Pacemaker Panic #2

• Broad complex tachycardia at 107 bpm.
• Extremely wide QRS complexes.
• Indeterminate QRS axis.
• Pacemaker spikes dissociated from QRS complexes.

here are a number of causes for a wide QRS complex, including:

• Bundle branch block
• Pacemaker
• Wolff-Parkinson-White syndrome
• Ventricular Rhythm
• Metabolic
• Sodium Channel Blockade
• Nonspecific Intraventricular Conduction Delay

However, when the QRS duration is greater than 200 ms, hyperkalemia should immediately move to the top of the differential. Hyperkalemia would also explain the pacemaker failure to capture. When the QRS becomes too wide, the pacemaker attempts to trigger during the refractory period and fails to capture.

• The ECG alone is neither particularly sensitive nor specific for diagnosing hyperkalemia.
• Serial blood draws should be used to track the patient’s potassium.
• A VBG using an ED-based gas analyser is often the most rapid way to get an initial potassium reading, and may give useful information about acid-base status.
• Urea and electrolytes should be checked to detect renal dysfunction.
• Her initial potassium is 8 mmol/L.

There are 3 goals in treating hyperkalemia: membrane stabilisation, shift potassium into cells, and increased potassium elimination from the body.

Membrane stabilisation

• Calcium chloride and gluconate are both effective. Remember that calcium gluconate does not have to be metabolised by the liver to work.

Shift potassium

• Sodium bicarbonate: alone does not lower potassium, and there is debate whether it will potentiate the effects of salbutamol / albuterol and insulin + dextrose.
• Insulin + Dextrose
• Salbutamol / Albuterol

Increase potassium elimination

• Diuretics such as furosemide
• Dialysis
• Kayexalate: while a mainstay of treatment, there is no evidence that kayexelate reduces potassium levels. The original research that promoted its has serious methodological flaws.

• Underlying rhythm is a dual chamber AV sequential pacemaker.
• Pacemaker rate: 100 bpm, Ventricular rate captured: 50 bpm.
• Pacemaker failure to capture
• Wide QRS complex
• ST-T wave abnormalities

• While the patient’s pacemaker has taken over, it is still unable to capture 100% of the time.
• The wide QRS from the underlying hyperkalemia is causing half the pacemaking impulses to fall during the refractory period of the QRS and fail to conduct.

• Yes.
• A blood draw confirms that the patient’s potassium level has dropped to 6.6 mmol/L.

• Furosemide is a loop diuretic that when administered alone may cause low potassium levels.
• As such, many patients on furosemide will be taking a potassium supplement.
• After additional interviewing, you find that the patient misunderstood the dosing instructions for the potassium and unintentionally overdosed.

• Martin TJ, Kang Y, Robertson KM, Virji MA, Marquez JM. Ionization and hemodynamic effects of calcium chloride and calcium gluconate in the absence of hepatic function. Anesthesiology. 1990 Jul;73(1):62-5.
• Wrenn KD, Slovis CM, Slovis BS. The ability of physicians to predict hyperkalemia from the ECG. Ann Emerg Med. 1991 Nov;20(11):1229-32. 
• Montague BT, Ouellette JR, Buller GK. Retrospective review of the frequency of ECG changes in hyperkalemia. Clin J Am Soc Nephrol. 2008 Mar;3(2):324-30.