In JVP, a wave is due to?

Atrial contraction REF: Harrison's Internal Medicine 17th edition Chapter 220 Physical Examination of the Cardiovascular System, http://en.wikipedia.org/wiki/Jugular_ venous_pressure JVP WAVEFORM: Classically three upward deflections and two downward deflections have been described. 1. The " a " wave corresponds to right Atrial contraction and ends synchronously with the carotid aery pulse. The peak of the 'a' wave demarcates the end of atrial systole. 2. The " c " wave corresponds to right ventricular Contraction causing the triCuspid valve to bulge towards the right atrium. 3. The " x " descent follows the 'a' wave and corresponds to atrial relaXation and rapid atrial filling due to low pressure. 4. The " x' " (x prime) descent follows the 'c' wave and occurs as a result of the right ventricle pulling the tricuspid valve downward during ventricular systole. The x' (x prime) descent can be used as a measure of right ventricle contractility. 5. The " v " wave corresponds to Venous filling when the tricuspid valve is closed and venous pressure increases from venous return - this occurs during and following the carotid pulse. 6. The " y " descent corresponds to the rapid emptYing of the atrium into the ventricle following the opening of the tricuspid valve. ABNORMAL JVP: 1. Raised JVP, normal waveform Bradycardia Fluid overload Hea Failure 2. Raised JVP, absent pulsation Superior vena cava syndrome 3. Large 'a' wave (increased atrial contraction pressure) Tricuspid stenosis Right hea failure Pulmonary hypeension 4. Cannon 'a' wave (atria contracting against closed tricuspid valve) Atrial flutter Premature atrial rhythm (or tachycardia) Third degree hea block Ventricular ectopics Ventricular tachycardia 5. Absent 'a' wave (no unifocal atrial depolarisation) Atrial fibrillation 6. Large wave (c-v wave) Tricuspid regurgitation 7. Slow 'y' descent Tricuspid stenosis 8. Parodoxical JVP (Kussmaul's sign: JVP rises with inspiration, drops with expiration) Pericardial effusion Constrictive pericarditis Pericardial tamponade