EKG Interpretation

Atrial Rhythms

• Are not classic “P-wave” rhythms, if equal/consistent/nonvarying P-waves are easily identified then the rhythm is NOT atrial in origin

• Atrial rhythms are routinely fast

• Ventricular rates can be controlled (<100) or uncontrolled (>100)

• Ventricular responses and rates can reach up to 220 – 240 ppm

• Ventricular regularity can be regular or irregular, depending on the rhythm:

- AFib, WAP & MAT = ALWAYS IRREGULAR

- Aflutter = Regular or Irregular

- SVT/PSVT, ATach = ALWAYS REGULAR

• QRS-complexes can be Narrow (<0.12 sec) or Wide (>0.12 sec). This is measured using the ECG paper (<0.12 = less than 3 small boxes; <0.12 = greater than 3 small boxes)

Atrial Rhythms & Associated Rates

• A-Fib: Atria Rate >350 – 500; Ventricular Rate >220 – 240 ppm

• A-Flutter: Atrial Rate >250 – 450; Ventricular Rate >220 – 240 ppm

• Atrial Tachycardia: Atria > 220 – 240; Ventricular Rate = Atrial Rate (1:1 ratio)

• Supraventricular Tachycardia: >150 – 160 ppm, even upwards of 220 – 240 ppm; Ventricular Rate = Atrial Rate (1:1 ratio)

• Wandering Atrial Pacemaker (WAP): Atrial Rate <100 ppm; Ventricular Rate = Atrial Rate

• Multifocal Atrial Tachycardia (MAT): Atrial Rate >100 ppm; Ventricular Rate = Atrial Rate

Premature Atrial Contraction (PAC)

Atrial ectopy (not a rhythm) similar to an ill timed hiccup within the atria, or the atria playing a game of interrupting cow.

Atrial Fibrillation (A-Fib)

Wavy and chaotic baseline, noted overall irregularity, AFib QRS complexes can be 'wide' or 'narrow'

Narrow QRS Complex

<0.12 seconds (3 small boxes)

Wide QRS Complex

>0.12 seconds (3 small boxes)

Atrial Flutter (A-Flutter)

Consistent atrial depolarization waves creating "flutter" or "saw-tooth" appearance on baseline.

Can be regular or irregular.

QRS complexes can be 'wide' or 'narrow'

Different ratios (2:1, 3:1, 4:1) possible

Atrial Tachycardia (A-Tach)

Atrial Tachycardia is caused when abnormal electrical signals inersect with signals coming from the SA node.

It can prevent the heart from filling normally and refuse the overall blood flow out of the heart due to rapid rate.

'Teeny-tiny' P's noted, FAST rate, narrow complexes and REGULAR

Supraventricular Tachycardia (SVT)

Abnormal heart rhythm arising from aberrant electrical activity in the heart; originates at or above the AV node

No P's noted, FAST rate, narrow complexes and REGULAR

Multifocal Atrial Tachycardia (MAT)

3 or more varying P-Waves, overall irregular and rate is >100 ppm. Note the DIFFERENT P’s presented.

Wandering Atrial Pacemaker (WAP)

3 or more varying P-Waves, overall irregular and rate is <100 ppm. Note the DIFFERENT P’s presented.

Heart Block Key Points

• 1st Degree - PRI is > 0.20sec and 1:1 (P-wave for every QRS-complex)

• 2nd Degree Type I – PRI will INCREASE, QRS’s will drop. Remember phrase: “Going…Going…Going…Gone!”

• 2nd Degree Type II – PRI will remain CONSTANT and QRS’s will drop.

• 2nd Degree High Grade Block – Repetitive QRS complexes are dropped.

• 3rd Degree (Complete Heart Block) – Occurs when impulses are not received from the atria into the ventricles. Atria and ventricles will each depolarize at individual rate

***RATES CAN VARY FOR EVERY TYPE OF BLOCK***

Heart Block Rhythms

When interpreting Heart Blocks, the P-wave is always present which means the Sinus Node is “firing”, so the underlying rhythm is typically “Sinus” in nature. In order to identify a “Heart Block”, find the P-waves! Heart block degree is based on the location of the P-waves and their relationships to the following QRS-complexes and their consistency.

