Physiology of arterial pressure:-
When the left ventricle ejects the blood into the aorta, the aortic pressure rises. The maximal aortic pressure following ejection is termed the systolic pressure (Psystolic). As the left ventricle is relaxing and refilling, the pressure in the aorta falls. The lowest pressure in the aorta, which occurs just before the ventricle ejects blood in to the aorta, is termed the diastolic pressure (diastolic pressure). Afterload is the pressure required by the ventricle to eject blood.
The lower the afterload, the lower stroke volume will be.
Stroke volume is quantity of blood pumped out of the left ventricle with every heart beat
Heart rate is number of times the heart beats every minute
Known as Q is a measure of the amount of blood that is pumped out of the heart (ventricle) in one minute.
The cardiac output is made of two components heart rate and stroke volume.
HR x SV = Q
An increase in HR, SV or both will increase Q.
When the Blood pressure is measured using sphygmomanometer on the upper arm, the systolic and diastolic pressures that are measured represent the pressure within the brachial artery, which is slightly different than the pressure found in the aorta or the pressure found in other distributing arteries.
When the myocardium becomes damaged, cardiac output is insufficient to meet the oxygenation demands of the body. Blood pressure falls, and the myocardium gets weaker as it struggles to provide vital organs with oxygenated blood. Pharmacologic intervention may not be enough, also it may increase the demand on the myocardium. In cases such as MI, cardiogenic shock, septic shock, and cardiac surgery myocardial support can be the solution.
In summary the indication for support device are:-
- Cardiogenic shock
- Hemodynamic support for high risk cardiac catheterization laboratory procedure
- Acute myocardial infarction complicated by papillary muscle dysfunction, severe mitral regurgitation, ventricular septal defect, continuing ischemia
- Intractable ventricular arrhythmias
- Hemodynamic support for high risk cardiac surgery ; following cardiac surgery
- Bridge to transplant
Devices used to support the heart as a conjunction with pharmacology therapy are:-
- Intra-Aortic Balloon Pump-IABP (Counterpulsation device)
- Percutaneous left ventricular assist device (nonpulsatile assist device)
- Tandem heart – used as an implantable device for patients in end stage heart failure awaiting a donor for transplantation
The IABP catheter is placed in the ascending aorta through femoral access, because the coronary arteries branches from the ascending aorta.
The intra-aortic balloon catheter has a double lumen, the inner lumen is designed for a guide wire passage or pressure monitoring, and the outer lumen is designed for helium transport. Helium is used to inflate and deflate the balloon. Sometimes the balloon catheter has a fiber optic sensor for monitoring pressure and timing of deflation and inflation of the balloon for added accuracy.
Inflating a balloon catheter within the aorta during diastole to augment coronary perfusion and improve hemodynamics. Inflation of the balloon during diastole increases systolic pressure and stroke volume, which lead to an increase of Q. Balloon deflation occurs during diastolic pressure rapidly reduces afterload, which leads to increase stroke volume and eventually increases Q.
The inflation and deflation of the balloon is triggered by ECG and arterial pressure waveforms.
Catheter designed to actively unload the ventricle, allowing the heart to rest and recover. The distal end of the catheter has a pig tail, which rests within the ventricle. The pump itself is within the body of the catheter it draws blood through inlet ports in the pigtail segment, and the outlet ports lie within the aorta. The IMPELLA has different types, the most commonly used is LP 2.5 and IMPELLA CP. The LP2.5 can unload the left ventricle of 2.5 liters per minute of blood flow, the CP can unload up to 4.1 liters per minute.
- IABP uses heparinized normal saline or normal saline is used to prep the catheter and pressurized flush. Some hospitals D\C heparin flush solutions due to concerns over heparin induced thrombocytopenia
- Impella The purge cassette delivers rinsing fluid to the Impella® Catheter. The purge fluid (typically 20% dextrose solution) flows from the purge cassette through the catheter to the microaxial blood pump to prevent blood from entering the motor.
|Impella (left ventricular assist device-LVAD)
||Produce continuous flow from the left ventricle to ascending aorta
|Intra-aortic balloon pump
||Increase coronary perfusion Impella:-ressure
||Reduce end diastolic pressure\afterload
Contraindication of using both devices:-
The most common between both devices is aortic valve regurgitation. The displacement of blood during diastole would force additional blood volume through the incompetent aortic valve, increasing the severity of the regurgitation.
- Vascular complications:-
- During insertion, failure to advance the catheter because of severe peripheral arterial disease
- Aortic dissection
- Arterial perforation
- Ischemia to the left subclavian and renal arteries caused by improper balloon placement within the aorta
- Immune reaction
- Embolism, thrombosis
- Vascular injury through to angionecrotomy
- Positioning problems
- Infection and septicemia
- Dislocation of the pump
- Cardiovalvular injuries due to extreme movement of the suction cannula in relation to the cardiac valve or as a result of attachment by suction of the pump to the valve system following incorrect positioning.
- Endocardial injuries as a result of attachment of the pump due to suction
- Pump failure, loss of pump components following a defect
- Patient dependency on the pump after use for support