Myocardial Performance Index (MPI) - Echocardiography for Beginners

 

Myocardial Performance Index (MPI) by Tissue Doppler Imaging (TDI): An Echo Practical Guide

The Myocardial Performance Index (MPI), also known as the Tei index, is a Doppler-derived echocardiographic parameter used to assess global ventricular performance by combining systolic and diastolic time intervals. It provides additional information about myocardial function beyond conventional measures such as left ventricular ejection fraction (LVEF).

With tissue Doppler imaging (TDI), MPI can be calculated using myocardial velocity waveforms recorded at the mitral or tricuspid annulus. This practical guide explains the formula, measurement technique, interpretation, and important clinical considerations for echocardiographers, cardiologists, and medical trainees.

Key Point

MPI = (Isovolumic Contraction Time + Isovolumic Relaxation Time) ÷ Ejection Time.

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1. What Is the Myocardial Performance Index?

The Myocardial Performance Index is a dimensionless ratio that combines isovolumic contraction time (ICT), isovolumic relaxation time (IRT), and ejection time (ET). It is designed to reflect aspects of both systolic and diastolic ventricular performance.

The index can be assessed using conventional Doppler echocardiography or tissue Doppler imaging. However, the measurement techniques differ, and values obtained using different methods should not automatically be considered interchangeable.

Why Is MPI Useful?

• Combines systolic and diastolic time intervals into a single index.
• Provides additional information about global ventricular performance.
• May complement LVEF when evaluating patients with suspected myocardial dysfunction.
• Can be measured using tissue Doppler waveforms obtained during a routine echocardiographic examination.

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2. Formula for TDI-Derived MPI

MPI = (ICT + IRT) / ET

The sum of the isovolumic time intervals divided by ejection time.

Parameter	Definition
ICT	Isovolumic contraction time
IRT	Isovolumic relaxation time
ET	Ejection time

All intervals can be recorded in milliseconds. Because the numerator and denominator are expressed in the same units, MPI is dimensionless.

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3. How to Measure MPI Using Tissue Doppler Imaging

Step 1: Obtain the Apical Four-Chamber View

Acquire a standard apical four-chamber view with adequate visualization of the left ventricle and mitral annulus. Optimize the image before activating tissue Doppler imaging.

Step 2: Position the TDI Sample Volume

Activate pulsed-wave tissue Doppler imaging and place the sample volume at the lateral mitral annulus for assessment of left ventricular performance. Align the Doppler beam as parallel as possible to the longitudinal motion of the annulus.

For right ventricular assessment, tissue Doppler measurements can be obtained at the tricuspid annulus using an appropriate acquisition technique.

Step 3: Identify the Myocardial Velocity Waves

The tissue Doppler tracing typically demonstrates three major myocardial velocity waves:

• s′ wave: Systolic myocardial velocity, occurring during ventricular ejection.
• e′ wave: Early diastolic myocardial velocity, associated with early ventricular relaxation and filling.
• a′ wave: Late diastolic myocardial velocity, associated with atrial contraction.

Step 4: Measure the Time Intervals

Interval	Measurement
ICT	From the end of the a′ wave to the onset of the s′ wave.
ET	From the onset to the end of the s′ wave.
IRT	From the end of the s′ wave to the onset of the e′ wave.

Important: Identify waveform boundaries consistently. The end of a′, onset and end of s′, and onset of e′ must be clearly defined on the recorded tracing for reliable interval measurement.

Step 5: Calculate the MPI

After measuring ICT, IRT, and ET, substitute the values into the formula:

Example:

ICT = 40 ms

IRT = 50 ms

ET = 300 ms

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MPI = (40 + 50) / 300 = 0.30

The calculated MPI is 0.30. This example illustrates the calculation only; clinical interpretation requires appropriate method-specific reference values.

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4. Interpretation of MPI

MPI should be interpreted in the context of the acquisition method, the patient's clinical condition, and other echocardiographic findings.

