Cardiac cycle
Cardiac function refers to the hearts capability to fulfill its task as the motor or pump of the blood circuit satisfying the bodies demands of oxygen and nutritive substances as well as the removal of waste products.
A direct measure of cardiac function is cardiac output which can be increased to 3-4 fold at strenuous exercise but only as long as the venous return will keep up at a similar rate.
The cardiac cycle can be described by the following phases (starting off from end-diastole) :
- closed atrioventricular valves
- isovolumetric contraction and intraventricular pressure buildup
- opening of the semilunar valves
- rapid ejection (maximal outflow, the build-up of systolic artery pressure)
- reduced ejection with a decline in ventricular tension after repolarization
- closure of the semilunar valves - end of systole
- isovolumetric relaxation - eventually leading to an atrioventricular pressure gradient
- opening of the atrioventricular valve
- rapid inflow or early filling due to the lower ventricular pressure
- slow filling and equalization of intraarterial and intraventricular filling pressures (diastasis)
- atrial contraction and late filling (about 15% of atrial volume)
- closure of the atrioventricular valves - end of diastole
Systolic function refers to the heart's ability to throw out a specific amount of blood in a certain amount of time. It is based on the following factors :
- preload filling volume and filling pressures (preload)
- vascular resistance and arterial pressure (afterload)
- myocardial contractility
- heart rate
Diastolic function refers to the capability of the cardiac chambers to fill adequately. It is characterized and dependent on different factors which include :
- end-systolic and end-diastolic volumes and filling pressures
- ventricular relaxation
- elastic recoil
- chamber stiffness
Radiographic features
Visual analysis
Includes the following features :
- hemodynamic interaction between the chambers
- synchrony/asynchrony, shunts, constriction etc.
- cardiac chamber size
- global and segmental wall motion assessment
- normokinesia, hyperkinesia, hypokinesia, akinesia, dyskinesia
Quantitative analysis
Basic quantitative methods for the evaluation of cardiac function include :
Systolic function
- cardiac chamber size (cardiac volumes)
- end-diastolic volume and end-diastolic volume index
- end-systolic volume and end-systolic volume index
- atrial chamber size
- myocardial wall thickness and wall thickening
- stroke volume and stroke volume index
- cardiac output and cardiac index
- ejection fraction
Diastolic function
- mitral inflow early diastolic velocity (E)
- mitral annular early diastolic velocity (e')
- E/A ratio and E/e’ ratio
- peak tricuspid regurgitation velocity
Additional or advanced functional measurements include the following :
- cardiac strain parameters e.g. global longitudinal strain or left atrial strain
- mitral annular plane systolic excursion (MAPSE)
- tricuspid annular plane systolic excursion (TAPSE)
- longitudinal wall fractional shortening (LWFS)
See also
