Diagnostic criteria

  Heart rate (ventricular rate, QRS rate) < 50/minute in adults.

  P wave is positive in D1 and D2.

  Every P wave is followed by a QRS complex.




Causes of sinus bradycardia

  During sleep

  Medications: beta blockers, verapamil, diltiazem, amiodarone, digoxine,

      ivabradine, clonidine, lithium, pyridostigmine, cisplatin, cytarabine, ticagrelor

  Myocardial ischemia or infarction

  Hyperkalemia

  Increased vagal tone

  Athlete's heart

  Hypothyroidism

  Increased intracranial pressure

  Hypothermia

  Advanced age

  Oculocardiac reflex, Aschner reflex, Trigeminovagal reflex (TVR)




Caution! Two other rhythms may mimick sinus bradycardia, at first glance:

  2:1 AV block may mimick sinus bradycardia, at first glance.

      If you see P waves and the heart rate (ventricular rate) is < 50/minute, then
search for a second P wave

      (not conducted to the ventricles)
before diagnosing sinus bradycardia.

      In this cases,
the configuration of P waves (both conducted and blocked) are similar,

      since both originate from the sinus node.

 
Atrial bigeminy with blocked atrial premature beats may also mimick sinus bradycardia, at first glance.

      In this case,
the configuration of conducted P waves and blocked P waves are usually different,

      since they originate from different atrial foci.




Remember

  Bradycardia is one of the triggers of atrial fibrillation
.



References

  Indian Pacing Electrophysiol J 2013;13(3):114-117.

  Heart Rhythm 2013;10(8):1192-1198.

  Congenit Heart Dis 2012;7(5):E82-84.

  Clin Cardiol 1979;2(2):126-130.





ECG 1. Sinus bradycardia.

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ECG 2. Sinus bradycardia due to concomitant ingestion of bisoprolol and diltiazem.

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ECG 3. Sinus bradycardia during acute inferior myocardial infarction. The heart rate is approximately 25/minute.
Inferior leads show ST segment elevation.
Immediately after recording of the above ECG, the patient underwent coronary angiography which revealed 99% stenosis of
the proximal Right Coronary Artery (RCA).

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ECG 4. The ECG above belongs to a 72 years-old woman with 2:1 AV block.
Some P waves are conducted to the ventricles while some P waves cannot be conducted to the ventricles.
One of every two P waves can be conducted to the ventricles.
Heart rate (
ventricular rate) is bradycardic (44/minute) but it is not sinus bradycardia since P wave rate (atrial rate) is 88/minute.
Atrial rate is normal but its conduction to the ventricles is the problem.
ECG machine inadvertently reported it as sinus bradycardia.
If you see P waves and the heart rate (ventricular rate) is < 50/minute, then
search for a second P wave
(not conducted to the ventricles)
before diagnosing sinus bradycardia.
Wide QRS complexes and increased PR interval (of the conducted P waves) in this ECG suggest Mobitz Type 2 block.
The conducted P waves and the blocked P waves have similar configurations, since they originate from the same focus.

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ECG 5. The ECG above belongs to a 85 years-old man with prolonged PR interval and 2:1 AV block.
Some P waves are conducted to the ventricles while some are blocked.
One of every two
P waves can be conducted to the ventricles.
Heart rate (ventricular rate) is bradycardic (33/minute) but it is not sinus bradycardia since P wave rate (atrial rate) is 66/minute.
Atrial rate is normal but its conduction to the ventricles is the problem.
If you see P waves and the heart rate (ventricular rate) is < 50/minute, then search for a second (blocked) P wave
before diagnosing sinus bradycardia.
The conducted P waves and the blocked P waves have similar configurations, since they originate from the same focus.

Click here for a more detailed ECG





ECG 6. The ECG above belongs to a 54 years-old man with systemic arterial hypertension.
Coronary angiography did not show significant coronary artery stenosis.
His only medication is Ramipril 2.5mg/day.
He is not taking any beta blocker, non-dihydropyridine calcium channel blocker or ivabradine.
His usual heart rate is below 50/minute.
This ECG shows a short-lasting episode of atrial fibrillation during
bradycardia (vagally-mediated atrial fibrillation).

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ECG 7. The ECG above is from a 68 years-old woman with systemic hypertension and atrial fibrillation.
The rhythm may seem like sinus bradycardia at first glance, but there are no P waves, QRS intervals are irregular:
The rhythm is atrial fibrillation with slow ventricular response.
She is taking Digoxin tablets.
Sagging-type ST segment depression is seen in most of the leads.
The ventricular response is slow due to Digoxin effect. RR intervals are irregular.
When a patient with atrial fibrillation and Digoxin intoxication developes bradycardia, irregularity of
RR intervals decrease, mimicking sinus bradycardia, at first glance.

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