Daily Bulletin 2016

Strain Analysis in Cardiac MRI May Help Diagnose Rare Type of Cardiomyopathy

Wednesday, Nov. 30, 2016

Strain analysis can be used in cardiac MRI to detect and quantify abnormalities in cardiac wall motion, offering a reliable way to help identify arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C), a rare, life-threatening condition that is often responsible for sudden death among young athletes, new research shows.

In their session on Tuesday, a team of Johns Hopkins researchers said ARVD/C is a genetic disease characterized by fibro-fatty replacement of the right ventricular myocardium. Patients are predisposed to potentially life-threatening ventricular arrhythmias and right ventricular dysfunction.

In about 10 percent of patients, sudden cardiac death is their first symptom. If detected early, physicians can treat ARVD/C by inserting a pacemaker and having the patient stop rigorous athletic activity. But so far, there has not been a reliable diagnostic test to distinguish ARVD/C from other cardiac conditions that cause arrhythmias.

Mounes Aliyari Ghasabeh, MD<

Mounes Aliyari Ghasabeh, MD

Patients at risk of ARVD/C are not easy to identify, said presenter Mounes Aliyari Ghasabeh, MD, postdoctoral research fellow in the Advanced Diagnostic and Interventional Radiology Research Center at Johns Hopkins Medical Center.

An international task forced devised five diagnostic criteria, most recently updated in 2010, including family history, histology, electrocardiogram results, arrhythmia, and structure — each one with sub-criteria. The task force criteria specify cardiac MR studies including right ventricle volume and ejection fraction, and wall motion. Assessing wall motion on images is highly subjective, and even experienced readers can make a false positive ARVD/C diagnosis, presenters said.

"Because our method is quantitative, it can add extra value," Dr. Ghasebeh said. The team performed strain analysis on short- and long-axis SSFP CMR sequences using myocardial tissue tracking software. The study assessed global and segmental longitudinal and circumferential strains in both ventricles.

Study Draws from Two Institutions

Because ARVD/C is relatively rare, most studies include only 50 to 100 patients, Dr. Ghasebeh said. Her team's study drew from patients at two centers, Johns Hopkins (which specializes in treating the condition at its Heart and Vascular Institute), and University Medical Center Utrecht in the Netherlands. The study enrolled 426 consecutive ARVD-suspected patients who had been referred to one of the two centers for evaluation. All the patients received CMR imaging with a protocol that included a stack of cine functional images in the horizontal long and circumferential short-axis planes, and also had a complete clinical workup using the 2010 task force criteria.

Based on those criteria, patients were divided into five groups: definite ARVD (69), at-risk (mutation positive without symptomatic disease) (84), structural heart disease (not ARVD) (57), electrical heart disease (87) and normal subjects (133). Regional and global strain analysis was performed on cine SSFP CMR images. Right and left ventricle longitudinal strains were measured on long-axis views. Short-axis views were used for circumferential strain measurements.

(Click to enlarge) Strain segmentation: RV longitudinal strain tracing in an ARVD patient.

(Click to enlarge) Strain segmentation: LV longitudinal strain tracing in a cardiomyopathy patient.

Right ventricle basal longitudinal strain was the best parameter for an ARVD diagnosis. A cutpoint of -27 was 82 percent sensitive and 83 percent specific for differentiating patients with ARVD from normal patients and from those with structural or electrical heart disease. (The at-risk group was excluded.)

Right ventricle global longitudinal strain was significantly worse in ARVD patients than in all the other groups. The at-risk group showed strain values between ARVD and normal patients. Left ventricle strain was worst in the structural heart disease group. Longitudinal strains showed stronger differences between groups than circumferential strains, for both ventricles.

Question of the Day:

The NRC dose limit for radiation workers is 50 mSv/yr. How much radiation do flight crews and astronauts get?

Tip of the day:

Typically, mammography units have an HVL of 1cm. This means that a woman with a 6cm thick compressed breast needs at least four times as much radiation as a woman with a 4cm thick compressed breast.

The RSNA 2016 Daily Bulletin is owned and published by the Radiological Society of North America, Inc., 820 Jorie Blvd., Oak Brook, IL 60523.