UCI Internal Medicine Mini-Lecture ECG for Interns UCI Internal Medicine Mini-Lecture

Learning Objectives Establish Consistent Approach to Interpreting ECGs Review Essential Cases for New Interns Provide Additional Resources for Future Learning The purpose of this mini-lecture is to teach the fundamentals of reading ECGs. This is to help beginning interns establish a consistent approach to interpreting the ECG. The ECGs that will be reviewed here are fundamental ECGs that will be seen over and over again during the course of the intern year. While some interns may readily recognize the pathology represented on the ECG, the instructor should help the intern go through the ECG in a methodological fashion. The mini-lecture is designed in a way so that each slide could be a quick lesson in itself that can be quickly squeezed into a free moment during the day. The instructor should start with the fundamentals of ECG interpretation, then proceed with interpreting individual cases using a consistent method as time permits through the course of the block.

ECG Interpretation What is your approach to reading an ECG? Rate Rhythm Axis Hypertrophy Intervals P wave QRS complex ST segment – T wave SLIDE STARTS WITH QUESTION ONLY Ask interns about their method for interpreting an ECG. Emphasize the importance of interpreting an ECG always in the same order so that nothing is missed. Question will appear first in presentation, then answers.

Rate Square Counting: 300-150-100-75-60-50-42A Count QRS in 10 second rhythm strip x 6 Rate — Ask interns to define normal rate, bradycardia and tachycardia. Square counting: 300-150-100-75-60-42 or count number of QRS complexes in rhythm strip and multiply by 6 (especially for atrial fibrillation).

Rhythm Are P waves present? Is there a P wave before every QRS complex and a QRS complex after every P wave? Are the P waves and QRS complexes regular? Is the PR interval constant? 1st Example: Normal sinus rhythm 2nd Example: Third degree heart block No P waves – atrial fibrillation

Axis Left or right axis deviation? Look at limb leads I and aVF. Normal: I +, aVF + LAD: I +, aVF – RAD: I -, aVF + Left Axis Deviation (LAD) Right Axis Deviation (RAD)

Hypertrophy LVH: S in V1 or V2 + R in V5 or V6 ≥ 35 mm. Hypertrophy – LVH: S wave in V1 or V2 + R wave in V5 or V6 ≥ 35 mm. RVH: V1 R/S ratio >1 or V6 S/R ratio >1. There are many other different criteria that can be used. These are the simplest. RVH: V1 R/S ratio >1 or V6 S/R ratio >1.

Intervals What is the normal PR interval? 0.12 to 0.20 s (3 - 5 small squares). Short PR – Look for Wolff- Parkinson-White. Long PR – 1st Degree AV block What is the normal QRS? < 0.12 s duration (3 small squares). Long QRS - look for bundle branch block, ventricular pre-excitation, ventricular pacing or ventricular tachycardia What is the normal QTc (QT/square root of RR)? < 0.42 s. Long QTc can lead to torsades to pointes. Questions and Responses will appear with each forward button. What are the normal PR, QRS, QT intervals? Short PR – Look for Wolff-Parkinson-White. Long PR - 1st degree AV block. Long QRS – look for bundle branch block, ventricular preexcitation, ventricular pacing, or ventricular tachycardia. Normal QTc varies. Males < Females. Prolonged QTc (QT/square root of RR) can lead to torsades de pointes. Prolonged QTc can be caused by MI, myocardial disease, hypocalcaemia, hypothyrodism, intracranial hemorrhage, drugs (e.g. sotalol, amiodarone), hereditary

P Waves Evaluate the shape, height and width of P waves. Multiple morphologies  Wandering pacemaker or Multifocal atrial tachycardia Notched (M-shaped) P-wave in I and II, > 0.12 s  P-mitrale seen in severe left atrial enlargement

QRS complex Poor R Wave Progression in V1 to V6: suggests prior anterior MI Pathologic Q wave: previous MI. Q wave amplitude 25% or more of the subsequent R wave, OR > 0.04 s in width + > 2 mm in amplitude in more than one lead Is there good R wave progression? Normal R wave progression: around V3 or V4, QRS transitions from predominately negative to predominately positive and R/S ratio becomes>1. Poor R wave progression suggests anterior MI, but not diagnostic Are Q waves present, suggestive of infarction?

ST segment & T wave ST segment – Elevation or depression indicates ischemia. Figure on right: Concave– Normal  smile. Convex – MI  frown. T wave - can diagnosis ischemia, hyperkalemia Now we are ready to start an ECG. a case day is workable.

Case #1 70 year old male with history of diabetes mellitus and hypertension occasionally feels lightheaded. He recently fainted while standing.

