The ECG Rhythms content is currently under development and is being updated by medical professionals.
Sinus bradycardia is defined as a sinus rhythm where the heart rate falls below 60 beats per minute in adults. This slower heart rate occurs because the sinoatrial (SA) node discharges electrical impulses at a rate slower than the typical range.
Analogy: “The heart’s tempo has slowed down, like a lullaby played at a gentle pace.”
On an ECG, sinus bradycardia is characterized by a regular rhythm with a heart rate below 60 bpm. A P wave precedes each QRS complex, and its morphology is usually normal and upright in lead II, confirming that the impulse originates from the SA node. The PR interval and the QRS complex duration are typically within normal limits. The primary distinguishing feature is the rate of the rhythm, which is slower than the standard range for sinus rhythm, while other ECG components remain consistent with a normal heartbeat.
Sinus bradycardia is often asymptomatic, particularly in healthy individuals and well-trained athletes who may have a naturally lower resting heart rate due to increased vagal tone. However, in some individuals, especially when the heart rate drops significantly, it can lead to symptoms such as fatigue, dizziness, lightheadedness, and even syncope (fainting). Sinus bradycardia can be a physiological response or may be caused by certain medications or underlying medical conditions.
“Like a resting heart during sleep, the heart is beating at a slower, more relaxed pace.”