(ALS) ECG Tips Fast Facts

ECG Lead Placement Review

• Lead I (bipolar) Right Arm (+) to Left Arm (-)
• Lead II (bipolar) Right Arm (+) to Left Leg (-)
• Lead III (bipolar) Left Arm (+) to Left Leg (-)
• V1 (precordial) 4th IC space right of sternum
• V2 (precordial) 4th IC space left of sternum
• V4 (precordial) 5th IC space midclavicular line
• V3 (precordial) halfway between V2 and V4
• V5 (precordial) 5th IC space anterior axillary line
• V6 (precordial) 5th IC space axillary line
• V4R (right) 5th IC space midclavicular on right
• V6R (right) 5th IC space axillary line on right
• V8 (posterior) 5th IC space midscapular
• V9 (posterior) 5th IC space between V8 & spine

Quick Tips (Lead Placement)

• Limb leads should be placed on the limbs.  Place them lateral to the shoulder joint in the arms and inferior to the inguinal folds in the legs.
• It is better to place leads on top of breast tissue than to attempt to move the breast and place them.  Movement often leads to incorrect final placement.

Definitions:

P wave: 1st positive wave of the electrocardiogram

PR Interval: Period that extends from the beginning of the P wave until the beginning of the QRS complex. Normally 0.12–0.20 seconds

Q wave: 1st negative deflection after the P wave

R wave: 1st positive deflection after the P wave

S wave: Negative deflection after an R wave

QRS is normally 0.08–0.12 seconds

T wave:  1st positive deflection after the R wave

J point: where the QRS complex ends and the ST segment begins.

ST segment: End of the QRS complex (J point) to the initial deflection of the T wave.  Normally isoelectric.

5 Steps of ECG Interpretation

1. Analyze the rate.
2. Analyze the rhythm.
3. Analyze the P waves.
4. Analyze the PR interval.
5. Analyze the QRS complex.

Quick Tips (ECG Interpretation)

• Consistently evaluate all 5 elements in every ECG.  Never skip steps or assume!
• Know at least two ways to identify rate.  Don’t trust the 6-second method exclusively.
• Always confirm regularity.  Fast rhythms can often hide subtle irregularity.
• Most dysrhythmias have at least one obvious recognition feature or rule.  Take time to notice these features and remember that the most obvious choice is likely the correct answer.

ECG Hints

(Note: These hints are not absolute or representative of every possibility.  They represent common and likely findings that typically lead to correct analysis.)

• Irregularly irregular rhythms – atrial fibrillation (most common), ventricular fibrillation, wandering atrial pacemaker, multifocal atrial tachycardia
• Regularly irregular rhythms – Look for ectopic beats such as PACs, PJCs and PVCs.
• Narrow complex tachycardia without P waves – If the rhythm is regular consider SVT (AVRNT or AVRT) or atrial flutter (particularly if the rate is 150).  If the rhythm is irregular consider atrial fibrillation.
• Narrow complex tachycardia with P waves – Always rule out sinus tachycardia (particularly if nature of the illness points to compensation).
• Wide complex rhythms – If the rhythm is fast and no P waves can be identified, consider ventricular tachycardia.  If the rhythm is slow consider idioventricular rhythms or other rhythms with aberrant QRS complexes (such as resulting from a bundle branch block).  Also consider PVCs.
• Extra P waves between QRS complexes – Consider an AV block (see AV block hints below)
• PR Interval Issues – If the PRI is long, consider 1st degree AV block, PAC or 2nd-degree type I block.  If the PRI is short, consider junctional rhythms or PJCs.

Common Rhythm Characteristics

Normal sinus rhythm – Rate 60-99, regular, PRI .12-.20, P wave for every QRS, QRS for every P wave.

Sinus bradycardia – All aspects of normal sinus rhythm with a rate less than 60.

Sinus tachycardia – All aspects of normal sinus rhythm with a rate greater than or equal to 100.

Atrial fibrillation – Irregularly irregular rhythm with typically narrow complex, no P waves but commonly fibrillation waves are present.

Atrial flutter – Typically a regular rhythm (although it can be irregular with changing conduction ratios), no P waves but commonly flutter (sawtooth) waves preceding the QRS complex.  The most common rate is 150.

Ventricular tachycardia – Typically a regular and fast (by definition greater than 100) rhythm.  Most commonly wide complex with no P waves present (although it can occasionally display retrograde P waves or capture beats).

Junctional Rhythm – Typically a regular and slow rhythm (commonly less than 60, but it can be accelerated at 60-100 or even tachycardia at greater than 100).  Most commonly narrow complex and associated with absent or retrograde P waves.  It can be associated with normal P waves but narrowed PRI.

SVT (more accurately AVRNT or AVRT) – A regular and fast rhythm.  Almost always narrow complex with no P waves present (although retrograde P waves can be displayed).

Idioventricular rhythm – Typically a regular and wide complex rhythm.  It is usually very slow (less than 40) with no P waves.

Polymorphic ventricular tachycardia (commonly referred to as Torsades de Pointes) – This is a wide complex rhythm similar to ventricular tachycardia but with varying amplitude of QRS complexes.  It typically displays a distinct pattern of a tall complex preceding very short or negative complexes.

