EKG

EKG Introduction

  • Presenter: Amgad Masoud, MD, PhD, MRCP, FACP, Associate Professor of Medicine, UMKC.

Objectives of EKG Study

  • Waves on EKG: Describe their relation to cardiac physiology.

    • P wave

    • QRS complex

    • T wave

  • Calculate Heart Rate: Importance of heart rate determination.

  • Lead Placement: Identify placements and anatomical basis.

  • Rhythm Identification:

    • Sinus rhythm

    • Sinus bradycardia

    • Sinus tachycardia

    • Supraventricular tachycardia

    • Junctional rhythm

    • Atrial fibrillation

    • Atrial flutter

    • Multifocal atrial tachycardia

    • Atrial Premature Complexes (APC)

    • Premature Ventricular Complexes (PVC)

  • Cardiac Axis: Identify and understand causes of deviation.

  • ST Segment Change Recognition: Recognize ST elevation and depression.

  • Myocardial Infraction Diagnosis: Different types of myocardial infarctions.

  • Cardiac Enlargement Features: Identification of cardiac enlargement.

EKG Use Cases

  • Main Uses of EKG:

    • Cardiac arrhythmias detection.

    • Diagnosis of myocardial ischemia and infarction.

    • Assessment of cardiac chamber enlargement.

    • Detection of electrolyte imbalances.

    • Evaluation of drug effects.

  • Limitations: EKG is not utilized for assessing overall cardiac function.

EKG Tracing Basics

  • Atrial Depolarization: Represented by the P wave.

  • Ventricular Depolarization and Repolarization:

    • Q, R, S, and T waves: Represent ventricular activity.

EKG Basics: Time Intervals

  • Box Measurement:

    • Each small box (1mm) = 0.04 seconds

    • Each big box (5mm) = 0.2 seconds = 200 milliseconds

Normal EKG Parameters

  • QRS Duration: 0.1 seconds

  • P-R Interval: 0.12 - 0.2 seconds

  • QT Interval: 0.44 seconds

  • T Wave Duration: 0.11 seconds

Lead Placement

Limb Leads

  • Placement includes:

    • Right Arm (RA)

    • Left Arm (LA)

    • Right Leg (RL)

    • Left Leg (LL)

  • Einthoven's Triangle: Recognizes placement of limb leads.

Chest Leads (Precordial Leads)

  • Placement Specifics:

    • V1: 4th intercostal space at right margin of sternum.

    • V2: 4th intercostal space at left margin of sternum.

    • V3: Midway between V2 and V4.

    • V4: 5th intercostal space at junction of midclavicular line.

    • V5: At horizontal level of V4 at left anterior axillary line.

    • V6: At horizontal level of V4 at mid-axillary line.

EKG Basics: Calculating Heart Rate

  • Regular Rhythms:

    • Identify R-R interval in big boxes.

    • Formula:

    • Heart rate = rac300extnumberofbigboxesperR−Rrac{300}{ ext{number of big boxes per R-R}}

    • Alternatively: $ rac{1500}{ ext{number of small boxes per R-R}}$

  • Box Correlation:

    • 1 box = 300 bpm

    • 2 boxes = 150 bpm

    • 3 boxes = 100 bpm

    • 4 boxes = 75 bpm

    • 5 boxes = 60 bpm

  • Irregular Rhythms: Count R waves in a 6, 10, or 15-second span and multiply accordingly to find the heart rate.

EKG Basics: Rhythm

Sinus Rhythm

  • Described as the normal rhythm from the Sinoatrial (SA) node. Heart rate is 60-100 beats/min.

  • P Wave: Normal morphology (upright in leads I, II, aVF; possibly biphasic in leads III, V1).

  • Rate Variants: Sinus tachycardia (HR > 100 bpm) and sinus bradycardia (HR < 60 bpm).

Premature Atrial Contraction (PAC)

  • Regularity: Irregular due to ectopic beat.

  • Rate: Depends on underlying rhythm.

  • P Wave: Each QRS has a P wave; PAC P wave differs in morphology.

  • PRI: Generally 0.12 to 0.20 seconds, may differ from underlying rhythm.

  • QRS: Duration < 0.12 seconds.

Premature Ventricular Contraction (PVC)

  • Regularity: Underlying rhythm is irregular.

  • Rate: Dependent on the baseline rhythm.

  • P Wave: No P wave precedes the PVC.

  • PRI: Cannot be measured (no P wave).

  • QRS: Duration > 0.12 seconds, typically wide and bizarre.

Atrial Fibrillation

  • Regularity: Irregularly irregular R-R intervals.

