What are the cardiac indices?

From the Guidelines

Cardiac indices are crucial measurements for assessing heart function, with the primary cardiac index calculated by dividing cardiac output by body surface area, and normal values ranging from 2.5 to 4.0 L/min/m², as supported by the European Society of Cardiology guidelines 1. The cardiac indices are essential in evaluating cardiovascular status, guiding fluid management, and assessing response to treatments.

• The primary cardiac index is a key measurement, with normal values ranging from 2.5 to 4.0 L/min/m².
• Other important cardiac indices include stroke volume index, left ventricular stroke work index, and systemic vascular resistance index.
• These measurements can be obtained using techniques such as pulmonary artery catheterization, echocardiography, or less invasive methods like arterial pulse contour analysis, as described in the European Heart Journal 1.
• Abnormal values may indicate conditions such as heart failure, shock, or valvular heart disease, making these indices valuable tools for diagnosing and managing cardiovascular disorders.
• The European Society of Cardiology guidelines provide a comprehensive overview of cardiac indices and their clinical implications, including parameters related to systolic function, diastolic function, valvular function, and other parameters such as RV function and tricuspid regurgitation peak velocity 1.
• The use of cardiac indices, such as the left ventricular ejection fraction, left ventricular fractional shortening, and left ventricular regional function, can help identify abnormalities in patients with heart failure, as outlined in the guidelines 1.

From the Research

Cardiac Indices

The cardiac indices are measures of cardiac function that can be used to assess the performance of the heart. Some of the key cardiac indices include:

• Cardiac index: a measure of cardiac output normalized to body surface area, typically expressed in units of L/min/m2 2
• Cardiac power output: a measure of the rate at which the heart performs work, typically expressed in units of watts 3
• Stroke volume index: a measure of the volume of blood pumped by the heart per beat, normalized to body surface area, typically expressed in units of mL/m2 4, 5
• Peak cardiac power output-to-left ventricular mass: a measure of the rate at which cardiac work is delivered respect to the potential energy stored in left ventricular mass, typically expressed in units of W/100 g 6

Determinants of Cardiac Indices

The determinants of cardiac indices can vary depending on the specific index being measured. Some of the key determinants include:

• Heart rate: an increase in heart rate can lead to an increase in cardiac output and cardiac power output 3, 5
• Stroke volume: an increase in stroke volume can lead to an increase in cardiac output and cardiac power output 3, 5
• Left ventricular mass: an increase in left ventricular mass can lead to a decrease in peak cardiac power output-to-left ventricular mass 6
• Body mass index: a higher body mass index can be associated with smaller increases in heart rate and stroke volume index during exercise 5

Clinical Significance of Cardiac Indices

The cardiac indices can have significant clinical implications, particularly in patients with heart failure. For example:

• A reduced cardiac index can be an independent predictor of poor prognoses in patients with hypertrophic cardiomyopathy 2
• A lower cardiac power output can be associated with adverse outcomes in patients with heart failure with preserved ejection fraction 3
• A peak cardiac power output-to-left ventricular mass can be a powerful independent predictor of outcome in patients with heart failure and depressed systolic function 6