The clinical significance of the fourth heart sound in aortic stenosis

It has previously been proposed that the presence of a fourth heart sound in an adult with discrete aortic stenosis predicts a peak systolic gradient of 75 mm Hg or more. A number of exceptions led us to reinvestigate this concept. Accordingly, 124 patients were studied in order to examine the significance of the fourth heart sound in the clinical assessment of severity in discrete obstruction to left ventricular outflow. Since both age and aortic stenosis are independent variables in the production of the fourth heart sound, the data were reviewed in this light. The results indicate that: (1) over age 40 years, the fourth heart sound is not a reliable index of severity in discrete aortic stenosis; (2) under age 40 years, a fourth heart sound is good evidence of a peak systolic gradient of 75 mm Hg or more; (3) absence of a fourth heart sound in any adult subject suggests that the peak gradient is less than 75 mm Hg and probably less than 60 mm Hg, provided that factors hindering detection of a fourth heart sound (such as very short P-R interval, emphysema or obesity) are taken into account. The essence of the problem can be concisely stated as follows: In severe aortic stenosis a fourth heart sound is almost always present, but the presence of a fourth heart sound in adults with aortic stenosis implies severity of disease only in subjects under 40 years of age.