Atrial Fibrillation as a Cardiomyopathy Equivalent?

A 35-year-old male was referred by his PCP with a history of a single episode of atrial fibrillation (AF) with a ventricular rate in the 160-170 range lasting over 24 hours, which had been documented before DCCV in an outside ER. In retrospect, he had noted similar short-lived and self-terminating symptoms on a few occasions in the past but with no clear patterns of occurrence. He had no other cardiovascular or respiratory complaints. He was active with no limitations. There were no symptoms suggestive of dysthyroidism and he was systemically well.

Figure 1
Figure 1: Atrial Fibrillation as a Cardiomyopathy Equivalent?
He had no past medical history. He was on no medications and had no allergies.

He was an outdoor activities instructor. He did not smoke, use alcohol or drugs.

Family history was notable for his paternal grandfather who had died of a heart attack at the age of 39. The patient's father had been diagnosed with hypertension but family history was otherwise unremarkable.
A comprehensive physical exam revealed no abnormalities.

Initial labs including TSH were normal.

The 12-lead ECG obtained immediately after the DCCV revealed an ectopic atrial rhythm and some diffuse non-specific ST and T wave abnormalities (Figure 1), but a subsequent ECG was completely normal.

Echocardiogram was normal including LA dimensions.

An ETT had been performed at the outside ER prior to discharge. This was terminated at 12 minutes with a peak heart rate of 170/min, with no symptoms and no evidence of reversible ischemia or arrhythmia.

What other potential etiologies for the atrial fibrillation must be considered in this case?

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