A Duke Health pilot project suggests that in the near future, a blood test could show whether arteries carrying blood to the heart are narrow or blocked, a risk factor for heart disease. According to the 40-person study, emergency patients who underwent a treadmill stress test and showed signs of decreased blood flow to the heart also had changes in five metabolites in their blood within two hours.
All study subjects had gone to the emergency department with symptoms of coronary disease, such as chest, jaw and shoulder pain.
The researchers hope a larger study could confirm that acute changes in these fatty acid and amino acid metabolites, which are energy sources for cells, could be an early biological indicator of restricted blood flow that could complement or even replace current tests.
“Cardiologists do a stress test to determine who’s at risk for having heart disease,” said lead author Dr Alexander T Limkakeng Jr, lead author of the study and an associate professor of emergency medicine at Duke. “It guides them on whether they need a more invasive study like a catheterisation. Augmenting the imaging of a stress test with metabolite biomarkers could make that process more accurate or more efficient.”
Previous research has suggested that metabolites could indicate heart disease, but scientists have yet to uncover the specific metabolomic signature to look for. For the Duke study, scientists evaluated the presence of more than 60 chemicals or compounds in the blood to identify the five specific metabolites that appeared to change in patients with abnormal cardiac stress tests.
The researchers hope to begin a larger study to further test this approach to detecting coronary artery disease, they said.
Background: The heart is a metabolically active organ, and plasma acylcarnitines are associated with long-term risk for myocardial infarction. We hypothesized that myocardial ischemia from cardiac stress testing will produce dynamic changes in acylcarnitine and amino acid levels compared to levels seen in matched control patients with normal stress tests.
Methods: We analyzed targeted metabolomic profiles in a pilot study of 20 case patients with inducible ischemia on stress testing from an existing prospectively collected repository of 357 consecutive patients presenting with symptoms of Acute Coronary Syndrome (ACS) in an Emergency Department (ED) observation unit between November 2012 and September 2014. We selected 20 controls matched on age, sex, and body-mass index (BMI). A peripheral blood sample was drawn <1 hour before stress testing and 2 hours after stress testing on each patient. We assayed 60 select acylcarnitines and amino acids by tandem mass spectrometry (MS/MS) using a Quattro Micro instrument (Waters Corporation, Milford, MA). Metabolite values were log transformed for skew. We then performed bivariable analysis for stress test outcome and both individual timepoint metabolite concentrations and stress-delta metabolite ratios (T2/T0). False discovery rates (FDR) were calculated for 60 metabolites while controlling for age, sex, and BMI. We built multivariable regularized linear models to predict stress test outcome from metabolomics data at times 0, 2 hours, and log ratio between these two. We used leave-one-out cross-validation to estimate the performance characteristics of the model.
Results: Nine of our 20 case subjects were male. Cases’ average age was 55.8, with an average BMI 29.5. Bivariable analysis identified 5 metabolites associated with positive stress tests (FDR < 0.2): alanine, C14:1-OH, C16:1, C18:2, C20:4. The multivariable regularized linear models built on T0 and T2 had Area Under the ROC Curve (AUC-ROC) between 0.5 and 0.55, however, the log(T2/T0) model yielded 0.625 AUC, with 65% sensitivity and 60% specificity. The top metabolites selected by the model were: Ala, Arg, C12-OH/C10-DC, C14:1-OH, C16:1, C18:2, C18:1, C20:4 and C18:1-DC.
Conclusions: Stress-delta metabolite analysis of patients undergoing stress testing is feasible. Future studies with a larger sample size are warranted.
Alexander T Limkakeng, Ricardo Henao, Deepak Voora, Thomas O’Connell, Michelle Griffin, Ephraim L Tsalik, Svati Shah, Christopher W Woods, Geoffrey S Ginsburg