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: Rupture of an abdominal aortic aneurysm is readily diagnosed when the triad of abdominal or back pain, shock and a pulsatile abdominal mass are present. Clinical diagnosis can be difficult, however, when patients present with chronic pain and an aneurysm which is not readily palpable. In these patients with confusing abdominal symptoms, CT scan provides a rapid, noninvasive diagnosis. The acute leaking AAA has been documented, but only rarely. This report identifies two patients who ruptured an aortic aneurysm several "months" prior to operation--a "contained chronic" rupture.
Solution:
Aged