Basics of ECG Interpretation

Royal College of Physicians Conference Student Track September 2018 Dr. Stephen Noe, DMS-c, MPAS, PA-C Objectives

• Explain how depolarization and repolarization of cardiac myocytes produces a predictable waveform patter on an ECG. • Identify patterns of myocardial ischemia, injury, and infarction on an ECG. • Explain how myocardial ischemia, injury, and infarction produce predictable waveform patterns on the ECG. • Explain the pathophysiology and clinical significance of atrioventricular block, bundle branch block, hypertrophy, and QT prolongation. • Identify atrioventricular block, bundle branch block, hypertrophy, and QT prolongation on an ECG. • Explain the pathophysiology and clinical significance of chronotropic incompetence, sinus pause, sinus exit block, and sick sinus syndrome. Cardiac Depolarization and Repolarization ECG Basics

• ECG complexes appear upright (Positive) if electricity is moving towards the area of the myocardium that ECG complex represents

• ECG complexes appear downright (Negative) if electricity is moving away from the area the myocardium that ECG complex represents Bipolar Limb Leads (I, II, III) Unipolar Limb Leads Chest Leads Chest Leads ECG Leads ECG Waveforms

PR Interval: Start of P wave to QRS Complex; time from SA node activation to AV node activation QT Interval: Start of QRS to end of Measurement Intervals Calculating Rate Calculating Axis

RCA: supplies the RV and the inferior portion of the LV, the AV node and the conal branch supplies the SA node

LAD: supplies the anterior portion of the LV, the interventricular septum, and the perforating branches supply the bundle branches

LCx: supplies the lateral wall of the LV, less commonly supplies the SA and/or AV node

Primary Reciprocal* (injury – ST segment elevation) (ST segment depression) Anterior (V1-V4) Inferior (II, III, aVF) Lateral (I, aVL, V5-V6) Inferior (II, III, aVF) Inferior (II, III, aVF) Lateral (I, aVL, V5-V6) Posterior Anterior (V1-V4)

First Degree AVB Consistent PR interval length > 200 ms (one large block) Second Degree Progressive lengthening of PR interval from cycle AVB Type I to cycle prior to a dropped QRS (Wenckebach) Second Degree Punctual P wave with unpredictable dropped AVB Type II QRS; consistent PR interval length Third Degree AVB Consistent P-P interval, consistent R-R interval, no association between P waves and QRS complexes

Consider BBB when QRS > 100 milliseconds V1 V6 LBBB QRS negative QRS positive Wide QS wave Tall R wave with no septal Q wave RBBB rSR’ qRS (slurred S in Lead I)

Sgarbossa criteria

• Used to diagnose myocardial infarction in patients with LBBB and paced ventricular rhythms • In LBBB, the QRS is always predominantly negative (deep S wave) and ST-segment elevation occurs in the right precordial leads • Modified Sgarbossa criteria have improved diagnostic accuracy over original Sgarbossa criteria • > 1 lead with > 1 mm of concordant ST-segment elevation • > 1 lead of V1-V3 with > 1 mm of concordant ST-segment depression • > 1 lead anywhere with > 1 mm ST-segment elevation and proportionally excessive discordant ST-segment elevation, as defined by > 25% of the depth of the preceding S wave modified: excessively discordant ST-segement elevation (> 25% of the depth of the preceding S wave)

Atrial enlargement: P waves in Leads II and V1

Ventricular Hypertrophy LVH S in V1 or V2 (which ever is taller) + R in V5 or V6 (which ever is taller) > 35 mm OR Any precordial lead > 45 mm R wave in aVL > 11 mm R wave in I > 12 mm R wave in aVF > 20 mm RVH R:S > 1 in V1 and/or V2

**voltage criteria cannot be used in the setting of abnormal conduction** main QRS vector main QRS vector

Prolonged QTi • QTc > 500 ms (normal QTi < 460 ms) • Primary causes • Genetic (LQT 1, 2, 3, Romano-Ward syndrome) • Acquired causes • (antibiotics, antifungals, antipsychotoics, antidepressants) www.qtdrugs.org • Electrolyte abnormalities (hypokalemia) • Risk for VT, VF, and R on T phenomenon (PVC falls at peak of T wave, may precipitate VT, VF) • Brugada syndrome • Association of characteristic ECG pattern w/ risk of ventricular tachyarrhythmias Disorders of the SA node

