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    8.8
    Home > ECG findings

    8.8

    Minnesota Code 8-8: sinus bradycardia below 50/min — often normal in athletes; medicines, sinus node disease and symptoms.

    Code 8.8 — Minnesota Code 8-8: sinus bradycardia. The rhythm arises normally in the sinus node, but the heart rate is slow. The Minnesota Code assigns 8-8 when the rate is below 50 beats per minute. The 2018 ACC/AHA/HRS bradycardia guideline also uses the 50/min threshold for clinically relevant sinus bradycardia, although many textbooks define bradycardia as a rate under 60/min. Slow heart rates are common and often normal in trained people and during sleep.

    Minnesota Code 8Heart rateBradycardia
    Code 8-8rate < 50 /min
    P wavenormal, before each QRS
    RR interval> 1200 ms
    Often normalathletes, sleep
    Rhythm strip with normal sinus rhythm at 75 beats per minute compared with sinus bradycardia at about 45 beats per minute Sinus rhythm 75/min RR 800 ms Sinus bradycardia 45/min RR ≈ 1330 ms
    Figure 1. Same time window: normal sinus rhythm at about 75/min (RR 800 ms, left) and sinus bradycardia at about 45/min (RR about 1330 ms, right).

    Causes

    • Physiological: endurance training, sleep, high vagal tone, youth
    • Medicines: beta-blockers, verapamil, diltiazem, digoxin, amiodarone, ivabradine, some antidepressants and sedatives
    • Sinus node dysfunction (sick sinus syndrome), often with pauses or alternating fast and slow rhythms
    • Hypothyroidism, hypothermia, high potassium, raised intracranial pressure, sleep apnoea, inferior myocardial infarction

    Clinical significance

    Bradycardia without symptoms usually needs no treatment. It becomes clinically important when it causes symptoms: dizziness, fainting, fatigue, reduced exercise tolerance, breathlessness or confusion. In that case the doctor first looks for reversible causes, particularly medicines and thyroid function. If symptomatic sinus node dysfunction persists, a permanent pacemaker may be indicated.

    Usually harmless

    Athlete, no symptoms, rate rises normally with exercise.

    Needs evaluation

    Fainting or near-fainting, fatigue, breathlessness, rate < 40/min while awake, pauses > 3 s, poor heart-rate response to exercise.

    Seek urgent care

    if a slow pulse is accompanied by fainting, chest pain, breathlessness or confusion.

    References

    1. Kusumoto FM, Schoenfeld MH, Barrett C, et al. 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay. Circulation. 2019;140(8):e382–e482. doi:10.1161/CIR.0000000000000628
    2. Prineas RJ, Crow RS, Zhang ZM. The Minnesota Code Manual of Electrocardiographic Findings. 2nd ed. London: Springer; 2010. doi:10.1007/978-1-84882-778-3

    This article is for general information and does not replace a consultation with a doctor. ECG findings must be interpreted by a physician together with symptoms and other tests.

    Published on 14 May 2019