I have atrial fibrillation, now in remission, that caused enlargement of my left atrium. This is a common artefact after having arrhythmia for a period, say more than 30-60 days, and particularly if it is persistent and constitutes a heavy burden over all.

One would have to assume that the measurement is 'accurate', but a second opinion might be in order here, including a second diagnostic, maybe an MRI or ultrasound. When I say that the first measurement is accurate, that was as far as the individuals performing the ECG are concerned, and based on the instruments' specs. Another, different, test, with another cardiologist/radiologist might have them telling you something different. But it might also be the same, or they might even find that the enlargement is closer to 'moderate'. My last assessment placed me in that category, but I had been battling AF for five years when it became a heavier burden suddenly, and this went on for almost two years before they beat it into submission with a catheter ablation of my pulmonary vein ostia.

Would you like to know one way or another? I would want a second assessment.