Missed Diagnosis due to No Flow Measurements (5 min)

AUDIO TRANSCRIPT: The other day, I was asked to provide a second opinion on a cardiac MRI study. The patient was a 57 year old man who had an echocardiogram that showed unexplained right ventricular enlargement.

The physician who interpreted the MRI had concluded that the right ventricle was enlarged, and that the right ventricular inferior and free walls were hypokinetic. He suggested the diagnosis of arrhythmogenic right ventricular dysplasia and recommended a cardiac CT to look for fat in the RV wall. The CT didn’t show any fatty infiltration.

Because the patient had no arrhythmias, no ECG abnormalities, and no family history of sudden death, the cardiologist was skeptical of the diagnosis of ARVD and asked for a second opinion on the cardiac MRI. So let’s take a look at it.

Here are some images. On the 4 chamber view, you can easily see that the right ventricle and right atrium are enlarged. There’s a brief jet of TR in early systole. RV systolic function looks pretty good.

On the short axis images, you can see why the primary reader might have thought there was inferior hypokinesis of the right ventricle. It actually looks dyskinetic to me in this view. But, sometimes through-plane motion can cause a deceiving appearance. And, that’s the case here. When you look at the orthogonal view, you can see clearly the inferior wall is contracting well.

So, what’s going on here? Let’s look at the quantification. The RV EF is 45%. The primary reader got an RV EF of only 34%, probably due to bad segmentation. He probably had a problem at the base of the RV. The nice thing about the segmentation done here is that it’s fully automatic. And, a really useful feature is that it can automatically determine the base of the right ventricle from the 4 chamber view, where it’s often easier to determine than on the short axis views. The segmentation results show that the right ventricular end-diastolic volume index is 129 ml/m2. That’s severe enlargement. Yet, left ventricular size and function are normal.

To my knowledge, there are only 3 things that give you asymmetric RV enlargement:

  1. The RV function is diminished. That’s not the case here.
  2. There is a regurgitant valve lesion, either tricuspid or pulmonic regurgitation
  3. There is a left to right shunt.

We saw TR in the 4 chamber view. It didn’t look significant, but TR can be difficult to quantify just by looking at the jet. I don’t recommend trying to do it that way. The easiest way to quantify tricuspid regurgitation is to calculate the regurgitant volume by subtracting the main pulmonary artery flow from the RV stroke volume. Unfortunately, the site didn’t acquire any flow data.

Another possibility is that there’s a left-to-right shunt, like an atrial septal defect.  That could also give you right atrial and right ventricular enlargement with a normal RV ejection fraction. Patients with substantial left to right shunts also have enlargement of their central pulmonary arteries. We do have pictures of those. Here, you can see the central pulmonary arteries are enlarged.

It would be nice if we had flow measurements of the aorta and main pulmonary artery. We make them routinely in our practice. If the site had made those flow measurements, I suspect they would have found a left-to-right shunt and reached a different diagnosis.

So, please consider making it routine to measure flow in both the aorta and main pulmonary artery — in all of your patients. I recommend measuring each at least twice to assess the reproducibility of the measurement. It’s quick and easy to do. And, it can help steer you to the right diagnosis.

If you enjoyed this video, there are more at cardiacmri.com.

Thank you.

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