ECG Basics

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

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

Strip of the Month