When the SA node fails as main pacemaker – therefore AV node takes over whereas the P-wave indicates the depolarisation sequence;

• P-wave in front of QRS = Atria depolarised before ventricles
• P-wave after QRS = Ventricles depolarised before atria
• P-wave hidden in QRS = Atria & ventricles depolarised together

• Damage to AV node
• Cardiomyopathy
• Drug toxicity
• Electrolyte disturbance
• Heart failure
• Hypoxia
• Myocarditis
• Reperfusion
• Valvular Heart Disease

• Light-headedness
• Palpations
• Chest pain symptoms
• Shortness of breath
• Weakness

Delayed impulse not from the atria but elsewhere in the AV junction – occurs when the SA node produces impulses slower than the AV node’s rate. This can due to a block.

• Severe Sinus bradycardia
• Sinus Arrest
• Sino-atrial exit block
• 2nd Degree AV block
• 3rd Degree AV block
• Hyperkalaemia
• Drug Toxicity

• Bradycardia
• Light-headedness
• Dizziness
• Hypotension
• Syncope

When inherent junction pacemaker site is stimulated faster than the normal rate – This is an excited junction rhythm. Again P-wave behaviour indicates depolarising sequence.

• Damage to AV node
• Cardiomyopathy
• Drug toxicity
• Electrolyte disturbance
• Heart failure
• Hypoxia
• Myocarditis
• Reperfusion
• Valvular Heart Disease

• Light-headedness
• Palpations
• Chest pain symptoms
• Shortness of breath
• Weakness

When inherent junction pacemaker site is stimulated faster than the normal rate – This is an excited junction rhythm. The tachycardia is caused by re-entry circuit allowing repeat transmission of the impulse through the AV node and surrounding structures.

• AV node damage
• Digitalis toxicity
• Electrolyte disturbance
• Heart failure
• Post-cardiac Surgery
• Valvular heart disease

• Light-headedness
• Palpations
• Chest pain symptoms
• Shortness of breath
• Weakness

Originate from ectopic sites closer to the AV node (cause absent P-waves) – Where little of this impulse is travelled through the atria tissue creating an inverted P-wave as impulse can travel backwards – Usually a precursor to other junctional rhythms.

• Digoxin toxicity
• Electrolyte imbalance
• Heart failure
• Hyperthyroidism
• Stimulants
• Pericarditis
• Stress
• Valvular Heart Disease

• Bradycardia
• Light-headedness
• Dizziness
• Hypotension
• Syncope
  

References

College of Pre-Hospital Care. (2015). 12-Lead ECG Analysis: Self-Directed Learning Package. Version 3. St John Ambulance Ltd.  

Curtis, K., & Ramsden, C. (2016). Emergency and trauma care for Nurses and Paramedics (2nd ed.). Elsevier Australia.

DeLaune, S. C., Ladner, P. K., McTier, L., Tollefson, J., & Lawrence, J. (2016). Australian and New Zealand fundamentals of nursing (1st ed.). Cengage Learning Australia Pty Limited.

ECG & ECHO Learning. (2020). Clinical ECG Interpretation. https://ecgwaves.com/topic/ecg-normal-p-wave-qrs-complex-st-segment-t-wave-j-point/

Life in the Fast Lane. (2020). ECG Library. https://litfl.com/ecg-library/

St John WA Ltd. (2017). Electrocardiography (ECG). Clinical Resources. https://clinical.stjohnwa.com.au/clinical-skills/assessment/vital-signs/electrocardiography-(ecg)

WikiEM. 2020. The Global Emergency Medicine Wiki. https://www.wikem.org