Читать книгу Manual of Equine Anesthesia and Analgesia - Группа авторов - Страница 84

 The impulse exits the AV node and electrical activation of the ventricles occurs.This results in the QRS complex on the ECG.

 Ventricular contraction begins shortly after electrical activation.Ventricular pressure quickly exceeds atrial pressure.

 The AV valves are forced closed, producing the high‐frequency first heart sound (S1).Following closure of the AV valves and prior to the onset of ventricular ejection, the ventricle contracts on a constant volume of blood (isovolumetric contraction).

 When left ventricular pressure exceeds aortic and pulmonary artery pressure the semilunar valves open and ventricular ejection (the ejection period) begins.The time between the onset of the QRS and the opening of the semilunar valves (the pre‐ejection period) can be measured by echocardiography and is an index of ventricular myocardial contractility.Normal functional systolic “flow” or ejection murmurs may occur during the early part of the ejection period.The arterial pulse can be palpated during the ejection period, but the actual timing of the pulse depends on the proximity of the palpation site relative to the heart.

  The audible “cardiac impulse” or “apex beat” occurs during early systole when the contracting heart twists slightly, causing the left ventricle to strike the chest wall just caudal to the left olecranon.A “c” wave will be observed during early systole due to bulging of the tricuspid valve into the right atrium or possibly due to pulsations from the carotid artery.Ventricular contraction causes the atria to collapse toward the ventricles (ventricular “suction”), which causes a brief collapse of the jugular vein and a decrease in atrial pressure (the “x” descent).

 Following this event, atrial filling begins.This generates the positive “v” wave.