ECG & Heart Diseases Notes

ECG & Heart Diseases

Objectives

• List the information gained from an ECG.

• List the indications for recording an ECG.

• Familiarize with a 12-lead ECG.

• Describe the basic PQRST nomenclature and how the leads relate to anatomy.

• Understand basic principles of ECG interpretation with examples.

What is an ECG?

• An "Elektrokardiogramm" is a trans-thoracic, non-invasive recording and amplification of electrical changes on the skin during heart muscle depolarization and repolarization.

• It records the underlying electrical activity of the heart over the skin.

• The recording quality depends on:

  • Body habitus

  • Skin contact

  • Muscle movement

  • Chest and limbs

• Types:

  • Bipolar: L1, L2, L3 (Leads I, II, and III)

  • Unipolar: aVR, aVL, aVF

12-Lead ECG

• Consists of:

  • 6 limb leads (I, II, III, aVR, aVL, aVF)

  • 6 chest leads (V1-V6)

• Includes a rhythm strip.

• Paper speed: 25 mm/sec, 1 cm/mV.

Understanding "Leads"

• Leads are not just physical cables.

• They are real and virtual sites where electrical activity is recorded.

Electrode Placement

• 10 electrodes are placed on the patient using ECG dots or electrode stickers.

• Four on the limbs (one is neutral).

• Six on the chest.

Standard Limb Leads (Bipolar) – Einthoven's Triangle

• Bipolar leads (I, II, and III) record the potential difference between pairs of electrodes.

  • Lead I: RA (-) to LA (+)

  • Lead II: RA (-) to LL (+)

  • Lead III: LA (-) to LL (+)

Cardiac Axis & Einthoven's Triangle

• Lead I: 0 degrees (LA - RA)

• Lead II: +60 degrees (LL - RA)

• Lead III: +120 degrees (LL - LA)

Augmented Limb Leads (Unipolar)

• Unipolar leads (aVF, aVL, and aVR) consist of a single positive electrode referenced to a combination of other limb electrodes.

  • aVR: -150 degrees

  • aVL: -30 degrees

  • aVF: +90 degrees

What Can the ECG Show?

1. Normal Heart Rate and Rhythm

2. Rhythm Disturbances

   • Sinus node dysfunction

   • Supra-ventricular & ventricular arrhythmias

   • AV node dysfunction

   • Intra-ventricular conduction

3. Myocardial Ischaemia / Infarction

• Examples:

  • Tachycardia (Ventricular Tachycardia example shown)

  • Bradycardia (Complete Heart Block example shown)

  • Acute Myocardial Infarction (STEMI example shown)

What Can the ECG Show? (2)

• Chamber hypertrophy/damage

• Congenital heart disease

• Inherited electrical disorders

• Secondary effects of:

  • Lung disorders

  • Systemic medical conditions

  • Environmental disturbance

Chamber Enlargement

• Left Atrial Enlargement

  • Lead II: P-mitrale: broad (\geq3mm), plus or minus notched.

  • V1: Negative deflection of P wave is broad (>1mm) & deep (> 1mm).

• Right Atrial Enlargement

  • Lead II: P-pulmonale: Tall (more than 2.5mm), Peaked.

  • V1: Positive deflection of P wave is tall (>1.5mm).

• Left Ventricular Enlargement (One method is enough to diagnose LVE):

  1. R in V5 or V6 (the taller) \geq 25mm

  2. R in V5 or V6 (the taller) + S in V1 >35mm

  3. R in V5 or V6 (the taller) + S in V2 >45mm

  4. R in V6 > R in V5

  5. R in aVL >11-13mm

  6. R in aVF >20mm

  • Strain pattern: ST depression plus or minus T wave inversion may be present in V5 & V6 due to pressure overload.

• Right Ventricular Enlargement

  • In lead V1: Tall R >7 mm or R/S ratio \geq 1

  • In lead V6: Deep S

  • Strain pattern: ST depression plus or minus T wave inversion may be present in V1 & V2 due to pressure overload.

Bundle Branch Blocks

• Left Bundle Branch Block (LBBB)

  • QRS complex:

    • Shape:

      • V1, V2: QS or rS

      • V5, V6, lead I: Monophasic (plus or minus notched) R

    • Width:

      • > 3mm: complete LBBB

      • 2.5-3mm: incomplete LBBB

    • T wave: Secondary T wave inversion in V5, V6

  • In LBBB, do not diagnose myocardial ischemia, myocardial infarction, ventricular enlargement, or hemiblock.

