Most common ecg in medicine

Reading File

Finding Sources

Reading File

Finding Sources

Loading Image

Finding Sources

Reading File

I now have excellent textbook content to give a thorough, well-structured answer. Here is the comprehensive guide:

Most Common ECGs in Clinical Medicine

ECG interpretation follows a systematic approach: rate → rhythm → axis → intervals → waveform morphology. Below are the most important and commonly encountered ECG patterns, grouped by category.

1. Normal Sinus Rhythm (Baseline Reference)

Rate: 60-100 bpm
Regular R-R intervals
P wave before every QRS, PR interval 120-200 ms, QRS < 120 ms
The P wave = atrial depolarization; QRS = ventricular depolarization; T wave = ventricular repolarization

How to read rate (quick method): Count large boxes between R waves - divide 300 by that number. Example: 4 large boxes = 75 bpm.

Medical Physiology, Box 21-2

2. Atrial Fibrillation (AF) - Most Common Sustained Arrhythmia

Classic ECG features:

Absent P waves - flat or chaotic/fibrillatory baseline
Irregularly irregular ventricular rhythm (no two R-R intervals the same)
Narrow QRS (unless pre-existing bundle branch block or pre-excitation)

Causes: Ischemic heart disease, valvular disease, cardiomyopathy, thyrotoxicosis, alcohol ("holiday heart"), blunt chest trauma.

Clinical risk: Loss of atrial kick → heart failure. Risk of thromboembolism increases with duration; >48 hours requires anticoagulation before cardioversion.

Atrial fibrillation and flutter ECG tracings

(Panel A: Lead II rhythm strip; Panel B: 12-lead ECG; Panel C: atrial flutter with irregular conduction)

Tintinalli's Emergency Medicine, Table 18-8

3. STEMI (ST-Elevation Myocardial Infarction)

Per the Fourth Universal Definition of MI, diagnostic STEMI criteria:

Lead	Threshold
All leads except V2-V3	New ST elevation ≥ 1 mm in ≥2 contiguous leads
V2-V3, females (any age)	≥ 1.5 mm
V2-V3, males < 40 years	≥ 2.5 mm
V2-V3, males ≥ 40 years	≥ 2.0 mm

Evolutionary sequence:

Hyperacute T waves - tall, broad-based, peaked (within minutes of occlusion; transient)
ST elevation - "tombstoning" pattern
Q wave formation - pathological Q waves develop (>40 ms wide or >25% of R wave height)
T wave inversion - during and after infarction
ST normalization - hours to days later

Localization by leads:

Inferior MI (RCA): II, III, aVF - reciprocal changes in I, aVL
Anterior MI (LAD): V1-V4
Lateral MI (LCx): I, aVL, V5-V6
Posterior MI (RCA/LCx): ST depression V1-V3 + tall R waves (mirror image)

Important: ST elevation establishes candidacy for emergent reperfusion (PCI or fibrinolysis). A single normal ECG does not rule out AMI - serial ECGs are required.

Rosen's Emergency Medicine, Chapter 64

4. NSTEMI / Unstable Angina ECG Findings

ST depression (horizontal or downsloping ≥ 0.5 mm)
T-wave inversions (deep symmetric inversions = Wellens pattern in LAD disease)
May have a normal ECG (up to 6% of MIs)
Troponin distinguishes NSTEMI from unstable angina

5. Left Bundle Branch Block (LBBB)

QRS ≥ 120 ms (broad)
Broad notched R in I, aVL, V5, V6 ("M" shape or plateau)
Deep S or QS in V1 (rS or QS pattern)
ST and T wave changes discordant (opposite) to the main QRS deflection
New LBBB + chest pain = treat as STEMI equivalent (Sgarbossa criteria)

6. Right Bundle Branch Block (RBBB)

QRS ≥ 120 ms
RSR' pattern ("rabbit ears") in V1-V2
Wide S wave in I, V5, V6
Common in pulmonary embolism, right heart strain, congenital disease, or incidental finding

7. Left Ventricular Hypertrophy (LVH)

Sokolow-Lyon criteria (most used):

S in V1 + R in V5 or V6 ≥ 35 mm
R in aVL ≥ 11 mm

Associated findings:

"Strain pattern" - ST depression + asymmetric T-wave inversion in lateral leads (I, aVL, V5, V6)
Left axis deviation
Increased QRS duration

Common in hypertension, aortic stenosis, hypertrophic cardiomyopathy.

8. AV Blocks

Type	PR interval	Dropped beats	QRS
1st degree	>200 ms, constant	None	Normal
2nd degree Mobitz I (Wenckebach)	Progressively lengthens	Yes, then resets	Normal
2nd degree Mobitz II	Fixed PR interval	Sudden drop (no warning)	Often wide
3rd degree (complete)	No relationship (AV dissociation)	All P waves blocked	Wide escape

Mobitz II and 3rd degree = serious, often require pacing
Symptom to Diagnosis, Chapter on Bradycardia

9. Ventricular Tachycardia (VT) vs. SVT with Aberrancy

VT features:

Wide QRS (≥ 120 ms), rate 100-250 bpm
AV dissociation (P waves independent of QRS) - pathognomonic
Fusion beats and capture beats (pathognomonic)
Brugada algorithm helps differentiate from SVT with aberrancy

VF: Completely chaotic, no discernible QRS - cardiac emergency.

10. Other High-Yield Patterns

Pattern	Key ECG Finding	Cause
Hyperkalemia	Peaked T waves → wide QRS → sine wave	Renal failure, ACE inhibitors
Hypokalemia	Flattened T waves, prominent U waves, QU prolongation	GI losses, diuretics
Pulmonary embolism	S1Q3T3 (S wave in I, Q wave + T inversion in III), sinus tachycardia, new RBBB	Large/submassive PE
Pericarditis	Diffuse saddle-shaped ST elevation, PR depression (all leads except aVR/V1)	Viral, autoimmune
Brugada syndrome	Coved-type ST elevation in V1-V2, RBBB morphology	Channelopathy, sudden death risk
Wolff-Parkinson-White (WPW)	Short PR, delta wave, wide QRS	Accessory pathway
Long QT	QTc > 450 ms (males), > 470 ms (females)	Drugs (amiodarone, antipsychotics), electrolyte abnormalities, congenital
Early repolarization	ST elevation with J-point notching in young athletes	Usually benign variant
Digoxin toxicity	"Reverse tick" ST scooping (Salvador Dali mustache), PVCs, bidirectional VT	Digoxin excess

Quick Systematic ECG Reading Approach

Rate - 300 / (number of large boxes between R-R)
Rhythm - regular? P before every QRS?
Axis - I and aVF both positive = normal axis
Intervals - PR (120-200 ms), QRS (<120 ms), QTc (<450 ms males / <470 ms females)
P wave - present, morphology, relationship to QRS
QRS - width, morphology, Q waves
ST segment - elevation or depression
T waves - inversion, hyperacuity
U waves - if present, think hypokalemia

Medical Physiology, Box 21-2 & Table 21-5
Rosen's Emergency Medicine
Tintinalli's Emergency Medicine

This is a shared conversation. Sign in to Orris to start your own chat.