Introduction Attenuated heart rate recovery (HRR) following exercise is an adverse prognostic marker in heart failure. Here we examine the relationship between HRR and response to cardiac resynchronisation therapy (CRT).
Methods 40 patients receiving biventricular pacemakers for conventional indications underwent functional assessments; cardiopulmonary exercise test (maximum oxygen consumption;Vo2max), 6-minute hall walk test (6MWT), and quality of life scoring, together with detailed echo analyses, before and at 3 months after implant. Heart rate recovery gradients were calculated at 30, 60, 90 and 120-s intervals following cessation of the baseline exercise test and compared with functional and echo markers of response to CRT. Functional response was defined as a 20% or greater improvement in two of the three functional assessments according to our “Cardiff functional index” and echo response defined as a 5% or greater increase in ejection fraction (EF).
Results 40 patients (aged 64 ± 9 years, 83% male) exercised for a total duration of 325 ± 144 s, achieving 74.3 ± 14.6% of their maximum predicted heart rate. Functional and echo assessments improved significantly at 3 months follow-up, and resulted in response rates of 60% and 72.5% according to our functional index and echo criteria, respectively. The heart rate recovery gradient at 30 s from the cessation of exercise (HRR30) was the strongest distinguisher of responder status (table 1), and correlated with an improvement in 6MWT and Vo2max (r = 0.41, p = 0.01 and r = 0.52, p = 0.002 respectively). In multiple regression analyses, which included preimplant QRS duration, EF, end-systolic volume (ESV), Vo2max, and 6MWT, HRR30 was the only significant predictor of functional and echo response to CRT (table 2). Receiver operator characteristic curve analysis (fig 1) demonstrates area under the curve for HRR30 in predicting functional and echo response to CRT of 0.76 and 0.80, respectively, and further confirms a HRR gradient cut-off of 2.75 at 30 s (equivalent to a 5% reduction in heart rate) to have the optimal sensitivity/specificity profile in both cases (see fig 2).
Conclusions Heart rate deceleration within the first 30 s after the cessation of exercise significantly predicts subsequent functional and echocardiographic responses to CRT. Application of this index in addition to established echo predictors of response may improve optimal patient selection and thus warrants application in larger numbers of patients.