**Easy Basics of ECG Learning ** is one the challenging for the medical students. While studying the medicine ECG is one of the important topic to master. ECG reading will be difficult if we don’t know the proper way or the basic . Here are some the basic things which can be easily reading the ECG .

### ECG -Basics

Normal Impulse Conduction

Sinoatrial node–AV node–Bundle of His–Bundle Branches–Purkinje fibers

The “PQRST”

► P wave – Atrial depolarization

QRS – Ventricular depolarization

T wave – Ventricular repolarization

The PR Interval

Atrial depolarization

+

delay in AV junction

(AV node/Bundle of His)

(delay allows time for the atria to contract before the ventricles contract)

Pacemakers of the Heart

► SA Node – Dominant pacemaker with an intrinsic rate of 60 – 100 beats/minute.

► AV Node – Back-up pacemaker with an intrinsic rate of 40 – 60 beats/minute.

► Ventricular cells – Back-up pacemaker with an intrinsic rate of 20 – 45 bpm.

The ECG Paper

► Horizontally

One small box – 0.04 s

One large box – 0.20 s

► Vertically

One large box – 0.5 mV

► Every 3 seconds (15 large boxes) is marked by a vertical line.

► This helps when calculating the heart rate.

### ECG 2 -How to Analyze a Rhythm

• Step 1: Calculate rate.

• Step 2: Determine regularity.

• Step 3: Assess the P waves.

• Step 4: Determine PR interval.

• Step 5: Determine QRS duration.

**Step 1: Calculate Rate**

• Option 1

– Count the # of R waves in a 6 second rhythm strip, then multiply by 10.

– Reminder: all rhythm strips in the Modules are 6 seconds in length.

Interpretation? 9 x 10 = 90 bpm

• Option 2

– Find a R wave that lands on a bold line.

– Count the # of large boxes to the next R wave. If the second R wave is 1 large box away the rate is 300, 2 boxes – 150, 3 boxes – 100, 4 boxes – 75, etc.

– Memorize the sequence:

300 – 150 – 100 – 75 – 60 – 50

**Step 2: Determine regularity**

• Look at the R-R distances (using a caliper or markings on a pen or paper).

• Regular (are they equidistant apart)? Occasionally irregular? Regularly irregular? Irregularly irregular?

Interpretation? Regular

**Step 3: Assess the P waves**

• Are there P waves?

• Do the P waves all look alike?

• Do the P waves occur at a regular rate?

• Is there one P wave before each QRS?

Interpretation? Normal P waves with 1 P wave for every QRS

**Step 4: Determine PR interval**

• Normal: 0.12 – 0.20 seconds.

(3 – 5 boxes)

Interpretation?0.12 seconds

**Step 5: QRS duration**

• Normal: 0.04 – 0.12 seconds.

(1 – 3 boxes)

Interpretation? 0.08 seconds

**Rhythm Summary**

• Rate 90-95 bpm

• Regularity regular

• P waves normal

• PR interval 0.12 s

• QRS duration 0.08 s

Interpretation? Normal Sinus Rhythm

### ECG 3-Normal Sinus Rhythm (NSR)

• Etiology: the electrical impulse is formed in the SA node and conducted normally.

• This is the normal rhythm of the heart; other rhythms that do not conduct via the typical pathway are called arrhythmias.

**NSR Parameters**

• Rate 60 – 100 bpm

• Regularity regular

• P waves normal

• PR interval 0.12 – 0.20 s

• QRS duration 0.04 – 0.12 s

Any deviation from above is sinus tachycardia, sinus bradycardia or an arrhythmia

**Arrhythmia Formation**

Arrhythmias can arise from problems in the:

• Sinus node

• Atrial cells

• AV junction

• Ventricular cells

**SA Node Problems**

The SA Node can:

fire too slow— Sinus Bradycardia

fire too fast— Sinus Tachycardia

**Atrial Cell Problems**

Atrial cells can:

• fire occasionally from a focus —Premature Atrial Contractions (PACs)

• fire continuously due to a looping re-entrant circuit —-Atrial Flutter

**Atrial Cell Problems**

Atrial cells can also:

• fire continuously from multiple foci Atrial Fibrillation

or

fire continuously due to multiple micro re-entrant “wavelets” Atrial Fibrillation

**AV Junctional Problems**

The AV junction can:

• fire continuously due to a looping re-entrant circuit–Paroxysmal Supraventricular Tachycardia

• block impulses coming from the SA Node–AV Junctional Blocks

**Ventricular Cell Problems**

Ventricular cells can:

• fire occasionally from 1 or more foci –Premature Ventricular Contractions (PVCs)

• fire continuously from multiple foci–Ventricular Fibrillation

• fire continuously due to a looping re-entrant circuit–Ventricular Tachycardia