1st Degree Heart Block

Actually only a “delay” so all waves are present on the strip. With a 1st Degree AV Block, there is a P-wave for EVERY QRS-complex. Thus, nothing is “missing” and the PRI is consistently >0.20sec (5 small boxes) as measured on the ECG/EKG paper. Remember, the PRI WILL NOT CHANGE!

2nd Degree Type I Heart Block

Missing QRS-complexes. The PRI will increase, resulting in a "dropped" QRS-complex. The PRI will reset and the process will start all over again. Remember the following phrase: "Going...Going...Going...Gone..." and this will help you remember the process of a 2nd Degree Type I (Wenckebach or Mobitz I). Remember the PRI CHANGES!

2nd Degree Type II Heart Block

Dropped QR complexes with the PRI remaining CONSTANT. PRI's will remain overall consistent and QRS-complexes are repeatedly drop from the rhythm. Defining characteristic of this heart block is that the PRI WILL NOT CHANGE!

2nd Degree High Grade Heart Block

2nd degree heart block becomes “high grade” when multiple QRS’s are consistently missing from the rhythm. These ratios are given when interpreting and documenting a 2nd High Grade Block:

• 2:1 - 2 P-waves for every QRS-complex present

• 3:1 - 3 P-waves for every QRS-complex present

• 4:1 - 4 P-waves for every QRS-complex present and so on…

Junctional Rhythm

The SA node is nonfunctional, P waves absent, inverted, or follow QRS's.

• Usually slow

• QRS-complexes can be narrow (<0.12 sec) or wide (>0.12 sec).

Junctional Rhythm Rates

• Junctional Escape: 40 – 60 ppm

• Junctional Bradycardia: < 40 ppm

• Accelerated Junctional: 60 – 100 ppm

• Junctional Tachycardia: > 100, upwards of 130 to 140 ppm

Automaticity

•Ability of pacemaker cells to initiate electrical impulse independent of external stimulation.

•Increased electrolytes decrease automaticity

•Decreased K+ and Ca++ in blood increase automaticity

Exitability "irritability"

Ability of cardiac cells to respond to outside stimulation.

Junctional Bradycardia

HR = 38

No apparent P-waves

Accelerated Junctional Rhythm

HR = 71

No apparent P-waves

Junctional Tachycardia

R = 125

No apparent P-waves

Sinus Rhythms

• Rhythms that originate in the SA node

• Upright & Consistent P-waves

• P-waves remain identical (except premature complexes)

• PRI remains constant (0.12 – 0.20 Seconds, or 3 – 5 small boxes on ECG paper)

• 1 P-wave for every QRS-complex (1:1 ratio)

• R to R (QRS to QRS) is typically regular, meaning at equal intervals. Only variations would be for premature/delayed complexes, sinus arrhythmias, or pauses of the SA Node

• QRS-complexes can be Narrow (<0.12 sec) or Wide (>0.12 sec). This is measured using the ECG paper (<0.12 = less than 3 small boxes; <0.12 = greater than 3 small boxes)

• Exception are pauses of the SA node. Sinoatrial Blocks and Sinoatrial Arrests occur, but do not change the underlying sinus rhythm.

Sinus Rhythm Rates

• Normal Sinus Rhythm: 60 to 100 ppm

• Sinus Bradycardia: <60 ppm

• Sinus Tachycardia: >100 ppm (up to 150 – 160, even as high as 180)

• Sinus Arrhythmia: fast or slow, bradycardic, normal, or tachycardic rates. The R to R (from QRS to next QRS) changes in rates typically due to cardio-respiratory response. However, there are instances where this is not respiratory related.

