MPI (Myocardial Performance Index, aka Tei Index) is the fraction of the sum of isovolumetric contraction time (IVCT) and isovolumetric relaxation time (IVRT) to the left ventricular ejection time (LVET).
In layman terms, the heartbeat has 2 phases – systole and diastole. Systole is the phase where the heart pumps blood into the body, diastole is the phase where the blood is coming into the heart for the next cycle of pumping. Systole consists of 3 phases – isovolumetric contraction (heart muscles contract to increase pressure before pumping out the blood), left ventricular ejection (when the aortic valve opens and the blood actually starts getting pumped out) and relaxation (after the blood has been pumped out, the heart relaxes to take in blood for the next cycle of pumping). The total time interval of systole is called Mitral valve Closing Opening Time (MCOT), because the systole starts when the mitral valve closes and ends when the mitral valve reopens.
MPI is a numerical measure of the amount of time the heart spends in getting ready to eject out the blood into the body as compared to the time the heart spends in the actual ejection process.
MPI is a measure of the fraction of time the heart spends in getting ready to pump out the blood – isovolumetric contraction time (ICT) + isovolumetric relaxation time (IRT) – to the time the heart spends in actually pumping out the blood – left ventricular ejection time (LVET).
MPI = (ICT + IRT) / LVET
A healthy heart spends less time getting ready to pump and more time in the actual ejection process. A weak heart spends more time getting ready to pump and less in the ejection process. So a healthy heart will have a lower MPI value and a weaker heart will have a higher MPI value.
There are numerous studies conducted by cardiological societies across the world, published in renowned medical journals that prove MPI to be an early predictor of many serious heart disorders like myocardial infarction, cardiac dysfunction, heart failure, and many other CVDs. MPI is also an important indicator of existing comorbidities in patients with existing disorders like diabetes and thyroid problems.
A lower MPI value shows a healthy heart and a higher MPI value shows an unhealthy heart. While there is no such universally accepted cutoff value between the two, and MPI value of less than 0.46 is considered to be of a healthy person and that of more than 0.46 is that of an unhealthy person.
Below is an image showing the cardiac cycle, identified in pressure signals, phonogram obtained from a digital stethoscope and ECG. The ICT, IRT, LVET, and MCOT can be seen.