Normal sinus rhythm

Debs Farr 2011

Course Objectives

• To recognize the normal rhythm of the heart - “Normal Sinus Rhythm.”

• Understand normal conduction of the heart

http://caribbean.scielo.org/img/revistas/wimj/v54n3/a12fig03.jpg

R.E.Mason.,I.Likar ( 1966)

Impulse Conduction & the ECG

Sinoatrial node

AV node

Bundle of His

Bundle Branches

Purkinje fibers

The “PQRST”

• P wave - Atrial depolarization

• T wave - Ventricular repolarization

• QRS - Ventricular depolarization

The PR Interval

Atrial depolarization

+

delay in AV junction

(AV node/Bundle of His)

(delay allows time for the atria to contract before the ventricles contract)

Qt Inteval

• QT – Represents time for both ventricularDepolarisation and repolarisation.

Pacemakers of the Heart

• SA Node - Dominant pacemaker with an intrinsic rate of 60 - 100 beats/minute.

• AV Node - Back-up pacemaker with an intrinsic rate of 40 - 60 beats/minute.

• Ventricular cells - Back-up pacemaker with an intrinsic rate of 20 - 45 bpm.

The ECG Paper

• Horizontally– One small box - 0.04 s– One large box - 0.20 s

• Vertically– One large box - 0.5 mV

The ECG Paper (cont)

• Every 3 seconds (15 large boxes) is marked by a vertical line.

• This helps when calculating the heart rate.

3 sec 3 sec

Calibration

Normal Sinus Rhythm

• “Normal sinus rhythm occurs when the impulse originates in the sino Atrial node and travels through the conduction system in a normal sequence ,at a normal and regular rate”American Heart Association,(2000).homepage:Availablehttp:/www.americanheart.org/warning.

Normal Sinus Rhythm

ECG Interpretation

• A mystery?

• An enigma?

• Confusing?

• Difficult?

Criteria - P wave

An upright rounded P-wave in leads II, III and AVF, and an inverted P-Wave in AVR which precede each QRS Complex.

• The P wave does not exceed 2.5mm in height.

• It does not exceed 3mm in width.• A biphid P wave is seen in lead V1.

Criteria - PR interval

• PR Interval

• 0.12 - 0.20seconds.

• Delay at AV node»Protect ventricles»Allow for ventricular filling

Criteria QRS complex

• Should not exceed 0.12 seconds in duration.

• Should not exceed 27mm in height.

• Sharp narrow complex

• RS in V1, QRS in V6

Criteria T wave

• The deflection produced by repolarisation of the ventricles.

• No clearly defined range

• General rule - T wave should not be more than 1/2 the height of the preceding QRS

Criteria - QT interval

• QTc Interval

• Should not exceed 0.42 seconds (QTc).

• QT interval corrected to the heart rate.

Correction Calculation

QTc = measured Qt interval

cycle length

Criteria U wave

• The origin is uncertain

• May represent repolarisation if the IVS

• May represent slow conduction of ventricular myocardium

• Prominent U waves are abnormal

• Usually most visible in V1-V4

Nomenclature - QRS

• The 1st negative deflection - Q

• The 1st positive deflection - R

• The 2nd negative deflection or If a negative follows a positive - S

Nomenclature -QRS

Nomenclature - QRS

Nomenclature - QRS

• Waves > 0.5mv (5mm) high• Capital letters e.g. QRS

• Waves < 0.5mv (5mm) high• Lower case e.g. qrs

Intervals

• P wave duration measured?

• PR interval measured?

• QRS interval measured?

• QT interval measured?

Amplitudes

• P wave height measured?

• QRS height measured?

Segments

• PR segment measured?

• ST segment measured?

Limb leads

• Measurements - lead II

• QRS Axis

• P wave Axis

Chest Leads

• Progression of R waves throughout the chest leads

• Transitional Zone

• Phases of Activation

Depolarisation Stages

1

2

3

Typical complexes in the Pre-cordial leads

V1 V2 V3 V4 V5 V6

RV RV IVS IVS LV LV

Progression of R waves throughout the chest leads

• Size of the R wave should increase from V1 to V6.

• V4 Usually at the Apex (Transitional Zone where the first negative wave appears).

R Wave Progression

Practical Challenges

Sinus Rhythms

• Sinus Bradycardia

• Sinus Tachycardia

• Sinus arrhythmia

NSR Parameters

• Rate60 - 100 bpm• Regularity regular• P waves normal• PR interval 0.12 - 0.20 s• QRS duration 0.04 - 0.12 s• QT interval not exceed 0.42

seconds. • U wave

Sinus Bradycardia

- Rate < 60 b pm

Etiology: SA node is depolarizing slower than normal, impulse is conducted normally (i.e. normal PR and QRS interval).

Sinus Tachycardia

- Rate > 100 bpm• Etiology: SA node is depolarizing faster than

normal, impulse is conducted normally.• Remember: sinus tachycardia is a response to

physical or psychological stress, not a primary arrhythmia.

Sinus arrythmia

• Rate – variable

Etiology: SA node is depolarizing t a variable rate , impulse is conducted normally (i.e. normal PR and QRS interval).

Normal Rhythms !!!

• *Sinus Arrest*

• Considered a ‘Sinus rhythm’ but is abnormal

Rhythm 1

130 bpm• Rate?• Regularity? regular

normal

0.08 s

• P waves?

• PR interval? 0.16 s• QRS duration?

Interpretation? Sinus Tachycardia

Rhythm 2

30 bpm• Rate?• Regularity? regular

normal

0.10 s

• P waves?

• PR interval? 0.12 s• QRS duration?

Interpretation? Sinus Bradycardia

ECG INTERPRETATION

• If the normal ECG is known then interpretation of abnormals becomes easier

EASY ?

References/Bibliography

• www.ecglibrary.com

• www.acc.org

• www.cardionetics.com

• www.coheadquarters.com

• www.RNCEUS.com

• www.tmc.edu/thi/arrhythm.html

• ctmed