Question 15.2

College answer

Syllabus topic/section:

2.1.4 Cardiovascular Intensive Care /Interpretation of the electrocardiogram: L1

Discussion:  

Overall answered well. Candidates are encouraged to practice interpreting ECGs of common or potentially life-threatening conditions where ECGs are key to diagnosis.

Discussion

No discussion is necessary for the interpretation here (this is a spot diagnosis - the QT interval is massively prolonged, even just measured with the unaided eyeball). This brainstem response was awarded only a half mark, which is probably fair. The causes of QT prolongation are rather numerous and it would not be practical to list all possible answers, but here is a good range of options from 

Harrigan & Chan (2009):

Non-drug-related causes

• Hypokalemia
• Hypocalcemia
• Hypomagnesemia
• Hypothermia
• Thiamine deficiency
• Cardiac ischaemia
• Congenital long QT syndrome

Additionally, one could list any of the approximately one million drugs that cause QT prolongation (see www.qtdrugs.org):

• Cardiac agents
  • Anti-arrhythmics (Type Ia, Ic, and III)
  • Calcium channel-blockers (some) (e.g. bepridil, isradipine, nicardipine)
• Anti-psychotic agents
  • Phenothiazines (some) (e.g. thioridazine, mesoridazine)
  • Butyrophenones (e.g. haloperidol, droperidol)
• Anti-depressants (some) (e.g. tricyclics, fluoxetine, sertraline, venlaflaxine)
• Anti-infective agents
• Fluoroquinolones (some) (e.g. sparfloxacin, gatifloxacin, moxifloxicin)
• Macrolides (some) (e.g. erythromycin, clarithromycin)
• Miscellaneous (pentamidine, amantadine, tetracyclines, foscarnet, quinine, chloroquine)
• Neurologic agents
  • Carbamazepine, fosphenytoin, sumatriptan, zolmitriptan, naratriptan
• Organophosphates
• Gastrointestinal agents (e.g. cisapride, ipecac, octreotide, dolasetron)
• Other (e.g. cocaine, diphenhydramine, methadone, tacrolimus, tamoxifen, probucol, tizanidine, salmeterol)