AUDIO TRANSCRIPT: I just finished a short video on how not having flow measurements contributed to the mistaken diagnosis of ARVD in a patient who likely had a left to right shunt. Since ARVD is such a rare disease, I thought it might be helpful to show a case example. But, before I do, here is some background information.
Arrhythmogenic right ventricular dysplasia is also called arrhythmogenic right ventricular cardiomyopathy. That’s probably a better name since it is thought to be the result of a genetic defect rather than a developmental abnormality. It’s often inherited as autosomal dominant, but doesn’t have to be, and there is variable penetrance. It primarily affects the right ventricle but in the later stages of the disease it can involve the left ventricle as well. It causes heart failure, ventricular arrhythmias, and sudden cardiac death. It’s a rare disease, with an incidence of 1 in 5,000. It is found in males more often than in females. The reason why it’s important is that it’s often associated with sudden cardiac death. Recognizing the diagnosis is important because patients can get an implantable defibrillator, which could save their life.
Pathologically, ARVD is characterized by myocardial atrophy, fibrofatty replacement of the myocardium – which typically progresses from epicardium to endocardium – inflammation and fibrosis, thinning of the wall, chamber enlargement, and aneurysms. Here, you can see a photograph of an autopsy specimen showing how the fat extends from the epicardium toward the endocardium. Below is an MRI of the same specimen, which again shows the bright fat extending from the epicardium. You can’t get high resolution MR images like this in living people because of respiratory and cardiac motion. As a result it is often very difficult to tell whether bright signal on MRI represents epicardial fat adjacent to the right ventricle or fat in the RV wall. In fact, as I’ll talk about shortly, the presence of visible fat is not a recommended criterion for diagnosing right ventricular dysplasia. In my experience from reviewing outside studies, the mistaken identification of fat in the right ventricular wall has led to a lot of false positive diagnoses.
Patients with ARVD typically have palpitations and syncope. One of the main problems a cardiologist confronts when presented with a patient with palpitations and syncope is differentiating ARVD from other more common diseases such as right ventricular outflow tract tachycardia, which is not associated with sudden cardiac death, and is not associated with structural heart abnormalities.
So, how do we make the diagnosis of ARVD? Probably the best way is to look at the 2010 Revised Task Force Criteria. The diagnosis depends on a variety of abnormalities including ventricular dysfunction, tissue characterization, repolarization abnormalities, conduction abnormalities, arrhythmias, and family history. According to these criteria, the only role for MRI is assessing ventricular dysfunction.
According to the Task Force, a patient needs 2 Major Criteria, 1 Major and 2 Minor, or 4 Minor criteria to make the diagnosis.
So, what role does MRI play in making the diagnosis? As far as the Task Force is concerned, it’s only to assess right ventricular function and size. One needs to find right ventricular akinesia, dyskinesia, or right ventricular dyssynchrony – along with an increase in right ventricular volume or a decrease in ejection fraction. Whether it’s a major or minor criterion depends on how big the RV is and on how bad its ejection fraction is.
So, keeping that in mind, let’s look at a look at a case.
This is a 19 year old man who had nonsustained ventricular tachycardia. You can see from the stack of axial images that the right ventricle is enlarged, hypokinetic , and dyssynchronous.
You can see the same thing on these short and long axis images, which is why we don’t acquire axial images any more. You can see how nicely the software has automatically segmented the left and right ventricular contours. You can see the volume vs. time curves here. The RV trace shown in grey here is elevated compared to the LV trace because the RV is dilated. You can see that the right ventricle has a 31% ejection fraction, and the end diastolic volume index is 112 ml/m2. So, this would be a major criterion towards the diagnosis of ARVD. Interestingly enough, the LV function is down slightly also. The LV EF is 48%. You can see the LV and the RV stroke volumes are close to being equal to each other, which is what you’d expect.
We also acquired late gadolinium images to look for fibrosis. You can see the RV wall actually lights up. You can see in many of the images, there are regions of the wall that are bright white, and this is indicative of fibrosis. However, this observation is not part of the Task Force criteria.
I hope this talk has helped you to better make the diagnosis of ARVD in your practice.
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