Oscillations in the right internal jugular vein, and often in the external jugular vein, reflect changing pressures in the right atrium. Careful inspection of these waveforms reveals two quick peaks and two troughs, diagrammed in Figure 1. Considerable practice and experience are required to discern these fluctuations.
■ The first elevation, the presystolic a wave, reflects the slight rise in atrial pressure that accompanies atrial contraction. It occurs just prior to S1 and before the carotid upstroke.
■ The following trough, the x descent, starts with atrial relaxation. It continues as the RV, contracting during systole, pulls the floor of the atrium downward, and ends just before S2. During ventricular systole, blood continues to flow into the right atrium from the venae cavae.
■ The tricuspid valve is closed, the chamber begins to fill, and right atrial pressure begins to rise again, creating the second elevation, the v wave. When the tricuspid valve opens early in diastole, blood in the right atrium flows passively into the RV, and right atrial pressure falls again, creating the second trough, or y descent.
FIGURE 1. Jugular venous pulsations. (Adapted with permission from Douglas G, Nicol F, Robertson C. Macleod's Clinical Examination, 13th ed. London: Elsevier, 2013.)
■ A simplified way to remember the three peaks is: a for atrial contraction, c for carotid transmission (although this may represent closure of the tricuspid valve),102 and v for venous filling. To the naked eye, the two descents, x and y, are the most visible events in the cycle of atrial contraction, atrial relaxation, atrial filling, and atrial emptying again followed by atrial contraction. Of the two, the sudden collapse of the x descent late in systole is more prominent, occurring just before S2. The y descent follows S2 early in diastole.
Observe the amplitude and timing of the jugular venous pulsations. To time them, feel the left carotid artery with your right thumb or listen to the heart simultaneously. The a wave just precedes S1 and the carotid pulse, the x descent can be seen as a systolic collapse, the v wave almost coincides with S2, and the y descent follows early in diastole. Look for absent or unusually prominent waves.
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