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Chapter: Clinical Anesthesiology: Anesthetic Management: Cardiovascular Physiology & Anesthesia

The Cardiac Cycle

The cardiac cycle can be defined by both electrical and mechanical events.

THE CARDIAC CYCLE

The cardiac cycle can be defined by both electrical and mechanical events ( Figure 20–2). Systole refers to contraction and diastole refers to relaxation. Most  diastolic ventricular filling occurs passively before atrial contraction. Contraction of the atria normally contributes 20% to 30% of ventricular filling. Threewaves can generally be identified on atrial pres-sure tracings (Figure 20–2). Theawave is due to


atrial systole. The c wave coincides with ventricular contraction and is said to be caused by bulging of the AV valve into the atrium. The v wave is the result of pressure buildup from venous return before the AV valve opens again. The x descent is the decline in pressure between the c and v waves and is thought to be due to a pulling down of the atrium by ventricular contraction. Incompetence of the AV valve on either side of the heart abolishes the x descent on that side, resulting in a prominent cv wave. The y descent fol-lows the v wave and represents the decline in atrial pressure as the AV valve opens. The notch in the aor-tic pressure tracing is referred to as the incisura and is said to represent the brief pressure change from transient backflow of blood into the lef t ventricle just before aortic valve closure.

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Clinical Anesthesiology: Anesthetic Management: Cardiovascular Physiology & Anesthesia : The Cardiac Cycle |


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