EKG

Reading: Klabunde, Cardiovascular Physiology Concepts Chapter 2 (Electrical Activity of the Heart) pages 27-37 Dubin, Rapid Interpretation of EKG’s, 6th Edition.

Check these hyperlinks out! http://www.themdsite.com/personal_reference.cfm Dubin’s EKG Pocket Guide

Basic Principles

Basic Principles The EKG records the electrical activity of contraction of the heart muscle Depolarization may be considered an advancing wave of positive charges within the heart’s myocytes

– + – + + – - - - - - - - - - - - + + + + + + + +

– + – + + – - - - - - - - - - - - - - - - - - - - - - - + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + - - - - - - - - - - - - - - - - - - - - - - + Depolarization Wave –

Depolarization Repolarization

Conduction System

AN Region N Region NH Region SA Node Right Atrial Tracts Anterior Internodal Pathway Middle Internodal Pathway Posterior Internodal Pathway Anterior interatrial myocardial band (Bachmann’s Bundle) Left Atrium AN Region N Region NH Region AV Node Bundle of His Right Bundle Branch Left Bundle Branch Anterior Division Posterior Division

Sinus Rhythm The SA (Sinus) Node is the heart’s dominant pacemaker. The ability of a focal area of the heart to generate pacemaking stimuli is known as Automaticity. The depolarization wave flows from the SA Node in all directions.

Atrio-Ventricular (AV) Valves Prevent blood backflow to the atria Electrically insulate the ventricles from the atria

AV Conduction AV node is situated on right side of interatrial septum near the ostium of the coronary sinus When the wave of depolarization enters the AV Node, depolarization slows, producing a brief pause, thus allowing time for the blood in the atria to enter the ventricles.

Rapid Repolarization Phase ST Segment Rapid Repolarization Phase Plateau

QT Interval Ventricular Systole

Recording the EKG

Limb Leads I II III AVR AVL AVF Chest Leads V1 V2 V3 V4 V5 V6

Autonomic Nervous System

Check for these on every EKG RATE Rhythm Axis Hypertrophy Infarction

Sinus Rhythm The SA (Sinus) Node is the heart’s dominant pacemaker. The generation of pacemaking stimuli is automaticity. The depolarization wave flows from the SA Node in all directions.

Sinus Rhythm The Sinus Node is the heart’s normal pacemaker Normal Sinus Rhythm: 60-100/min. Sinus Bradycardia: Less than 60/min. Sinus Tachycardia: More than 100/min.

Automaticity Foci Level Inherent Rate Range Atria AV Junction Ventricles Inherent Rate Range 60-80/min. 40-60/min. 20-40/min.

Overdrive Suppression

RATE Say “300, 150, 100” …“75, 60, 50” But for bradycardia: rate = cycles/6 sec. strip ✕ 10

Check for these on every EKG Rate RHYTHM Axis Hypertrophy Infarction

RHYTHM Identify the basic rhythm, then scan tracing for prematurity, pauses, irregularity, and abnormal waves. Check for: P before each QRS. Check for: QRS after each P. Check: PR intervals (for AV Blocks). Check: QRS interval (for Bundle Branch Block)

Sinus Rhythm Origin is the SA Node (“Sinus Node”) Normal sinus rate is 60 to 100/minute Rate more than 100/min. = Sinus Tachycardia Rate less than 60/min. = Sinus Bradycardia

Sinus Bradycardia

Sinus Tachycardia

Arrhythmias Irregular rhythms Escape Premature beats Tachy-arrhythmias

Irregular Rhythms Sinus Arrhythmia Wandering Pacemaker Multifocal Atrial Tachycardia Atrial Fibrillation

Sinus Arrhythmia Irregular rhythm that varies with respiration. All P waves are identical. Considered normal.

Wandering Pacemaker Irregular rhythm. P waves change shape as pacemaker location varies. Rate under 100/minute

Multifocal Atrial Tachycardia Irregular rhythm. P waves change shape as pacemaker location varies. Rate greater than 100/minute

Atrial Fibrillation Irregular ventricular rhythm. Erratic atrial spikes (no P waves) from multiple atrial automaticity foci. Atrial discharges may be difficult to see.

Escape Escape Rhythm Escape Beat Atrial Escape Rhythm Junctional Escape Rhythm Ventricular Escape Rhythm Escape Beat Atrial Escape Beat Junctional Escape Beat Ventricular Escape Beat

Premature Beats Premature Atrial Beat Premature Junctional Beat Premature Ventricular Contraction (PVC)

Atrial Bigeminy

PVC’s

Bigeminy

Tachyarrhythmias

Paroxysmal Atrial Tachycardia (Supraventricular Tachycardia) An irritable atrial focus discharging at 150-250/min. produces a normal wave sequence, if P’ waves are visible.

P.A.T. with block (Supraventricular Tachycardia) Same as P.A.T. but only every second (or more) P’ wave produces a QRS.

Paroxysmal Junctional Tachycardia AV Junctional focus produces a rapid sequence of QRS-T cycles at 150-250/min. QRS may be slightly widened.

Paroxysmal Ventricular Tachycardia Ventricular focus produces a rapid (150-250/min) sequence of (PVC-like) wide ventricular complexes.

Atrial Flutter A continuous (“saw tooth”) rapid sequence of atrial complexes from a single rapid-firing atrial focus. Many flutter waves needed to produce a ventricular response.

Ventricular Flutter A rapid series of smooth sine waves from a single rapid-firing ventricular focus Usually in a short burst leading to Ventricular Fibrillation.

Atrial Fibrillation Multiple atrial foci rapidly discharging produce a jagged baseline of tiny spikes. Ventricular (QRS) response is irregular.

Ventricular Fibrillation Multiple ventricular foci rapidly discharging produce a totally erratic ventricular rhythm without identifiable waves. Needs immediate treatment.

