Question 20

College answer

Syllabus topic/section:

2.1.4    Cardiovascular Intensive Care: Mechanical supports IABP: L1

Discussion: 

Listing the indications and complications was well done by candidates that knew the topic.

Candidates that did well for part ii) were able to outline the haemodynamic effects and relate them to the indications they had listed in part i). For example, describing how an IABP may be beneficial in acute MR or VSD provided candidates with a good structure to their answer. It also ensured they outlined the effects rather than just listing them which scored less marks as the question asked candidates to “outline (provide a summary of the important points) the haemodynamic effects” not just list them which some candidates did, and as a result scored lower marks.
A number of candidates mixed up the 2 traces in part b) or gave the right haemodynamic consequence but the wrong explanation and sometimes appeared to have written down the wrong word e.g. inflation instead of deflation or early instead of late. Due to the mark allocations in the question candidates could still achieve a pass without having to interpret the IABP traces correctly.
 

Discussion

a)

i) Indications for IABP:

Cardiogenic shock:

• Failure to come off bypass
• Severe MR
• ventricular septal defect
• Ischaemic coronary disease while waiting for PCI

Prophylactic use

• High risk CABG patients (pre-op)
• High-risk PCI patients (pre-op)

Controversial indications:

• Takotsubo cardiomyopathy
• Neurogenic stress cardiomyopathy of subarachnoid haemorrhage
• Severe aortic stenosis

ii) Haemodynamic effects, as an outline rather than list, because 4 marks:

• The balloon inflates in diastole:
  • displaces aortic blood into the coronary arteries
  • myocardial perfusion and therefore contractility improves
  • plus small volume of aortic blood is displaced into the systemic circulation
  • Net effect is an increased cardiac output
• The balloon deflates before systole:
  • decreases aortic pressure
  • reduces LV afterload
  • thereby decreases LV workload and improves directional flow across a regurgitant mitral valve or VSD

iii). Complications:

• Poor operation of the device
  • Mis-timing
  • Haemolysis
  • Mechanical failure
• Common complications
  • Mild limb ischaemia - 2.9%
  • Balloon leak - 1.0%
  • Major limb ischaemia - 0.9%
  • Haemorrhage - 0.8%
  • Leg amputation due to ischaemia - 0.1%
• Rare complications
  • Atheromatous cholesterol emboli
  • Aortic or arterial dissection
  • Cerebrovascular accident
  • Thrombocytopenia
  • Haemolysis
  • Helium embolism

b) Explain the haemodynamic consequences of these waveforms:

i)

This is early inflation. Early balloon inflation results in:

• Increased LV oxygen demand, due to increased afterload
• Decreased LV oxygen supply, due to decreased diastolic perfusion
• Decreased cardiac output, due to decreased stroke volume

ii) 

This is late deflation. Late balloon deflation causes:

• increased aortic end-diastolic pressure
• thus increased afterload and left ventricular oxygen consumption