Thursday, September 15, 2005

Another important cause of dilated cardiomyopathy

On July 27 I discussed familial dilated cardiomyopathy (DCM). There is another under-appreciated form of DCM that must not be missed because it can be completely reversible. I’ll start with a case. This is not a real patient, but a composite of some memorable ones I’ve seen.

A 66 yo male presents with dyspnea and leg edema, progressive over three weeks. He had no prior history of heart disease, diabetes or hypertension and had never consumed alcohol. Physical exam revealed bilateral lung crackles, lower extremity edema, ascites, neck vein distension and an S3 gallop. The electrocardiogram revealed rapid atrial fibrillation. The patient was not aware of his irregular cardiac rhythm.

He was admitted and underwent diuresis, rate control and anticoagulation with subsequent clinical improvement. An echocardiogram showed global hypokinesis, an ejection fraction of 15%, and no significant valvular abnormalities. The patient was discharged on digoxin, furosemide, warfarin and potassium supplement. (This was before the era of ACE inhibitors and beta blockers!).

After a few weeks of anticoagulation he returned for cardioversion followed by cardiac catheterization, which showed an ejection fraction of 20% and no significant coronary artery disease. He was diagnosed as “idiopathic dilated cardiomyopathy, possibly due to viral myocarditis.”

During long term follow up he maintained sinus rhythm and clinical improvement, and was able to have his diuretic discontinued. At one year all manifestations of his heart failure seemed to have disappeared and a repeat echo was totally normal, with an ejection fraction of 65%. What’s going on? What is the most likely etiology of his cardiomyopathy?

Answer: chronic tachycardia-induced cardiomyopathy.

Here’s a review of the topic from the American Journal of Medicine (only the abstract linked here is available for free; the full text is well worth the read if you can obtain it). This phenomenon was occasionally reported for decades but remained largely under the radar screen until publication of series like this one from the Mayo Clinic in 1992. (American Journal of Cardiology). These patients, some of whom were on the transplant list, were thought to have atrial fibrillation secondary to idiopathic DCM. The interesting finding in the series was that after rate or rhythm control the patients exhibited striking reversibility. Instead of atrial fibrillation secondary to DCM, the reverse appeared to be true. These patients likely started out with nothing more than “lone” atrial fibrillation. Is there anything unique about certain atrial fibrillation patients that predisposes them to this complication? Perhaps it’s that they lack tachycardia awareness, thus allowing them to maintain the arrhythmia for long periods without seeking medical attention. (That seemed to be a common thread in the Mayo series).

As explained in the American Journal of Medicine review, animal models of this condition produced by prolonged rapid pacing have demonstrated evidence of chronic myocardial energy depletion and numerous ultrastructural changes, all reversible after cessation of pacing.

What are the take home points?
1) When your new case of “idiopathic” DCM happens to have atrial fibrillation don’t be hasty and write it off as irreversible.
2) Chronic tachycardia can be the sole etiology of DCM (which may have originated as merely lone atrial fibrillation in a patient lacking tachycardia awareness) or a contributing etiology (in which case aggressive rate control will improve the patient’s heart failure).

1 comment:

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