University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

139

Pages:

2
Author:

Mariam A. A.

• Cardiac ventricles • Left ventricle: dual motion o Constrict circular muscle layers ↓ diameter of the progressing from the apex → base o Power/pressure stroke Contract spiral muscles o Pulls the mitral valve ring toward the apex o Shortening ▪ Conical shape ▪ Smaller surface-to-volume ratio 1. 2. 3. 4. 5. 6. Atrial depolarisation begins: signal spreads from SA node depolarises the atria Atrial depolarisation complete: atrial systole begins Ventricle begins to depolarise at apex → atria repolarises → atrial diastole Ventricular depolarisation is complete → ventricular systole Ventricles begin to repolarise at apex, before ventricular diastole Ventricular repolarisation complete, ventricular diastole Ventricular repolarisation • Repolarisation spreads less quickly from: o Apex → base o Epicardium → endocardium ▪ Opposite charge (negative) ▪ Opposite direction (epi-endo) • Negative wave moving away from positive electrode (double –ve) • Same as vector as a positive wave moving towards + electrode • Positive deflection same as QRS • • Theory o Epi-endoprogression: contraction → compression of subendocardium delaying repolarisation o Repolarisation slower/disperse in time: progression not coordinated by purkinje fibres by local mechanism If ventricular repolarisation begins at the same location and travelled in the same direction as the depolarisation wave (from the endocardium where Purkinje fibres are situated) and goes across the wall to the epicardium → slow negative wave occurring in the direction opposite to the depolarisation wave o Directly superiorly to the right and anteriorly, with the mean T wave vector being opposite to the QRS vector o This is not the case with the whole heart because repolarisation occurs in from epicardium to endocardium leading to a T wave having the same direction as the depolarisation wave o Repolarisation is a slower process → fewer cells are being repolarised at any moment and the repolarisation wave (T wave) is longer (which could be displayed as more vectors per unit time) and is of lower amplitude than the depolarisation wave o One theory for the opposite direction of repolarisation holds that the buildup of pressure by contraction of the left ventricle compresses the subendocardial (inner wall) tissue, thereby delaying repolarisation in that area