Jugular venous pressure, JVP, also known as jugular venous pulse, is the pressure within
the jugular vein.
Because the right internal jugular vein communicates directly with the right atrium via the superior
vena cava, JVP essentially reflects the central venous pressure; and its cyclic changes with
each heartbeat accurately mirror the dynamics of blood flow to the right atrium.
JVP can be recorded precisely by inserting a central line; or assessed, non-invasively,
by observing the pulsation of the vein on the right side of the patient’s neck.
The mean JVP, measured at the highest point of jugular pulsation, serves as an indicator
of fluid status.
A higher than normal JVP indicates hypervolemia, while lower values are associated with hypovolemia.
Generally, fluid overload is diagnosed when the jugular vein is distended to the jaw in
upright position.
A normal JVP waveform has 3 positive waves: A, C and V, of which only A and V can be seen
by looking at the vein; and their corresponding descents.
Reminder: blood flows from higher to lower pressure; contraction increases the pressure
within a chamber, while relaxation lowers the pressure.
The A wave represents atrial contraction, which actively pushes blood into the right
ventricle.
Contraction increases pressure inside the atrium, pushing blood both downward and upward,
creating a distension in the jugular vein.
The X descent is generated by the subsequent relaxation of the right atrium.
The resulting reduced pressure pulls the blood down from the jugular vein.
As the right ventricle starts to contract, blood pushes against the closed tricuspid
valve, causing it to bulge into the right atrium.
This slightly raises right atrial pressure, producing the small positive C wave in the
middle of the X descent.
V wave reflects the passive rise in pressure and volume of the right atrium as it fills,
reaching the peak right before the tricuspid valve reopens.
Opening of tricuspid valve allows blood to flow down the ventricle, emptying the right
atrium, reducing its pressure, and resulting in the Y descent.
Abnormalities in JVP waveforms can help with diagnosis of a number of cardiac and pulmonary
diseases: - Absence of proper atrial contraction, such
as in atrial fibrillation, leads to absence of A waves.
- Abnormally large A waves occur when the right atrium contracts against a higher-than-usual
resistance.
Examples include right ventricular hypertrophy, tricuspid valve stenosis, and obstruction
of right ventricular outflow.
These conditions produce giant A waves that are uniform and occur on every beat.
- Cannon A waves, on the other hand, are also large, but occur intermittently, and usually
of various height.
Cannon A waves typically result from cardiac arrhythmias, when there is a disconnection
between atrial and ventricular activation, and the right atrium contracts against a closed
tricuspid valve, in some but not all beats.
Examples include premature beats, complete atrioventricular block, and ventricular tachycardia.
- A large V wave occurs when there is increased atrial filling during ventricular contraction.
The most common cause is tricuspid regurgitation.
Because regurgitation begins during C wave (when the ventricle starts to contract), the
large V wave is commonly FUSED with C wave, forming a so-called CV wave.
Atrial septal defects may also result in larger V waves.
- Unusually steep X and Y descents can be observed as abrupt collapse of the neck vein,
in conditions such as constrictive pericarditis.
The reduced elasticity of the pericardial sac raises atrial pressure while also limiting
ventricular filling to early diastole.
- Cardiac tamponade, on the other hand, attenuates the Y descent as it impedes ventricular filling.