Given a passage, construct a question on the basis of the information present in the passage. Construct the question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) it answer uses text phrases from the passage. Avoid creating questions that (i) can't be answered correctly without actually understanding the passage and (ii) uses the same words or phrases given in the passage.

[EX Q]: Class III antiarrhythmic agents exhibit reverse rate-dependent lengthening of the action potential duration (APD). In spite of the several theories developed so far to explain this reverse rate dependency (RRD), its mechanism has not yet been clarified. The aim of the present work was to further elucidate the mechanisms responsible for reverse rate-dependent drug effects.', 'Action potentials were recorded from multicellular canine ventricular preparations and isolated cardiomyocytes, at cycle lengths (CLs) varying from 0.3 to 5 s, using conventional sharp microelectrodes. APD was either modified by applying inward and outward current pulses, or by superfusion of agents known to lengthen and shorten APD. Net membrane current (I(m)) was calculated from action potential waveforms. The hypothesis that RRD may be implicit in the relationship between I(m) and APD was tested by numerical modelling. Both drug-induced lengthening (by veratrine, BAY-K 8644, dofetilide, and BaCl(2)) and shortening (by lidocaine and nicorandil) of action potentials displayed RRD, i.e. changes in APD were greater at longer than at shorter CL. A similar dependency of effect on CL was found when repolarization was modified by injection of inward or outward current pulses. I(m) measured at various points during repolarization was inversely proportional to APD and to CL. Model simulations showed that RRD is expected as a consequence of the non-linearity of the relationship between I(m) and APD.
[EX A]: Is reverse rate dependency an intrinsic property of canine cardiac preparations?

[EX Q]: Extracorporeal membrane oxygenation (ECMO) support is often required in the management of perioperative congenital heart surgery (CHS) patients. However, 24-hour in-hospital congenital cardiac surgical coverage (24-CCSC) is not available at all institutions. The purpose of this study is to evaluate the effect of 24-CCSC on perioperative ECMO outcomes in CHS patients.', "An institutional review board approved, retrospective review of 128 perioperative CHS ECMO patients at a single, quaternary care children's hospital between January 2003 and December 2012 was performed. Primary endpoints evaluated were mortality in children supported with ECMO after undergoing cardiac surgery and ECMO-related morbidity after initiation of 24-CCSC with advanced congenital cardiac surgical fellows. Patients were divided into 2 groups based on whether 24-CCSC was absent (cohort 1: January 2003 to July 2007) or present (cohort 2: August 2007 to December 2012) at the time of ECMO management.", 'The surgical procedures performed were similar in both cohorts based on STAT Mortality Categories (5 Society of Thoracic Surgeons-European Association for Cardio-Thoracic Surgery Congenital Heart Surgery Mortality Categories). The overall mortality rate in children supported with ECMO after undergoing cardiac surgery was 53%. This mortality was significantly reduced from 68% to 43% (p\xa0= 0.007) with\xa024-CCSC. Multivariate logistic regression analysis revealed that 24-CCSC (p\xa0= 0.009) and lower STAT Mortality Category (p\xa0= 0.042) were independent predictors of operative survival. Cardiac arrhythmias (36% to 16%; p\xa0= 0.012) and pulmonary complications (32% to 8%; p < 0.001) were significantly reduced with 24-CCSC.
[EX A]: Does twenty-four hour in-hospital congenital cardiac surgical coverage improve perioperative ECMO support outcomes?

[EX Q]: Syndromic forms of osteosarcoma (OS) account for less than 10% of all recorded cases of this malignancy. An individual OS predisposition is also possible by the inheritance of low penetrance alleles of tumor susceptibility genes, usually without evidence of a syndromic condition. Genetic variants involved in such a non-syndromic form of tumor predisposition are difficult to identify, given the low incidence of osteosarcoma cases and the genetic heterogeneity of patients. We recently mapped a major OS susceptibility QTL to mouse chromosome 14 by comparing alpha-radiation induced osteosarcoma in mouse strains which differ in their tumor susceptibility.', 'Tumor-specific allelic losses in murine osteosacoma were mapped along chromosome 14 using microsatellite markers and SNP allelotyping. Candidate gene search in the mapped interval was refined using PosMed data mining and mRNA expression analysis in normal osteoblasts. A strain-specific promoter variant in Rb1 was tested for its influence on mRNA expression using reporter assay.', 'A common Rb1 allele derived from the BALB/cHeNhg strain was identified as the major determinant of radiation-induced OS risk at this locus. Increased OS-risk is linked with a hexanucleotide deletion in the promoter region which is predicted to change WT1 and SP1 transcription factor-binding sites. Both in-vitro reporter and in-vivo expression assays confirmed an approx. 1.5 fold reduced gene expression by this promoter variant. Concordantly, the 50% reduction in Rb1 expression in mice bearing a conditional hemizygous Rb1 deletion causes a significant rise of OS incidence following alpha-irradiation.
[EX A]:
Does a Rb1 promoter variant with reduced activity contribute to osteosarcoma susceptibility in irradiated mice?