(USMLE topics, cardiology) Understanding JVP waveforms and interpretation of JVP abnormalities.

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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.
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.