Normal sinus rhythm

Jump to: navigation, search
Animation of a normal ECG wave


WikiDoc Resources for Normal sinus rhythm

Articles

Most recent articles on Normal sinus rhythm

Most cited articles on Normal sinus rhythm

Review articles on Normal sinus rhythm

Articles on Normal sinus rhythm in N Eng J Med, Lancet, BMJ

Media

Powerpoint slides on Normal sinus rhythm

Images of Normal sinus rhythm

Photos of Normal sinus rhythm

Podcasts & MP3s on Normal sinus rhythm

Videos on Normal sinus rhythm

Evidence Based Medicine

Cochrane Collaboration on Normal sinus rhythm

Bandolier on Normal sinus rhythm

TRIP on Normal sinus rhythm

Clinical Trials

Ongoing Trials on Normal sinus rhythm at Clinical Trials.gov

Trial results on Normal sinus rhythm

Clinical Trials on Normal sinus rhythm at Google

Guidelines / Policies / Govt

US National Guidelines Clearinghouse on Normal sinus rhythm

NICE Guidance on Normal sinus rhythm

NHS PRODIGY Guidance

FDA on Normal sinus rhythm

CDC on Normal sinus rhythm

Books

Books on Normal sinus rhythm

News

Normal sinus rhythm in the news

Be alerted to news on Normal sinus rhythm

News trends on Normal sinus rhythm

Commentary

Blogs on Normal sinus rhythm

Definitions

Definitions of Normal sinus rhythm

Patient Resources / Community

Patient resources on Normal sinus rhythm

Discussion groups on Normal sinus rhythm

Patient Handouts on Normal sinus rhythm

Directions to Hospitals Treating Normal sinus rhythm

Risk calculators and risk factors for Normal sinus rhythm

Healthcare Provider Resources

Symptoms of Normal sinus rhythm

Causes & Risk Factors for Normal sinus rhythm

Diagnostic studies for Normal sinus rhythm

Treatment of Normal sinus rhythm

Continuing Medical Education (CME)

CME Programs on Normal sinus rhythm

International

Normal sinus rhythm en Espanol

Normal sinus rhythm en Francais

Business

Normal sinus rhythm in the Marketplace

Patents on Normal sinus rhythm

Experimental / Informatics

List of terms related to Normal sinus rhythm

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]

Overview

An impulse (action potential) that originates from the SA node at a rate of 60 - 100 beats/minute (bpm) is known as normal sinus rhythm.

The sinus node (SA) is located in the upper part of the wall of the right atrium. When the sinus node generates an electrical impulse, first the cells of the right atrium depolarise, then the cells of the left atrium, the AV node (atrioventricular) follows and at last the ventricles are stimulated via the His bundle.

Criteria for normal sinus rhythm (see also Basics)
  • A P wave (atrial contraction) precedes every QRS complex
  • The rhythm is regular, but varies slightly while breathing
  • The frequency ranges between 60 and 100 beats per minute
  • The P waves maximum height is 2.5 mm in II and/or III
  • The P wave is positive in I and II, and biphasic in V1

Sinus Tachycardia

If SA nodal impulse occur at a rate exceeding 100 bpm, the consequent rapid heart rate is sinus tachycardia.

Sinus Bradycardia

If SA nodal impulses occur at a rate less than 60 bpm, the heart rhythm is known as sinus bradycardia. Sinus bradycardia may not always be indicative of disease. Trained athletes, for example, often have heart rates < 60 bpm when not exercising.

Non Sinus Rhythms

If the SA node fails to initialize the AV junction can take over as the main pacemaker of the heart. The AV Junction "surrounds" the AV node (the AV node is not able to initialize its own impulses) and has a regular rate of 40 to 60 bpm. These "Junctional" rhythms are characterized by a missing or inverted P Wave. If both the SA node and the AV Junction fail to initialize the electrical impulse, the ventricles can fire the electrical impulses themselves at a rate of 20 to 40 bpm and will have a QRS complex of greater than 0.12 seconds.

Depolarization and the ECG

See also: Electrocardiogram
The EKG complex. P=P wave, PR=PR interval, QRS=QRS complex, QT=QT interval, ST=ST segment, T=T wave

SA node: P wave

Under normal conditions, electrical activity is spontaneously generated by the SA node, the physiological pacemaker. This electrical impulse is propagated throughout the right and left atria, stimulating the myocardium of the atria to contract. The conduction of the electrical impulse throughout the atria is seen on the ECG as the P wave.

As the electrical activity is spreading throughout the atria, it travels via specialized pathways, known as internodal tracts, from the SA node to the AV node.

AV node/Bundles: PR interval

The AV node functions as a critical delay in the conduction system. Without this delay, the atria and ventricles would contract at the same time, and blood wouldn't flow effectively from the atria to the ventricles. The delay in the AV node forms much of the PR segment on the ECG. And part of atrial repolarization can be represented by PR segment.

The distal portion of the AV node is known as the Bundle of His. The Bundle of His splits into two branches in the interventricular septum, the left bundle branch and the right bundle branch. The left bundle branch activates the left ventricle, while the right bundle branch activates the right ventricle. The left bundle branch is short, splitting into the left anterior fascicle and the left posterior fascicle. The left posterior fascicle is relatively short and broad, with dual blood supply, making it particularly resistant to ischemic damage.

Purkinje fibers/ventricular myocardium: QRS complex

The two bundle branches taper out to produce numerous Purkinje fibers, which stimulate individual groups of myocardial cells to contract.

The spread of electrical activity through the ventricular myocardium produces the QRS complex on the ECG.

Ventricular repolarization: T wave

The last event of the cycle is the repolarization of the ventricles.

Sinus arrhythmias

Some variants of sinusrhythm exist:

If the heart rate exceeds 100 bpm, the tachycardia flow chart should be followed.

Additional resources

References

  1. Hammill S. C. Electrocardiographic diagnoses: Criteria and definitions of abnormalities, Chapter 18, MAYO Clinic, Concise Textbook of Cardiology, 3rd edition, 2007 ISBN 0-8493-9057-5

Examples & Diagrams










Linked-in.jpg