Tutoriales cardiacos

ATRIAL SYSTOLE
The end of diastole
| Heart:Prior to atrial systole, blood has been flowing passively from the atrium into the ventricle through the open AV valve. During atrial systole the atriumcontracts and tops off the volume in the ventricle with only a small amount of blood. Atrial contraction is complete before the ventricle begins to contract. |
| Atrial pressure:The "a" waveoccurs when the atrium contracts, increasing atrial pressure (yellow). Blood arriving at the heart cannot enter the atrium so it flows back up the jugular vein, causing the first discernible wave in thejugular venous pulse. Atrial pressure drops when the atria stop contracting. |
| ECG:An impulse arising from the SA node results in depolarization and contraction of the atria (the right atriumcontracts slightly before the left atrium). The P wave is due to this atrial depolarization.The PR segment is electrically quiet as the depolarization proceeds to the AV node. This brief pause beforecontraction allows the ventricles to fill completely with blood. |
| Heart sounds:A fourth heart sound (S4) is abnormal and is associated with the end of atrial emptying after atrial contraction. Itoccurs with hypertrophic congestive heart failure, massive pulmonary embolism, tricuspid incompetence, or cor pulmonale. |
Next phase

ISOVOLUMETRIC CONTRACTION
The beginning of systole
|Heart:The atrioventricular (AV) valves close at the beginning of this phase.Electrically, ventricular systole is defined as the interval between the QRS complex and the end of the T wave (the Q-Tinterval).Mechanically, the isovolumic phase of ventricular systole is defined as the interval between the closing of the AV valves and the opening of the semilunar valves (aortic and pulmonary valves). || Pressures & Volume:The AV valves close when the pressure in the ventricles (red) exceeds the pressure in the atria (yellow). As the ventricles contract isovolumetrically -- their volume does not...