Survivors of cardiac arrest seek answers through imaging tests

Cardiac arrest – when the heart suddenly stops pumping normally – can result from several causes. Doctors use a variety of imaging techniques to diagnose the cause, which then determines treatment.

Cardiac arrest can kill in a few minutes if a normal heartbeat isn’t restored with a defibrillator, according to the National Library of Medicine. The on-field collapse of Buffalo Bills safety Damar Hamlin last month, due to cardiac arrest, attracted national attention. Cardiac arrests outside of a hospital occur about 356,000 times annually, the American Heart Association says.

Hamlin survived, and doctors likely put him through a battery of tests to determine why he was stricken. Choosing which type of imaging should be used first depends upon several factors, including the patient’s age, said Tendoh F. Timoh, MD, a cardiologist who specializes in cardiac imaging at Cape Cod Hospital’s Cardiovascular Procedural Services in Hyannis. Older patients are more likely to have heart problems caused by years of accumulated plaque inside their blood vessels (atherosclerosis), he said, while young athletic patients may have thickened heart muscle or were born with abnormal coronary arteries.

“Ischemic heart disease (atherosclerosis) is a disease of the elderly, but we do see it in young people with diabetes,” Dr. Timoh said.

Dr. Timoh described three non-invasive techniques used to examine cardiac arrest patients. He said the most commonly employed is an echocardiogram, which uses ultrasound.

Echocardiogram (echo or transthoracic echocardiography)

“An echocardiogram gives us two things: We look for muscle dysfunction and left ventricular ejection fraction (a percentage of the amount of blood pumped out with each beat compared with the amount left in this chamber, according to the American Heart Association),” he said.

This test can show if one portion of the heart’s muscle is working less effectively than the rest, he said. If so, coronary heart disease may be obstructing blood flow to one section of the organ. If the entire heart is not performing properly, then something other than blocked heart blood vessels is likely at fault.

Cardiac MRI (magnetic resonance imaging)

“Echo looks at pumping function,” Dr. Timoh said. “MRI looks at muscle of the heart, for fibrosis of the heart.”

An MRI will also give the overall pumping function of the heart, he added.

MRI uses radio waves and a magnetic field to make two-dimensional and three-dimensional pictures in great detail. It doesn’t use ionizing radiation, such as X-rays. Sometimes a contrast agent is injected into the blood stream to better detect certain structures, according to the American Heart Association.

Young athletes who suffer cardiac arrest may have a condition called hypertrophic cardiomyopathy, Dr. Timoh said.

“Muscle is thickened, sort of overgrown,” he said. “Leads to lots of fibrosis in muscle.”

The fibrosis, in turn, leads to tachycardia, in which the heart beats too fast, which can cause cardiac arrest, Dr. Timoh said.

By using a contrast agent or dye, cardiac MRI can highlight areas of fibrosis in the heart muscle, he said. Patients with poor kidney function may be ineligible for contrast.

According to a September 2017 article in Circulation Research, hypertrophic cardiomyopathy is a genetic disorder that causes muscle overgrowth in the left ventricle. It can be benign, but is sometimes fatal, especially for young people and athletes. In addition to ventricular tachycardia, the condition may cause atrial fibrillation (or AFib). AFib means the heart beats irregularly (arrhythmia), and may beat too quickly or too slowly, a possibly deadly situation, according to the Centers for Disease Control and Prevention.

Cardiac CT (CAT scan, computed tomography or computerized axial tomography)

A CT scan uses information from X-rays taken at different angles to produce highly detailed images of the target area, according to the National Cancer Institute. Injected or swallowed contrast may be used.

Some young survivors of cardiac arrest may have been born with abnormal coronary arteries, called congenital coronary anomalies or anomalous coronary arteries. The condition is rare and often only found during imaging or after death in an autopsy, according to a March 2021 article in Frontiers in Cardiovascular Medicine.

“Cardiac CT, in these young patients, is very good for looking at blood vessels of the heart, Dr. Timoh said.

In patients with this condition, the coronary arteries that supply the heart with oxygen don’t follow normal paths.

“The coronaries go off into weird areas,” Dr. Timoh said.

Cardiac Imaging at Cape Cod Hospital

Depending upon the findings of initial imaging using these techniques, more invasive procedures may be employed, such as cardiac catheterization, Dr. Timoh said. In this procedure, a very thin tube is put into a blood vessel and guided to the heart. Once there, dye may be injected and X-rays taken of cardiac blood vessels. It can also be used to take tissue samples (biopsies) or perform other tests, according to the National Heart, Lung and Blood Institute.

Cardiac imaging at Cape Cod Hospital extends beyond that used for in-house cardiac arrest patients. Many outpatients are referred for imaging by area cardiologists for a range of problems, Dr. Timoh said.

Some cardiac patients may undergo a nuclear stress test, Dr. Timoh said. In this procedure, a radionuclide tracer is injected and images taken during periods of exercise and rest, according to the National Library of Medicine. Nuclear stress tests are more often done on outpatients, Dr. Timoh said.

“We see a lot of patients a day – a fair amount of echoes a day,” he said.