Decreased Heart Rate (Bradycardia)

What counts as a low heart rate

A normal adult resting heart rate is 60 to 100 beats per minute (bpm). Anything under 60 is technically bradycardia, but that number alone does not mean a problem.

Children have higher normal rates, so a rate that is normal for an adult can be slow for a child.

To measure your pulse, sit quietly for 5 minutes, then count beats at the wrist or neck for 30 seconds and double it. Check a few times on different days.

Is a low heart rate dangerous?

A slow heart rate is a problem only when the heart cannot pump enough blood for the body's needs. The brain is most sensitive to this. Signs that a slow rate is causing trouble:

• dizziness or lightheadedness
• fainting or nearly fainting
• unusual tiredness and weakness
• breathlessness or poor exercise tolerance
• chest pain
• confusion or memory problems, especially in older adults

If you feel well, a resting rate in the 40s or 50s is often a sign of a fit, efficient heart.

Causes of a decreased heart rate

Normal (physiological) causes

• Fitness: endurance training strengthens the heart and increases vagal tone, slowing the resting rate. Some marathon runners rest in the 30s and 40s.
• Sleep: heart rate normally falls during sleep.
• Age: the rate tends to be lower in some older adults.
• Vasovagal reactions: pain, fear or straining can briefly slow the heart and drop blood pressure, causing a faint.

Heart conditions

• Sinus bradycardia: a regular slow rhythm from the heart's natural pacemaker. It can be normal or caused by other conditions.
• Sick sinus syndrome: age-related wear of the natural pacemaker, causing slow rates, pauses and sometimes alternating fast rhythms.
• Heart block: electrical signals are delayed or blocked between the upper and lower chambers. Higher-grade block can cause very slow rates and fainting.
• Heart attack, especially affecting the lower (inferior) wall of the heart.
• Heart surgery, inflammation (myocarditis) and infections such as Lyme disease.

Medicines

• beta-blockers (metoprolol, atenolol, bisoprolol), including eye drops for glaucoma
• calcium channel blockers (verapamil, diltiazem)
• digoxin, amiodarone and other heart rhythm drugs
• clonidine, donepezil, lithium and opioids

Do not stop these medicines without medical advice, as stopping some suddenly is dangerous.

Other medical causes

• Underactive thyroid
• High potassium (hyperkalemia), often with kidney disease or some medicines
• Hypothermia
• Sleep apnea, which causes slowing during breathing pauses at night
• Raised pressure in the skull after head injury, with high blood pressure and abnormal breathing
• Eating disorders and severe malnutrition

How a slow heart rate is diagnosed

A doctor will ask about symptoms, fitness, medicines and family history, check your pulse and blood pressure, and listen to your heart.

• ECG: shows the rate and rhythm and whether heart block is present
• Holter monitor: records every heartbeat for 24 hours to 2 weeks
• Event monitor or implantable loop recorder: for infrequent symptoms
• Exercise test: checks whether the heart speeds up normally with exertion
• Blood tests: thyroid function, potassium and other electrolytes, digoxin level if relevant
• Echocardiogram: heart ultrasound to check structure and pumping
• Sleep study if sleep apnea is suspected

Treatment

• No symptoms, normal ECG: no treatment, just periodic review.
• Medicine-related: the dose is lowered, or the medicine switched.
• Underlying cause: thyroid hormone for hypothyroidism, correcting potassium, treating sleep apnea or Lyme disease.
• Pacemaker: a small device placed under the skin of the chest, with a lead into the heart, that triggers a beat when the rate drops too low. It is the main treatment for symptomatic sick sinus syndrome and higher-grade heart block. Fitting takes about an hour under local anesthetic.
• Emergency treatment of a dangerously slow rate with symptoms may include atropine, medicines given through a vein and temporary pacing.

Frequently asked questions

What is a dangerously low heart rate?

There is no single number. A resting rate under 40 beats per minute while awake, or any slow rate with fainting, chest pain, breathlessness or confusion, needs urgent care. Many healthy people, especially athletes, rest in the 40s and 50s without any problem.

Is a heart rate of 50 normal?

For many adults, yes. A resting heart rate of 50 is common in active people and older adults and is usually normal if you feel well. If you also have dizziness, fainting or unusual tiredness, see a doctor for an ECG.

What causes a sudden drop in heart rate?

Common causes are a vasovagal reaction to pain or fear, new or increased heart medicines, a heart attack, high potassium and heart block. A sudden drop with fainting or chest pain needs emergency assessment.

Can a low heart rate cause tiredness?

Yes, if the heart is not pumping enough blood to meet the body's needs, especially during activity. Tiredness with a slow pulse can also point to an underactive thyroid or medication side effects, which are easily checked with blood tests.

How is bradycardia different from sinus bradycardia?

Bradycardia means any heart rate under 60. Sinus bradycardia is the most common kind, where the heart's natural pacemaker fires normally but slowly. Other kinds, such as heart block, involve faulty electrical conduction and are more likely to need treatment.