2025 – PAGE 123 – CARDIOLOGY

2025 – Core Study Guide 05 – Cardiology 2025 – PAGE 123 – CARDIOLOGY

PROLONGED QT

Prolonged QT can lead to TORSADES DE POINTES. It can be caused by hypOcalcemia, hypOmagnesemia (which can lead to hypocalcemia), hypOkalemia, tricyclic antidepressants (TCAs), Levofloxacin, and Erythromycin.

  • PEARL: Think about Prolonged QT in ANY patient who presents for loss of consciousness (LOC), drowning, syncope, and even seizure. The patient may have had a prolonged QT and gone into Torsades!
  • FAMILIAL PROLONGED QT SYNDROME: Prescribe a beta-blocker.
  • TORSADES: You may try to prevent this with a beta blocker or a defibrillator (AICD). Treat with MAG­NESIUM SULFATE. You can also consider overdrive pacing for treatment.
  • MNEMONICS:
    • “MELT PC’s because they take too LONG! Buy an Apple instead.” Problems with low Magnesium, Erythromycin, Levofloxacin, TCAs, low Potassium, and low Calcium can result in a LONG
    • LOW electrolytes result in a sLOW interval.

HEART BLOCKS (AV BLOCKS OR AVB)

FIRST DEGREE AV BLOCK

In first degree AV block (AVB), everything looks normal except for a prolonged PR interval. It is diagnostic if greater than 0.20s (5 small blocks, 1 large block). It is considered benign.

SECOND DEGREE AV BLOCK

In second degree AV Block, some P waves are blocked from initiating a QRS complex. There are two types of second degree AVB:

  • TYPE 1 = MOBITZTYPE I = WENCKEBACH: PR interval widens until there is a dropped QRS complex. It is benign.
    • MNEMONIC: “Won (one) = Widening = Wenckebach
  • TYPE 2 = MOBITZ TYPE II: Normal looking EKG except for intermittent non-conducted P waves (dropped QRS). This can progress rapidly to complete heart block, so a PACER might be indicated.

THIRD DEGREE AV BLOCK = COMPLETE HEART BLOCK

In third degree AV block (AVB), P waves and QRS complexes are completely independent of each other. A PACER may be indicated. Here are the specific indications:

  • Persists > 7 days after surgery
  • Congenital third degree AVB with symptoms
  • Congenital third degree AVB with CONGENITAL HEART DISEASE (CHD) and HR < 75
  • Congenital third degree AVB without CHD and HR < 55
  • PEARL: For third degree AVB, look for a child who is bradycardic except for when he or she is crying.
  • PEARL: Remember that patients born to mothers with SLE can develop third degree heart block.
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