The Parasternal Long Axis View (PLAX):
©Walter Rasmussen, R.D.C.S.
Above: Imaging plane.
Below: An ideal PLAX image.
The Parasternal Long Axis View is found by placing the transducer at the 4th or 5th, left intercostal space and is the usual starting point for beginning an adult echocardiographic examination.
1. The transducer index mark should be pointing generally toward the patient’s right shoulder. Slight adjustments will be necessary for each patient because the axis of the heart can be either more horizontal or more vertical. Adjust the TGC, LGC or Auto Gain control so that the image appears evenly-lit.
2. The ideal parasternal long axis should include the following anatomical features however this is not always possible.
Aortic root and valve and a portion of the ascending aorta.
Mitral valve and left ventricular outflow tract.
Portions of the right ventricle.
Interventricular septum (basal to mid regions).
Left ventricular chamber (basal to mid regions).
Posterior left ventricular wall (basal to mid regions).
Anterior and Posterior Pericardium.
Descending Thoracic Aorta.
3. It is important to thoroughly explore the parasternal area in order to assure good beam penetration resulting in the clearest, most focused image possible for the condintions encountered. Ideal conditions are found in the medical office clinic, where the patient can cooperate fully and the exam table allows effective patient positioning.
The image illustrated above displays the ideal coverage of anatomy in the parasternal long axis view and is achieved in perhaps only half of the patients scanned. It is often the case however, that a more limited section of anatomy will be revealed, principally because of the narrowness of the intercostal spaces and the heart’s distance from the transducer.
After finding the clearest parasternal long axis window, adjust the transducer so that the heart appears as horizontal as possible within the sector.
If the cardiac apex still points steeply vertically, this is because the window is low relative to the heart’s position. It can be helpful to attempt to make it point more horizontally by moving the transducer superiorly up one intercostal space.
Above: A Low Parasternal Long Axis view. Although it is technically less desirable to record the initial PLAX from a low intercostal space, it is sometimes unavoidable. A low PLAX view can however, be routinely recorded as an additional view, because it can give extended long axis views that include the apical region.
Above: An M-Mode cursor is placed at the mitral valve from a low parasternal view. This will not yield a good M-Mode recording.
A major goal of echocardiography is to record as many anatomical features as clearly as possible for each view. Because not all of the anatomical features of the parasternal long axis are typically seen clearly from only one transducer position, it may be necessary to make more than one parasternal long axis recording.
Above: The transducer was moved one intercostal space downward on the chest to feature the left ventricle.
Instructing the patient to exhale and hold their breath out for a few cardiac cycles often makes it possible to move the transducer to a better place that will yield higher image quality. This is particularly helpful to get in better position for placing the M-Mode cursor perpendicular to the left ventricle or aorta.
In many cases, all of the components of the parasternal long axis will not completely fit within a typical 90 degree sector. If possible, those portions of the heart not well seen should be featured on an additional separate clip. For example, if in the PLAX, the left ventricle is clearly demonstrated, yet by comparison, the aorta and left atrium are faint or cut-off, another clip at a higher intercostal space should be recorded to clarify those features as well. Respiratory maneuvers are an essential tool for obtaining the highest quality ultrasound images of the heart and in most cases, having the patient completely exhale all of their residual air can substantially clear an image without having to move the transducer.
In some patients, the image will fade in and out of view with each respiration, or a clear horizontal image of the heart cannot be obtained. Positioning the patient more steeply on their left side and directing the patient exhale all of the remaining air from their lungs and holding it out for a few seconds, while searching for the best image, often helps. In some cases, it is necessary to have the patient exhale and hold the breath out for every single clip recorded. Although tedious and time-consuming, this extra effort often pays-off with a good quality echocardiogram that would have otherwise been of low quality. The patient should be allowed to catch their breath between each image acquired.
Always take into consideration the patient’s health and ability before having them do any respiratory maneuvers. Observe the patient’s physiologic state and don’t hesitate to ask the patient if they are having any difficulty with the exercise. Exercise caution and do not stress patients who are pregnant, in heart failure, as well as those with lung disease.
Occasionally, a patient will develop bradycardia or frequent PVC’s with sustained suspension of respiration. Many elderly and hospitalized patients cannot understand or follow instructions for regulating their breath. If the patient cannot communicate due to a language barrier, it may be very difficult to give the patient specific directions even if a translator is present.
Muscular pain or arthritis can cause many patients to have significant pain during an echocardiogram and so it is always best to allow for such sensitivities by subjecting them to as little discomfort as possible. Aggressive use of the probe is rarely necessary and as pointed out in an earlier section, can be avoided by getting to know how to use the various, “facets” of the probe as well as effective patient positioning and breath control.