Introduction to Electrocardiography Aaron J. Gindea, MD, FACP, FACC Associate Professor of Cardiology Hofstra North Shore LIJ School of Medicine Hempstead, NY

How to use this workbook The beginning of the workbook can be used in conjunction with the recommended readings as an introduction to EKG interpretation. Beginning with page 58, there are a large series of unknowns. The unknowns encompass a large (but not exhaustive) list of EKG abnormalities. A complete interpretation of each EKG is included in comments section of each EKG. We recommend that you try to interpret each EKG on your own before looking at the interpretation. On page 57 is a list of specific abnormalities on particular EKG’s. The minimum number of EKG’s that we recommend that you review are also listed on page 57. We will be providing 4-6 extended office hour sessions to review EKG’s that present persistent problems.

Definitions An electrocardiogram is a graphic representation of the propagation of electrical vectors in the heart Vectors (as you remember from college physics) are representations of force/energy that have magnitude and direction

Review of vectors, and how we graph them on an EKG

Graphing the Vectors Time Electrical force Towards lead Away from lead

The Electrical Pathways of the Heart 1)SA node 2)AV node 3)Bundle of His 4)Left Bundle 5)Left posterior hemifascicle 6)Left anterior hemifascicle 7)Left ventricle 8)Interventricular septum 9)Right ventricle 10)Right bundle

With the Heart Removed

A Single Beat: PQRST The morphology will vary depending on the lead

Lead Systems: 1 The leads give the viewer an opportunity to trace the propagation of the impulses from multiple different axes.

Lead Systems: Standard & Augmented (aV) leads

Lead Systems: Precordial Leads

Electrocardiogram

How It Works

A Few Important Points Because of the intercalated discs, myocardial muscle functions as an electrical syncytium so that even when the normal pathways are interrupted, the cardiac muscle can still be activated (albeit in an abnormal manner). Pacemaker cells (cells that initiate heart beat) are regular in nature. Since normal propagation of the impulses is down & to the left, lead II will generally be the best lead to look at to determine the atrial rhythm. There is a delay in the normal EKG after the P wave which is the time it takes for the impulse to get through the AV node to the Bundle of His (called the A-H interval) and from the Bundle of His to the ventricles (called the H-V interval). This is called the PR interval.

A Few Important Points (Continued) The more rapidly you stimulate the AV node, the longer it takes to repolarize. This is called decremental conduction and it’s “REALLY IMPORTANT”!! The His Purkinje system is a specialized conduction system that allows for very efficient impulse conduction. Impulses that go down that pathway result in narrow complex QRS. There is a delay in the normal EKG after the QRS complex which is the time it takes for the ventricle to repolarize for the next beat. The commonly used interval extends from the beginning of the QRS to the end of the T wave and is called the QT interval.

Dissecting an EKG interpretation: Every interpretation should have the phrases below or a phrase to replace the respective colored phrase Normal sinus rhythm at 60, normal electrical axis, normal intervals, good R wave progression with no significant repolarization abnormalities Atrial rhythm and rate Axis Conduction (includes AV and interventricular) R wave progression (includes infarcts and hypertrophy) repolarization abnormalities (ischemia, infarction, hypertrophy, etc.)

Calculating Heart Rate The scale of a standard EKG is: Time axis: 1 small box = 40 msec 1 big box = 5 small boxes = 200 msec Voltage axis: 2 big boxes = 10 small boxes = 1 mV

Sinus rhythm: The SA node is located in the high right atrium and the impulse is transmitted down and to the left. The wave formed is called the P wave and will be positive (upright) in leads that look down and/or to the right. SINUS RHYTHM HAS NOTHING TO DO WITH CONDUCTION TO THE VENTRICLES. Normal sinus rhythm: There are reproducible upright P waves in I and II at a rate of Sinus bradycardia: There are reproducible upright P waves in I and II at a rate of Sinus tachycardia: There are reproducible upright P waves in I and II at a rate >100 Normal sinus rhythm at 60, normal electrical axis, normal intervals, good R wave progression with no significant repolarization abnormalities