• Sick sinus syndrome: • resting bradycardia, prolonged pauses, and chronotropic incompetence; may also have tachy- brady syndrome (sinus or junctional bradycardia interrupted by paroxysms of tachycardia, usually SVT; termination of the tachycardia is often followed by a slow recovery of )) • Chronotropic incompetence: • inability of the sinus node to effectively increase the sinus rate and allow for physiologic demand that is present with activity; associated with fatigue and exercise intolerance • Sinus pause: • failure of impulse formation; sinus node fails to pace for at least one cycle before (sinus arrest – pause of > 3 seconds without atrial activity) resuming normal function; all P waves have the same morphology, P-P interval including the pause is unrelated to the underlying P-P interval; this is a form of sick sinus syndrome; may cause syncope • Sinus exit block: • dysfunction of conduction of the action potential generated in the SA node to the surrounding myocardium; classified like AV block (1st, 2nd type I, 2nd type II, 2:1, 3rd); the P-P interval of the pause is a multiple of the underlying P-P interval Expect next PQRST here 5 large boxes = 5 large boxes 5 large boxes 5 large boxes 1 sec = 1 sec = 1 sec = 1 sec

sinus arrest (> 3 seconds) 800 ms 2600 ms

Pause is > 3 P-P intervals and less than 4 P-P intervals; therefore not sinus exit block

References • • • • • • • • Harrison’s Principles of Internal Medicine, 19 EKGs for the NursePractitioner and Physician Assistant, 2 Current Medical Diagnosis & Treatment: Cardiology, 5 Hurst’s: The ,14 Cardiovascular Physiology, 8 Physiology, 4 Pathophysiology of Disease, 7 Ganong’s • • • • • • • • • • • • • • • • • • • • • • • • • • • • Chapter Chapter 278e: Chapter 277: Chapter 276: Chapter 275: Chapter 274: Chapter 273e: Chapter 269e: Chapter 268: Chapter 52: Chapter 14: Chapter 13: Chapter 12: Chapter 11: Chapter 87: Chapter 86: Chapter 85: Chapter 84: Chapter 83: Chapter 82: Chapter 80: Chapter 79: Chapter 78: Chapter 4: Chapter 2: Chapter 4: Chapter 1: Chapter 10: Chapter 29: Review Review of Medical Physiology, 25 th edition (Costanzo) Functional Anatomy Heart Anatomy of Functional the Muscle of Cells Cardiac Characteristics Cardiovascular Physiology CellularPhysiology Palpitations and Pacing Disorders Cardiac Conduction Ventricular Tachycardia Atrial Fibrillation Supraventricular Antiarrhythmic Bradyarrhythmias Ventricular Arrhythmias Wolf and Tachycardia: Reentry, Nodal Atrioventricular Supraventricular Atrial Tachycardia, Atrial Fibrillation, Atrial and Atrial Tachycardia Flutter, Invasive Electrophysiology Diagnostic Geneticsof Disturbances MechanismsArrhythmias Conduction and Cardiac of Electrophysiologic Disease Cardiovascular Disorders: Heart Electrical the Origin& Activity ofHeart of the Heartbeat the Ventricular Arrhythmias Ventricular Supraventricular The The Atlas Arrhythmias of Cardiac Principles of Electrophysiology Atlas of Electrocardiography th edition ( Bradyarrhythmias Bradyarrhythmias th th edition ( Channelopathies edition (Hammer, et. al) Fuster Tachycardias Tachyarrhythmias Anatomy Mohrman , et. al) : Node Disorders Atrioventricular the of : Node Disorders Sinoatrial the of th th edition (Barrett, et. al) and Clinical and Implications edition (Kasper, et.al) , et. al) th edition (Crawford, et. al) nd edition (Knechtel) - Parkinson - White White Syndrome