Page 403 - fbkCardioDiabetes_2017

Cardio Diabetes Medicine 2017 379

ECMO system is distinct from all the other devices by 80 and 50%, and marked improvement in symptoms
very effectively providing circulatory support (mean and quality of life. While the traditional indications for
arterialpressure will increase). However, by directly implantation were divided into bridge to transplanta-
transferring venous blood intothe systemic circula- tion, bridge to decision and destination therapy, the-
tion, afterload goes up and the left ventricle has to improved reliability of today’s devices and the lack
work harder. As such, VA ECMO in isolation will not of available organs for transplantationhas led to a
unload the left ventricle and would need the addi- paradigm shift where future device will be designed/
tion of pharmacological (e.g. inotropes), mechanical tested for short or long term use, without a transplant
(e.g.intra-aortic balloon pump, Impella) or surgical (e.g. associated label.
direct left atrial or ventricularvent) unloading. In addi- First generation positive displacement pulsatile de-
tion, there are limited data to understand the effect vices (e.g. Thoratec HeartMateXVE, Novacor LVAS)
of VAECMO on coronary perfusion pressure.A clear used a diaphragm and unidirectional valves to mimic
understanding of each device strengths and weak- the pulsatile cardiac cycle through diastolic filling and
ness is crucial,since the complications are not trivial. systolic emptying of the pump.The use of HeartMate
Patients are kept on support until end organ function XVE in the Randomized Evaluation of Mechanical As-
has improved and a decision of weaning for recovery sistance for the Treatment of Congestive Heart Fail-
or proceeding to permanent support is achieved, or ure (REMATCH) trial opened the door for mechanical
palliative withdrawal is instituted.
circulatory support for long-term use in transplant
The initial approach is to quickly achieve normal in eligible patients (“destination therapy”). However,
perfusion (mean arterial pressure above 65 mmHg, due to their size, adverse events and limited dura-
lactate level below 2 mmol/L),while maintaining the bility (18-24 months), their use was very limited and
acid base equilibrium (pH 7.3-7.4), adequate tissue these pumps were eventually discontinued in mid to
oxygenation(hematocrit above 30 %), and urine out- late 2000s.
put (greater than 1.5-2 mL/kg/h). All patients should Second and third generation continuous flow pumps
be anticoagulated with intravenous heparin, targeting are smaller, enjoy simpler implantation, and have
partial thromboplastin time of 45-60 s or unfraction- more limited blood contacting area with fewer mov-
ated heparin level of 0.3-0.5 U/mL. When hemo- ing parts and without valves, air vents and com-
dynamicsimprove (right atrial pressure below 10-12 pliance chambers, leading to longer durability and
mmHg, pulmonary capillary wedge pressures below reduced risks for thromboembolism, infection, and
20 mmHg), echocardiography guided weaning ofthe malfunction. They use a permanent magnetic field
support is attempted. The amount of support should designed to rapidly spin a single impeller supported
gradually be decreased (from full support of4-5 L to by mechanical,hydrodynamic (using a layer of blood
minimal support of 1-1.5 L), while paying attention to – blood bearing – to lift the rotor) or magnetic bear-
left ventricular size,severity of mitral regurgitation, ings (using magnetic bearings to levitate the rotor).
right ventricular function (fractional area change, Second-generation axial pumps have the impeller
freewall s’) and hemodynamics (mean arterial pres- outflow directed parallel to the axis of rotation with
sure, right atrial pressure and pulmonary capillary the rotor spinning on mechanical (Abbott HeartMate
wedge pressures). If the weaning is successful, the II,Jarvik 2000, Reliant Heart HeartAssist 5) or con-
temporary mechanical circulatory support is removed tact-free bearings (Berlin Heart Incor). Third-gener-
and patients are bridged via inotropes to oral heart ation centrifugal pumps have the impeller outflow
failure therapies. If the weaning is unsuccessful, the perpendicularto the axis of rotation (Medtronic Heart-
patients are then implanted with durable ventricu- Ware Ventricular Assist Device [HVAD] and Abbott
larassist devices.
HeartMate III) or use a mixed design, where blood
flows along the axis of rotation but exits perpendicu-
Durable (Permanent) Mechanical Circulatory lar to the inflow (Medtronic HeartWare miniatureven-
Support Devices tricular assist device [MVAD]).
Durable ventricular assist devices are evolving into
an effective and reasonably cost-effective therapy Underlying Physiologic Principles of
for a growing population of patients with advanced Continuous Flow Devices
heart failure.They provide significant left ventricular The pump blood flow is directly proportional to the
unloading and increased cardiac output and improve rotor speed and inversely proportional to the pres-
end-organ function. Patients supported with ventric- sure differential across the pump (i.e. head pressure,
ular assist device enjoy one and 5-year survival of
the pressure difference between the left ventricle and

Cardio Diabetes Medicine