Can anaerobic threshold be used as an end-point for therapeutic trials in heart failure?: Lessons from a multicentre randomized placebo-controlled trial

‘Anaerobic threshold’ (AT), proposed as a non-invasiveindex of exercise tolerance, independent of patient motivation,is considered more reliable than exercise duration in assessingthe effect of drug therapy in chronic heart failure (CHF). However,inter-observer variation in patients may be more difficult thanin normal subjects. In a multicentre study, 85 patients from10 centres performed a total of 331 bicycle maximal tests (rampprotocols, 10 watts. min^–1) with respiratory gas analysisby different systems. A central committee reviewed all the tests.Percentages of AT determination ranged from 34% to 71% dependingon the method used. Apart from the respiratory exchange ratio(RER=1) method, which yielded the lowest rate of determination.and the crossing point (when RER=1), which yielded the highestrate, 71%, other methods of determination, such as carbon dioxide(42%), minute ventilation (52%) or ventilatory equivalents plottedvs time (57%), did not dtffer in the rate of AT determination. Thus, even among trained physicians, AT determination was notreliable. The crossing point may nevertheless be a valuableindex from a pragmatic standpoint, although it occurs afterthe actual AT Peak oxygen uptake should remain the main end-pointin assessment of exercise capacity.