Introduction 123 1 2 123 3 11 123 12 13 123 14 123 123 Materials and methods Study design 123 15 123 123 123 123 The primary efficacy objective of the original trial was to determine the prognostic significance of the late H/M ratio in relation to occurrence of major cardiac events (MCE), defined as either: 1) cardiac death due to all causes, including myocardial infarction (MI), progressive heart failure and sudden cardiac death (SCD); 2) cardiac transplant; 3) potentially fatal arrhythmic event, including resuscitated cardiac arrest or appropriate internal cardiac defibrillator (ICD) discharge. Results of that analysis have been published. For the purposes of this paper, H/M thresholds associated with low-, intermediate- and high-risk for MCEs were defined to provide the basis for the multivariate analysis described below. Image analysis 1 Fig. 1 123  Statistical analysis 123 R 2 F p Results 2 p Fig. 2 p p p  1 123 n Table 1 123   N Late H/M N N N Patient characteristics  Male/Female 237/53 39/12* 117/26* 81/15*  Age (years) 53 ± 11 (21–83) 55 ± 10‡ 54 ± 10‡ 49 ± 11  NYHA (II/III/IV) 165/116/9 11/34/6† 85/55/3† 69/27/0†  LVEF (%) 32 ± 14 (7–85) 23 ± 9† 31 ± 13‡ 39 ± 14*  Etiology of heart failure (isch/non-isch) 121/169 20/31‡ 70/73‡ 31/65‡ Scintigraphic parameters  Collimator type (LEGP/LEHR/ME) 50/216/24† 24/25/2† 24/104/15† 2/87/7†  Activity (MBq) 164 ± 53 (72–370) 145 ± 31† 173 ± 64 160 ± 41  Delay after injection (h) 4.3 ± 0.6 (1.9–6.9) 4.1 ± 0.5‡ 4.3 ± 0.5‡ 4.5 ± 0.6  Duration of acquisition (min) 9.6 ± 3.3 (1–15) 11.3 ± 4.3† 9.2 ± 3.4 9.4 ± 2.0* Data are presented as mean ± standard deviation (range). NYHA LVEF Isch Non-isch LEGP LEHR ME MBq h min p p p p p p 123 n 123 1 2 p Table 2 N Variables b b P  Constant 0.549 0.411   LVEF 0.015 0.02 <0.001  Collimator type 0.531 0.087 <0.001  Duration of acquisition 0.045 0.014 0.001  NYHA −0.121 0.055 0.028  Age −0.006 0.003 0.034 R 2 P 3 p 4 p 5 p Table 3 N Variables b b P  Constant 1.680 0.161   NYHA −0.055 0.027 0.049  Delay after injection −0.068 0.030 0.031 R 2 P Table 4 N Variables b b P  Constant 1.370 0.078   LVEF 0.004 0.001 0.001  Collimator type 0.086 0.030 0.005 R 2 P Table 5 N Variables b b P value  Constant 0.022 1.376   Duration of acquisition 0.119 0.057 0.040 R 2 P Discussion 123 3 11 123 123 3 12 16 18 19 20 13 123 Acquisition duration was one of the independent predictors of late H/M. The positive correlation suggests that a longer acquisition time is associated with a higher late H/M. However, it is more likely that this association reflects that a longer acquisition time results in a higher number of counts and the allied improvement of count statistics. In particular, in patients with reduced myocardial uptake (i.e. heart failure patients), the higher signal-to-noise ratio for a longer acquisition (≥10 min in the present study) plays a pivotal role in the accurate assessment of late H/M. In addition, delay after injection was in high-risk subjects (late H/M <1.4), an independent predictor of late H/M. The negative correlation suggests that a longer acquisition time is associated with a lower late H/M. However, in analogy to acquisition duration, it is more likely that this association reflects that a longer delay results in a lower number of counts and the allied deterioration of count statistics. In particular, in patients with reduced myocardial uptake (i.e. heart failure patients), the higher signal-to-noise ratio for a shorter delay after injection plays a pivotal role in the accurate assessment of late H/M. 123 123 21 123 14 21 22 123 123 123 15 23 123 24 34 123 35 36 123 3 11 23 37 38 39 40 123 123 15 123 The primary limitation of the present study has already been noted, namely, that the largest influence on the H/M is cardiac disease status rather than image acquisition parameters. Although collimation and acquisition duration were independent predictors of late H/M, their individual contributions to measurement variance were <10% each. Because of the retrospective nature of this multi-centre study, it was not possible to control for the effects of numerous variables that might have had undetected impact on late H/M. Studies using phantoms have already established the effect of collimator selection on H/M, and similar studies could be performed to examine the influence of count rate and total counts. Additional patient studies that included multiple acquisitions of different durations and times post-injection could establish the effect of these parameters on H/M with greater clarity. 123 123 123 123