What does an M-mode echocardiogram measure?

An M-mode echocardiogram is primarily used to measure and provide a time-based graphical representation of cardiac dimensions, particularly the dimensions and motion of the heart structures over time. This form of echocardiography is particularly useful in assessing the size and function of the heart chambers, as well as the movement of the heart valves, by producing a single-dimensional view of the structures as they change during the cardiac cycle.

M-mode captures high temporal resolution images, which can help detail the timing of contractions and relaxations of the heart. This allows clinicians to quantify parameters such as chamber sizes and wall motion, facilitating the assessment of cardiac function more effectively than some other types of echocardiographic techniques.

In contrast, the other choices pertain to different dimensions of cardiac assessment. Blood flow velocity is measured using Doppler echocardiography, while 3D volumetric measurements of the heart involve more complex imaging techniques to assess overall heart volume and shape. Changes in heart rhythm are monitored through electrocardiography, which specifically captures the electrical activity of the heart rather than structural measurements.