• left atrium;
  • histology;
  • atrial fibrillation

Objective: The goal of this study was to determine the relationship between left atrial (LA) size and pathology in humans. Methods: We evaluated 14 patients (age 60 ± 14 years, range 25–77, 9 males) who had died at our hospital. Eight patients were in sinus rhythm, 3 had paroxysmal atrial fibrillation (PAF), and 3 were in established atrial fibrillation (AF). LA size was calculated at transthoracic echocardiography (TTE) prior to death. At autopsy, histology of the dissected LA was examined at the appendage (APP), transverse sinus (TS), oblique sinus (OS), crux, and oval fossa. The severity of hypertrophy (HTY) and fibrosis (FIB) was determined by histochemistry. Results: Mean LA weight was 37 ± 11 g. One patient with PAF had amyloid. LA size by TTE was associated with LA weight (R = 0.6, P = 0.029). Increased age was associated with less severe APP FIB (P = 0.04). Younger patients tended to have less severe APP HTY (P = 0.09), and TS FIB (P = 0.12). Severity of atrial HTY and FIB was similar in APP and TS (P = NS). There was no relationship between abnormal atrial histology with LA volume or cardiac rhythm. Five patients had LA dilatation (LA end systolic volume index >30 ml/m2). Of those patients with normal LA size, 6 (75%) had APP FIB, 8 (100%) had APP HTY, 7 (88%) had TS FIB, 8 (100%) had TS HTY, and 7 (88%) had OS HTY. Conclusions: Abnormal LA histology is common in patients who have normal LA size by TTE. Microscopic atrial disease is associated with aging, and may represent a precursor state for LA dilatation or AF.