• Right Bundle Branch Block (RBBB)

  • QRS complex:

    • Shape:

      • V1, V2: RsR' or RR'

      • V5, V6, lead I: QRS with slurred S

    • Width:

      • > 3mm: complete RBBB

      • 2.5-3mm: incomplete RBBB

    • T wave: Secondary T wave inversion in V1, V2

  • In RBBB, do not diagnose myocardial ischemia or ventricular enlargement.

Intraventricular Conduction Delay

• Wide QRS but the pattern is not consistent with LBBB or RBBB.

Electrolyte Disturbance (K^+)

What the ECG Can't Show

• Cardiac Function - e.g., Pulseless Electrical Activity or PEA during cardiac arrest can have an almost normal ECG and a non-beating heart!

• Underlying coronary artery disease

• Any intermittent conduction problems

• Static snapshot in time

Clinical Indications for ECG

• Investigation of symptoms or signs:

  • Palpitations, chest pain, SOB, syncope

• Investigation of a sick patient.

• Monitoring therapy.

• Choice of therapy.

• Routine medical.

• Risk stratification.

• Family screening.

Recommendations for the Standardization and Interpretation of the Electrocardiogram

• Approximately 190 primary statements, 30 secondary statements, 60 modifiers.

Basic Electrocardiography

• A wave of depolarization traveling towards a positive electrode results in a positive deflection.

• A wave of depolarization traveling away from a positive electrode results in a negative deflection.

ECG Nomenclature

• P - Atrial depolarization

• Q - 1st negative deflection

• R - 1st positive deflection

• S - 1st negative deflection after a +ve deflection

• T - Ventricular repolarization

• U - After polarization

• Intervals: PR & QRS intervals

Normal Conduction

• AV node conduction determines PR interval (120-200ms).

• His-Purkinje network ensures rapid and synchronized ventricular depolarization (large magnitude and short duration QRS complex).

• Abnormal conduction results in an abnormal ECG.

His-Purkinje Network & QRS Complex

• Narrow QRS complex (<120msec): normal ventricular activation

• Broad QRS complex (\geq120msec): abnormal ventricular activation

  • Bundle branch block

  • Ventricular pre-excitation

  • Independent ventricular activation

  • Ventricular tachycardia

Rate

Nomenclature & Anatomy

• Understanding the anatomical correlation to ECG lead placement allows for identifying areas of ischemia or infarction.

  • Anterior leads: V1-V4

  • Inferior leads: II, III, aVF

  • Lateral leads: I, aVL, V5, V6

ECG Interpretation

1. Rate

2. Rhythm

3. P wave

4. PR interval

5. QRS complex

6. ST segment

7. T wave

8. QT interval

9. Axis

10. Put it all together and summarize

Heart Rate Calculation

• Heart rate/min = 300 ÷ number of large squares between beats

• (Paper speed is 25mm/s = 1500mm/min = 300 big squares/min)

Rhythm

• Assess for bradycardias and tachycardias.

Normal Sinus Rhythm Criteria

1. Each QRS preceded by a normal P wave indicating SA node origin

2. PR interval 120 - 200msec indicating intact AV node conduction

3. 1:1 P:QRS complex indicating no evidence of AV block

4. QRS shape normal and duration <120msec indicating rapid + synchronised ventricular depolarisation

Bradycardia Causes

• Failure of impulse generation (SA node disease).

• Failure of impulse propagation (AV node or His Purkinje disease).

AV Blocks

• 1st Degree AV Block: All P waves conducted but with prolonged PR interval.

• 2nd Degree AV Block: Some P waves not conducted (dropped beats).

• 3rd Degree AV Block (Complete)

  • No P waves are conducted.

  • QRS escape rhythm.

  • Reliability of escape rhythm depends upon site.

Tachycardia Classification

• Narrow complex (<120msec): Conduction via intact conduction system

  • (sinus tachycardia)

  • (supra-ventricular tachycardia, SVT)

• Broad complex (>120msec): Conduction system impaired or bypassed

  • (sinus tachycardia or SVT with Bundle Branch Block)

  • (ventricular tachycardia, VT)

Axis Determination

• Normal Axis, Left Axis Deviation (LAD), Right Axis Deviation (RAD), or Northwest Axis.

Rapid axis determination

• I +ve, aVF +ve = Normal.