• Higher MPI: Generally associated with poorer global ventricular performance, reflecting longer isovolumic intervals relative to ejection time.
• Lower MPI: Generally associated with better global ventricular performance when interpreted within the appropriate reference range.

Clinical Caution

There is no single universal abnormal cutoff applicable to every TDI technique, ventricular chamber, and patient population. Avoid interpreting MPI in isolation or applying reference limits derived from a different measurement method.

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5. Clinical Pearls for Echocardiographers

MPI Complements LVEF

LVEF primarily reflects the proportion of end-diastolic ventricular volume ejected during systole. MPI provides complementary information by combining systolic and diastolic time intervals. Neither parameter provides a complete assessment of myocardial function on its own.

Consider Loading Conditions

Although MPI has historically been described as relatively independent of loading conditions, it can be influenced by preload, afterload, heart rate, and changes in ventricular loading. These factors should be considered during interpretation.

Be Careful in Arrhythmias

Atrial fibrillation, frequent ectopic beats, and variable cycle lengths can affect interval measurements. When technically appropriate, use representative cardiac cycles and a consistent measurement approach.

Consider Conduction Abnormalities

Bundle branch block, ventricular pacing, and other conduction abnormalities can alter the timing of myocardial contraction and relaxation. These conditions may affect MPI and should be documented.

Do Not Confuse TDI-MPI With Conventional Doppler MPI

Conventional Doppler MPI and TDI-derived MPI use different waveform landmarks and measurement approaches. Their values may differ, so the method used should be specified in the echocardiography report or study protocol.

Integrate MPI With Comprehensive Echocardiography

Interpret MPI alongside LVEF, global longitudinal strain (GLS), tissue Doppler velocities, conventional diastolic parameters, chamber dimensions, and the patient's clinical presentation.

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6. Common Measurement Pitfalls

• Using poorly defined waveform boundaries.
• Incorrect positioning or alignment of the TDI sample volume.
• Measuring intervals from technically inadequate Doppler tracings.
• Comparing values obtained with different Doppler techniques without accounting for methodological differences.
• Ignoring irregular heart rhythms or significant conduction abnormalities.
• Interpreting MPI without considering the clinical context and other echocardiographic findings.

Practical Tip

For serial follow-up, use the same acquisition site, Doppler technique, and measurement conventions whenever possible. This improves consistency when comparing results over time.

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7. Frequently Asked Questions

What is the formula for the Myocardial Performance Index?

MPI = (ICT + IRT) / ET, where ICT is isovolumic contraction time, IRT is isovolumic relaxation time, and ET is ejection time.

Can MPI be measured using tissue Doppler imaging?

Yes. TDI-derived MPI can be calculated from the timing of the a′, s′, and e′ myocardial velocity waves recorded at an appropriate annular site.

Is MPI affected by heart rate?

MPI may be influenced by heart rate and rhythm, as well as loading conditions and conduction abnormalities. These factors should be considered during acquisition and interpretation.

Can MPI replace LVEF?

No. MPI is an adjunctive parameter and should be interpreted alongside LVEF, GLS when available, and a comprehensive echocardiographic assessment.

Is the same abnormal cutoff used for all MPI methods?

No. Reference ranges depend on the acquisition method, ventricular chamber, population, and clinical setting. Use appropriate method-specific reference values.

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Conclusion

The Myocardial Performance Index is a useful adjunct in echocardiography for evaluating global ventricular performance through the integration of systolic and diastolic time intervals. TDI-derived MPI can be measured using the a′, s′, and e′ myocardial velocity waves at the appropriate annular site.

Reliable results depend on technically adequate Doppler recordings, consistent measurement of waveform boundaries, and interpretation using method-specific reference ranges. MPI should complement, rather than replace, established measures of ventricular function and comprehensive echocardiographic assessment.

Key Takeaway

TDI-MPI = (ICT + IRT) / ET. Measure the intervals carefully, understand the limitations, and interpret the result in the context of the complete echocardiographic examination.

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