  • Atrial Rate: Usually exceeds 350 bpm.

  • Ventricular Rate: Rates 60-100 bpm indicate controlled A-Fib; > 100 bpm indicates uncontrolled A-Fib.

  • P Wave: Absent due to rapid atrial firing.

  • QRS: < 0.12 seconds.

Atrial Flutter

  • Regularity: Atrial rate is regular; Ventricular rate varies based on AV conduction.

  • Rate: Atrial rates 250-350 bpm, commonly resulting in ventricular rates of 150 bpm or less.

  • P Wave: Sawtooth pattern with well-defined morphology.

  • QRS: < 0.12 seconds.

Supraventricular Tachycardia (SVT)

  • Regularity: R-R intervals are regular.

  • Rate: Atrial and ventricular rates commonly 150-250 bpm.

  • P Wave: Often indistinct due to simultaneous atrial and ventricular activation.

  • QRS: < 0.12 seconds.

Junctional Rhythm

  • Regularity: No P waves preceding QRS complexes.

  • P Wave: May occur retrograde or in the ST segment/T wave.

  • Rate: Junctional escape rhythm if slower than usual AV or fast = junctional tachycardia.

Multifocal Atrial Rhythm

  • Diagnosis: Three or more different P wave morphologies indicate multifocal atrial pacing.

  • Associated Conditions: Often occurs in chronic lung disease.

  • Rate: > 100 bpm indicated as multifocal atrial tachycardia.

Myocardial Infarction Identification

Types of Myocardial Infarction

  1. ST-Elevation Myocardial Infarction (STEMI):

    • ECG Features: Hyperacute T waves (tall, peaked), ST segment elevation in contiguous leads.

    • Q Waves: Can develop after ST segments return to baseline.

  2. Chronic Q Wave MI:

    • Initial Changes: Deep Q waves (>1mm wide, >0.04 seconds).

    • Associated T Waves: May have inverted T waves.

  3. Non-ST Elevation Myocardial Infarction (NSTEMI):

    • ST Changes: T wave flattening/inversion and ST segment depression.

    • Q Waves: Typically absent; elevated troponin indicates myocardial injury.

Q Waves and Significance

  • Detection Criteria: Q waves > 1 small box (0.04 seconds or deep > 1 mm) are indicative of myocardial infarction.

  • Inferior Infarction Leads: Q waves visible in leads II, III, aVF; lateral leads (I, aVL) for lateral infarction.

ST Elevation Recognition

  • Diagnosis Criteria: New ST segment elevation at J point in two contiguous leads.

  • Elevation Measurements: ≥ 0.1 mV in all leads except V2-V3 (which require higher cut points).

ST Depression Recognition

  • Clinical Context: Can signify ischemia or non-ST elevation MI.

  • Measurement Significance: Typically significant at > 1 mm depression.

Infarction vs. Pericarditis Identification

  • Pericarditis:

    • Diffused ST-T changes.

    • ST segment elevation has a concave morphology; no reciprocal changes.

    • Often presents with PR segment depression.

  • STEMI:

    • ST-T changes localized to specific leads involved in the infarction.

    • ST elevation displays convex morphology.

    • Reciprocal ST changes indicative of infarction.

Cardiac Enlargement Criteria

Right Atrial Enlargement (RAE)

  • Measurement: Amplitude > 2.5 mm in lead II or > 1.5 mm in lead V1.

  • Identifying Features: Notable right atrial P waves.

Left Atrial Enlargement (LAE)

  • Measurement: Duration > 0.12 seconds in lead II.

  • Identifying Features: Biphasic P in V1; notched P waves in limb leads.

Ventricular Enlargement

Right Ventricular Hypertrophy (RVH)

  • Criteria:

    • R in lead V1 > 7 mm or ≥ S wave amplitude.

    • Inversion of T in lead V1.

    • Right axis deviation.

Left Ventricular Hypertrophy (LVH)

  • Criteria:

    1. Limb leads: R in lead I + S in lead III > 25 mm.

    2. Precordial leads: S in lead V1 + R in lead V5 or V6 > 35 mm.

    3. ST-T abnormalities in lateral leads (I, aVL, V4-V6).

    4. R wave in lead aVL > 11 mm.

    5. Left atrial enlargement indicated by a wide P wave.

References and Resources

  • Various educational and clinical resources on EKG interpretation and guidelines for cardiac health assessment is included for further reading and study.

  • It is essential to engage with both practice questions and clinical cases to refine interpretation skills and diagnostic confidence in EKG reading.