Mechanical haemodynamic support strategies in brief summary

This is a brief overview of the mechanical strategies in haemodynamic support. It was the topic of several past paper SAQs:

  • Question 20 from the first paper of 2025
  • Question 4 from the first paper of 2017
  • Question 19 from the second paper of 2012 (virtually identical)
  • Question 13 from the first paper of 2007 (briefly and vaguely touched upon)

Given the awesomeness of these strategies, one could really go on and on about them. However, the time-poor exam candidate would not appreciate any extensive rambling digressions on this issue. A brief point-form review is probably called for. Fortunately, a good resource for this exists in the 2010 article by Cove and MacLaren. Together with the official college answer, this article was used as the basis of the table offered below.

 Mechanical Haemodynamic Support Strategies
Strategy Advantages Limitations

Positive pressure ventilation:
the use of positive pressure to decrease LV preload and afterload (by manipulating LV transmural pressure)
  • Easy to apply
  • Minimally invasive
  • Added benefit of improved oxygenation and gas exchange
  • Invasive ventilation has the added benefit of anaesthesia +/- paralysis, which decreases whole-body oxygen demand
  • Preload reduction may result in hypotension in the volume-depleted patient
  • Increased intrathoracic pressure increases RV afterload, exacerbating right heart failure
  • Positive pressure may result in barotrauma and volutrauma
  • All the risks of mechanical ventilation apply, eg. VAP
Temporary transcutaneous pacing:
Increase cardiac output crudely, as CO = HR × SV
  • Requires minimal skill to apply
  • Minimally invasive
  • Cardiac output will increase in proportion to hear rate
  • Requires a substantial amount of analgesia and sedation
  • Uncomfortable for the patient
  • May cause significant tissue damage
  • Not a long-term solution
  • Poor A-V synchrony with 

Temporary transvenous pacing

Increase cardiac output crudely, as CO = HR × SV
  • Comparatively easy to insert
  • Dual-chamber pacing may improve A-V synchrony and restore the "atrial kick".
  • Not only does it work in bradycardia, but also by "overdrive pacing" in tachycardia, where the slowed heart rate allows for longer diastolic filling
  • Requires some expertise to manage and troubleshoot
  • Invasive, with all the risks of large-bore central venous access
  • Generally, one can only pace the ventricle, which means A-V synchrnoy will be lost; the "atrial kick" may be sorely missed by patients with severe valve dysfunction
Cardiac resynchronisation therapy: biventricular pacing with precise timing improves the synchrony between ventricles, making their activity more efficient 
  • Restores synchrony to ventricular contraction in patients with severe heart failure
  • There is strong evidence that CRT reduces mortality and hospitalisation  (i.e. it is superior to AICD or medical therapy).
  • Requires specialist skill to insert and adjust; hardly an emergency procedure
  • To benefit, one must have LBBB, a wide QRS, and an LVEF less than 35%.
  • Generally, only about 5-10% of heart failure patients will benefit
  • There is a "heterogeneity of effect" in patients  who do not meet the recognised criteria (read: it does them no good)
Intra-aortic balloon pump: Inflates a balloon in the aorta during diastole, improving coronary filling; deflates it during systole, reducing afterload.
  • Decreases LV afterload
  • Improves coronary arterial filling in diastole
  • Improves forward flow though defective mitral valves
  • Nowadays, little adjustment is required (automatic timing is usually satisfactory)
  • "Severe" cardiogenic shock is still not very well investigated, and there may be an unrecognised  mortality benefit in this group.
  • Violently invasive
  • Requires a certain level of expertise to place correctly.
  • Significant complications are associated with its use, including a non-zero rate of death and limb loss.
  • The mortality benefit in most patients might either be marginal or altogether absent, depending on what you read. Certainly, the IABP-SHOCK II trail did not demonstrate any survival improvement.
  • Does not benefit the right ventricle.
  • Contraindicated in aortic regurgitation
  • Poor effect in AF, particularly rapid AF
Ventricular assist devices: bypass the native LV, RV or both, to pump blood into the pulmonary and systemic circulation
  • Decreases myocardial workload
  • Offers a bridge to heart transplantation
  • Effective temporary support for myocardial stunning
  • May afford a period of outpatient management
  • Highly invasive
  • Requires surgical expertise to implement
  • Requires significant anticoagulation
  • Substantial risk of infection (50%)
  • Does not oxygenate the blood
  • In spite of anticoagulation, there is a significant risk of thrombosis

VA- ECMO: 

extracts venous blood, oxygenates it, and returns it under pressure into the systemic circulation (retrograde flow)
  • Not only decreases myocardial workload- it may take over all of the circulatory workload.
  • Attends to both circulation and gas exchange
  • Easier to implement (percutaneous technique does not require surgical expertise)
  • Unloads the RV and LV by transferring some preload to the circuit
  • Highly invasive
  • Requires expertise to implement
  • Requires significant anticoagulation
  • In spite of anticoagulation, there is a significant risk of thrombosis
  • All the complications of large-bore arterial and venous access
  • Can increase LV afterload and cause LV dilatation

Impella microaxial flow pump

Traverses the aortic valve, pumping blood from the LV into the aorta
  • Can be inserted percutaneously
  • Decompresses LV, decreases afterload 
  • Capable of substantial cardiac output (~ 5L)
  • Placement requires skill set which is not widely available
  • Expensive even for an ECMO type device
  • May not achieve enough cardiac output to satisfy demand
  • Does not oxygenate the blood

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.

References

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.

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