Measures of cardiac contractility variability during ischemia

Acute myocardial infarction (AMI) is one of the leading causes of death in the US. While heart rate variability (HRV) has been widely studied for ischemia detection, the changes in cardiac contractility variability have not yet been explored. This paper presents novel variability analysis using 23 linear and non-linear measures during myocardial ischemia. Multiple physiologic measures of cardiac contractility and heart rate variability are analyzed and compared before and after acute coronary artery occlusion in a swine model. Change in the spread of the Poincare plot of RR intervals was highly negatively correlated with the change in contractility reflective of ischemia (r=-0.92, p<0.05). The change in approximate entropy of the S1 heart sound intensity was also highly correlated (r=0.96, p<0.05) with the change in contractility due to ischemia. These preliminary results show the potential utility of nonlinear measures of variability to detect changes in the autonomic tone due to ischemia. These parameters, if measured continuously, may be used for early detection of AMI events in patients with implantable devices. Further research in a larger clinical study is warranted to confirm these findings.