Carotid Pulse Synchrony with Heart Sounds
The carotid pulse is synchronous with the first heart sound (S1), not with S2. Specifically, the carotid upstroke coincides precisely with the onset of S1, occurring approximately 43 milliseconds after aortic valve opening 1.
Timing Relationships
The carotid arterial pulse demonstrates the following precise temporal relationships:
- The carotid upstroke is exactly coincident with the onset of the first carotid arterial sound (CaS1), which corresponds to S1 1
- The mean interval from QRS onset to the carotid arterial sound is Q-CaS1 = 131 ± 15 ms 1
- The dicrotic notch of the carotid pulse (representing aortic valve closure) coincides with S2, not the main upstroke 1
- The second carotid arterial sound (CaS2) occurs at Q-CaS2 = 412 ± 36 ms, corresponding to aortic valve closure and S2 1
Physiologic Mechanism
The synchrony between the carotid pulse and S1 reflects the mechanical events of ventricular systole:
- S1 occurs with completion of atrioventricular valve closure, with M1 (mitral component) occurring at 0.06 ± 0.003 seconds from the Q wave 2
- The carotid upstroke represents the rapid ejection phase immediately following aortic valve opening 1
- The delay between S1 and the carotid upstroke is approximately 43 ± 6 ms, representing the time for the pressure wave to travel from the aortic valve to the carotid artery 1
Clinical Relevance for Physical Examination
When palpating the carotid pulse during cardiac auscultation:
- The palpable carotid upstroke helps identify S1 versus S2, particularly useful when heart sounds are difficult to distinguish 1
- In severe aortic stenosis, the carotid pulse demonstrates a delayed, dampened upstroke (pulsus parvus et tardus), which can help confirm the diagnosis when combined with a soft or absent A2 component of S2 3
- Carotid bruits may indicate atherosclerotic disease and should prompt evaluation for underlying coronary artery disease 4
Common Pitfall
A common misconception is that the carotid pulse coincides with S2 because both relate to aortic events. However, the palpable carotid upstroke represents the systolic ejection wave and thus synchronizes with S1, while the dicrotic notch (not typically palpable) corresponds to S2 1.