Discuss the potential mechanical strategies for supporting myocardial function in a 45-year-old male presenting with cardiogenic shock post-revascularisation for an acute anterior myocardial infarction.
In your answer include the physiological rationale for each strategy.
Positive End Expiratory Pressure
This can either be delivered invasively or non-invasively. By increasing the positive pressure within
the thoracic cavity, venous return to the heart is reduced thereby reducing cardiac preload to
facilitate movement back to the optimal point on the Starling Curve. Also reduces afterload by
reducing pressure gradient across the myocardial (left ventricular) wall. Also reduces work of
breathing (reduces cardiac work) and improves PaO2 (O2 delivery to coronary blood flow).
Intra-Aortic Balloon Pump
The inflation of the intra-aortic balloon pump at the time of diastole increases coronary perfusion to
increase cardiac contractility and reduces the after load at the commencement of systole as the
Emergency transcutaneous, temporary transvenous and permanent multi-chamber pacing. Improves
cardiac output by optimising the heart rate and/or synchronising A-V conduction optimising “atrial
kick”. Increasing the heart rate to normal in profound bradycardia as CO = SV x HR. Overdrive
pacing in tachyarrhythmias to re-establish normal conduction and then slow the heart improves
cardiac output by increased ventricular filling and improved coronary artery perfusion in diastole.
Ventricular Assist Devices
This provides either a continuous or pulsatile pumping of blood from the left ventricle directly into the
aorta (LVAD) or from right atrium or right ventricle directly to pulmonary artery (RVAD) or functions
as both (BIVAD).
Decreases workload of the heart whilst maintaining adequate flow and blood pressure.
Indicated if potentially reversible myocardial stunning or as a bridge to transplantation or for support
during high-risk revascularisation procedures. In this patient as a bridge to transplantation may allow
management as outpatient. Requires cardiac surgical expertise for insertion and so not available in
Veno-Arterial Extra Corporeal Membrane Oxygenation
Venous blood is extracted, oygenated externally and then pumped and returned to the arterial
system providing both oxygenation and circulation. Decreases workload of heart and lungs whilst
maintaining flow, blood pressure and oxygenation.
Requires expertise for insertion and maintenance and not available in all ICUs.
This question is virtually identical to Question 19 from the second paper of 2012. To simplify revision and sabotage SEO, this table is copied here without any alteration.
Positive pressure ventilation:
|Temporary transcutaneous pacing:|
|Temporary transvenous pacing|
|Cardiac resynchronisation therapy: biventricular pacing|
|Intra-aortic balloon pump:|
|Ventricular assist devices:|
Though strictly speaking it is a "mechanical haemodynamic support strategy", the author still could not bring himself to include manual cardiac compressions in the list above.
Cove, Matthew E., and Graeme MacLaren. "Clinical review: mechanical circulatory support for cardiogenic shock complicating acute myocardial infarction." Crit Care 14.5 (2010): 235.
Boehmer, John P., and Eric Popjes. "Cardiac failure: mechanical support strategies." Critical care medicine 34.9 (2006): S268-S277.
Cooper, David S., et al. "Cardiac extracorporeal life support: state of the art in 2007." Cardiology in the young 17.S4 (2007): 104-115.
Brignole, Michele, et al. "2013 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy." European heart journal (2013): eht150.