Sinus Bradycardia on ECG

Introduction

Sinus bradycardia is a condition where the heart rate is slower than normal, typically below 60 beats per minute in adults. While it can be normal in athletes and during sleep, it may also indicate underlying medical conditions.

ECG Characteristics of Sinus Bradycardia

On an electrocardiogram (ECG), sinus bradycardia is identified by the following features: 1. Regular rhythm – The time between consecutive heartbeats (R-R intervals) is consistent. 2. P waves present – Every QRS complex is preceded by a normal, upright P wave in lead II, confirming that the rhythm originates from the sinoatrial (SA) node. 3. Slow heart rate – Less than 60 beats per minute. 4. Normal PR interval – Typically 120-200 ms. 5. Normal QRS complex – Duration is usually less than 120 ms unless another conduction abnormality is present.

Causes of Sinus Bradycardia

Sinus bradycardia can occur due to various reasons: - Physiological causes: Seen in athletes and during sleep. - Medications: Beta-blockers, calcium channel blockers, digoxin, and other drugs can slow heart rate. - Increased vagal tone: Vagal nerve stimulation can slow heart rate, seen in vasovagal syncope. - Hypothyroidism: Reduced thyroid hormone levels slow metabolism, including heart rate. - Electrolyte disturbances: High potassium levels (hyperkalemia) or imbalances in calcium and magnesium. - Cardiac causes: Sinus node dysfunction, myocardial infarction, or myocarditis. - Neurological causes: Increased intracranial pressure, brainstem strokes, or head trauma.

Symptoms

Many people with sinus bradycardia have no symptoms. However, if bradycardia is significant or associated with an underlying condition, patients may experience: - Dizziness or fainting (syncope) - Fatigue - Shortness of breath - Chest pain (if due to ischemia) - Confusion or memory problems (in older adults)

Treatment

Treatment depends on the underlying cause and symptoms: - If asymptomatic, no treatment is needed. - Addressing underlying conditions such as hypothyroidism or medication side effects. - In symptomatic cases, atropine can be given to increase heart rate. - Severe cases may require a pacemaker to regulate heart rhythm.

Conclusion

Sinus bradycardia is common and often benign, but in some cases, it may require further investigation and treatment. If you experience symptoms, consult a cardiologist for a thorough evaluation.

Source recommendations

1. American Heart Association Guidelines on Bradycardia and Conduction Disorders

1. https://www.heart.org/en/health-topics/arrhythmia/about-arrhythmia/conduction-disorders
2. https://www.ahajournals.org/doi/10.1161/CIR.0000000000000628
3. https://www.heart.org/en/health-topics/arrhythmia/about-arrhythmia/bradycardia--slow-heart-rate
4. https://pubmed.ncbi.nlm.nih.gov/30412709/
5. https://www.jacc.org/guidelines/bradycardia

2. European Society of Cardiology (ESC) Guidelines for Cardiac Pacing and Resynchronization Therapy

1. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Cardiac-Pacing-and-Cardiac-Resynchronization-Therapy
2. https://academic.oup.com/eurheartj/article/42/35/3427/6358547
3. https://pubmed.ncbi.nlm.nih.gov/34455430/
4. https://academic.oup.com/eurheartj/article/34/29/2281/401445
5. https://pubmed.ncbi.nlm.nih.gov/23801827/