Block Sinus Block AV Block Bundle Branch Block Hemiblock

Sinus (SA) Block An unhealthy Sinus (SA) Node misses one or more cycles (sinus pause) The Sinus Node usually resumes pacing However, the pause may evoke an “escape” response from an automaticity focus

1° AV Block PR interval is prolonged to greater than 0.2 sec (one large square)

1° AV Block

2° AV Block (Some P waves without QRS Response) Wenkebach PR gradually lengthens with each cycle until the last P wave in the series does not produce a QRS

2° AV Block (Some P waves without QRS Response) Mobitz Some P waves don’t produce a QRS response. Intermittent may cause an occasional QRS to be dropped. More advanced may produce a 3:1 pattern or higher AV ration.

2° AV Block (Some P waves without QRS Response) May be Mobitz or Wenkebach.

2° AV Block

3° AV Block (“Complete” Block) P waves of SA node origin QRS’s if narrow, and if the ventricular rate is 40-60/min., then origin is a junctional focus.

3° AV Block (“Complete” Block) P waves of SA node origin QRS’s if PVC-like, and if the ventricular rate is 20-40/min., then origin is a ventricular focus.

3° AV Block

Bundle Branch Block Find R, R' in right or left chest leads Always check: Is QRS within 3 tiny squares?

Left Bundle Branch Block

Right Bundle Branch Block

Hemiblock Block of Anterior or Posterior Fasicle of the Left Bundle Branch Always check: Has Axis shifted outside normal range? Anterior Hemiblock: Axis shifts leftward > L.A.D. Look for Q1S3 Posterior Hemiblock: Axis shifts rightward > R.A.D. Look for S1Q3

Left Anterior Hemiblock

Check for these on every EKG Rate Rhythm AXIS Hypertrophy Infarction

Using Vectors to Represent Electrical Potentials A vector is an arrow that points in the direction of the electrical potential generated by current flow The arrowhead of the vector is in the positive direction The length of the arrow is drawn proportional to the voltage of the potential

N W E S

+ + + – + – + – + + – + – + + – – + + + + – – + + – + + – + – + + + – + – + + – – + + + + + + + + +

LV RV

+ + + – + – + – + + – + – + + – – + + + + – – + + – + + – + – + + + – + – + + – – + + + + + + + + +

Lead I – +

Axis QRS above or below baseline for Axis Quadrant (Normal vs. R or L Axis Dev.) For Axis in degrees, find isoelectric QRS in a limb lead Axis rotation in the horizontal plane (chest leads) find “transitional” (isoelectric) QRS

Causes of Axis Deviation Change of the position of the heart in the chest Hypertrophy of one ventricle Myocardial infarction Bundle branch block

Check for these on every EKG Rate Rhythm Axis HYPERTROPHY Infarction

Hypertrophy P wave for Atrial hypertrophy R wave for Right Ventricular Hypertrophy S wave depth in V1 + R wave height in V5 for Left Ventricular Hypertrophy

Right Atrial Hypertrophy Large, diphasic P wave with tall initial component Seen in lead V1

Left Atrial Hypertrophy Large, diphasic P wave with wide terminal component Seen in lead V1

Right Ventricular Hypertrophy R > S wave in V1 R wave gets progressively smaller from V1-V6 S wave persists in V5-V6 RAD with slightly widened QRS Rightward rotation in the horizontal plane

Left Ventricular Hypertrophy mm of S in V1 + mm of R in V5 Total: If more than 35 mm there is LVH

Left Ventricular Hypertrophy LAD with slightly widened QRS Leftward rotation in the horizontal plane Inverted T wave Slants downward gradually, but up rapidly

Hypertrophy Left Ventricle and Left Atrium

Check for these on every EKG Rate Rhythm Axis Hypertrophy INFARCTION (and Ischemia)

Infarction Scan all leads for: Q waves Inverted T waves ST segment elevation or depression Find the location of the pathology and then identify the occluded coronary artery

Necrosis = Q wave (significant Q’s only) Significant Q wave: One mm wide (0.04 sec in duration) or 1/3 the amplitude (or more) of the QRS Omit lead AVR when looking for significant Q’s Old infarcts: Q waves remain for a lifetime

Injury = ST elevation Signifies an acute process ST elevation associated with significant Q waves indicates an acute (or recent) infarct ST depression (persistent) may represent a “subendocardial infarction”

Ischemia = T wave inversion Inverted T wave (of ischemia) is symmetrical Normally T wave is upright when QRS is upright, and vice versa Usually in the same leads that demonstrate signs of acute infarction (Q waves and ST elevation)

Inferior Infarction

Inferior Infarction (+ LBBB)

Anterior Infarction

Postero-Lateral Infarction

Miscellaneous

Digitalis EKG appearance with digitalis Salvador Dali mustache T waves depressed or inverted QT interval shortened

Digitalis Digitalis Excess (Blocks) Digitalis Toxicity SA Block P.A.T. with Block AV Blocks AV Dissociation Digitalis Toxicity (Irritable foci firing rapidly) Atrial Fibrillation Junctional or Ventricular Tachycardia Multiple PVS’s Ventricular Fibrillation

Calcium

Decreased Potassium (Hypokalemia)

Hyperkalemia

Pulmonary Embolism S1Q3T3 Acute Right Bundle Branch Block Wide S in I, large Q and inverted T in III Acute Right Bundle Branch Block R.A.D. and clockwise rotation Inverted T waves in V1 – V4 ST depression in II

Pulmonary Embolism

Pacemakers

Wolf-Parkinson-White Syndrome

Wolf-Parkinson-White Syndrome

Review the 12-lead EKG on top in the next slide (EKG b). Anything unusual about it?

The End