Ectopic atrial rhythm: There are P waves but they’re not upright in I and II Wandering atrial pacemaker: There are at least three different morphologies of P waves Atrial flutter: There are flutter waves (classically looking like a sawtooth pattern) at a rate of Atrial fibrillation: There appears to be an undulating baseline but no discernable P waves (-often atrial fibrillation is diagnosed by noting an irregularly irregular ventricular pattern) No atrial activity: This phrase would be replaced by the phrase defining the origin of the ventricular rhythm e.g. junctional rhythm, ventricular tachycardia) Normal sinus rhythm at 60, normal electrical axis, normal intervals, good R wave progression with no significant repolarization abnormalities

Electrical Axis: Describes the vector direction of the electrical activation of the ventricles Normal electrical axis: -30 degrees to +90 degrees; the net QRS vector is upright in leads I and II Left axis deviation: <-30 degrees; the net QRS vector is upright in I and down in II Right axis deviation: >+90 degrees; the net vector is down in I Normal sinus rhythm at 60, normal electrical axis, normal intervals, good R wave progression with no significant repolarization abnormalities

Electrical Axis Normal electrical axis Left axis deviation (A) Right axis deviation (B) Indeter minate axis I++- II+- III A: left anterior hemifascicular block, inferior wall myocardial infarction B: left posterior hemifascicular block, pulmonary disease sometimes

PR segment: from beginning of P wave to beginning of QRS complex; normally between msec (3-5 small boxes) –Short PR: either the impulse is coming from an ectopic location close to the AV node so the time to get to the ventricle is shorter or there is an accessory pathway that bypasses the AV node (Wolf Parkinson White or Lown Ganong Levine syndromes) Normal sinus rhythm at 60, normal electrical axis, normal intervals, good R wave progression with no significant repolarization abnormalities

–Long PR: the impulse is taking longer to get to the ventricle. First degree AV block: Every P wave is generating a QRS complex, but the PR interval is greater than 200 msec –Variable PR second degree AV block, Type I (also known as Mobitz type I or Wenckebach): Every P wave conducts through the AV node progressively more slowly (i.e. with a progressively longer PR interval) until a P wave occurs which is blocked in the AV node and doesn’t generate a QRS complex) second degree AV block, Type II (also known as Mobitz II): A P wave is not conducted to the ventricle but there is no preceding progressive prolongation of the PR interval Third degree or complete heart block: No P wave generates a QRS complex. The P wave rhythm and the QRS rhythms are independent Normal sinus rhythm at 60, normal electrical axis, normal intervals, good R wave progression with no significant repolarization abnormalities

QRS interval: from beginning of Q wave to end of S wave; normally less than 120 msec (3 small boxes) –normal: will only occur if the impulse is propagated through the highly efficient, specialized His Purkinje system –Bundle branch block: either the left bundle of His or the right bundle of His is blocked. Impulses travel efficiently down the still-working bundle and propagate to the distribution of the other bundle through the intercalated discs but because that’s not as efficient, the QRS complex generated is wide (>120 msec) and has specific morphologies depending on which bundle is blocked Normal sinus rhythm at 60, normal electrical axis, normal intervals, good R wave progression with no significant repolarization abnormalities

Right bundle branch block: The ventricular impulse passes along the left bundle and initially activates the interventricular septum in a left to right direction. This causes a small R wave in lead V1. Then the impulse propagates left (-the right bundle is not active), giving a deep S wave. After the left bundle distribution has been depolarized, the right bundle distribution is depolarized (without competition from the left sided forces) resulting in a large second R wave in V1 (known as an R’)—this is called an rSR’. The late rightward forces can also be seen as a deep terminal S wave in left facing leads like I and V6. Normal sinus rhythm at 60, normal electrical axis, normal intervals, good R wave progression with no significant repolarization abnormalities

Right Bundle Branch Block

Left bundle branch block: The ventricular impulse passes along the right bundle so the normal left to right activation of the septum is lost. This causes a loss of the septal Q (the small initial negative deflection in I, aVL and V6 and the small positive deflection in V1). Then the impulse propagates to the septum (-the left bundle is not active), and leftward through the septum. After the left bundle distribution has been depolarized, the right bundle distribution is depolarized (without competition from the left sided forces) resulting in a large second R wave in V1 (known as an R’); this is called an rSR’. The late rightward forces can also be seen as a deep terminal S wave in left facing leads like I and V6. Normal sinus rhythm at 60, normal electrical axis, normal intervals, good R wave progression with no significant repolarization abnormalities

