Indirect Estimation of the First Ventilatory Threshold in Beta-Blocked Cardiac Patients: A Diagnostic Accuracy Study

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AimsCardiopulmonary exercise testing (CPET) is the gold standard for determining the first ventilatory threshold (VT1), a key marker for prescribing exercise-training intensity, but is not routinely available in cardiac rehabilitation.We evaluated the accuracy of commonly used indirect methods for estimating VT1 in beta-blocker (BB) treated cardiac patients. Methods and resultsTwenty-six BB treated patients with cardiovascular disease underwent maximal CPET.VT1 estimations derived from the original and modified Karvonen formulas, rating of perceived exertion (Borg scale, target 12-14), and the dyspnea threshold were compared with CPET derived VT1 and VT2.Agreement was assessed using Lin's concordance correlation coefficients and Bland-Altman analysis.The original Karvonen formula (ρ c = 0.90; 95%CI 0.81-0.95;bias+5 bpm) showed the best agreement with VT1.The dyspnea threshold showed moderate agreement (ρ c = 0.86; 95%CI 0.71-0.93;bias +7 bpm), whereas perceived exertion showed poor agreement with VT1 (ρ c = 0.73; 95%CI 0.53-0.85;bias +12 bpm).The modified Karvonen formula had the poorest estimation of VT1 (ρ c = 0.68; 95%CI 0.50-0.85;bias+16 bpm) but closely matched VT2 (ρ c = 0.94; 95%CI 0.87-0.97;bias+0.3bpm). ConclusionIn the absence of CPET, the original Karvonen formula and the dyspnea threshold could be preferred for guiding exercise intensity in BB treated patients, whereas the modified Karvonen formula consistently overestimates VT1 by approximating VT2, making it unsuitable for secure exercise-intensity prescription.

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