The cardio vascular system is made up of three main sections:
a. The Heart: the driving organ which provides the exact amount of blood momentarily required, it provides strokes of blood which are energy loaded, in a governed rate and shape.
b. The Vascular bed: This is the distribution system of the blood to the various organs, in accordance with the specific needs of each of them. It also acts as collecting system and general reservoir for blood, towards its reallocation to the heart, to be distributed on a beat by beat basis, in accordance with the integrated needs of the entire body.
c. The control: The control system is made up of subsystems which control the various organs via feed-back loops. All these controlled loops are part of the Central Nervous Systems (CNS), where they are evaluated and integrated. The CNS then operates the vascular flow towards the heart to provide the exact amount of blood to be circulated on the next beat and activates the heart to provide that volume of "blood stroke" at a predetermined rate and shape.
The heart's ventricles are operated by the following parameters, which are governed by the heart's own control system:
1. Preload: the pressure of the atrium preceding the acting ventricle, which defines the volume of the next stroke; PA0 2. Afterload: the "pressure head" against which the ventricle has to act; PA0 3. Contractility: the capability of the myocardium (the heart's muscle) to apply the needed force to reach the required stroke; PA0 4. Rate the heart's beats per minute which together with the stroke volume define the cardiac output.
The coordinated performance of all these above operators is manifested in the Cardiac-Output, which provides the amount of blood per beat, at the right pressure wave.
In case of heart failure, the entire flow system is disturbed. Such disturbance is manifested by an inadequate Cardiac Output and damming of blood behind the defective heart chambers.
Depending on the kind, rate of development, and severity of the heart failure, a whole set of compensating mechanisms is activated in the vascular system by its control system, reallocating and affecting pressures, directing the reduced flow to the various organs, bringing the whole vascular system to a new balance point. This new balance point is in accordance with the central control system, operating the heart's controls as well.
However, in acute heart failure (such as acute myocardial infarction, AMI) a reduction in cardiac output and acute damming of blood behind the affected ventricles occurs. This effect might be too big to be regulated by those compensatory mechanisms and thus be fatal.
If all conventional therapeutic treatments of the heart failure mechanical support of the heart and circulation is required, and more specifically, Ventricular Assistance.
This form of sustained life assist might either be temporary or permanent.
A temporary heart assist system can, for example, be applied to patients who cannot be resuscitated (such as at AMI, or the end of an open heart operation) while recovery of the ventricular function is anticipated. If this does not happen, the device serves as a "bridge to transplantation" until a donor heart will be available.
The permanent ventricular assistance should be applied to patients who sustain permanent damage, where recovery is not anticipated, and the patient is not a candidate for heart transplantation, for any reason.