Because the y descent is the fall in the RA pressure in diastole immediately following the opening of the tricuspid valve, it is necessary that the RV pressure in fact falls close to zero as it does normally with the early rapid filling phase of diastole. In other words, the ventricle should not have any restriction during this early rapid filling phase of diastole, even if it does have restriction during the later phases of diastole. This automatically excludes cardiac tamponade, which implies total diastolic restriction resulting from high fluid pressure in the pericardial sac, which allows very little or no expansion of the ventricle during diastole.
The steepness of the y descent will depend on the v wave pressure head that is present at the time of the tricuspid valve opening. The higher the v wave pressure head, the steeper and more prominent is they descent, assuming of course that there is no tricuspid obstruction as in tricuspid stenosis (Fig. 11). The latter condition is very rare, and if significant it could be expected to slow the y descent (18).
The normal v wave pressure being low, the y descent is usually not very prominent (Fig. 9). The corresponding diastolic flow velocity in the jugulars is also slow and low. Although the small y descent may be seen in the RA pressure pulse, it is not usually seen in the jugular venous pulse. This is because of the capacitance function of the normal
1. Increased v wave pressure head with NO restriction to ventricular filling during rapid filling phase, e.g., a. High sympathetic tone as in young children, anxiety, anemia, pregnancy, thyrotoxicosis b. Hypervolemia c. Extra source of venous filling as in atrial septal defect d. Pericardial effusion with some restriction e. Constrictive pericarditis f. Pulmonary hypertension with elevated RV diastolic pressure g. Ischemic and/or infarcted RV
Excludes cardiac tamponade:
2. Decreased right atrial capacitance function, e.g., a. Post-cardiac surgery
3. Bernheim effect in severe mitral regurgitation0
a Rare occurrence.
right atrium. The reservoir function of the atrium is such that it is able to empty into the ventricle without the top of the column actually falling much. When the right atrium gets stiff and behaves like a conduit as in post-cardiac surgery patients who have had their right atrium cannulated during surgery and therefore traumatized, this capacitance function is lost. In these patients even the normal v wave pressure allows recognition of the y descent in the jugulars (17,29,42,52) (see JVP Videofiles 1- 3 on the Companion CD).
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