FRAILTY PREDICTS MORTALITY AND BASELINE CARDIAC OUTPUT IN THE ISOLATED RAT HEART

Abstract

Elderly patients represent the fastest growing population presenting for cardiac surgery. While advanced age is associated with adverse postoperative outcomes, the wide variation in the health status of elderly patients suggests that chronological age (CA) does not necessarily reflect physiological age (PA). Frailty, a geriatric syndrome associated with impaired resiliency to acute stress, is an indicator of PA that predicts negative health outcomes following cardiac surgery. To better understand the impact of CA and frailty on hearts undergoing surgical procedures, there is a need to develop an animal model of frailty in which ischemia-reperfusion injury following cardioplegic arrest can be studied. Our objective was to develop a frailty index (FI) for rats, and assess the impact of age and frailty on cardiac function and recovery from cardioplegic arrest. We followed male F344 rats (n=36) from middle age (13 months) into old age (21 months). Data on survival and 45 variables in health systems known to change with age were serially collected to develop a 30-item FI (table 1). Mean FI scores increased with age from 0.07±0.05 at 13 months to 0.15±0.09 at 17 months and 0.25±0.10 at 21 months (p<0.05). Overall survival was 50%. A high FI score (>0.250) was associated with an increase in mortality (p<0.05) (figure 1). In the isolated working heart, we compared functional recovery following delivery of Del Nido cardioplegia. Young adult rats (9 months, n=7) served as a control. Baseline CO was similar between young adult and aged rats (11.2±0.5 vs. 9.6±0.5 ml*min-1*cm tibia length-1). Percent recovery following cardioplegic arrest did not differ by age (83 vs. 84%). In contrast, frail rats (FI score >0.250, n=5) had a reduced baseline CO relative to less frail rats (FI score <0.250, n=18) (8.0±0.6 vs. 10.7±0.4 ml*min-1*cm tibia length-1, p<0.05). Recovery of CO was similar between groups (91 vs. 82%). Eighty percent of frail hearts exhibited tachyarrhythmia in baseline working heart, while only 11% of rats in the less frail group presented with arrhythmia (p<0.05). We created a 30-item FI that predicts mortality in F344 rats. Frail hearts had a reduced CO and were more likely to be arrhythmic at baseline. Further study in a larger group of frail animals is required to elucidate the impact of frailty on functional recovery from cardioplegic arrest.View Large Image Figure ViewerDownload (PPT)