ECG Basics Anatomy of the Heart 1 Sinus

ECG Basics

Anatomy of the Heart 1. Sinus Node (SA node) – the primary pacemaker of the heart; 2. Atrioventricular Node (AV node) – slows and transmits electrical signal from atria to ventricles. 3. Bundle of His – rapidly sends electrical signal through ventricles 4. Right and Left Bundle branches – carry fast electrical signals through the ventricles 5. Bundle Branches (bundles of Purkinje fibers)

Where is the Rate Determined? SA node – pacemaker of the heart; rate of 60 - 100 bpm if SA node fails, then the Atrial foci will pace the heart; rate of 60 -80 bpm If the Atrial foci fail, then the AV node (Junctional foci) will pace the heart, send electrical activity up through the atria and down through the ventricles; rate of 40 -60 bpm If the Junctional foci fail, then the Purkinje fibers (ventricular foci) will pace; rate of 20 -40 bpm

Breaking Down an EKG – What It All Means

• P wave – Atrial Depolarization (atrial contraction) • < 0. 11 seconds • PR interval – Time from atria to Purkinje fibers • 0. 12 - 0. 20 seconds • QRS complex – Ventricular Depolarization (ventricular contraction) • • First negative deflection – Q wave First Positive deflection – R wave Negative following the R wave – S wave 0. 05 – 0. 10 seconds • ST segment – Ventricle remains depolarized • 0. 04 seconds • T wave – rapid ventricular repolarization • QT interval – repolarization • • Ventricular contraction last from Q wave to end of T wave < 0. 42 seconds • U wave – Purkinje fibers repolarization -usually present with post-MI patients • R-R interval – duration of one heart beat

What else to consider? What is the heart rate? Atrial HR – number of P waves Ventricular HR – number of QRS complexes Normally – should be equal Is the rhythm regular or irregular? Are the R-R interval equally spaced? Is there a P wave for every QRS? Yes – sinus rhythm No – more information needed

It’s all about the paper Each small square is 1 mm tall by 1 mm wide Time x amplitude Between two thick black lines is 0. 20 seconds, therefore 5 thick line boxes equal 1 minute. Can use a 6 second strip to calculate rate and rhythm.

Let’s Practice! P wave = ____ PR interval = ____ QRS interval = _____ ST segment = ____ T wave = ____ P wave = 0. 10 * PR interval = 0. 16 * QRS interval = 0. 04 * ST segment = 0. 14 * T wave = 0. 18

What is the heart rate? 60 bpm * Is this rhythm regular or irregular? Regular * Is there a P wave for every QRS complex? Yes * Is this a sinus rhythm? Yes Is there a P wave for every QRS complex? Is this a sinus rhythm? Is this rhythm regular or irregular? What is the heart rate? More Practice!

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