Given a passage with a context and an answer, 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]: Context: Transcatheter aortic valve implantation (TAVI) without predilatation has fewer procedural steps and thereby potentially fewer complications. This has been demonstrated for the antegrade transapical access; however, whether TAVI can be safely performed without predilatation using the retrograde transfemoral route is unknown.', 'We postulated that TAVI is feasible with a balloon-expandable device without predilatation using the retrograde transfemoral route.', 'Twenty-six consecutive patients with stenosis of the native aortic valve (AV) undergoing transfemoral TAVI with the Edwards SAPIEN XT prosthesis without predilatation were enrolled in this retrospective study and compared with 30 patients treated previously with predilatation.', 'The procedure was successfully performed in all 26 patients, irrespective of the AV area and the extent of AV calcification. At baseline mean AV area, mean AV gradient, and median left ventricular ejection fraction were 0.7 ± 0.2 cm(2) , 36.0 ± 17.3 mm Hg, and 55.0% (interquartile range [IQR], 35.0-60.0], respectively; prior to discharge these values were 1.7 ± 0.3 (P < 0.001), 9.8 ± 6.1 mm Hg (P < 0.001), and 57.5% (IQR, 38.7-60.0) (P = not significant). Postdilatation was required in 3 patients due to aortic regurgitation > 2°; this was reduced by the procedure to < 2° in all cases. Radiation dose and amount of contrast dye were significantly reduced in comparison with the predilatation group. No periprocedural neurological adverse events occurred. Mortality at 30 days was 0%.
Answer: TAVI without predilatation using the transfemoral Edwards SAPIEN XT valve is feasible and safe. Larger studies are required to further evaluate this approach.
[EX A]: Is transfemoral aortic valve implantation of Edwards SAPIEN XT without predilatation feasible?

[EX Q]: Context: Histamine-related drugs are commonly used in the treatment of vertigo and related vestibular disorders. The site of action of these drugs however has not been elucidated yet. Recent works on amphibians showed that histamine H3 receptor antagonists, e.g. betahistine, inhibit the afferent discharge recorded from the vestibular nerve. To assess the expression of H3 histamine receptors in vestibular neurons, we performed mRNA RT-PCR and immunofluorescence experiments in mouse Scarpa's ganglia.", 'RT-PCR analysis showed the presence of H3 receptor mRNA in mouse ganglia tissue. H3 protein expression was found in vestibular neurons characterized by large and roundish soma, which labeled for calretinin and calbindin.
Answer: The present results are consistent with calyx and dimorphic, but not bouton, afferent vestibular neurons expressing H3 receptors. This study provides a molecular substrate for the effects of histamine-related antivertigo drugs acting on (or binding to) H3 receptors, and suggest a potential target for the treatment of vestibular disorders of peripheral origin.
[EX A]: Do calyx and dimorphic neurons of mouse Scarpa 's ganglion express histamine H3 receptors?

[EX Q]: Context: Pacemaker lead implantation can cause thrombosis, which can be associated with serious local morbidity and complicated by pulmonary embolism. Few reliable estimates of the incidence of thrombosis have been reported. The contribution of established risk factors to venous thrombosis in patients with implanted pacemaker leads is unknown.', 'One hundred forty-five consecutive patients n = 145) underwent routine clinical and Doppler ultrasound evaluation for thrombosis before and 3, 6, and 12 months after lead implantation. Established risk factors for venous thrombosis were assessed in detail for all patients. Clinical outcome, including clinically manifest thrombosis, pulmonary embolism, associated pacemaker lead infection, complicated reinterventions, and death, was evaluated. Thrombosis was observed in 34 (23%) of 145 patients. Thrombosis did not cause any signs or symptoms in 31 patients but resulted in overt clinical symptoms in 3 patients. The absence of anticoagulant therapy, use of hormone therapy, and a personal history of venous thrombosis were associated with an increased risk of thrombosis. The risk of thrombosis increased in the presence of multiple pacemaker leads compared to a single lead.
Answer: Established risk factors for venous thrombosis and the presence of multiple pacemaker leads contribute substantially to the occurrence of thrombosis associated with permanent pacemaker leads. Risk factor assessment prior to implantation may be useful for identifying patients at risk for thrombotic complications. Preventive management in these patients is warranted.
[EX A]:
Does incidence and risk factors of early venous thrombosis associated with permanent pacemaker lead?