Parasternal long axis view (PLAX)

The parasternal long axis view is obtained by (usually) placing the probe next to the sternum, on the left part of the chest, at 2nd intercostal space. In this view, we can observe the left ventricular (LV) free wall, the mitral valve with its attachement to the LV free wall, the fibrous continuity between the aortic valve and the mitral valve. Anteriorly, we can see the right ventricular outflow tract (RVOT) and the septum seperating the LV from the RVOT. This is a good view to evaluate for septal hypertrophy (example: infant of diabetic mother), or obstruction of the LV outflow tract (LVOT).

RVOT: Right ventricular outflow tract

Ao: Aorta

LV: Left ventricle

MV: Mitral valve

LA: Left atrium

DesAo: Descending aorta

In this view, there is a sweep initially towards the posterior aspect of the heart (inflow - tricuspid valve - right atrium / right ventricular junction). The sweep then goes towards the outflow tract of the RV. These are good views to observe the relationship between the cardiac structures. It is also a good sweep to do with a colour box (evaluate blood flow through the mitral, aortic, tricuspid and pulmonary valves). You may attempt to detect tricuspid regurgitation jet (TRJ) or pulmonary insufficiency (PI) from this view, and obtained a continuous wave Doppler (CW) for appreciation of gradient velocities between RV-RA by the TRJ, or PA-RV by the PI. The aortic valve (AV) and mitral valve (MV) are each displayed, as is the proximal aorta. The ventricular septum should be seen 2/3 to the apex. The septum is nearly horizontal when looking at the LV-MV-AV.

In these view, we may also observe the descending aorta in cross-section just below the left atrium.

2D image at the level of aortic valve, aortic root and cusps. Aortic valve, aortic root and ascending aorta measurements can be done in the PLA view. This is an excellent view to assess LVOT diameter by 2D. Colour Doppler on the aortic valve should also be done to assess for presence of aortic insufficiency or flow acceleration.

The measurement of the LVOT should be at the hinge point of the aortic valve, at valve opening.

The anterior sweep anterior will show the RV outflow tract (pulmonary valve and pulmonary artery) – 2D anatomy. Colour Doppler on pulmonary valve, as well as pulmonary artery, allows to indicate laminar flow through the valve. Doming of the PV may be associated with some acceleration. Pulmonary stenosis, atresia can be evaluated in this view. Pulmonary insufficiency allows for estimation of pulmonary arterial pressure in diastole. Pulsed-Wave (PW) Dopplers at pulmonary valve leaflets attachment and in the MPA are usually done to assess for pulmonary acceleration time (on RV ejection time ratio), as well as evaluating the PA-velocity time integral (a marker of stroke distance).

Another view showing the Pulmonary valve open nicely. In this view, the main pulmonary artery is nicely delineated and may allow for measurement. Main PA may dilate in the presence of increased RV afterload. In the case of dilation, one may also see some swirling effect of the blood by colour Doppler.

M-Mode of the LA:Ao relationship. The measurement of the LA:Ao (left atrium to aorta) ratio can be done in the PLA or PSA. The measurement has been described as a way to estimate left atrial dilation in the context of a large patent ductus arteriosus. With the increased pulmonary blood flow, the left atrium may start dilating. A ratio of >1.4 has been associated with larger PDA diameters. There are caveats to this measurement. A) If there is a large inter-atrial defect, the left atrium will unload in the right atrium and may not dilate, B) if the aorta is hypoplastic, the ratio will be increased even if the left atrium is within normal size, C) the line of interrogation needs to be appropriately positioned to obtain the M-Mode.

From this view: M-mode at the closure of aortic valve and with line of interrogation perpendicular to aorta for: Left atrial on aorta ratio (detection of signs of LV overload, or small aortic valve). Evaluation of LV ejection time from opening to closure of aortic valve.

The M-mode from the LV at the mitral valve leaflet level may be useful to measurement: a) the diastolic inter-ventricular septum, b) the diastolic posterior wall of the LV. These may be indicators of septal or LV hypertrophy. In this view, you may also measurement the shortening fraction, where SF = (End-diastolic diameter of the LV - End-systolic diameter of the LV)/end-diastolic diameter of the LV. Beware of newborns where the pulmonary vascular resistances are still high and where there is flattening of the inter-ventricular septum. In this situation, the septal geometry will be distorted and the SF will be affected, and as such is not a reliable marker of LV function. Furthermore, M-modes are highly susceptible to angle of interrogation. As such, there are many caveats in relying solely on these measurements.

From this view: M-mode of left and right ventricle at the level of tip of mitral valve with line of interrogation perpendicular to interventricular septum for measurement of shortening fraction (SF) and measurements of LV / RV / Septum / Posterior wall thickness (only valid in normal biventricular anatomy), measurement of R-R interval.

Example of colour box on the RVOT-PV-MPA

Example of Pulsed-Wave Doppler at the tip of the pulmonary valve.

Example of Pulsed-Wave Doppler at the tip of the pulmonary valve in a patient with congenital diaphragmatic hernia. Here, the indicator "R chest", shows that the transducer is on the right of the chest. Furthermore, the VTI is traced (velocity time integral). The axis indicate time (x axis) and velocity (y axis). As such, the area under the curve of the VTI estimates stroke distance at the sampled area.

It is important to see blood flow actually going through the valve. In the case of pulmonary valve atresia, blood will be seen in the main pulmonary artery (from the patent ductus arteriosus). As such, to confirm no atresia or stenosis of the valve, one may need to pay attention to see blood flow crossing the RVOT.

Example of pulmonary insufficiency jet obtained with the CW-Doppler from the RVOT. More examples are provided in the section dedicated to pulmonary hypertension.

Created by Gabriel Altit - Neonatologist / Créé par Gabriel Altit (néonatalogiste) - © NeoCardioLab - 2020