Cardiac Motion and Imaging Planes

Objectives

After completing this chapter, the student will be able to:

Identify the types of cardiac motion
Identify the cardiac axis planes
Identify the transthoracic windows
Identify the imaging planes
Describe the anatomy in each transthoracic view
Correlate each transthoracic view with the transesophageal views
Describe the normal transthoracic exam order

Introduction

The heart is a three dimensional structure that is displayed on a two dimensional angiographic image. Echocardiography cuts a tomographic plane in space, through which, the heart moves. Since the heart may have slightly different orientation from patient to patient, standard views have been developed that allow comparison from intra-study and inter-study images.

The anatomic view of the heart depends upon the acoustic window, the cardiac plane, and the cardiac structure of the ultrasound beam. Acoustic windows can be either transthoracic, transesophageal, epiaortic or epicardial. The ASE-SCA has developed standard nomenclature and views for transesophageal and transthoracic acoustic windows

Cardiac Motion

When the heart is imaged with ultrasound, the probe position is static but the heart is not. The heart will exhibit motion in the imaging plane. Some of the motion may be within the imaging plane but other motions will move through the plane or rotate through the imaging plane. The types of motion that the heart will exhibit are:

Translation
Rotation
Torsion

Translation motion occurs when the heart moves in a single direction that is not in the imaging plane. When imaging the heart, as it contracts, the heat may appear to move through the imaging plane.

Animation 1. Translation

Video 1. 3D Translation

Rotation motion occurs when the heart contracts and twists through the imaging plane.

Animation 2. Rotation Animiation

Video 2. Rotation Video

Torsion is the wringing motion that the heart exibits where the base will twist less than the apex of the heart. When imaging a myocardial wall from base to apex, the base will rotate less through the imaging plane whereas the apical wall will have more rotation.

Animation 3. Torsion Animation

Video 3. Torsion Video

Interpreting myocardial motion, where excessive cardiac motion occurs, can result in a misdiagnosis of the myocardial abnormality. The heart may exhibit normal wall motion but the area of the heart that is normally imaged may have moved out of the imaging plane and have abnormal motion that is not detected. Therefore, imaging all of the walls of the heart in multiple views and angles can prevent misdiagnosis of abnormal wall motion.

Cardiac Axis Planes

When viewed in the anatomical position, the major axis, or long axis of the left ventricle (LV), is obliquely positioned and rotated leftwards ~60° away from the horizontal plane (axial or transverse plane) in the normal adult (Figure 1). The axis serves as the anatomical reference for the standard echocardiographic imaging planes (Figures 1, 2):

Long Axis (LAX)
Four Chamber (4C)
Short Axis (SAX)

The long axis runs from the apex of the heart through the base of the heart and the long axis of the aortic valve. The 4 chamber axis is perpendicular the the long axis but includes all four chambers of the heart. The short axis is perpendicular to the long axis and the 4 chamber axis.

The cardiac imaging planes are established referenced planes, whether the heart is viewed from the esophagus (as in TEE), or from the chest wall (as in TTE).


Figure 1. Anatomical planes and the cardiac imaging planes compared. Image source: Echocardiography Pocket Guide: The Transthoracic Examination. Bulwer BE, Jones and Bartlett Publishers, 2011.	Figure 2. The standard orthogonal echocardiography imaging planes: long-axis (LAX), short-axis (SAX), and four-chamber (4C) planes. Image source: Echocardiography Pocket Guide: The Transthoracic Examination. Bulwer BE, Jones and Bartlett Publishers, 2011.