Effects of environmental stress following myocardial infarction on behavioral measures and heart failure progression: The influence of isolated and group housing conditions

Background.  Heart failure (HF) prognosis is negatively influenced by adverse environmental conditions associated with psychological distress and depression. The underlying mechanisms are not well understood because of insufficient experimental control in prior clinical and epidemiological studies. Using a validated animal model we examined whether distress-producing environmental manipulations (social isolation and crowding) increase HF progression following myocardial infarction (MI). Methods.  MI was induced using coronary artery ligation in 8-week old male Wistar rats (N = 52) and results were compared to sham surgery (N = 24). Housing conditions were randomly assigned at 5 days post MI or sham surgery (1/cage = isolation, 2/cage = standard reference condition, or 4/cage = crowding) and continued for 17 weeks until the end of observation. The open field test was used to test behavioral responses. Echocardiograms were obtained at weeks 8 and 16, and left ventricular (LV) weight at week 17. Results. Housing conditions increased behavioral markers of distress (p = 0.046) with the strongest effects for the isolated (1/cage) (p = 0.022). MI did not increase distress-related behaviors compared to sham. MI-surgery resulted in characteristic HF indices (left ventricular ejection fraction (LVEF) at week 16 = 46 ± 12% vs. 80 ± 7% in sham, p  0.10). Conclusions.  Adverse environmental conditions, particularly isolated housing, produce increases in some of the behavioral indicators of distress. No effects of housing were found on post-MI progression of HF. The distress–HF associations observed in humans may therefore reflect common underlying factors rather than an independent causal pathway. Stronger environmental challenges may be needed in future animal research examining distress as related HF progression. Keywords, Heart failure, Social stress, Cardiac function, Housing conditions, Myocardial infarctio