We often describe the left and right sides of the heart. When we think of them in this way, most people imagine the heart standing up on the apex with the septum exactly in the middle. Some might even imagine that the AV valves are more superior and the apex is inferior as depicted in Figure 1.
Unfortunately, it is not that simple. The heart is positioned at an oblique angle in the chest with the apex downward and left compared to the base. As a result, orientation can become very confusing.
Figure 1: Idealized anatomic descriptions of the heart
Figure 2: Transverse CT image of the heart in the thorax
Looking at Figure 2, you can appreciate the following observations:
Even more importantly, bear in mind that:
We describe the location of the image intensifier with respect to the patient’s body, but the object of interest is actually the heart. Because the heart is oriented obliquely in the thorax, these orientations can become confusing. We will go through these one at a time, but this is summarized in the following table.
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| With respect to body | With respect to heart |
|---|---|
| Left anterior oblique | Anterior |
| Right anterior oblique | Right lateral |
| Anteroposterior | Right anterior oblique |
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Figure 3-1: Left anterior oblique
In order to look at the anterior heart (as shown in Figure 1), the image intensifier is positioned off to the patient’s left side.
This is referred to as left anterior oblique, or more simply LAO.
On the other hand, if we want to look at the lateral heart (as imagined from the perspective of Figure 1), the image intensifier is positioned off to the patient’s right side.
This is referred to as right anterior oblique, or more simply RAO
Figure 3-2: Right anterior oblique
Figure 3-3: Anteroposterior
Sometimes, we want to look at the heart halfway in between these two views.
If the image intensifier is directly in front of the patient with no left or right angulation, this is called anteroposterior or AP.
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The easiest way to identify the left-right angulation is by looking at the position of the heart with respect to the spine.
In additional to left/right angulation, the image intensifier can be moved toward or away from the patient’s head. Moving the image intensifier toward the head is “cranial” angulation, and moving it away from the head is “caudal” angulation.
Figure 4-1: Cranial angulation
Imaging the heart with cranial angulation “lays out” the vessels which course from base to apex as shown below. This axis is represented by the dashed blue line.
This is referred to as cranial angulation, often abbreviated in spoken language just using the first two syllables “crani.”
Figure 4-2: Caudal angulation
Changing our viewing angle to a more caudal perspective, we will now instead be “laying out” the vessels coursing through the AV groove. This axis is represented by the dashed orange line.
This is referred to as caudal angulation.
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Cranial images are identified because they include the diaphragm. As an example, see the diaphragm annotated with a dotted black line in the following AP cranial image.
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