Renal failure & the ECG

Answer: The peaked T waves, broad QRS in the absence of a bundle branch block and absence of P waves concerning for Hyperkalaemia changes to the ECG.

 

Hyperkalaemia & the ECG

Increasing plasma K+ concentration reduces the ration of intracellular to extracellular potassium –therefore reduces the resting voltage potential to make it LESS negative.

 

 

Resulting ECG features of Hyperkalaemia

 

1. Tall & Narrow – Peaked T waves

• • The increased extracellular K+ activates voltage depended K+ rectifier currents, which are responsible for allowing K+ efflux and repolarisation of myocytes.

 

• • With more K+ voltage gates open, repolarisation becomes more rapid and this results in our FIRST ECG feature “Tall & narrow T waves”

 

2. Wide QRS complex

• The elevated baseline voltage reduces the pool of available (voltage dependent) Na+ channels which can open with depolarisation.

 

• This contributes to conduction velocity slowing resulting in our second ECG change “Widened QRS complex”.

 

• Eventually, conduction velocity slowing widens the QRS to resemble the T wave, producing the so-called “sine wave” pattern with an alternating QRS and T wave which look similar.

 

 

3. Prolonged PR interval

• Reduced conduction velocity also explains our 3rd ECG feature – Prolonged PR interval since conduction through the AV node and His purkinjie system slows.

 

4. P wave flattening

• Reduced Voltage Na+ channels opening also results in a reduced depolarisation voltage being generated – accounting for our 4th ECG feature- P wave flattening.

 

• • In fact, P wave flattening tends to be an early manifestation because atrial myocytes have fewer Na+ channels.

 

Potential lethal arrhythmias

• Eventually, this weak atrial depolarisation can eventuate into Atrial Standstill potentially lethal unless a junctional or ventricular escape rhythm occurs.

 

• Ventricular Standstill can also occur in the ventricles due to weak ventricular depolarisation

 

• Conduction velocity of the purkinjie system may become so severely reduced that bilateral bundle branch block or His bundle block may occur, resulting in potentially lethal sudden ventricular standstill or complete heart block.

 

 

 

Do ECG changes always occur in the context of Hyperkalaemia?

• In severe Hyperkalaemia, particularly when serum K+ is >8mmol/L, around 100% of  patient show ECG abnormalities and the majority will experience adverse arrhythmic episodes if untreated.

 

• The graph demonstrates that ECG abnormalities become more prevalent with worsening hyperkalaemia.

 

Why does Hyperkalaemia occur?

• Usually associated with Chronic Kidney Disease/Renal Failure where there are insufficient nephrons (the functional unit of the kidney) or reduced nephron function, resulting in insufficient K+ filtration/excretion.

 

• Therefore patients with renal failure & poor GFR, are more likely to experience hyerkalaemia due to K+ retention.

 

Heart failure & Pharmacological causes

• Low GFR can also occur in the context of heart failure which causes low glomerular perfusion pressure, resulting in less blood being filtered and therefore less K+ being excreted –
  • this has been somewhat criminally oversimplified, but you get the point – sorry to the Nephrologists out there :(

 

• ACE inhibitors (end in “..pril”) and Angiontensin II blockers (end in “…sartan”) are pillars of heart failure management, but they can also exacerbate hyperkalaemia by blocking aldosterone, which is a hormone that would normally assist in K+ excretion, but potentially worsen heart failure progression & symptoms

 

• • So there’s a balancing act between heart failure treatment & managing the side effects

 

My two cents:

• Untreated hyperkalaemia can result in lethal arrhythmias such as ventricular standstill.

 

• ECG changes occur loosely in proportion to worsening hyperkalaemia severity.

 

• ECG changes begin with Peaked T waves & flattened P waves and progresses to prolonged QRS & PR interval until it resembles a sine wave, where risk of lethal arrhythmia is high.

 

• Hyperkalaemia is often associated with chronic kidney failure or kidney injury as a result of heart failure &/or poly-pharmacological effects.

 

• It’s therefore important for people treating cardiac patients to be cognisant of the signs of Hyperkalaemic changes on the ECG.

 

Thanks for tuning in :)
Cheers
Mitch & CPiP Team

Electrolyte abnormalities & ECG changes is covered in our EP in Practice – Complete Curriculum. 

References:

• Durfey N, Lehnhof B, Bergeson A, Durfey SN, Leytin V, McAteer K, Schwam E, Valiquet J. Severe hyperkalemia: can the electrocardiogram risk stratify for short-term adverse events? West J Emerg Med. 2017;18:963. doi: 10.5811/westjem.2017.6.33033.
• Kuvin JT. Electrocardiographic changes of hyperkalemia. N Engl J Med. 1998;338:662. doi: 10.1056/NEJM199803053381005.
• Wong R, Banker R, Aronowitz P. Electrocardiographic changes of severe hyperkalemia. J Hosp Med. 2011 Apr;6(4):240.
• Dittrich KL, Walls RM. Hyperkalemia: ECG manifestations and clinical considerations. J Emerg Med. 1986;4(6):449-55.
• Jayawardena S, Burzyantseva O, Shetty S, Niranjan S, Khanna A. Hyperkalaemic paralysis presenting as ST-elevation myocardial infarction: a case report. Cases J. 2008 Oct 10;1(1):232.