• I +ve, aVF -ve = LAD

• I -ve, aVF +ve = RAD

• I -ve, aVF -ve = North West

Axis Deviations: Causes

• Left Axis Deviation (LAD): Left Anterior Hemiblock, Left Ventricular Hypertrophy, Q wave MI, Emphysema, Hyperkalemia, WPW - right sided, Tricuspid Atresia, Primum ASD, Pacing.

• Right Axis Deviation (RAD): Right Ventricular Hypertrophy, Lung disease, Myocardial Infarction, Left Posterior Hemiblock, Pulmonary Embolism, Wolf Parkinson White, Atrial Septal Defect, Ventricular Septal Defect.

• Causes of Northwest Axis: Lead transposition, VT, Emphysema, Pacing, Hyperkalaemia.

ECG Interpretation Example

• 70-year-old man with hypertension.

• Rate, rhythm, axis, PR interval, QRS duration, complexes.

• Findings suggest left ventricular hypertrophy due to longstanding hypertension.

How to Interpret ECG?

• I - General look to ECG can give an idea about the major abnormality.

• II - Look in the following sequence:

  1. Look for the long strip (usually lead II) if available or 12 lead ECG (If no long strip): To identify the rate/rhythm and for diagnosis of Arrhythmia (by identifying the pacemaker of the heart) or heart block (the key is PR interval).

  2. Look for 12 lead ECG to diagnose:

     • Atrial enlargement (look for lead II, V1)

     • Bundle branch block (wide QRS) (look for V1,V2-V5,V6)

• If there is bundle branch block, do not search for: Myocardial ischemia/myocardial infarction (except if RBBB), Hemiblock (except if RBBB), Ventricular enlargement.
  * Ventricular enlargement: look for V1,V2-V5,V6
  * Axis (Look for lead I, lead III, AVF)
  * Hemiblock (In limb leads)
  * Myocardial ischemia/infarction
  * Others:
  * Pre-excitation
  * Pericarditis
  * Low voltage (look for lead I,II,III)
  * Electrolyte imbalance (Eg: hyperkalemia)
  * Drug effect: eg digitalis

How to Write ECG Report?

1. Rate

2. Rhythm

3. Waves:

   • P wave

   • PR interval

   • QRS (Axis, width, amplitude, waves)

   • ST segment

   • T wave

   • QT interval

4. Final diagnosis

Question 1

A 68-year-old hypertensive patient presents for a routine evaluation. His 12‑lead ECG shows in lead II a P wave that is broad (≥3 mm in duration) with a notched appearance and, in lead V1, a prominent broad negative deflection (≥1 mm deep). Which abnormality is most consistent with these findings?

a. Right atrial enlargement b. Left atrial enlargement c. Left ventricular hypertrophy d. Right ventricular enlargement e. Intraventricular conduction delay

Question 2

A 55-year-old patient with chronic lung disease undergoes an ECG. Lead II reveals tall, peaked P waves exceeding 2.5 mm, and lead V1 shows a tall positive P wave (>1.5 mm). This pattern most likely indicates which of the following?

a. Left atrial enlargement b. Right atrial enlargement c. Atrial fibrillation d. Left ventricular enlargement e. Normal variant in athletes

Question 3

A 60-year-old man with long-standing hypertension is evaluated by ECG. One of the criteria for diagnosing left ventricular enlargement is an R wave amplitude in lead V5 or V6 exceeding 25 mm. Which of the following additional measurements is also considered diagnostic for left ventricular enlargement?

a. R in V5 or V6 plus S in V1 greater than 35 mm b. QRS duration >120 ms in any lead c. R in V1 greater than 20 mm d. Negative T waves in lead aVL e. P wave duration >120 ms

Question 4

A 62-year-old woman with poorly controlled hypertension has an ECG that reveals ST depression and T wave inversion in leads V5 and V6. What do these findings most likely represent?

a. Acute myocardial infarction b. Left ventricular strain pattern due to pressure overload c. Normal variant in elderly d. Right ventricular hypertrophy e. Pericarditis

Question 5

A 50‑year‑old man suspected of having right ventricular enlargement has an ECG in which lead V1 shows an R wave amplitude of 9 mm with an R/S ratio ≥1 while lead V6 displays a deep S wave. Which diagnosis does this pattern most strongly support?

a. Left ventricular hypertrophy b. Right ventricular enlargement c. Left atrial enlargement d. Right bundle branch block e. Intraventricular conduction delay

Question 6

An ECG of a patient reveals in leads V1 and V2 a QS or rS pattern and in leads V5, V6, and lead I, a monophasic R wave (with possible notching). The QRS width measures 3 mm. This pattern most likely corresponds to which of the following?

