You will be given a definition of a task first, then an example. Follow the example to solve a new instance of the task.
Given an abstract, generate a keyword (a noun phrase) that best describes the focus or contribution of the paper. Such keywords can be directly from the given abstract or outside it.

Abstract: Some patients converted from ventricular fibrillation to organized rhythms by defibrillation - trained ambulance technicians(EMT - Ds) will refibrillate before hospital arrival.The authors analyzed 271 cases of ventricular fibrillation managed by EMT - Ds working without paramedic back - up.Of 111 patients initially converted to organized rhythms, 19(17 % ) refibrillated, 11(58 % ) of whom were reconverted to perfusing rhythms, including nine of 11(82 % ) who had spontaneous pulses prior to refibrillation.Among patients initially converted to organized rhythms, hospital admission rates were lower for patients who refibrillated than for patients who did not(53 % versus 76 % , P = NS), although discharge rates were virtually identical(37 % and 35 % , respectively).Scene - to - hospital transport times were not predictively associated with either the frequency of refibrillation or patient outcome.Defibrillation - trained EMTs can effectively manage refibrillation with additional shocks and are not at a significant disadvantage when paramedic back - up is not available.
Solution: Ventricular Fibrillation
Why? This term is directly present in the abstract and it is one of the main topic in it. So can be chosen as the medical subject heading.

New input: Abstract: We have examined the effects of nonsteroidal antiestrogens (AEs) and estradiol (E) on dopamine (DA) levels and turnover rates in the medial basal hypothalamus (MBH) and on serum and pituitary PRL to gain insight into DA-PRL-E/AE interrelationships. In 21-day-old female rats, E was found to increase MBH DA levels and turnover and serum PRL concentrations in a time- and concentration-dependent manner. Changes were observed by 1 day, and after 3 days of E treatment (1 microgram/day), MBH DA levels increased 2-fold (to 1300 pg/mg tissue), and DA turnover rates increased 5-fold (to 1170 pg/mg tissue . h). The AEs tamoxifen, monohydroxytamoxifen, CI628, and LY117018 (50 micrograms/day for 3 days) weakly stimulated uterine weight gain and significantly suppressed the uterotropic action of E. The AEs LY117018, monohydroxytamoxifen, CI628, and tamoxifen competed with E for binding to the MBH estrogen receptor and displayed relative binding affinities of 190%, 185%, 6.7%, and 1.4%, with E set at 100%; these affinities are similar to those found for uterine estrogen receptors. The AEs increased DA turnover rates only 2-fold, and they antagonized the E-induced 5-fold increase in DA turnover rates very successfully. In animals treated with bromocriptine, E and AE failed to increase the low serum PRL levels, yet they evoked significant (approximately 2-fold) increases in DA turnover rates and nearly 2-fold increases in MBH DA content. Hence, a part of the actions of E and AE on MBH DA appears to be exerted independently of changes in circulating PRL and may occur by direct action of these compounds on the estrogen receptor system present in the MBH. In addition, these studies reveal that AEs behave as partial estrogen agonists/antagonists in terms of their effects on MBH DA turnover.
Solution:
Age Factors