Download Chapter XII Mechanical assistance

CHAPTER XII – Mechanical Assistance of Circulation - Marian GASPAR
12. 1. History of Mechanical Assistance of Circulation
The need to sustain the heart mechanically has emerged with the introduction of extracorporeal
circulation in open heart pathology approach. In 1953, J. Gibbon used in surgical practice for
the first time the heart-lung machine to repair an interatrial defect. About 5% of patients
operated on heart require mechanical support for overcoming the critical period after the pump
to improve the depressed function of the heart or to heart transplant. The attempt to replace the
heart with a mechanical heart has concerned scientists since before open heart operations, at
least experimentally. In 1937, Demikhov implanted the first artificial heart in dogs.
Introduction. Incidence of heart failure has increased both due to the process of growing old
and by more efficient methods of treatment, by increasing life expectancy in cardiac patients
(coronary, valvular, congenital). Therefore, many of them get to the stage of end-stage heart
failure which has the only efficient method of treatment- the heart transplantation. However,
the small number of donors cannot meet these needs so that many come to be supported for
various periods of time by mechanical devices while waiting for a transplant or recovery of
cardiac function.
12. 2. Major indications of mechanical assistance of circulation
There are two main categories of patients who need MAC: a) - those who expect a recovery in
temporarily lost cardiac function, b) - those who decompensate on the waiting list of a heart
transplant.
12. 3. Intraaortic balloon counterpulsation (IABC)
It is the easiest way to support the heart in contractility depression, for a short period of hours
or days. It can even be installed outside the operating room, in cardiac catheterization rooms
and in specialized ambulance service.
Technical presentation. The device consists of a mobile computer console that displays
hemodynamic parameters and controls the frequency and amplitude of a chamber filled with
polyurethane, inserted in descending thoracic aorta. The balloon itself is attached to the end of
a catheter ranging between 7 to 12 French in size, with helium filling volume of 4 - 40 ml,
(chosen according to patient’s size, adult or child).
Hemodynamic effects of counterpulsation balloon
The balloon is inserted through the femoral artery punction up to the descending thoracic aorta,
2-4 cm below the origin of the left subclavicular artery.
The synchronization with patient’s ECG ensures the beginning of the gonflation once the aortic
valve is closed (ventricular diastole) and deflated, immediately before the start of ventricular
systole. This ensures a reduction of left ventricle work and coronary flow increase. Thus, LV
reduces postload, rhythmic work, to restore the depressed contractile capacity. By means of
counterpulsation balloon, cardiac output increases about 20%.
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IABC Indications
The criteria for mechanical circulation support become objective by patient monitoring, who
presents a systolic blood pressure below 90 mmHg, cardiac index is reduced below 2 L/min/
m2, pressure in right or left atrium is over 20 mmHg and urine output is below 20 ml / h, by all
maximum means of pharmacologic support. This hemodynamic configuration can be met in:
• left ventricular failure under ECC
• cardiogenic shock after acute myocardial infarction
• heart support in angioplasty procedures in hemodynamically unstable patients
•set angina pectoris, unresponsive to complex therapy
• preoperatively in hemodynamically unstable patients
• cardiac contusion
• heart transplant candidates who become unstable.
It is contraindicated in patients with aortic dissection and those with aortic valve regurgitation.
Complications
Complications may occur both due to the insertion maneuvers and use of up to 20% IABC.
Thevascular, local complications, at punction level, acute lower limb ischemia (by thrombosis,
embolism, dissection, hematoma) require surgical intervention, infection, femoral nerve lesion
or on the trajectory of the advancing catheter, iliac arteries, abdominal aorta and thoracic aorta:
dissections, distal embolisms, visceral ischemia, which can be serious or even fatal. These
complications occur particularly in patients that also present associated vascular lesions. They
must be identified in time and properly resolved.
IABC is maintained until the recovery of contractile function, several hours or days, then
gradually reduced and stops when haemodynamic stability permits.
12. 4. Extracorporeal Membrane Oxygenation (ECMO).
Definition.
ECMO ajuta plamanul si cordul pe perioada critica prin preluarea partiala a functiei acestora,
dar nu se adreseaza direct bolii de baza.
ECMO is a special procedure of supporting pulmonary and cardiac function with
extracorporeal circulation pumps. It is used especially in infants and children with severe lung
damage but also in adults with cardiorespiratory failure.
The purpose of this method is to provide a mechanical support to the function of blood
oxygenation, remove the CO2 excess and, thus, improve cardiac function.
ECMO helps the lung and heart during critical time by taking over their partial function, but it
does not directly address the disease.
Technical presentation.
ECMO is composed of: a mobile centrifugal pump which regulates hemodynamic parameters
(flow, volume, blood temperature), oxygenator and the piping connecting special cannulae
inserted into patient’s arterial and venous system.
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There are two types of ECMO: veno-arterial which supports the lungs and heart and venovenous which only supports pulmonary function.