a. Right bundle branch block b. Left bundle branch block (complete) c. Intraventricular conduction delay d. Left ventricular hypertrophy e. Normal variant

Question 7

A 45-year-old man’s ECG shows in leads V1 and V2 an RsR′ (or rSR′) pattern with a QRS width of 3 mm and in leads V5 and V6, a QRS with a slurred S wave. What is the most likely diagnosis?

a. Left bundle branch block b. Right bundle branch block (complete) c. Intraventricular conduction delay d. Pre-excitation syndrome e. Left ventricular hypertrophy

Question 8

An ECG presents with a markedly wide QRS complex; however, the pattern does not clearly fulfill the criteria for either left bundle branch block or right bundle branch block. This finding is best described as:

a. Left ventricular hypertrophy with strain b. Intraventricular conduction delay c. Atrial fibrillation d. Normal variant in the elderly e. Bifascicular block

Question 9

When evaluating an ECG for possible arrhythmias or conduction disturbances, which of the following is the most critical initial step?

a. Analyze the long lead strip (preferably lead II) for rate, rhythm, and the PR interval b. Immediately focus on ST segment deviations in precordial leads c. Measure the QRS duration exclusively d. Assess solely the T wave morphology e. Evaluate only the QT interval

Question 10

A systematic approach to writing an ECG report is essential. Which of the following outlines the correct sequence of components that must be addressed in such a report?

a. Rate, rhythm, wave analysis (P wave, PR interval, QRS complex including axis and width, ST segment, T wave, QT interval), then final diagnosis b. Only the heart rate and rhythm c. QRS duration only d. ST segment and T wave interpretation only e. Axis deviation followed by final diagnosis

Question 11

Which of the following measurements is most critical for the diagnosis of heart block and arrhythmias on an ECG?

a. PR interval b. QRS duration c. QT interval d. ST segment e. R wave amplitude

Question 12

In patients with a left bundle branch block, which of the following diagnoses should be approached with caution because the abnormal depolarization alters secondary repolarization changes, making it unreliable on the ECG?

a. Myocardial ischemia/infarction b. Right ventricular hypertrophy c. Atrial enlargement d. Ventricular tachycardia e. Pre-excitation syndrome

Question 13

Which ECG finding is most characteristic for diagnosing left atrial enlargement?

a. Tall, peaked P waves in lead II b. Broad, notched P waves (P mitrale) in lead II with a deep, broad negative component in V1 c. Atrial fibrillation d. RsR′ pattern in V1 e. Prolonged QRS duration

Question 14

In the evaluation of right atrial enlargement, which of the following ECG features is most indicative?

a. P mitrale in lead II b. P pulmonale: tall, peaked P waves >2.5 mm in lead II and a tall positive P wave in V1 c. Deep S waves in lead V6 d. Prolonged PR interval e. Notched R waves in lead I

Question 15

Which of the following represents the recommended sequence in the standard ECG interpretation algorithm?

a. Begin with rate and rhythm assessment using a long lead strip (often lead II), then sequentially analyze P waves, PR interval, QRS complex, ST segment, T waves, QT interval, and finally, provide a final diagnosis b. Start with QRS duration and then evaluate the T wave c. Focus solely on lead V1 for conduction abnormalities and ignore limb leads d. Assess only the axis deviation before reaching a conclusion e. Immediately issue a final diagnosis based solely on QRS morphology

Answer Key

1. b. Left atrial enlargement

2. b. Right atrial enlargement

3. a. R in V5 or V6 plus S in V1 greater than 35 mm

4. b. Left ventricular strain pattern due to pressure overload

5. b. Right ventricular enlargement

6. b. Left bundle branch block (complete)

7. b. Right bundle branch block (complete)

8. b. Intraventricular conduction delay

9. a. Analyze the long lead strip (preferably lead II) for rate, rhythm, and the PR interval

10. a. Rate, rhythm, wave analysis (P wave, PR interval, QRS complex including axis and width, ST segment, T wave, QT interval), then final diagnosis

11. a. PR interval

12. a. Myocardial ischemia/infarction

13. b. Broad, notched P waves (P mitrale) in lead II with a deep, broad negative component in V1

14. b. P pulmonale: tall, peaked P waves >2.5 mm in lead II and a tall positive P wave in V1

15. a. Begin with rate and rhythm assessment using a long lead strip (often lead II), then sequentially analyze P waves, PR interval, QRS complex, ST segment, T waves, QT interval, and finally, provide a final diagnosis