What waveform feature marks the beginning of diastole on a pulmonary artery pressure (PAP) tracing?

Dicrotic Notch Marks the Beginning of Diastole on Pulmonary Artery Pressure Tracing

The correct answer is (a) dicrotic notch—this waveform feature universally demarcates the end of systole and the beginning of diastole in the pulmonary artery pressure tracing. 1

Physiological Basis

• The dicrotic notch represents the point of pulmonary valve closure, which physiologically defines the transition from systolic ejection to diastolic filling 1
• At the moment of the dicrotic notch, right ventricular ejection is completed, and pulmonary artery diastolic pressure begins 2
• The dicrotic notch occurs when pulmonary artery pressure equals mean pulmonary artery pressure in mechanically ventilated critically ill patients 2

Clinical Validation

• Studies using Swan-Ganz catheters in critically ill, mechanically ventilated patients demonstrate that dicrotic notch pressure (31.8 ± 10.4 mm Hg) precisely equals mean PA pressure (32.1 ± 10.2 mm Hg), with excellent correlation (r = 0.989, p < 0.001) 2
• The dicrotic notch is clearly identifiable in 94% of patients (30 of 32) using standard fluid-filled pressure monitoring systems 2
• This feature can be tracked using pulse wave imaging techniques, which capture the wavefront generated upon closure of the pulmonary valve at dicrotic notch pressure 3

Why Other Options Are Incorrect

• The a wave represents atrial contraction during late diastole, not the beginning of diastole 3
• The x descent reflects atrial relaxation and downward displacement of the tricuspid annulus during ventricular systole, occurring during systole rather than marking diastolic onset 3
• The systolic peak represents maximum right ventricular pressure during ejection, occurring in mid-to-late systole, not at the systolic-diastolic transition 2

Practical Application

• When analyzing pulmonary artery pressure tracings, identify the sharp downward deflection (notch) following the systolic peak—this marks valve closure and diastolic onset 1, 4
• The dicrotic notch can be used to calculate systolic phase duration (from systolic onset to the notch) and diastolic phase duration (from the notch to the next systolic upstroke) 4
• In patients with pulmonary regurgitation, the dicrotic notch marks where diastolic flow reversal begins, as documented by holodiastolic jets starting at this point 3