Cardiac MRI: A Better Look at Pulmonary Hypertension, Ischemic Heart Disease & 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 in enabling the detection of ischemic heart disease, characterized by reduced blood and oxygen supply to the heart muscle that can result in damage to the heart.
W. Gregory Hundley, MD, assistant professor, department of internal medicine - cardiology, of Wake Forest University School of Medicine in Winston-Salem N.C., notes the utilization of both cardiac MR and stress testing for the diagnosis of ischemic heart disease as being a “unique application,” as MR can highlight the disease at its most critical points for physicians.
After the stress test is employed, an MR exam can be used to diagnose ischemic heart disease by looking for abnormalities of heart muscle perfusion or heart muscle function. “When you find either of those, you are highly suspicious that the reason for the abnormality is due to a blockage in a coronary artery that supplies the heart muscle,” Hundley says.
Among the symptoms that bring on suspicion of ischemic heart disease are chest pressure, shortness of breath and unexplained sweating—particularly any of these after some level of exertion, says Hundley. For cases physicians determine to be more serious, catheterization may be recommended, or, if the physician is unsure of the need for invasive heart catheterization, stress testing can be employed along with a cardiac MR exam.
Additionally, Hundley warns that women can present symptoms of ischemic heart disease that are very different than men. He notes, “Women have different issues that need to be addressed, and that’s where MR images are useful.”
Despite the benefits of the utilization of cardiac MRI on this particular patient population, Hundley suggests that the testing method that should be employed within this patient population is specific to the community’s strengths, and the standard in which they are practicing may be the best bet. Hundley believes this can be attributed to a variance in worldwide expertise.
“In capable, trained hands, this is an excellent technique and in comparative studies had been performing better,” concludes Hundley.
A noninvasive paradigm
Prevention of future events is the objective of utilizing cardiac MR to study patients presenting with sudden cardiac death (SCD), or cardiac arrest.
Peter Hunold, MD, of the Department of Radiology and Nuclear Medicine at the University Hospital Schleswig-Holstein, in Luebeck, Germany, says that in 14 of the 18 cases of sudden cardiac death and normal coronary arteries that he and his colleagues reported in a 2009 study, cardiac MRI could define the diagnosis based on the typical imaging features of myocardial pathology.
In contrast to other disease stages of the heart, compounded by the fact that sudden cardiac death comes on very rapidly and without warning, the time-point for MRI is not as critical for SCD as the imaging features can be found days after an acute event, explains Hunold. “The patient should first be clinically stabilized and then be scanned,” he says.
Additionally, Hunold stresses that while cardiac MR can determine severity of sudden cardiac death in certain respects, a more important feature he notes is “disease or not, rather than how much disease.”
In terms of markers for this disease state that physicians can visualize through the utilization of cardiac MRI, Hunold offers, “Inflammation and cardiomyopathies, meaning black-blood prepa red T2-weighted imaging and late gadolinium enhancement.”
“In the special case of primary myocardial disease, i.e. not coronary artery disease or coronary occlusion/infarction, there is no better non-invasive way to diagnosis,” says Hunold. “MRI might play an important role in preventing new events in survivors.”
A work in progress
While Vogel-Claussen, Hundley and Hunold all agree that a 1.5T MRI scanner is sufficient in cardiac imaging each of these patient-populations, each physician has his or her own considerations for respective areas of heart disease research.
Vogel-Claussen notes that further clinical research for pulmonary hypertension has emerged suggesting that patients with higher ventricular mass index have poor survival rates compared to those with smaller ventricular mass indexes, and hopes that in the future, indicators such as this one that is visible through cardiac MR will hold more prognostic power.
With regard to ischemic heart disease, Hundley concludes, “Active research is ongoing in this area—with emphasis on patient selection, technique improvement, cost and expense to healthcare systems and comparators of MR determinations vs. other imaging image modalities. MRI is very unique, and can acquire multiple pieces of information at the same time,” he says, noting the cardiac MRI allows physicians to view multiple indicators of the disease in one single test.