Results
We screened 252 and successfully recruited 57 patients, two of which were subsequently excluded (one patient because of a diagnosis of chronic kidney disease (stage IV) and another because of pulmonary hypertension). Fifty-five patients underwent the first CPET, 25 in the chronically beta-blocked group and 30 in the acutely beta-blocked group. Seven patients dropped out of the study between the first and the second CPET. Forty-eight patients underwent a second CPET at a median of 7 days (IQR 7–9 days) after the first CPET (20 in the 'chronic' and 28 in the 'acute' group) and completed the study (Fig. 1). Patients in the 'chronic' group were on the after beta-blocker medications: bisoprolol (15), atenolol (7) and propranolol (3). Table 1 shows patients' characteristics in the two groups. Supplementary Table S1 http://bja.oxfordjournals.org/content/114/6/878/suppl/DC1 shows the patients' baseline cardiovascular medications. Ischaemic heart disease and left ventricular failure were more prevalent in the chronically beta-blocked group, and lower haemoglobin values were also found.
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Figure 1.
CONSORT diagram; Cardio Pulmonary Exercise Test (CPET).
Table 2 shows a summary of the whole group CPET derived variables split according to whether the individual was prescribed ('on') or not prescribed ('off') beta-blockers before the test. Each group was subsequently divided according to whether the individual was normally prescribed a beta-blocker ('chronic') or not normally prescribed a beta-blocker ('acute'). Interobserver agreement between the two CPET reporters was very high (98%). Figure 2 illustrates changes in V̇O2 at
(A) and in V̇ O2 at peak (B) whilst being on beta-blocker medications. An overall significantly lower resting and exercising heart rate was observed on treatment, indicating that significant beta-blockade was achieved. No adverse CPET or drug related events were recorded during the whole of the study.
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Figure 2.
Pair plots showing changes in V̇O2 at
(a) and V̇ O2 at peak (b) measured while beta-blocked in the 48 subjects who completed the study. *Patients are ranked according to performance on beta blockers.
The results from the multivariable regression analyses and the effect of beta-blockade on the whole groups' CPET variables are shown in Table 3. After adjustment for confounding variables, we found that taking beta-blockers resulted in no difference in V̇O2 at
and V̇ O2 at peak. However, there was a significant decrease in V̇ E/V̇ CO2 at
and peak in patients taking beta-blockers in comparison to those not taking beta-blockers and a significant increase in workload at
, but not at peak. Finally, a significantly higher O 2 pulse at
and peak was found during CPET in those taking beta-blockers along with a significant decrease in heart rate at
and peak. The increase seen in O 2 pulse was primarily related to a change in heart rate rather than a change in absolute V̇ O2: at
, the decrease in heart rate was associated with a 12.4% increase in O 2 pulse compared with a 2.4% increase associated with a change in absolute V̇ O2 (similarly at peak: 8.1 vs 0.3% increase).
Table 3 also shows the effect of beta-blockade on CPET variables in patients usually prescribed ('chronic') vs those not usually prescribed ('acute') beta-blockers. After adjustment for confounding variables, a significantly lower V̇O2 at
and V̇ O2 at peak was found in patients in the 'chronic' beta-blockade group compared with those in the 'acute' beta-blockade group. We found no difference between the groups in the remaining CPET variables.