Left Bundle Branch Block

Normal sinus rhythm at 60, normal electrical axis, normal intervals, good R wave progression with no significant repolarization abnormalities Normal sinus rhythm Sinus bradycardia Sinus tachycardia Wandering atrial pacemaker Atrial flutter Atrial fibrillation Junctional rhythm Ventricular rhythm Normal electrical axis Left axis deviation Right axis deviation A. Normal intervals First degree AV block Mobitz type I Mobitz type II Complete heart block B. Left bundle branch block Right bundle branch block C. Normal QT Prolonged QT Short QT A B C Good R wave progressionEarly R wave progression Late R wave progressionQ waves consistent with MI (indicate location of MI) 4 No significant repolarization abnormalitiesST segment elevations ST segment depressionsT wave inversions Peaked T waves 5

Normal ECG Normal sinus rhythm at 72, normal electrical axis, normal intervals, good R wave progression with no significant repolarization abnormalities

From the collection of Dr. A Bornstein Sinus bradycardia at 38, normal electrical axis, normal intervals, good R wave progression with no significant repolarization abnormalities

Sinus tachycardia at 110, normal electrical axis, normal intervals, good R wave progression with no significant repolarization abnormalities

Right Atrial Enlargement &/or Left Atrial Enlargement

Normal sinus rhythm at 80, normal electrical axis, First degree AV block but otherwise normal intervals, good R wave progression with no significant repolarization abnormalities

Normal sinus rhythm at 90, normal electrical axis, Mobitz type I second degree AV block, good R wave progression with inverted T waves in V5 and V6

Reading an EKG: AV Conduction (Continued) Second degree AV block –Type II (also called Mobitz II)- A P wave is not conducted but there is no preceding progressive prolongation of the PR interval

Normal sinus rhythm at 94, normal electrical axis, Mobitz type II, second degree AV block, right bundle branch block,, early R wave progression with nonspecific repolarization abnormalities

Sinus tachycardia at 105,, normal electrical axis, complete heart block with junctional escape at 40 beats a minute, good R wave progression with no significant repolarization abnormalities

Sinus bradycardia at 58, normal electrical axis, first degree AV block, right bundle branch block,, early R wave progression with no significant repolarization abnormalities

LBBB QRS >120 msec, QS or rS in V1, notched R wave in V6 and discordant T waves

Ventricular Hypertrophy

Ectopy (beats that don’t originate from the sinus node) Atrial premature contractions ([APC’s]) also known as atrial premature beats[APB’s], premature atrial contractions [PAC’s] Since these impulses originate in the atrium and conduct through the His Purkinje system, the resulting QRS complex is usually normal Ventricular premature contractions ([VPC’s]) also known as ventricular premature beats[VPB’s], premature ventricular contractions [PVC’s] Since these impulses originate below the His Purkinje system, the resulting QRS complex is usually wide and bizarre

Arrhythmias Most arrhythmias occur through a reentrant mechanism:

Arrhythmias are often based on location of reentrant circuit(s) 1-2 circuits in the atrium: atrial flutter 3-5 circuits in the atrium: atrial fibrillation 1 circuit in the AV node: AV nodal reentrant tachycardia 1 circuit in the ventricle: monomorphic ventricular tachycardia

From collection of Dr. A. Bornstein

Myocardial Infarction (MI) Acute changes: ST elevations in the affected leads & reciprocal ST depressions in some of the other leads

Localizing MIs Location of MI Leads with ST elevations Coronary artery usually involved Anterior Wall MI V 1 -V 3 Left anterior descending Septal MI V 1, V 2 Left anterior descending Lateral Wall MI V 4 -V 6 and often I & aVL Left circumflex Inferior Wall MI II, III, aVF Right coronary Posterior Wall MI ST depressions in V 1 & V 2 Right coronary Right ventricular MI V 1, V 4 R Right coronary

Evolutionary Changes in MI Leakage of potassium from the injured cells lowers the resting potential of the cells. Because the EKG uses the TP interval as the baseline and systolic ion shifts continue to occur, what we’re really seeing is a drop in the resting potential (during the TP interval) rather than an ST elevation. In ischemia, the ischemic tissue is usually subendocardial (watershed) and results in a higher resting potential so we see ST depressions relative to the baseline

