Basic: Rate:

Intervals:

PR – 0.12 - 0.20 seconds (3 - 5 boxes)

< 0.12 s 0.12-0.20 s > 0.20 s

High NE/E statesWolff-Parkinson-White

NormalAV nodal

blocks

WPW syndrome 1st Degree AV Block (delta-wave)

QRS – 0.04 - 0.12 seconds. (1 - 3 boxes)

< 0.10 s 0.10-0.12 s > 0.12 s

NormalIncomplete

Bundle Branch Block (BBB)

BBBPVC

Ventricular rhythm

QTc – QT interval α to heart rate. Faster heart beats Faster ventricles repolarize Shorter QT interval. I.e., “normal” QT varies with heart rate.

For each heart rate, calculate an adjusted QT interval, called the:

“corrected QT” (QTc)

Normal ; < 0.44 sLong QT : > 0.44 s

Tip: QT > half RR interval ≈ long.

A prolonged QT may predispose a type of ventricular tachycardia called Torsades de Pointes. Causes include drugs, electrolyte abnormalities, CNS disease, post-MI, and congenital heart disease.

3rd degree AV block with ventricular escape rhythm

Incomplete bundle branch block

Heart Arrhythmias1. Sinus Rhythms

Sinus Tachycardia Rate: > 100 bpmSinus Bradycardia Rate: < 60 bpm

2. Premature Contraction / Beats

Atrial (PACs)

Contour of P, PR interval, timing differ from normal pulse from SA node and QRS will be narrow (0.04 - 0.12 s) (normal impulse conduction in ventricles)

Ventri-cular (PVCs)

Wide and bizarre QRS complex(es).a. Uniform : look alike, b. Multiform : look different

3. Supraventricular Arrhythmiasa. Atrial Fibrillation (AF)

No normal P waves, Flutter wave. (No organized atrial depolarization, impulses are not from sinus), atrial activity is chaotic (irregular rate). Common, affects 2-4%, up to 5-10% if > 80 years old.Due to multiple reentry between LA and RA.

b. Paroxysmal SupraventricularTachycardia (PSVT) HR suddenly speeds up, often due to PAC and the P waves are lost. Due to reentry in AV node.

c. Atrial Flutter No P waves, “saw tooth” pattern at 250 - 350 bpm. Only some impulses conduct through AV node (usually every other impulse). Due to reentry in RA with every 2nd, 3rd or 4th impulse generate a QRS (others are blocked in AV node as node repolarizes).

4. Ventricular Arrhythmiasa. Ventricular Fibrillation

Completely abnormal. Ventricular cells are excitable and depolarizing randomly. Causes rapid drop in CO and death

b. Ventricular Tachycardia Impulse originates in ventricles (no P waves, wide QRS). Due to reentry in ventricle.

5. AV Junctional Blocks

a. 1st Degree AV Block PR Interval: > 0.20 s, Prolonged conduction delay in the AV node or Bundle of His.

b. 2nd Degree AV Block, Type I (Mobitz I/ Wenckebach) PR interval progressively lengthens, then impulse is completely blocked (P wave not followed by QRS). Each atrial impulse causes longer delay in AV node until one impulse (usually 3rd or 4th) fails to conduct to AV node.

c. 2nd Degree AV Block, Type II / Mobitz II Occasional P waves are completely blocked (P wave not followed by QRS). Conduction is all or nothing (no prolongation of PR interval); typically block occurs in the Bundle of His.

d. 3rd Degree AV Block P waves are completely blocked in the AV junction; QRS originate independently from below

QRS Complexes

I (L) II (R) Axis+ + normal+ - left axis deviation- + right axis deviation- - right superior axis deviation

MI Location

MI Lead

Anterior V1 - V4

Lateral I, aVL, V5 - V6

Inferior II, III aVF

the junction. (Ventricles pacemaker: around 30-45 bpm, conduction through ventricles is inefficient and the QRS will be wide and bizarre.)

Axis

Axis refers to the mean QRS axis (or vector) during ventricular depolarization. An abnormal axis can suggest disease such as pulmonary hypertension from a pulmonary embolism.

The QRS axis is determined by overlying a circle,in the frontal plane. By convention, the degrees of the circle are as shown. A quick way to determine the QRS axis is to look at the QRS complexes in leads I and II.

Diagnosing a Myocardial Infarction (MI)

One way to diagnose an acute MI is to look for elevation of the ST segment.

Heart Hypertrophy

Left atrial enlargement (LAE)

• P wave - atrial depolarization• II : P > 0.04 s (1 box) between

notched peaks, or• V1 : P Neg. deflection > 1 x1 box• Cause : LVH from hypertension.

Types of MI:

ST (Transmural / Q wave) Non-ST (Subendocardial / Non-Q-wave)

IschemiaST depression, peaked T-waves, then T-wave inversion ST depression & T-wave inversion

Infarct ST elevation & appearance of Q-waves Fibrosis ST and T-waves normalize, Q-waves persist ST normalize, but T-wave inversion persists

Right atrial enlargement (RAE) • II : P >2.5mm, or• V1/V2 : P >1.5mm• Cause : RVH from pulmonary hypertension

Left ventricular hypertrophy (LVH)

• R in V5 (or V6) + S in V1 (or V2) > 35 mm, • or avL: R > 13 mm • Cause: hypertension.

Right ventricular hypertrophy (RVH)

• R wave is normally small in V1, V2 because RV does not have a lot of muscle mass. But in RVH the R wave is tall in V1, V2.

• Right axis deviation, and V1 : R >7mm tall• Cause: left heart failure.

Bundle Branch Blocks (BBB)

QRS complex widen because when the conduction pathway is blocked it will take longer for the electrical signal to pass throughout the ventricles.

Left Bundle Branch Blocks (LBBB) Right Bundle Branch Blocks (RBBB)

V1-V2 : Broad, deep S waves / W wave V1-V2 : “Rabbit Ears”

/ M wave

Bifascicular block = RBBB + left bundle hemiblock, manifest as an axis deviation, eg LAD in the case of left ant. hemiblock. Trifascicular block = bifascicular block + 1st degree heart block.