Purpose:
To measure right ventricular (RV) trabecular complexity by its fractal dimension
(FD) in healthy subjects and patients with pulmonary hypertension (PH) and assess its
relationship to hemodynamic and functional parameters, and future cardiovascular events.
Materials and methods:
This retrospective study used data acquired from May 2004 to
October 2013 for 256 patients with newly-diagnosed PH that underwent cardiac magnetic
resonance (CMR) imaging, right heart catheterization and six-minute walk distance testing
with a median follow-up of 4.0 years. 256 healthy controls underwent CMR only.
Biventricular FD, volumes and function were assessed on short-axis cine images.
Reproducibility was assessed by intraclass correlation coefficient, correlation between
variables was assessed by Pearson’s correlation test, and mortality prediction compared by
univariable and multivariable Cox regression analysis.
Results:
RV-FD reproducibility had an intraclass correlation coefficient of 0.97 (95%
confidence interval [CI]: 0.96, 0.98).
RV-FD was higher in PH patients than healthy subjects
(median 1.310, inter-quartile range [IQR] 1.281-1.341 vs 1.264, 1.242-1.295,
P
<.001) with
the greatest difference near the apex. RV-FD was associated with pulmonary vascular
resistance (r=0.30,
P
<.001). In univariable Cox regression analysis, RV-FD was a significant
predictor of death (hazards ratio [HR]: 1.256, CI: 1.011, 1.560,
P
=.04), but in a multivariable
analysis did not predict survival independently of conventional parameters of RV remodeling
(HR: 1.179, CI: 0.871, 1.596,
P
=0.29). Conclusion:
Fractal analysis of RV trabecular complexity is a highly reproducible measure
of remodeling in PH associated with afterload, although the gain in survival prediction over
traditional markers is not significant.