***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
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    Input: Background Maximal hyperemia is the critical prerequisite for fractional flow reserve ( FFR ) assessment . Despite intravenous ( IV ) adenosine currently being the recommended approach , intracoronary ( IC ) administration of adenosine constitutes a valuable alternative in everyday practice . However , it is surprisingly unclear which IC strategy allows the achievement of FFR values that are comparable to IV adenosine . Objectives This study sought to compare increasing doses of IC adenosine versus IV adenosine for FFR . Methods 30 intermediate coronary stenoses undergoing FFR measurement were prospect ively and consecutively enrolled . Hyperemia was sequentially induced by bolus of IC adenosine ( ADN ; 150 μg ) followed by IV adenosine ( IVADN ) infusion over 3 minutes at dose of ( 140 μg/kg/min ) . FFR values , symptoms , and development of atrioventricular block were recorded . Results 150 μg doses of IC adenosine were well tolerated and associated with fewer symptoms  than IV adenosine . Intracoronary adenosine doses induced a significant decrease of FFR compared with baseline levels ( P < 0.01 ) . Among the 6 patients with FFR values less than 0.80 identified by IVADN , 4 were correctly identified also by 150 μg bolus IC adenosine . Larger r and omized studies with cross-over design are necessary to verify the results . Conclusions This small pilot study suggests that IC adenosine might be an alternative to IV adenosine . Larger r and omized studies with a cross-over design are necessary Adenosine is a potent vasodilator used extensively to study the coronary circulation of animals . Its use in humans , however , has been hampered by lack of knowledge about its effects on the human coronary circulation and by concern about its safety . We investigated in humans the effects of adenosine , administered by intracoronary bolus ( 2 - 16 micrograms ) , intracoronary infusion ( 10 - 240 micrograms/min ) , or intravenous infusion ( 35 - 140 micrograms/kg/min ) on coronary and systemic hemodynamics and the electrocardiogram . Coronary blood flow velocity ( CBFV ) was measured with a 3F coronary Doppler catheter . The maximal CBFV was determined with intracoronary papaverine ( 4.5 + /- 0.2.resting CBFV ) . In normal left coronary arteries ( n = 20 ) , 16-micrograms boluses of adenosine caused coronary hyperemia similar to that caused by papaverine ( 4.6 + /- 0.7.resting CBFV ) . In the right coronary artery ( n = 5 ) , 12-micrograms boluses caused maximal hyperemia ( 4.4 + /- 1.0.resting CBFV ) . Intracoronary boluses caused a small , brief decrease in arterial pressure ( similar to that caused by papaverine ) and no changes in heart rate or in the electrocardiogram . The duration of hyperemia was much shorter after adenosine than after papaverine administration . Intracoronary infusions of 80 micrograms/min or more into the left coronary artery ( n = 6 ) also caused maximal hyperemia ( 4.4 + /- 0.1.resting CBFV ) , and doses up to 240 micrograms/min caused a minimal decrease in arterial pressure ( -6 + /- 2 mm Hg ) and no significant change in heart rate or in electrocardiographic variables . Intravenous infusions in normal patients ( n = 25 ) at 140 micrograms/kg/min caused coronary vasodilation similar to that caused by papaverine in 84 % of patients ( 4.4 + /- 0.9.resting CBFV ) . At submaximal infusion rates , however , CBFV often fluctuated widely . During the 140-micrograms/kg/min infusion , arterial pressure decreased 6 + /- 7 mm Hg , and heart rate increased 24 + /- 14 beats/min . One patient developed 1 cycle of 2:1 atrioventricular block , but otherwise , the electrocardiogram did not change . In eight patients with microvascular vasodilator dysfunction ( delta CBFV , less than 3.5 peak/resting velocity after a maximally vasodilating dose of intracoronary papaverine ) , the dose-response characteristics to intracoronary boluses and intravenous infusions of adenosine were similar to those found in normal patients . ( ABSTRACT TRUNCATED AT 400 WORDS Background — Magnetic resonance myocardial perfusion imaging ( MRMPI ) has a number of advantages over the other noninvasive tests used to detect reversible myocardial ischemia . The majority of previous studies have generally used quantitative coronary angiography as the gold st and ard to assess the accuracy of MRMPI ; however , only an approximate relationship exists between stenosis severity and functional significance . Pressure wire – derived fractional flow reserve ( FFR ) values < 0.75 correlate closely with objective evidence of reversible ischemia . Accordingly , we have compared MRMPI with FFR . Methods and Results — One hundred three patients referred for investigation of suspected angina underwent MRMPI with a 1.5-T scanner . The stress agent was intravenous adenosine ( 140 & mgr;g · kg−1 · min−1 ) , and the first-pass bolus contained 0.1 mmol/kg gadolinium . In the following week , coronary angiography with pressure wire studies was performed . FFR was recorded in all patent major epicardial coronary arteries , with a value < 0.75 denoting significant stenosis . MRMPI scans , analyzed by 2 blinded observers , identified perfusion defects in 121 of 300 coronary artery segments ( 40 % ) , of which 110 had an FFR < 0.75 . We also found that 168 of 179 normally perfused segments had an FFR ≥0.75 . The sensitivity and specificity of MRMPI for the detection of functionally significant coronary heart disease were 91 % and 94 % , respectively , with positive and negative predictive values of 91 % and 94 % . Conclusion — MRMPI can detect functionally significant coronary heart disease with excellent sensitivity , specificity , and positive and negative predictive values compared with FFR Background —PTCA of a coronary stenosis without documented ischemia at noninvasive stress testing is often performed , but its benefit is unproven . Coronary pressure-derived fractional flow reserve ( FFR ) is an invasive index of stenosis severity that is a reliable substitute for noninvasive stress testing . A value of 0.75 identifies stenoses with hemodynamic significance . Methods and Results —In 325 patients for whom PTCA was planned and who did not have documented ischemia , FFR of the stenosis was measured . If FFR was > 0.75 , patients were r and omly assigned to deferral ( deferral group ; n=91 ) or performance ( performance group ; n=90 ) of PTCA . If FFR was < 0.75 , PTCA was performed as planned ( reference group ; n=144 ) . Clinical follow-up was obtained at 1 , 3 , 6 , 12 , and 24 months . Event-free survival was similar between the deferral and performance groups ( 92 % versus 89 % at 12 months and 89 % versus 83 % at 24 months ) but was significantly lower in the reference group ( 80 % at 12 months and 78 % at 24 months ) . In addition , the percentage of patients free from angina was similar between the deferral and performance groups ( 49 % versus 50 % at 12 months and 70 % versus 51 % at 24 months ) but was significantly higher in the reference group ( 67 % at 12 and 80 % at 24 months ) . Conclusions —In patients with a coronary stenosis without evidence of ischemia , coronary pressure-derived FFR identifies those who will benefit from PTCA OBJECTIVES This study sought to compare increasing doses of intracoronary ( i.c . ) adenosine or i.c . sodium nitroprusside versus intravenous ( i.v . ) adenosine for fractional flow reserve ( FFR ) assessment . BACKGROUND Maximal hyperemia is the critical prerequisite for FFR assessment . Despite i.v . adenosine currently representing the recommended approach , i.c . administration of adenosine or other coronary vasodilators constitutes a valuable alternative in everyday practice . However , it is surprisingly unclear which i.c . strategy allows the achievement of FFR values comparable to i.v . adenosine . METHODS Fifty intermediate coronary stenoses ( n = 45 ) undergoing FFR measurement were prospect ively and consecutively enrolled . Hyperemia was sequentially induced by incremental boli of i.c . adenosine ( ADN ) ( 60 μg ADN60 , 300 μg ADN300 , 600 μg ADN600 ) , by i.c . sodium nitroprusside ( NTP ) ( 0.6 μg/kg bolus ) and by i.v . adenosine infusion ( IVADN ) ( 140 μg/kg/min ) . FFR values , symptoms , and development of atrioventricular block were recorded . RESULTS Incremental doses of i.c . adenosine and NTP were well tolerated and associated with fewer symptoms than IVADN . Intracoronary adenosine doses ( 0.881 ± 0.067 , 0.871 ± 0.068 , and 0.868 ± 0.070 with ADN60 , ADN300 , and ADN600 , respectively ) and NTP ( 0.892 ± 0.072 ) induced a significant decrease of FFR compared with baseline levels ( p < 0.001 ) . Notably , ADN600 only was associated with FFR values similar to IVADN ( 0.867 ± 0.072 , p = 0.28 ) . Among the 10 patients  with FFR values ≤0.80 with IVADN , 5 were correctly identified also by ADN60 , 6 by ADN300 , 7 by ADN600 , and 6 by NTP . CONCLUSIONS Intracoronary adenosine , at doses higher than currently suggested , allows obtaining FFR values similar to i.v . adenosine . Intravenous adenosine , which remains the gold st and ard , might thus be reserved for those lesions with equivocal FFR values after high ( up to 600 μg ) i.c . adenosine doses BACKGROUND Fractional flow reserve ( FFR ) is a measure of coronary stenosis severity that is based on pressure measurements obtained at maximal hyperemia . The most widely used pharmacologic stimulus for maximal coronary hyperemia is adenosine , administered either as a continuous intravenous ( IV ) infusion or intracoronary ( IC ) bolus . IV adenosine has more side effects and is more costly than IC adenosine but has a more stable and prolonged hyperemic effect . METHODS We compared the efficacy of IC and IV adenosine administration for the measurement of FFR in a multicenter trial . Fifty-two patients with 60 lesions underwent determination of FFR with both IV and IC adenosine . IV adenosine was administered as a continuous infusion at a rate of 140 microgram/kg per minute until a steady state hyperemia was achieved . IC adenosine boluses were administered at a dose of 15 to 20 microgram in the right and 18 to 24 microgram in the left coronary artery . FFR was calculated as the ratio of the distal coronary pressure ( from pressure guide wire ) to the aortic pressure ( guide catheter ) at maximal hyperemia . RESULTS A total of 26 left anterior descending , 23 right , 9 left circumflex , and 3 left main coronary arteries were evaluated . Mean percent stenosis for both groups was 55.8 % + /- 23.6 % ( range 0 % to 95 % ) , and mean FFR was 0.78 + /- 0.15 ( range 0.41 to 0.98 ) . There was a strong and linear correlation between FFR measurements with IV and IC adenosine ( R = 0.978 , y = 0 . 032 + 0.964x , P < .001 ) . The agreement between the 2 sets of measurements was also high , with a mean difference in FFR of -0.004 + /- 0.03 . However , a small r and om scatter in both directions of FFR measurements was noted with 5 lesions ( 8.3 % ) where FFR with IC adenosine was higher by 0.05 or more compared with IV infusions , suggesting a suboptimal hyperemic response in these patients . Changes in heart rate and blood pressure were significantly higher with IV adenosine . Two patients with IV , but none with IC adenosine , had severe side effects ( bronchospasm and severe nausea ) . CONCLUSION These results suggest that IC adenosine is equivalent to IV infusion for the determination of FFR in the majority of patients . However , in a small percentage of cases , coronary hyperemia was suboptimal with IC adenosine Background : We evaluated the prognosis of  deferred and revascularized coronary stenoses after fractional flow reserve ( FFR ) measurement to assess its revascularization threshold in clinical practice . Methods : The IRIS-FFR registry ( Interventional Cardiology 
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Meta-regression analysis did not show any significant interaction between the way of adenosine administration and main clinical features .
Intracoronary adenosine was associated with a higher incidence of atrioventricular blocks , whereas angina and /or systemic symptoms were more frequent with intravenous adenosine .
Conclusion Intracoronary adenosine might be as effective as intravenous adenosine to measure FFR , provided that adequate doses are used .