Relationship of auscultatory fourth heart sound to the quantitated left atrial filling fraction

The fourth heart sound (S4) has been associated with vigorous atrial contraction. However, the presence of S4 has not been previously correlated with quantitated left atrial filling fraction. In this study, the presence of an auscultatory S4 was compared with the Doppler echocardiographically quantitated left atrial filling fraction in 41 consecutive patients in whom S4 was judged to be present or absent according to the consensus of cardiologists. Left atrial filling fraction in patients with S4 was 49% and was significantly greater than 33% found in patients without S4 (p<0.005). Using atrial filling fraction of 35% as a dividing line, S4 had a sensitivity of 84% and a specificity of 75% for determining left atrial filling fraction ≥ or <35%. Furthermore, of 25 patients with S4, 21 (84%) had atrial filling fraction ≥35%, and of 16 patients without S4, 12 (75%) had atrial filling fraction <35%. Thus, the presence or the absence of S4 is quantitatively related to the left atrial filling fraction and appears to predict atrial filling fraction ≥ or <35% reasonably well.