Cardiac MRI has distinguished itself as a tool for diagnosing heart disease, namely in examining the size and thickness of heart chambers, viewing the extent of damage from progressive heart disease, detecting plaque buildup and assessing a patient’s recovery following treatment. Recent improvements in speed, image quality, reliability and increased applications are positioning cardiac MR as a practical and powerful clinical tool. Here we take a look at its applications in imaging pulmonary hypertension, ischemic heart disease and sudden cardiac death.
Specific disease markers cannot hide
Pulmonary hypertension is a condition characterized by an increase in blood pressure in the pulmonary artery, pulmonary vein, or pulmonary capillaries. Cardiac MR is key in visualizing right ventricular (RV) remodeling, the heart’s first response to pulmonary hypertension. The response is characterized by the RV becoming thicker, as it needs more muscle to accommodate for the increased workload of the pulmonary artery.
In cases of pulmonary hypertension (PH), researcher Jens Vogel-Claussen, MD, assistant professor of radiology at Johns Hopkins University in Baltimore, says that specific indicators can be found by way of 1.5T or 3T cardiac MRI that can lead physicians to a diagnosis, as well as follow-up of the disease state.
With the increased pressure put on the RV, Vogel-Claussen says, “the relationship between RV mass and left ventricular (LV) mass has changed, and this is what we can see on the MRI.”
Vogel-Claussen explains that cardiac MRI enables the measurement of the ventricular mass index-RV mass divided by LV mass. “If the index rises, we can see the changed relationship,” he says.
Severity also can be determined by way of cardiac MR. “If [the disease] is chronic—which many patients have—the pulmonary hypertension gets more severe over time,” Vogel-Claussen says. “What then happens is the RV will decompensate because it is worn out after a while. We can then quantify the function of the RV and LV with MRI.”
Noninvasively, cardiac MRI is thought to be the “gold standard” in determining RV and LV mass function, says Vogel-Claussen. However, most physicians still utilize right-heart catheterization for a definitive diagnosis when they first suspect pulmonary hypertension.
Despite the need for an invasive diagnostic method, why should we continue to eye cardiac MR? “For the non-invasive monitoring of cardiac function and mass, [cardiac MRI] is better than right-heart catheterization,” he says.
Aside from cardiac MRI and right-heart catheterization, Vogel-Claussen notes Doppler ultrasound is widely used as a noninvasive method in the treatment and diagnosis of various types of heart disease. Unlike cardiac MRI, it is especially difficult to assess the condition of the RV through this method, as the measurements are not always accurate and pre-existing conditions such as emphysema can interfer with the results.
A recent study Vogel-Claussen participated in confirmed his theory. The study subjects had undergone cardiac MR and some of the resulting images clearly pointed to pulmonary hypertension. “What we see is a scar at the attachment site [where the RV is attached to the LV]. This hinge point gets stressed if the RV is under pressure. We found scarring at the attachment site to be quite a specific finding for PH.”
Vogel-Claussen notes, however, that the scarring does not present on all cases of pulmonary hypertension. In the study group, only one of the 12 individuals suspected to have PH presented with scarring.
After diagnosis of PH, physicians should treat their patients according to what has been proven to be reliable in the past, Vogel-Claussen says. “At the time of diagnosis, one could do an MRI to assess the cardiac function and remodeling status of the RV and then follow it up with non-invasive treatments to see if the heart remodels, decompensates or gets better over time.”
Cardiac MR + stress testing = diagnosis
Outside of evaluating pulmonary hypertension, cardiac MR also is making its mark