Sinus bradycardia

Sinus bradycardia

Description, Causes and Risk Factors:

Sinus bradycardia can be defined as a sinus rhythm with a resting heart rate of 60 beats per minute or less. However, few patients actually become symptomatic until their heart rate drops to less than 50 beats per minute. The action potential responsible for this rhythm arises from the sinus node. The sinus node is the pacemaker of the heart. It is responsible for generating the electrical impulses that stimulate the heart muscle to contract.

The sinus node is very carefully regulated by the brain. During normal activity, the firing rate of the sinus node is maintained according to the metabolic needs of the body. The body's nervous system stimulates the sinus node to fire more quickly during times of increased activity, for example during exercise. Likewise, the sinus node firing rate slows down during times of decreased metabolic rate, for example during sleep.

The pathophysiology of sinus bradycardia is dependent on the underlying cause. Commonly, sinus bradycardia is an incidental finding in otherwise healthy individuals, particularly in young adults or sleeping patients. Other causes of sinus bradycardia are related to increased vagal tone.

Physiologic causes of increased vagal tone include the bradycardia seen in athletes. Pathologic causes include, but are not limited to, inferior wall myocardial infarction, toxic or environmental exposure, electrolyte disorders, infection, sleep apnea, drug effects, hypoglycemia, hypothyroidism, and increased intracranial pressure.

Sinus bradycardia may also be caused by the sick sinus syndrome [SSS], which involves a dysfunction in the ability of the sinus node to generate or transmit an action potential to the atria. Sick sinus syndrome includes a variety of disorders and pathologic processes that are grouped within one loosely defined clinical syndrome. The syndrome includes signs and symptoms related to cerebral hypoperfusion in association with sinus bradycardia, sinus arrest, sinoatrial (SA) block, carotid hypersensitivity, or alternating episodes of bradycardia and tachycardia.


Symptoms may include:


  • Dizziness.

  • Lightheadedness.

  • Chest pain.

  • Shortness of breath [SOB].

  • Exercise intolerance.

  • Decreased level of consciousness.

  • Cyanosis.

  • Peripheral edema.

  • Pulmonary vascular congestion.

  • Dyspnea.

  • Poor perfusion.


Following laboratory values are very essential while evaluation of sinus bradycardia:

    Electrolyte levels.

  • Glucose level.

  • Calcium level.

  • Magnesium level.

  • Thyroid function tests.

  • Toxicologic screen.

Other Tests:

    Electrocardiogram: a test that records the heart's activity by measuring electrical currents through the heart muscle.

  • Echocardiogram: a test that uses high-frequency sound waves (ultrasound) to examine the size, shape, and motion of the heart.

  • Holter monitor or event monitor: a portable, continuous heart rhythm monitor that you wear as you perform normal daily activities.

  • Exercise stress test: a test that records the heart's electrical activity during increased physical activity.

  • Nuclear scanning: radioactive material is injected into a vein and observed as it is distributed through the heart muscle to look for coronary artery disease.

  • Coronary angiography: X-rays taken after a dye is injected into the arteries; this allows the doctor to look for abnormalities in the coronary arteries of the heart.


The first step in treating sinus bradycardia is to determine whether it has a reversible underlying cause. If the sinus bradycardia is due to increased vagal tone, drug therapy, an infectious disease, pericarditis, myocarditis or hypothyroidism, then addressing the underlying problem is usually the only treatment that is necessary.

But if the sinus bradycardia is caused by intrinsic sinus node disease, or by some other medical problem that cannot be easily reversed, then treatment will require the placement of a pacemaker.

So if you have sinus bradycardia, you will need to work with your doctor to determine why you have it, and whether it is causing symptoms. While most people with sinus bradycardia do not require a pacemaker, if you do have symptoms from sinus bradycardia, you can be confident that a pacemaker will completely eliminate those symptoms.

NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.


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