Papillary muscle contribution to ventricular ejection in normal and hypertrophic ventricles: a transesophageal echocardiographic study.

BACKGROUND: The interrelationship between left ventricular (LV) volume, stroke volume, and papillary muscle (PM) volume have not been studied. These volumes are relevant in understanding LV ejection mechanics in normal chambers and ascertaining whether differences exist between normal and hypertrophied LV chambers. METHODS AND
RESULTS: PM basal areas were measured in short-axis transesophageal echocardiographic views and lengths were measured in long-axis views. PM volume was estimated by the formula for volume of a cone: 1/3 x PM base area x PM length. The formula for LV volume was as follows: LV volume = 2/3 x LV area x LV length. Of the initial 82 subjects with normal LV function studied by TEE, data on 71 are presented in this report. Thirty-two patients had normal LV size and wall thickness, and 39 had LV hypertrophy (LVH). PM volume/LV volume % in end-diastole (ED) and end-systole (ES) in normal muscles was 3.1 +/- 1.0 and 9.6 +/- 4.9, respectively. In LVH, the respective values were 5.1 +/- 2.0 (P < 0.05) and 13.5 +/- 4.9 (P < 0.05). For those with severe LVH, the values were 7.1 +/- 2.5 (P < 0.001) and 15.9 +/- 4.1 (P < 0.001), respectively, for ED and ES. Similar trends were seen in the PM volume/stroke volume relationships in normal and hypertrophic ventricles.
CONCLUSIONS: PMs are larger and form a larger fraction of LV volume in LVH than in normal muscles. In patients with severe LVH, the contribution of PMs to ventricular ejection is more pronounced. PMs may, therefore, play a larger role in LV ejection in LVH than in normal ventricles (i.e., hypertrophied PM enhance the pump efficiency of LV ejection).