Question 14

Question 13 and Question 14 both relate to the following clinical scenario:

A 71-year-old man is transferred to your intensive care unit following a mechanical aortic valve replacement and coronary artery bypass surgery.

The anaesthetist reports that he came off bypass readily, has not required any inotropic support, and has epicardial pacing wires in situ. However, shortly after arrival his blood pressure falls to 60/30.

Question 13 was as follows:

a) Outline your differential diagnosis for his hypotension

His blood pressure improves rapidly with a fluid bolus, and examination is otherwise unremarkable. However, he is noted to lose 250ml of blood from his mediastinal drains over the next 30 minutes.

b) List 4 likely causes of, or contributors to, excessive post-operative bleeding in this setting, and outline your immediate management.

Question 14 continues from the above.

Twenty four hours later, he develops a new-onset tachycardia as shown in the ECG below. (again, the college has removed the images from their paper, but I have found an alternative (hopefully equivalent) image)

a) What is your interpretation of the ECG?

b) Outline your initial management of the tachycardia

c) List 3 primary non-cardiovascular causes of the above tachycardia.

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College Answer

a) What is your interpretation of the ECG?

Atrial fibrillation (vent rate approx. 170) LAD

LVH

Lateral T inversion.

b) Outline your initial management of the tachycardia

Attention to airway, breathing and circulation.

Identify and rectify reversible factors as above
Fluid bolus if hypovolaemic
Correct electrolyte abnormalities
Check pacemaker
Treat pain

Consider MgSO4

Assess for haemodynamic compromise.
- If significant haemodynamic compromise, early mechanical cardioversion.
- If tolerating arrhythmia haemodynamically, options are rate-control or pharmacological cardioversion.
- Rate-control – IV Digoxin or beta-blocker
- Pharmacological cardioversion – Amiodarone, Sotalol, Class 1A or 1C

c) List 3 primary non-cardiovascular causes of the above tachycardia.

Hyperthyroidism

Alcohol binge

Sepsis /Pneumonia

Carbon monoxide poisoning

Association with Friedrich’s ataxia although this is due to a cardiomyopathy.

Discussion

Though the previous question for this scenario was more related to the consequences of cardiothoracic surgery, this question focuses on the generic features of managing AF in the ICU.

First of all, let us lament again the absence of ECG images from the papers. I had to steal my material from this source. If their lawyers ever contact me, I will be very upset.

Now, lets examine the college answer for the management of AF.

The first seven points are hardly sophisticated. This seems to have required a registrar-level answer.

Attention to airway, breathing and circulation.
Identify and rectify reversible factors as above
Fluid bolus if hypovolaemic
Correct electrolyte abnormalities
Check pacemaker
Treat pain
Consider MgSO4

No geniuses needed here.

The next section deals with the discrimination between haemodynamically stable and haemodynamically unstable AF. This refers to the arrhythmia algorithm in the pre-arrest management section of the ARC ALS Handbook, and is therefore based on ILCOR Guidelines. The ARC book is not available online, but the UK version thankfully is. Again - its nothing special; you shock the unstable ones, and the stable ones give you plenty of time to debate the choice of rhythm or rate control medications.

As for the non-cardiac causes of AF- only 3 are asked for; however the list is enormous. This British publication contains Table 1.2 (on page 6) briefly lists 6 causes. To the college answer, they would add lung cancer, pulmonary embolism, and pleural effusion. Much larger tables of causes exist in the atrial fibrillation chapter of the Required Reading section for cardiology. To simplify revision, they are reproduced below:

Causes of Atrial Fibrillation Organised by System
Vascular: Myocardial infarction Pulmonary embolism Pulmonary hypertension Subarachnoid haemorrhage Infectious: Sepsis Myocarditis Pericarditis Infective endocarditis Neoplastic: Cardiac mass, eg. myxoma Drug-induced: Catecholamines Alcohol Caffeine Idiopathic: Infiltrative disease, eg. amyloidosis Age-related fibrotic changes	Idiopathic: Infiltrative disease, eg. amyloidosis Age-related fibrotic changes Congenitial: Atrial septal defect Familial AF Autoimmune: Autoimmune myocarditis Traumatic: Cardiac contusion Cardiac surgery Endocrine/environmental: Hypothermia Hyperthyroidism Haemochromatosis/iron overload Phaeochromocytoma Electrolyte derangement

Causes of Atrial Fibrillation Organised by Pathophysiology
Catecholamine excess Exogenous (eg. adrenaline infusion) Endogenous: Subarachnoid haemorrhage Stress Phaeochromocytoma Thyrotoxicosis (indirectly) Atrial distension Pulmonary hypertension: Obstructive sleep apnoea Pulmonary embolism Primary pulmonary hypertension Pulmonic valve disease Septal defects Valvular disease, including infective endocarditis	Abnormality of conducting system Congenital cardiac disease, eg. septal defect Infiltrative cardiac disease, eg. amyloidosis Ischaemic heart disease Age-related fibrotic changes Haemochromatosis/iron overload Hypothermia Increased atrial automaticity Alcohol Caffeine Catecholamines Electrolyte derangement Myocarditis

References

Frederick A. Hensley, Jr., M.D., Donald E. Martin, M.D., Glenn P. Gravlee, M.D. A Practical Approach to Cardiac Anaesthesia, 3rd ed. Sibylle A. Ruesch and Jerrold H. Levy. CHAPTER 9. The Postcardiopulmonary Bypass Period: A Systems Approach. 2003 by LIPPINCOTT WILLIAMS & WILKINS

National Collaborating Centre for Chronic Conditions (Great Britain). "Atrial fibrillation: national clinical guideline for management in primary and secondary care." Royal College of Physicians, 2006.

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