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Misrepresentation of left ventricular contractile function by endocardial indexes: clinical implications after
T L Gentles1, S P Sanders, S D Colan
1Department of Cardiology, Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA.
Insights
Endocardial function indexes overestimate left ventricular shortening after coarctation repair. Midwall shortening indexes reveal enhanced contractility, especially with residual obstruction.
Area of Science:
- Cardiology
- Pediatric Cardiology
- Cardiovascular Surgery
Background:
- Left ventricular (LV) function indexes can overestimate myocardial fiber shortening due to geometric effects related to wall thickness.
- This study investigates if elevated LV contractile function indexes post-coarctation repair are influenced by these geometric factors.
Purpose of the Study:
- To evaluate left ventricular (LV) contractile function after coarctation repair.
- To determine if endocardial indexes overestimate myocardial fiber shortening compared to midwall indexes.
- To assess the relationship between LV contractility and residual obstruction.
Main Methods:
- Echocardiograms from 57 patients (1.2-32 years) post-coarctation repair and 305 controls were analyzed.
- Chamber dimensions and wall thickness were measured to calculate midwall and endocardial shortening indexes.
- The stress-velocity index (SVI), a load-independent measure of contractility, was derived and expressed as z scores.
Main Results:
- Endocardial-derived SVI was significantly higher than midwall-derived SVI post-repair (P =.01).
- Endocardial SVI correlated with end-systolic thickness/dimension ratio, while midwall SVI did not.
- Midwall SVI was elevated in patients with residual gradients, significantly so in those with >15 mm Hg obstruction (P =.03).
Conclusions:
- Endocardial indexes overestimate LV fiber shortening and contractility after coarctation repair.
- Midwall shortening indexes provide a more accurate assessment of LV contractility.
- Enhanced midwall contractility is evident post-repair, particularly in patients with residual coarctation.
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), 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.