Kussmaul's sign and the y descent separate them
Expansion
| Tamponade | Constriction | |
|---|---|---|
| Onset | Acute | Chronic |
| JVP y descent | Absent | Steep and prominent |
| Kussmaul’s sign | Classically absent | Present |
| Pulsus paradoxus | Marked | Usually absent |
| Extra sound | None | Pericardial knock |
| Calcification | No | Often on imaging |
| Treatment | Drainage | Pericardiectomy |
“Tamponade has no y, constriction has a steep one.”
The physiological reason: in tamponade the pericardium is under pressure throughout diastole, so the ventricle cannot fill at any point and the y descent is lost. In constriction early filling is rapid and unimpeded until the rigid pericardium is reached, giving a steep y descent that stops abruptly, the “dip and plateau” or square root sign.
Kussmaul’s sign, a rise in JVP on inspiration, occurs in constriction because the rigid pericardium cannot accommodate the increased venous return.
Causes of constriction: tuberculosis worldwide, and in the UK previous cardiac surgery, radiotherapy, connective tissue disease and recurrent pericarditis.
Restrictive cardiomyopathy is the main mimic, and is distinguished by cardiac MRI and haemodynamic study rather than by clinical signs.