Infarctions Subacute changes: biphasic  inverted T waves in the affected leads Chronic changes: Q waves in the affected leads

Infarctions

Unknowns Sinus rhythms: 2, 7, 11, 12, 13, 14, 15, 16, 17, 18, 22, 24, 25, 32, 41, 42, 45, 54, 55 Atrial arrhythmias: 1, 4, 6, 8, 10, 20, 27, 46, 53, 56 AV block: 23, 26, 31, 41, 42, 44 Bundle branch blocks: 4, 10, 12, 14, 16, 17, 21, 28, 31, 32, 34, 35, 37, 39, 41, 45, 57 Myocardial infarctions: 11, 13, 19, 30, 40, 44 Ventricular arrhythmias: 3, 7, 29, 33 Pacemakers: 5, 16 Hypertrophy: 57 We recommend that you try the following EKGs (at a minimum): 1, 2, 3, 10, 11, 22, 27, 33, 34, 42

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Unknown # 47 A 60-year-old "walk-in" patient without a primary care physician arrives at your clinic. The patient is not on any medications and has not seen a physician in years. The patient complains of several hours of severe chest pressure. Although the vital signs were remarkable only for some bradycardia, the medical assistant is concerned that the patient appears ill. A stat ECG was done and you are asked to see this patient immediately. The following ECG is handed to you as you are on your way to see this patient.

Unknown # year-old patient comes in to get your advice on starting a new exercise program to get back into shape. The program involves heavy aerobic workouts and he needs a form filled out that he is medically cleared to participate in this workout program. In talking to him you learn he has cardiac risk factors for smoking, positive family history, high cholesterol and hypertension. He has a sedentary lifestyle and has not participated in any strenuous physical activity for years. Although his cardiorespiratory review of systems is (-), you are concerned that his activity level is very limited and he has significant risk factors. As part of the workup you obtain the following ECG to interpret: 55-year-old patient comes in to get your advice on starting a new exercise program to get back into shape. The program involves heavy aerobic workouts and he needs a form filled out that he is medically cleared to participate in this workout program. In talking to him you learn he has cardiac risk factors for smoking, positive family history, high cholesterol and hypertension. He has a sedentary lifestyle and has not participated in any strenuous physical activity for years. Although his cardiorespiratory review of systems is (-), you are concerned that his activity level is very limited and he has significant risk factors. As part of the workup you obtain the following ECG to interpret:

Unknown # year-old patient, with a history of hypertension, comes to see you. She is currently on a diuretic prescription and is complaining of a few days of "skipped heart beats". She has felt slightly dizzy lately but does not have any other symptoms. Overall she has been feeling well, her only medical issue has been hypertension. Previous electrocardiograms in her chart show normal sinus rhythm and are otherwise unremarkable. Her exam shows an irregular pulse in the 130 rate range but the rest of the exam is unremarkable. You obtain the following electrocardiogram:

Unknown # year-old man comes into your office as a new patient. He is concerned about his elevated blood pressure. A year ago, in a physicians office, he had a reading of 150/100. A month ago, while being evaluated for bronchitis at a walk-in clinic, his blood pressure was 150/105. At today's office visit his blood pressure is 155/105. He is asymptomatic and currently takes no medications. His cardiac exam is remarkable for a laterally displaced PMI and an S4. As part of the workup, you obtain the following electrocardiogram:

Unknown # year-old, man with no significant past medical history, comes in with fatigue and feeling light headed. He denies any chest pain, current medication usage, or syncope. He has had to limit his physical activity since this fatigue started about a week ago. His vital signs are remarkable for a pulse of 40 and a blood pressure of 100/60 which he states is a bit low for him. Exam is unremarkable except for the bradycardia. Because of the bradycardia an electrocardiogram is ordered as part of the initial assessment.

Unknown # year-old, female patient comes in for a get acquainted visit. She has a history of severe chronic obstructive pulmonary disease and is on multiple medications and home oxygen. During the physical she is noted to be tachycardic with an irregularly irregular pulse. An electrocardiogram is taken for further evaluation. 65-year-old, female patient comes in for a get acquainted visit. She has a history of severe chronic obstructive pulmonary disease and is on multiple medications and home oxygen. During the physical she is noted to be tachycardic with an irregularly irregular pulse. An electrocardiogram is taken for further evaluation.

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