Acute alterations in blood lactate in the setting of transient stress induced myocardial ischaemia

Abstract
Background
An elevation in resting venous blood lactate levels ([La-]b) in conditions of myocardial hypoperfusion is associated with adverse prognosis and survival. This investigation aimed to assess changes in venous [La-]b levels induced by dobutamine stress in the presence and absence of myocardial ischaemia and adverse outcomes at 1-year.

Methods
404 consecutive patients (mean age 70±10 years, 243 male) reporting chest pain underwent dobutamine stress echocardiography and were categorised as ischaemic (IS) or non-ischaemic (NI) responders. Conventional and global longitudinal strain (GLS) echocardiographic measures were recorded at rest. Venous [La-]b samples were acquired at rest, peak stress and 1, 3, 5 and 10-minutes into recovery using a commercially available Lactate Pro 2 device.

Results
There were no significant differences in [La-]b concentrations between IS (1.75±0.76 mmol×L-1) and NI (1.73±0.60 mmol×L-1) responders at baseline (p=0.592). However, [La-]b concentrations were significantly greater at peak stress (1.83±0.57 vs. 1.68±0.60 mmol×L-1), 1 (1.90±0.56 vs. 1.73±0.71 mmol×L-1), 3 (1.97±0.56 vs. 1.73±0.71 mmol×L-1), 5 (1.98±0.60 vs. 1.74±0.70 mmol×L-1), and 10-minutes (2.01±0.63 vs. 1.76±0.71 mmol×L-1) into recovery between IS and NI responders (all p<0.001), respectfully. GLS was significantly lower in IS compared to NI responders (-15.5±2.9 vs -16.2±2.7%, p=0.02) at baseline. In patients who experienced an adverse cardiac event during 1-year of follow-up, GLS (-14.4±2.7 vs -16.1±2.8%, p<0.001) and [La-]b concentrations were significantly lower at baseline (1.54±0.55 mmol×L-1 vs. 1.78±0.70 mmol×L-1, p=0.02), as were [La-]b concentrations at 5 (1.68±0.55 mmol×L-1 vs. 1.88±0.68 mmol×L-1, p=0.04) and 10-minutes (1.70±0.56 mmol×L-1 vs. 1.93±0.71 mmol×L-1, p=0.02) into recovery compared to patients who did not experience an adverse event, respectively. GLS (HR 1.21; 95% CI 1.11 to 1.33, p<0.001) and [La-]b concentrations at 10-minutes into recovery (HR 0.54; 95% CI 0.33 to 0.85, p=0.01) were significant independent predictors of an adverse event.

Conclusions
Transient myocardial ischaemia is associated with a significant elevation in [La-]b concentrations, which extends into the recovery period, compared to NI responders. A blunted metabolic response to dobutamine stress and attenuated longitudinal myocardial mechanics are independently associated with short-term adverse events.