wave Alternans (MTWA), measures a tiny heart beat irregularity believed to cause SCA. It is administered much like a stress test, on a treadmill. Specialized sensors are applied to a patient’s skin and within minutes, a readout shows the doctor if more testing or preventive measures are required.

In Miller’s case, the test showed the irregularity, indicating elevated risk for SCA. Miller’s cardiologist, Steven Korotkin, MD, of Bingham Farms, Michigan, ordered further testing, then surgical implantation of a defibrillator to administer an electric shock to restart Miller’s heart, should it abruptly stop functioning.

Prediction and prevention are critically important when it comes to SCA, an event that occurs without warning. According to the American Heart Association, 95 percent of cardiac arrest victims in the US die before reaching the hospital, resulting in nearly 300,000 deaths each year.

According to Theodore Chow, MD, an electrophysiologist, 50 percent of patients with some form of heart disease will die from SCA if not diagnosed and treated.

Chow believes that as in Miller’s case, many of those deaths can be prevented. That is why, this month, he is opening what may be the nation’s first clinic to focus on preventing SCA.

Located in San Jose, the new Silicon Valley Institute for Cardiac Arrest Prevention offers several tests, including MTWA, that can determine whether patients are at risk of sudden death.

“These technologies are very helpful in determining which patients are at risk for SCA and can potentially save many lives,” said Chow, who has written many medical journal articles and led national studies on SCA prevention tools.

“For example, five minutes after a patient starts walking on the treadmill, the MTWA test shows whether more invasive testing or preventive measures may be needed,” Chow said. “Equally important, if the MTWA level is normal, the test shows that patients can safely exercise and carry out daily activities without worry.”