Bradycardia and Heart Block: Recognition, Adverse Features and Nursing Response

Bradycardia means a heart rate below 60 beats per minute. In a fit young athlete asleep at night, a heart rate of 45 may be perfectly normal. In an older patient who has fainted, it may signal life-threatening heart block. Nurses are often first to notice a slow pulse; knowing which patients need urgent action is essential.

Common causes

• Physiological: athletes, sleep.
• Medicines: beta-blockers, rate-limiting calcium channel blockers (verapamil, diltiazem), digoxin, amiodarone, some eye drops.
• Heart disease: myocardial infarction (especially inferior MI), conduction system degeneration with age, sick sinus syndrome.
• Electrolytes: high potassium.
• Hypothyroidism, hypothermia.
• Raised intracranial pressure (with hypertension and irregular breathing: Cushing’s response).
• Hypoxia in children, a pre-arrest sign.
• Vagal stimulation: vomiting, suctioning, straining.
• Infections such as Lyme disease and, rarely, typhoid can cause relative bradycardia.

Types of heart block

• First-degree AV block: prolonged PR interval (over 0.20 seconds), every P wave followed by QRS. Usually benign.
• Second-degree Mobitz I (Wenckebach): PR interval gets progressively longer until a beat is dropped. Often benign.
• Second-degree Mobitz II: constant PR interval with sudden dropped beats. Risk of progressing to complete heart block.
• Third-degree (complete) heart block: no relationship between P waves and QRS complexes; often a slow, wide-complex escape rhythm. Dangerous.

See our ECG basics guide.

Assess for adverse features

Following the Resuscitation Council UK bradycardia algorithm, check for:

• Shock: hypotension, pallor, sweating, cold peripheries, confusion.
• Syncope (fainting).
• Myocardial ischaemia: chest pain, ischaemic ECG changes.
• Heart failure: breathlessness, crackles, oedema.

Nursing response

1. A–E assessment; call for help if adverse features.
2. Oxygen if hypoxic; IV access.
3. 12-lead ECG and continuous cardiac monitoring.
4. Check blood glucose, electrolytes (especially potassium), and review medicines. Hold rate-slowing medicines and inform the prescriber.
5. If adverse features: atropine IV (commonly 500 micrograms, repeated up to a maximum of 3 mg) as prescribed or per protocol.
6. If no response, further options include adrenaline or isoprenaline infusions and transcutaneous pacing, while arranging transvenous pacing. Be ready to assist.
7. Even without adverse features, Mobitz II, complete heart block, recent asystole, or ventricular pauses over 3 seconds carry a risk of asystole and need expert review.

Transcutaneous pacing

Pads are placed on the chest (and back), and the defibrillator delivers pacing impulses. It’s uncomfortable, so patients usually need analgesia and sedation. Check for both electrical capture on the monitor and mechanical capture (a palpable pulse at the paced rate).

Permanent pacemakers

Patients with symptomatic or high-grade heart block often need a permanent pacemaker. After insertion, nurses monitor the wound site, check for pneumothorax symptoms, restrict arm movement on the device side as instructed, and teach patients about follow-up checks and device safety.

Based on Resuscitation Council UK Adult Bradycardia Algorithm (2021) and ESC pacing guidelines. Educational content: follow local protocols.