The ECG Rhythms content is currently under development and is being updated by medical professionals.
Normal sinus rhythm (NSR) represents the heart’s fundamental and healthy electrical activity, originating from the sinoatrial (SA) node, which acts as the heart’s natural pacemaker. This rhythmic activity ensures the coordinated contraction of the heart’s chambers, facilitating efficient blood circulation throughout the body. The SA node initiates the electrical impulse that triggers each heartbeat, setting the pace for the entire cardiac cycle.
Analogy: “The heart’s natural metronome, keeping a steady and reliable beat.”
On an ECG, normal sinus rhythm exhibits specific characteristics. The rhythm is regular, meaning the time interval between consecutive heartbeats is consistent. The heart rate in adults typically falls within the range of 60 to 100 beats per minute. A P wave is present before every QRS complex, indicating that each ventricular depolarization is preceded by atrial depolarization originating from the SA node. The morphology (shape) of the P wave is typically upright in leads I and II, and negative in lead aVR, and it may be biphasic (partially positive and partially negative) in lead V1. The PR interval, which represents the time for the impulse to travel from the atria to the ventricles, remains consistent and falls within the normal range of 0.12 to 0.20 seconds (3 to 5 small squares on the ECG paper). The QRS complexes, representing ventricular depolarization, are typically narrow, with a duration of less than 0.12 seconds (less than 3 small squares). These characteristics collectively indicate that the heart’s electrical conduction system is functioning properly, with the SA node effectively pacing the heart. The P wave specifically reflects the atrial depolarization that originates in the SA node.
In most cases, normal sinus rhythm is asymptomatic, meaning individuals experiencing this rhythm do not typically feel any unusual sensations or symptoms related to their heartbeat. It is the expected and healthy rhythm of the heart.
“Like a well-conducted orchestra, each section (atria and ventricles) plays its part in perfect timing and harmony.”