The A Wave or Palpable Atrial Hump

1. How does a cineangiogram show the effect of a contracting atrium on the ventricle?

ANS: With contrast material in the LV, a cineangiogram can show that the LV suddenly expands at the end of diastole in response to atrial contraction.

2. When is this end-diastolic or presystolic expansion of the LV palpable?

ANS: The normal A wave is not palpable. Only a very strong left atrial contraction can expand the LV with enough force to cause a palpable presystolic hump on the LV impulse.

Note: If the atrial hump, or A wave, is too close to the outward movement of the ventricular contraction, it may be impalpable even if it is very high. This can be caused by a short P-R interval.

A short P-R of about 80 ms due to a preexcitation abnormality has caused the atrial hump (A) to be too close to the major ventricular movement to be palpable.

3. What is the cause of a left atrial contraction strong enough to make a palpable LV hump at the LV impulse?

ANS: Severe loss of LV compliance (i.e., loss of distensibility of the LV).

Note: The strong atrial contraction effect on the LV is often called the "atrial kick" or booster-pump effect. The reason for this is that the expansion of the LV just before its contraction produces an increased energy of ventricular contraction via the Starling effect. The A wave has the same significance as does the S4.

4. How does the left atrium "get the message" to contract harder when the LV is stiffer?

ANS: In diastole, the mitral valve is open and the left atrium and ventricle are in continuity (i.e., they are, in effect, an atrioventricle). When the ventricle is stiff, the atrioventricle is also stiff, and when blood pours into a stiff chamber, the pressure rises steeply. If the atrium is under high pressure at the end of diastole, then, due to the Starling effect, it will contract more strongly.

Note: The atrium will hypertrophy in response to its continued strong contractions and will then contribute to the stiffness of the atrioventricle.

Normal atrioventrlcle Stiff atrioventricle

A stiff ventricle must be transmitting its loss of compliance to the atrium during diastole when the AV valves open.

Normal atrioventrlcle Stiff atrioventricle

A stiff ventricle must be transmitting its loss of compliance to the atrium during diastole when the AV valves open.

5. What is the most common cause of chronic increased stiffness of the LV? What is the next most common?

ANS: LVH, secondary to hypertension. The next most common cause is coronary disease (i.e., the confluent patchy areas of fibrosis or infarction plus the tendency to hypertrophy of the remaining healthy myocardium can cause a stiff LV).

6. Why is it important to palpate for an A wave?

ANS: The S4 may be inaudible, or the S4, Sl may be mistaken for an Sl, ejection sound. You may be able to palpate an A wave but not hear an S4 because the frequency of vibrations may be too low for audibility but not for palpation.

7. What does an atrial kick feel like to the palpating fingers?

ANS: When it is strong and far from the ventricle outward movement, it feels like a double outward movement. When it is slight or close to the ventricular outward movement, it feels like a notch, vibration, or hesitation on the apical upstroke.

Note: These movements are best felt by the part of the hand near the fingertips with the patient in the left lateral decubitus position. Occasionally a suspected faint atrial kick can be confirmed by observing a double outward movement of the patient's skin, or of your stethoscope on the LV impulse. An atrial hump may only be felt with light finger pressure unless there is much muscle or fat, in which case it will be necessary to press firmly.

Atrial Kick

Far from

Close to lv movement

Atrial Kick

Far from

Close to lv movement

Notch or Double hesitation outward on upstroke movement

Notch or Double hesitation outward on upstroke movement

If only a notch or slight hesitation is present on the upstroke, the tips of the fingers must be used to perceive it. If a large double movement is felt, it must be distinguished from a mid-systolic dip.

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