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[Effect of systolic-diastolic displacement of the base of the heart on M-mode echocardiography].

M-mode-beam detects only structures moving in a direction parallel to them. The purpose of this study was to examine those movements of the heart which cannot be recorded by M-mode. We examined ten normals, ten patients with left ventricular volume overload, and ten patients with left ventricular pressure overload by M-mode and two-dimensional echocardiography (parasternal long axis view) simultaneously. We looked at the movement of particular structures during the cardiac cycle. A systolic movement of the base of the heart toward the apex is perpendicular to the M-mode beam and can therefore not be recorded. This shift is marked in patients with volume overload. End-diastolic diameter was measured too far apically in relation to the end-systolic diameter. We measured the amount of this dislocation of the end-diastolic diameter and corrected it. The new end-diastolic diameter was lower than the usual one. The difference was: -2.2 +/- 1.9 mm in normals (p less than 0.02); -6.9 +/- 2.6 mm in left ventricular volume overload (p less than 0.005); and -0.8 +/- 2.2 mm in pressure overload (n.s.). The overestimation of the fractional shortening was 12.4 +/- 13.3% in normals (p less than 0.02) and 21.4 +/- 7.4% in volume overload (p less than 0.005), expressed as a percentage. In conclusion, the static M-mode beam does not cross the same parts of the heart during systole and diastole because of movements of the base of the heart in relation to the beam. Misinterpretations of left ventricular function are the consequence. These depend on the extent of the movements and the configuration of the left ventricle.