Background The equilibrium radionuclide angiogram (ERNA) is an imaging method that can be used to assess left ventricular (LV) function and synchrony. Each pixel of an ERNA is defined by its phase (ø) and amplitude (Amp), which together define its vector; the Amp gives the vector's length. The vector sum of all Amps, based on the angular distribution of ø, divided by the scalar sum of the length of all the vectors defines a new parameter, synchrony (S). The degree of randomness or disorder in the LV based on the Shannon information measure normalized for the number of ø in the LV region defines another new parameter, entropy (E). With complete synchrony, S = 1 and E = 0; with complete dyssynchrony, S = 0 and E = 1. We evaluated S and E in patients requiring cardiac resynchronization therapy (CRT) to determine if these measures can be correlated with a clinical benefit from CRT.
Methods We studied 14 patients (9 males, mean age 66 ± 15 years) with advanced congestive heart failure, LV ejection fraction (EF) ≤ 35% and QRS ≥ 120 ms. ERNA was performed before and within 10 weeks after CRT. Assessment of clinical status was made based on NYHA classification assessed before and within 10 weeks of CRT. Patients were graded 2 (n = 5), 1 (n = 5) or 0 (n = 4) if they improved 2, 1, or 0 NYHA classes, respectively. This was then correlated to changes in LVEF, SD ø, S, and E after CRT using a Pearson correlation.
Results The patients classified 2 showed large improvements in S and E, less in SD of ø, and least in LVEF. S and E were best correlated with outcome and were strongest when combined (multiple R = .87). One patient classified 2 had improved S and E but not LVEF or SD ø. Most patients without clinical improvement, nonetheless, had an improved LVEF. Changes in LVEF or SD of ø could not differentiate among clinical groups.
Conclusions S and E seem to measure different functional characteristics than LVEF. They show promise to be the best and most reproducibly correlated with functional status after CRT.
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