Misrepresentation of left ventricular contractile function by endocardial indexes: clinical implications after coarctation repair.

BACKGROUND

Endocardial function indexes overestimate myocardial fiber shortening, a geometric effect proportional to wall thickness. We hypothesized that elevated endocardial indexes of left ventricular contractile function after repair of isolated coarctation of the aorta could be related to this effect.

METHODS

Chamber dimensions and wall thickness were measured from 59 echocardiograms in 57 patients aged 1.2 to 32 years, 8.5 +/- 5.6 years after coarctation repair, and in 305 normal controls aged 1 to 35 years. Midwall and endocardial shortening indexes and end-systolic fiber stress were calculated. The stress-velocity index (SVI), a load-independent index of contractility, was derived from these variables. All values were expressed as z scores.

RESULTS

After coarctation repair, the midwall-derived SVI was elevated, but significantly less so than the endocardial-derived SVI (0.6 +/- 1.6 vs 1.3 +/- 2.6; P =.01). The endocardial-derived SVI correlated with the end-systolic thickness/dimension ratio (P <.0001), but the midwall-derived SVI did not. There was no linear relation between the midwall-derived SVI and the residual blood pressure gradient. The mean midwall-derived SVI was higher compared with the normal population in those with a minor residual blood pressure gradient (</=15 mm Hg) and in those with more significant obstruction (>15 mm Hg), but this achieved statistical significance only in the latter group (0.5 +/- 1.6, P =.08; and 0.8 +/- 1.7, P =.03, respectively).

CONCLUSIONS

Endocardial indexes of function and contractility overestimate fiber shortening after coarctation repair. Nevertheless, midwall shortening indexes demonstrate enhanced contractility, particularly in those with residual coarctation.