Table. Indications of ECMO use
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• child and adult respiratory distress syndrome
• severe pulmonary hypertension
• aspiration of meconium at birth
• severe respiratory failure caused by severe trauma, embolisms or infections
• postoperative myocardial dysfunction (coronary, valvular, congenital, posttransplant)
• postprocedural cardiogenic shock to angioplasty
• severe intoxication
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Installing ECMO. It can be installed in the operating room, catheterization laboratory or
intensive care, usually by percutaneous puncture of femoral vessels, femoral artery and vein
using special cannulae which connect to the piping that leads to oxygenator. It provides blood
oxygenation and CO2 removal. Blood circulation in tubular circuits and oxygenator is
provided by a mobile centrifugal pump (Medtronic).
Fig. ECMO installed in the right femoral vein and artery, which provided mechanical support
temporarily until a biventricular Thoratec Assist Device was installed (patient of 24 years with
acute myocarditis and cardiogenic shock-Innsbruck 2002).
Complications of ECMO. The main complications of ECMO are: bleeding, infection,
thrombosis and cerebral embolism, technical deficiencies of the machine.
12. 5. Mechanical ventricular assist (MVA)
Definition. The support of severely depressed cardiac function, for a period of time, by taking
over the pumping activity by a mechanical system in order to recover ventricular function
"bridge to recovery" or to sustain life until heart transplantation" bridge to transplantation ".
MVA Indications.
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• low cardiac output syndrome after heart surgery, which cannot take medication, or by
IABC, ECMO
• severe postinfarction cardiogenic shock with severely impaired cardiac function
• post-procedural cardiogenic shock, angioplasty, stent placement with major
complications
• acute myocarditis with severe cardiogenic shock
• patients on the waiting lists with end-stage heart failure who are acutely
decompensated.
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Mechanical systems of circulation assist
Mechanical circulatory assist pumps are of two types: rotary and deplacing The deplacing
pumps work by periodical change of the work space which ensures transfer of energy and give
a pulsatile flow, IABC, Novac, Medos, Thoratec, Berlin Heart. In rotary pumps enegy transfer
into the blood is ensured through velocitary changes given by a spiral system: Impella,
centrifugal Vienna Biopump.
Based on the placement of the pumps outside or inside the body, they are divided into
extracorporeal pumps, (nonpulsatile, ECMO, extracorporeal pulsatile Abiomed) and
implantable pulsatile (Novac Therumo).
Fig. Berlin Heart paracorporeal circulation assist pump for adults and children, pump, cannulae
and driving control system. (First Berlin Heart implant at a young boy, 14 years old, in
Innsbruck, Austria, 2001)
Types of pumps. 1) pulsatile pump. It works like a sac of blood on which it is operated by
external compression of gas, a) - pneumatic pump (Abiomed, Thoratec, Heart Mate) or an
electrically driven membrane in b) - motor pump (Novac). Unidirectional blood flow pump is
provided like natural heart by mechanical or biological valves that regulate blood direction
(Fig.)
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Fig. Pneumatic pulsatile pump with monodisc mechanical valve that regulates unidirectional
blood flow
2)-Nonpulsatile centrifugal pumps. They use the centrifugal force, provided by a spiral
system which aspires blood from the heart and then pushes it into the arterial system
(BioMedicus, Medtronic, Sarns). There are no valves to ensure unidirectional closure of the
circuit, which is open and only set by centrifugal force.
Implantation technique.
MVA implantation is made through median sternotomy, usually under the ECC to ensure heart
decompression without its stop. Depending on the need, left ventricular system is implanted
only (LVAD-Left Ventricular Assist Device) or / and right (RVAD-Right Ventricular Assist
Device, both BVAD). The principle is simple, with a cannula which is connected to LA or LV,
blood is aspirated from the heart during diastole by the pump which then pumps it in the
ventricular systole, in ascending aorta. Thus, LV is put at rest for recovery.
If RVAD, a cannula which incorporates the blood is placed in RA and then is ejected by the
pump in pulmonary A. through the cannula connected to this level. Once MVA installed, the
ECC stops, optimum operating pump parameters are established and the pump is still
supervised by highly specialized staff, cardiotechnicians and therapists the whole period until
explantation. Some systems are fixed and the patient remains in hospital over this period or the
new portable systems where patients can be left during the months before heart transplantation
(Fig.).
Fig. Driving control unit, fixed and mobile (Berlin Heart Assist Device)
MVA Complications
During this period a number of complications can occur. The most considerable ones are:
bleeding, infection, thrombotic embolic cerebrovascular accidents and mechanical systemic
deficiencies of the device.
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12. 6. Total Artificial Heart
It is a biventricular device (TAH, Total Artificial Heart, CardioWest) which incorporates heart
activity that is totally explanted, like the heart transplant process. There are two systems: the
pneumatic and electric systems which function as an artificial heart, in "full-to-empty" mode.
Implantation is done in the same way as in cardiac transplantation using ECC, bicaval
cannulation. Among the used devices, the Jarvik-7-100 system has worked the most, 620 days.
The system is encumbered by a number of serious complications, bleeding, thrombosis,
infections leading to patient’s death.
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