Case #1 ECG Ask interns to go through all the steps of interpretation: Rate: Emphasize counting boxes between R-R interval. Divide 300 by # large boxes or count QRS complexes x 6. HR: 45 bpm. Bradycardia Rhythm: Regular. Axis: Normal Hypertrophy: LVH Intervals: Prolonged PR interval 240 ms – 1st degree AV block. This may be difficult to count. P waves: Normal morphology. QRS complex: Good R wave progress. No pathologic Q waves. ST segment – T wave: Normal. Answer: Sinus bradycardia with 1st degree heart block causing symptomatic syncope. Next Step? Ask the patient if he takes anti-hypertensive medications that cause bradycardia. If not, the patient should be evaluated for symptomatic bradycardia with a Holter monitor. He may need a pacemaker.

Case #2 58 year old female with no significant past medical history presents with fatigue, lightheadedness and shortness of breath.

Case #2 ECG Ask interns to go through all the steps of interpretation: Rate: Count QRS complexes and multiply by 6. HR 120. Tachycardia. Rhythm: Any P-waves present? None, so A fib. Axis: Normal Hypertrophy: LVH Intervals: Normal P waves: None. Atrial fibrillation. QRS complex: Normal. ST segment – T wave: Normal. Answer: Atrial fibrillation with rapid ventricular response. Symptoms are often vague. Palpitations are not always felt. Next Step? Treatment for rate control with CCB, BB, digoxin or amiodarone.

Case #3 78 year old female with history of HTN, DM, HL, CAD admitted for syncope complains of palpitations and lightheadedness.

Case #3 ECG Ask interns to go through all the steps of interpretation even if answer may be obvious. Rate: HR 150. Tachycardia. Rhythm: Any P-waves present? Not a supraventricular rhythm. Axis: Unable to determine. Hypertrophy: Unable to determine. Intervals: QRS > 120 ms indicates wide complex tachycardia from ventricular pacing. P waves: None. QRS complex: Unable to determine R wave progression or Q waves. ST segment – T wave: Unable to determine. Answer: Monomorphic V Tach. Interns should recognize this immediately as a life threatening emergency. Next step? ACLS algorithm for unstable tachycardia. Call rapid response code and get ready to cardiovert.

Case #4 67 year old male with history of diabetes, hypertension, COPD presents with chest pain.

Case #4 ECG Ask interns to go through all the steps of interpretation. Rate: HR 96 Rhythm: Regular. Axis: Normal Hypertrophy: LVH Intervals: Normal P waves: Normal morphology. P waves follows pacemaker spike indicating atrial pacing.. QRS complex: Good R wave progression. No pathologic Q waves. ST segment – T wave: Non-specific ST, T-wave changes. Answer: Atrial pacemaker. The pain is reproducible with palpitation. The patient had been doing some heavy lifting. The patient neglected to say that he has a pacemaker. Plus the intern auscultated the patient’s heart through the shirt.

Case #5 38 year old female with history of DM, HTN, CKD presents with 2 days of nausea and abdominal pain.

Case #5 ECG Rate: HR 60 Rhythm: Regular. Axis: Normal Hypertrophy: LVH Intervals: Normal P waves: Normal morphology QRS complex: Normal. ST segment – T wave: Would they prick you finger? Yes. Peaked (tented) T-waves. Answer: Hyperkalemia. Serum K+ 7.7. Teaching point: As hyperkalemia progresses, PR interval increases, QRS widens, P waves disappear. An ominous sign is the appearance of a sine wave pattern. Next step? Calcium gluconate (stabilizes cell membrane), Insulin and D50 (drives K+ into cells), and kayexalate (removes potassium) and possibly albuterol inhaled or lasix.

Case #6 60 year-old man with history of HTN, HL, CAD presents with nausea, shortness of breath and chest pain.

Case #6 ECG Rate: HR 55 Rhythm: Regular. Axis: Normal Hypertrophy: LVH Intervals: Normal P waves: Normal morphology and size. QRS complex: Good R wave progression. ST segment – T wave: ST elevations in the inferior (II, III, aVF) and apical/lateral (V5-V6) leads. ST depressions consistent with reciprocal changes are seen in leads aVL and V1-V2. Answer: STEMI Next step? Give ASA. Order 15 lead ECG to check for right ventricular MI. Call cardiology to activate the cath lab. Which vessel is most likely occluded? Right coronary artery.

Additional Resources Websites: http://en.ecgpedia.org/ http://ecg.utah.edu http://ecg.bidmc.harvard.edu/maven/ Apps: ECG Guide by QxMD (iPad and iPhone) ECG Interpret (iPhone) Books: 12-Lead ECG: The Art of Interpretation, Tomas Garcia (perhaps the best book on ECGs with detailed explanations and physiology.) Arrhythmia Recognition, Tomas Garcia

Summary Always keep a consistent approach. Do not rely upon machine reads. Practice makes perfect.