• Sinoatrial Block: rates vary; but periodically PQRS-T complexes are ‘dropped’, but resume normally/on time

• Sinoatrial Arrest: rates vary; but periodically PQRS-T complexes are ‘dropped' but resume at unpredictable intervals

Normal Sinus Rhythm

Ventricular rate: 60-100

Conduction

Ability of a cardia cell to receive and relay an electrical signal

Contractility

Ability of cardiac muscles to contract the heart

Phases of cardiac cellular conduction

Polarized- cells are charged with energy

Depolarized- cells are discharging energy and causing physical contraction

Repolarization- cells are recharging

Electrical conduction of the heart

SA Node --> AV Node --> Bundle of His --> Purkinje Fibers --> Contraction of ventricles

(Stab A Big Pickle)

PPM

Paces per minute

Cardiac output cannot be determined by conductivity, hence "BPM" is incorrect when referring to rates

Bundle branches

DO NOT produce any rhythms, are only the "power lines" between AV and Purkinje fibers

SA node

Pacemaker of the heart

Relays electrical impulses from atria into ventricles

Inherent rate 60-100ppm

Creates P-wave

AV node

Gatekeeper of electrical impulses

Speed bump function, can hold onto electrical impulses to control a rate when SA node fires too quickly

Backup pacemaker; can take over if SA node fails

Inherent rate 40-60ppm

Purkinje fibers

Tertiary pacemaker

Inherent rate <40ppm

Can only sustain cardiac output for short time

Eintoven's Triangle

Based on triangle formed with LA, RA, LL 9red, black, and white)

Triangle is the basis for limb lead tracings (I, II, III, aVR, aVL, and aVF)

Each lead tracing is bipolar, one positive and one negative

Shows frontal plane of cardiac conduction

Lead Placement Prep

Clean with soap and water if possible

Do not place on bony prominences if possible

If you need to shave, you need to shave!

Alcohol dries the skin AND electrode leading to low quality read

Floating lead

Brown lead (chocolate in your heart)

Traditional placement is right 4th intercostal space

Small EKG box

0.04 seconds

Large EKG box

0.2 seconds

5 Large Boxes

1 second

15 Large Boxes

3 seconds

Sometimes demarked by tic marks

300 Large Boxes

1 minute

Regular rhythm

Measure the intervals between P to P waves or R to R waves

If the intervals vary by less than 0.06 seconds or 1.5 small boxes, we can consider the rhythm to be regular

Baseline

Represents resting cardiac potential -90mV

Line is most visible when patient is in asystole

P wave

Atrial depolarization (contraction)

Normally from SA node

Usually rounded but can appear pointed, notched, or even biphasic (above and below baseline)

PR interval

Measurement from beginning of P wave to beginning of QRS complex

Normally 0.12-0.20 seconds (3-5 small boxes)

Q wave

First negative deflection of QRS

R wave

First positive deflection of QRS

S wave

First negative deflection after R wave

QRS complex

<0.12 seconds

Even if waves are missing, still referred to as QRS complex

Only complex with straight lines

ST segment

Early stage of repolarization

Measured J point to beginning of T wave

Usually 0.04 seconds (one small box)

J point

Junction between end of QRS complex and start of ST segment

T wave

Ventricular repolarization and relaxation

Should be pointing in same direction as QRS complex whether positively or negatively deflected

QT interval

Refractory period

Measures from beginning of QRS to end of the T wave

Normally 0.44 seconds or half of the R-R interval (can change based on age and gender)

The longer the QT, the greater chance of ventricular depolarization during ventricular repolarization, resulting in chaotic and lethal rhythm such as Torsade's

QTc interval

Measure of time between start of Q wave and end of T wave in cardiac cycle

Absolute Refractory Period

"Safe zone

Cells cannot be stimulated to conduct an electrical impulse, no matter how strong

Relative Refractory Period

Danger zone

Cardiac cells can be stimulated to depolarize if the stimulus is strong enough

This is why cardioversion has a sync button to time the shock exactly; shocking during RRP could cause a patient to go into V-fib a lethal rhythm

U wave

Associated with bradycardic rhythms and hypokalemia

Delayed repolarization of Purkinje fibers

Same direction as T wave

7 Step Interpretation

Regularity

Rate

P waves

PR interval

QRS complex

QT interval

ST segments

1500 Method

Count number of small squares between two consecutive R-waves and divide that number by 1500

Most accurate only if regular rhythm

P-P Interval

Used to determine atrial rate and regularity

Measure from beginning of one P wave to the beginning of the next

Artifact

Readings produced by external activity rather than cardiac electrical current

J-Point

Point where the QRS complex and ST segment meet