Cardiopulmonary Exercise Testing in Aortic Stenosis.


Dan Med J. 2017 May;64(5). pii: B5352.

Patients with moderate to severe aortic stenosis (AVA <1.3 cm2) who were judged,
by a referring cardiologist, as asymptomatic or equivocal symptomatic from the
aortic stenosis were included in the study. Patients with left ventricular
ejection fraction <50% were not included. Twenty-nine percent of the referred
patients were judged asymptomatic and 71% equivocal symptomatic from their valve
disease. The mean age was 72 years and 90% of the patients had an AVA-index <0.6
cm2/m2. By clinical evaluation in the outpatient clinic, 48% were judged as
having functional limitation corresponding to NYHA≥II. The study participants had
cardiopulmonary exercise testing (CPX) at inclusion, and, if relevant, pre- and
nine months post-aortic valve replacement (AVR). CPX was feasible in 130 of 131
study participants recruited across 19 months. The coefficient of variability by
test-retest was 5.4% and 4.6% for peak oxygen consumption (pVO2) and peak oxygen
pulse (pO2pulse= pVO2/peak heart rate), respectively. The stroke volume generally
increased with exercise, also in those with peak flow velocity across the aortic
valve (Vmax) >5 m/s, >4 m/s, and <4 m/s but with high valvuloarterial impedance
(Zva >5.5 mm Hg/(mL·m2 )). This was found both when assessed by inert gas
rebreathing and by the pO2pulse/hemoglobin index. Both resting and exercise
stroke volume were lower for the latter group, with Vmax <4 m/s but high
valvuloarterial impedance. A pVO2 <83% of the predicted, which corresponds to the
lower 95% percentile found in the healthy sedentary population, was predicted
independently by lower stroke volume during exercise, lower heart rate during
exercise, lower FEV1, and by higher ventilation/carbon dioxide exhaustion rate
(VE/VCO2), but not by the severity of the aortic stenosis as determined by
echocardiography. According to the CPX results, the patients were prospectively
grouped into 3 groups, as follows: 1) normal pVO2 (>83% of predicted) and
pO2pulse (>95% of predicted); 2) subnormal pVO2 or pO2pulse that according to CPX
could be explained by causes other than hemodynamic compromise; 3) subnormal pVO2
and pO2pulse. Groups 1 and 2 followed an initial conservative strategy, whereas
Group 3 was referred for angiogram and Heart Team evaluation for AVR. The
patients were followed for an average of 24 months and, in Groups 1 and 2, one
patient (0.9%) suffered cardiac death and seven were hospitalized with heart
failure (6.7%). The patient who died and another patient with heart failure had
both previously, during the study, declined AVR. For Groups 1 and 2, the rate of
the combined endpoint progression to cardiac death, hospitalization with heart
failure, or AVR was 37.5%, which seems lower than what was reported in the
literature by conventional assessment and strategy for younger asymptomatic
patients with comparable echocardiographic severity of aortic stenosis. The
endpoint progression to cardiac death, hospitalization with heart failure, or AVR
with improvement in pVO2 or in the Physical Component Score of the SF-36
health-related quality of life score was reached in 25.6% in Groups 1+2 and in
62.5% in Group 3 (p=0.003). A decreased pO2pulse, which expresses stroke volume
at peak exercise, predicted this endpoint. In 73 operated patients without left
ventricular dysfunction and no coronary stenosis, including 37 patients from the
above-mentioned study, a CPX 9 months post-AVR showed that the pVO2, on average,
was less than that predicted (mean 89% of the predicted ) and 35% of the patients
had a subnormal pVO2 (<83% of that predicted). A preoperative mean gradient <40
mm Hg across the aortic valve, the presence of atrial fibrillation, and a
permanent pacemaker post-AVR all predicted a post-AVR pVO2 <83% of that
predicted. For the 37 patients with a pre-AVR CPX, a postoperative decrease >10%
in the absolute pVO2 was noted in 30% and an increase >10% in 24% of patients. A
decrease >10% in pVO2 was predicted by preoperative mean gradient <40 mm Hg and
an increase in pVO2 was predicted by preoperative AVAI <0.4 cm2/m2 and
preoperative pO2pulse <the median in the study population (<98% of that
predicted).CONCLUSIONS: In this group of patients, where clinical assessment is
difficult and conventional exercise testing is regarded as less useful, CPX
showed high feasibility and reproducibility. CPX therefore has potential as a
useful tool for serial monitoring. In general, the stroke volume increased during
exercise, including in patients with severe aortic stenosis or decreased resting
stroke volume. CPX gives information on hemodynamics and the physiologic
components that determine decreased pVO2. CPX seems useful to identify 1)
patients with a low risk of cardiac death and low risk of progression to symptoms
from the aortic stenosis, and 2) patients with hemodynamic compromise who improve
in functional capacity after AVR. Patients with a preoperative mean gradient <40
mm Hg across the aortic valve, with the presence of atrial fibrillation or who
have a permanent pacemaker, postoperatively seem to benefit less from AVR,
whereas the benefit seems larger in those with more severe aortic stenosis and a
decreased pO2pulse. These findings may be of importance for decisions and
information of patients before AVR.