Question 12

College comments

Syllabus topic/section: 2.1.4 Cardiovascular Intensive Care: Valvular Heart Disease L1

Discussion: 

Systolic anterior motion (SAM) of the mitral valve is weh and is an important consideration in such patients who are shocked on return from theatre.

When defining SAM, candidates who scored higher marks were able to provide physiological consequences of SAM, including mitral regurgitation. This shows a greater understanding of the disorder.

If time permits, when describing management strategies, candidates could improve their answers by providing a brief rationale for individual therapies: For example: Fluid bolus to improve preload and decrease LVOT obstruction; Increased vasopressor support to increase SVR and afterload, maintaining increased LV volume at the end of systole and reduce LVOT obstruction.

Generally speaking, candidates should ensure their handwriting is legible.
 

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Interpretation

a)    Define systolic anterior motion (SAM) of the mitral valve (2 marks)

SAM is defined as "displacement of the distal portion of the anterior leaflet of the mitral valve toward the left ventricular outflow tract" - Lasala et al (2017)

This definition was somehow not enough to score full marks. The examiners also expected "physiological consequences of SAM, including mitral regurgitation", which would have shown a greater understanding of telepathy by the candidates. One may take heart in the knowledge that for the majority of the other CICM exam questions in the new era, the asked question represents the examined content, and there should be no need to game the answer to guess what the examiners are thinking.

Those physiological consequences are:

• LVOT obstruction
  • thus, a low cardiac output state occuring in the presence of a higher cardiac contractility
• Mitral regurgitation (eccentric)
  • thus, pulmonary oedema

b)    List the risk factors for SAM (3 marks)

• These are few:
  • Asymmetric septal hypertrophy
  • Small LV chamber volume (low preload)
  • Low afterload (allows the outflow tract to collapse)
  • High contractility
  • Atrial fibrillation (a variant of low preload, it keeps the ventricle underfilled by loss of atrial kick)
• Additionally, these congenital abnormalities can be listed together as "congenital abnormalities" because who would remember them all, for example:
  • Redundant anterior leaflet
  • Redundant posterior leaflet
  • Papillary muscle displacement 
  • Anatomical anomaly of the chordae
  • Undersized mitral annulus
  • Anterior displacement of the mitral valve (congenitally, surgically or by disease)
  • Low anterior-posterior length ratio of the valve (i.e. ovoid valve)

c)    Outline the specific management of SAM causing hemodynamic instability in a patient post cardiac surgery (5 marks)

Five marks conveniently matches five main strategies:

• Increase preload. Insufficient diastolic filling pressure is said to contribute to LVOT obstruction. Give fluid boluses until euvolaemia is achieved.
• Decrease heart rate to increase diastolic filling time (as much as is permitted by the relatively fixed stroke volume, i.e. the less heart rate the less cardiac output there will be)
• Maintain sinus rhythm. Atrial contraction contributes to LV diastolic filling and reduces MR.
• Reduce contractility; wean inotropes.
• Maintain a high afterload; aim for a higher MAP target to maintain LVOT patency during systole

Lastly,  if the SAM has occurred because of a new mitral valve, one other (unpalatable) option is to re-do the valve.