AV Block Differentiation Characteristics

Quick Tip: With the exception of a 1st-degree block, all AV blocks create P waves without QRS complexes (extra P waves).  Use this feature to help identify when an AV block is likely.

1st degree AV block – A P wave for every QRS but a prolonged PRI (greater than .20)

2nd degree AV block type I – Extra P waves between QRS complexes.  An inconsistent PRI where present.  It commonly presents as Wenckebach phenomenon with the shortest PRI following dropped QRS, then lengthening PRI leading to the next dropped QRS.  The pattern leads to an irregular rhythm.

2nd degree AV block type II – Extra P waves between QRS complexes.  Although QRS complexes are dropped, there are consistent PRIs when P waves and QRS complexes are present.  Technically it must have 2 consecutively conducted beats to identify a consistent PRI.  The pattern leads to an irregular rhythm.

3rd degree AV block – No correlation between P waves and QRS complexes.  Most often it presents with a regular P to P interval and a regular R to R interval but no clear association between the two.  Because the R to R interval is ventricular escape and therefore regular, the overall rhythm is typically regular.

Premature Beat Differentiation Characteristics

Quick Tips (Premature Beats)

• By definition, all premature beats occur before their expected timing.  Beware confusing them with pauses or delayed conduction.
• Premature contractions can occur in patterns such as bi- or trigeminy.  When regularly irregular rhythms are identified, suspect ectopic beats.

Premature atrial contraction – Early occurring complex with P wave and a normal or prolonged PR interval.  It is typically similar in morphology to other normally occurring QRS complexes.  Commonly has a narrow complex.

Premature junctional contraction – Early occurring, typically narrow complex QRS.  It can have an absent or retrograde P wave but also may present with a P wave but shortened PR interval.  Differentiate this from PAC by an absent or shortened PRI.  Differentiate this from PVC by the narrow complex.

Premature ventricular contraction – Early occurring typically wide complex QRS and an absent P wave.

Diagnosing a 12-Lead ECG

Quick Tip: Always assess more than one 12-lead ECG as symptoms evolve over time.

1. Diagnose the rhythm using the 5-step method discussed previously.
2. Identify the J point and examine the ST segment.
3. Consistently examine contiguous lead groupings to ensure all areas of the heart are assessed – inferior, septal, anterior, lateral, posterior.
4. Look for patterns that suggest ischemia (inverted T waves, ST segment depression).
5. Look for patterns that suggest injury (ST elevation).
6. Assess for reciprocal changes – inferior to lateral, anterior/septal to posterior.
7. Rule out common STEMI mimics (see STEMI mimics below).

Contiguous ECG lead groupings

• Inferior – Lead II, III, AVF (reciprocal to lateral)
• Septal – V1, V2 (reciprocal to posterior)
• Anterior – V3, V4 (reciprocal to posterior)
• Lateral – Lead I, AVL, V5, V6 (reciprocal to inferior)
• Posterior – V8, V9 (reciprocal to anterior and septal)

Common STEMI Mimics

• Bundle Branch Block – QRS greater than .12 in precordial leads, presence of R prime.
• Hyperkalemia – Tall T waves, wide QRS, absent P waves.
• Pericarditis – Global concave ST elevation, PR depression, sinus tachycardia common.  Patient has a history of fever.
• Left Ventricular Hypertrophy – Extremely tall (often greater than 35 mm) QRS complexes in precordial leads.

Static Cardiology Testing

Quick Tip: There is no substitute or trick that will replace learning the key recognition features of the common dysrhythmias.  Preparation starts and ends here.

• Review key recognition features of common dysrhythmias.  Focus attention on those that occur more frequently.
• Practice early and often.  Remember that timing is a key success strategy.  Be prepared to be succinct and manage your time.
• Take a deep breath.
• Take time to read the situation/symptoms.  Often clues to diagnosis will be found there.
• Take care to utilize the five steps for every rhythm.  DON’T GUESS!  Beware the subtleties of rate and rhythm.  Don’t make the mistake of calling a sinus bradycardia a normal sinus rhythm just because you forgot to count the rate.
• Be brief in your treatment descriptions.  Stick to key interventions as opposed to fine detail.
• Although any rhythm is possible, beware anchoring on obscure or rare dysrhythmias.  They are less likely to be correct.
• It is very unlikely you will see two of the same rhythms.  If you find this situation, go back and double check previous diagnoses.
• You can pass on a rhythm, but be aware of time limits.  Do not change your answer unless you have a specific cause to change it.

Dynamic Cardiology Testing

• Review key recognition features of common dysrhythmias.  Focus attention on those that occur more frequently.
• Review relevant protocols and treatment algorithms.
• Review the operation of the monitor/defibrillator you will test with.  Never walk into a test unfamiliar with the device you will use.
• Always consider safety.  Be sure to properly clear all defibrillations and cardioversions.
• Practice using the energy doses you will be expected to use during the test.
• Always verbally identify the rhythm before treating it, especially if there has been a rhythm change.
• Remember that you may print an ECG strip to assist in recognition.