Steps in evaluation

Step one: verify tachycardia and hemodynamic stability. If unstable refer to ACLS algorithms please.

Step two: determine whether the QRS is narrow complex or wide complex

Step three: if narrow complex determine whether irregular or regular rhythm

Step four: if wide complex tachycardia, determine whether monomorphic or polymorphic

Algorithm for the initial ECG review and differential diagnosis of tachycardia

ECG: electrocardiogram; AVNRT: atrioventricular nodal reentrant tachycardia; AVRT: atrioventricular reciprocating (bypass-tract mediated) tachycardia; AT: atrial tachycardia; SANRT: sinoatrial nodal reentrant tachycardia; AF: atrial fibrillation; AV: atrioventricular; VT: ventricular tachycardia; SVT: supraventricular tachycardia; WPW: Wolff-Parkinson-White.
* A narrow QRS complex is <120 milliseconds in duration, whereas a wide QRS complex is ≥120 milliseconds in duration.
¶ Refer to UpToDate topic reviews for additional details on specific ECG findings and management of individual arrhythmias.
Δ Monomorphic VT accounts for 80% of wide QRS complex tachycardias; refer to UpToDate topic on diagnosis of wide QRS complex tachycardias for additional information on discriminating VT from SVT.

Algorithm for the evaluation of narrow QRS complex tachycardia in stable patients

Overview of Dubin’s Method for Reading EKG’s

1. RATE (pp. 65-96)

Estimate using “300, 150, 100…”

Bradycardia: rate = cycles/6 sec. strip × 10

2. RHYTHM (pp. 97-202)

Identify basic rhythm, scan for prematurity, pauses, irregularity, abnormal waves. Check for:

P before each QRS, QRS after each P

PR intervals (AV Blocks)

QRS interval (BBB)

If Axis Deviation, rule out Hemiblock.

3. AXIS (pp. 203-242)

QRS above or below baseline for Axis Quadrant (Normal vs. R. or L. Axis Deviation).

Find isoelectric QRS in a limb lead for Axis in degrees using the “Axis in Degrees” chart.

Axis rotation (horizontal plane): find “transitional” (isoelectric) QRS.

4. HYPERTROPHY (pp. 243-258)

Check P wave (atrial hypertrophy).

Check R wave in V₁ (Right Ventricular Hypertrophy).

Check S wave depth in V₁ and R wave height in V (Left Ventricular Hypertrophy).

5. INFARCTION (pp. 259-308)

Scan leads for:

Q waves

Inverted T waves

ST segment elevation/depression

Find location of pathology and identify the occluded coronary artery.

Further discussion

Rate (pp. 65-96)

Determine rate by observation using the triplet method (300-50).

Fine division/rate association reference chart provided.

Bradycardia: cycles/6 second strip × 10 = rate

Sinus Rhythm: SA Node origin; normal rate 60-100/min.

100/min = Sinus Tachycardia

<60/min = Sinus Bradycardia

Determine independent (atrial/ventricular) rates if co-existing rhythms are present

Dissociated Rhythms: sinus or atrial rhythm can co-exist with an independent rhythm from a focus of a lower level

Irregular Rhythms: note average ventricular rate (QRS’s/6-sec strip x 10)

Rhythm (pp. 97-111)

Identify basic rhythm, then scan tracing for pauses, premature beats, irregularity, and abnormal waves.

Always check: P before each QRS, QRS after each P; PR intervals, QRS interval; QRS vector shift outside normal range

Irregular Rhythms:

Sinus Arrhythmia: Irregular, varies with respiration, all P waves identical

Wandering Pacemaker: Irregular, P waves change shape, rate < 100/minute

Multifocal Atrial Tachycardia: Rate >100/min; otherwise similar to Wandering Pacemaker

Atrial Fibrillation: Irregular ventricular rhythm, no P waves (erratic atrial spikes)

Rhythm – continued (pp. 112-172)

Escape (pp. 112-121) – The heart’s response to a pause in pacing.

An unhealthy Sinus (SA) Node fails to emit a pacing stimulus (“Sinus Block”).

A sick Sinus (SA) Node may cease pacing (“Sinus Arrest”).

Escape Beats can be: Atrial, Junctional, or Ventricular.

Premature Beats (pp. 122-145) – From an irritable automaticity focus.

Premature Beats can be: Atrial, Junctional, or Ventricular.

Tachyarrhythmias (pp. 146-172)

Paroxysmal – rate: 150-250/min.

Flutter – rate 250-350/min

Fibrillation – rate 350-450/min

Rhythm (Heart Blocks) (pp. 173-202)

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

AV Block: Blocks that delay or prevent atrial impulses from reaching the ventricles.

1st AV Block: Prolonged PR interval

2nd AV Block: Some P waves without QRS response

Wenckebach

Mobitz

3rd AV Block: No P wave produces a QRS response

Axis (pp. 203-242)

General determination – is QRS (+) or (-) in leads I and AVF

First determine axis quadrant

if the QRS is positive in I and AVF = Normal

Axis in Degrees

After locating the Axis Quadrant, find the limb lead where QRS is most isoelectric

Axis rotation (left/right) in the Horizontal Plane:

Find transitional (isoelectric) QRS in a chest lead

Hypertrophy (pp. 243-258)

Atrial Hypertrophy

Right Atrial Hypertrophy: Large, diphasic P wave with tall initial component

Left Atrial Hypertrophy: Large, diphasic P wave with wide terminal component

Ventricular Hypertrophy

Right Ventricular Hypertrophy

Left Ventricular Hypertrophy

Infarction (pp. 259-308)

Q wave = Necrosis (significant Q’s only)

ST segment elevation = (acute) Injury (also Depression)

T wave inversion = Ischemia

Always obtain patient’s previous EKG’s for comparison!

Infarction Location/Coronary Vessel Involvement

Know Coronary Artery Anatomy.

Posterior

Lateral

Inferior

Miscellaneous (pp. 309-328)

Pulmonary Embolism

Artificial Pacemakers

Electrolytes:

Potassium

Calcium

Digitalis

Quinidine

Practical Tips

Dubin’s Quickie Conversion: Patient’s weight in kg. = Half of patient’s wt. (in lb.) minus 1/10 of that value.

Modified Leads for Cardiac Monitoring.

Zulfiqar Rana, MD, MPH, FACP

Board Certified in Internal Medicine

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