Introduction to Electrocardiography

Introduction to Electrocardiography

Class Objectives: Introduction to ECG monitoring Discuss principles of interpretation Identify the components and measurements of the ECG ECG analysis

ECG Monitoring Recording of Electrical Activity Uses Bipolar or Unipolar leads The ECG DOES NOT provide a recording or evaluation of Mechanical Activity!!!

ECG Monitoring Bipolar Leads 1 positive and 1 negative electrode RA always negative LL always positive Traditional limb leads are examples of these Lead I Lead II Lead III Provide a view from a vertical plane

ECG Monitoring Unipolar Leads 1 positive electrode 1 negative reference point calculated by using summation of 2 negative leads Augmented Limb Leads avr, avf, avl vertical plane Precordial or Chest Leads V1-V6 V6 horizontal plane

ECG Monitoring Einthoven s Triangle Each lead looks from a different perspective Can determine the direction of electrical impulses Upright electrical recording indicates electricity flowing towards the positive (+) electrode positive deflection

Standardized Methods ECG Paper Device Paper Speed Most run at 25 mm/sec Device Calibration and Devices 10 mm (10 small boxes) = 1 millivolt Electrode Placement 3, 4, 12, 15, or 18 lead placement Remember, variations do exist! Check calibration and paper speed.

Standardized Methods & Devices ECG Graph Paper Vertical axis - voltage 1 small box = 1 mm = 0.1 mv Horizontal axis - time 1 small box = 1 mm = 0.04 sec. Every 5 lines (boxes) are bolded Horizontal axis - 1 and 3 sec marks

Horizontal boxes measure time in seconds. 1 small box=0.4 seconds, large box=5 small boxes=0.20 seconds Vertical boxes measure amplitude in milliamps. 1 small box=0.1 mv, large box=5 small boxes=0.5 mv.

1 mm = 0.1mv.04 sec..2 sec.

Standardized Methods ECG Paper Examples Vertical Axis No. of mm in 10 small boxes? No. of small boxes in 2 mm? Horizontal Axis and Devices No. of seconds in 5 small boxes? No. of small boxes in 0.2 second? No. of small boxes in 1 second?

Standardized Methods and Devices Electrode Placement Standardization improves accuracy of comparison ECGs 3 or 4 Lead and 12 Lead placement are most common Assure good conduction gel Prep the area, shave hair and remove oil from skin Avoid Bone Large muscle mass or hairy areas Limb vs. Chest placement

Electrode Placement RA and LA. Traditionally placed anywhere on the arm. Alternate placement to reduce muscle artifact is at the wrist or between the elbow and shoulder. RL and LL. Traditionally placed a few inches above the ankle. Alternate placement to reduce muscle artifact is on the upper leg, but below the umbilicus.

Electrode Placement V 1 4 th intercostal space at the right sternal border V 2 4 th intercostal space at the left sternal border V 3 Midway between V2 and V4 V 4 At the left mid-clavicular line in the 5 th intercostal space V 5 At the left anterior axillary line on the same horizontal level as V4 V 6 At the left mid-axillary line on the same horizontal level as V4 and V5.

Supplemental 15 and 18 Lead Electrode Placement

Calculating the Rate The 6 Second Method 6 sec. 0.20 seconds X 30 = 6 seconds Rate can be calculated by counting the number of QRS complexes in a 6 second strip and multiplying by 10.

Another way to calculate rate is measuring the R R interval: 300 divided by number of big blocks between R R interval (must be a regular rhythm) i.e. 300/4 = 75

300 150 100 75 60 50 43 37 33 30 The triplicate method assigns a value to each large box and counts backward: 300, 150, 100, 75, 60, 50, etc. between R waves. To work, the rhythm must be regular.

ECG Components Components and Their Representation P, Q, R, S, T, U, and J Waves PR Interval QRS Interval ST Segment QT Segment

P Wave First upward deflection Represents atrial depolarization Usually 0.10 seconds or less Less than 2.5 mm in height Smooth, rounded, upright in Leads I, II, avf with normal axis Do they look the same? Usually followed by QRS complex

P Wave The normal P wave represents the sum of the depolarizations of the right and left atria. Because the sinoatrial node is located in the right atrium, right atrial depolarization begins slightly before left atrial depolarization. Therefore, the initial portion of the P wave primarily reflects right atrial depolarization, and the terminal portion of the P wave reflects left atrial depolarization. You would think that this should produce a notched P wave, but depolarization in both atria occurs so closely in time that the P wave usually has a smooth or blunted apex. Notched P waves can be seen with Sick Sinus Syndrome or conduction problems in the atria.

P Wave Abnormal P Waves changes from the normal P wave morphology may be due to hypertrophy, dilation, or altered electrical activation.

P Wave P Wave in Right Atrial Enlargement Tall, peaked P waves (> 2.5 millimeters high or 0.25 millivolts amplitude) with a vertical axis seen in II, III, AVF - associated with lung disease, pulmonary embolus, or other causes of pulmonary hypertension. P-pulmonale

P Wave P Wave in Left Atrial Enlargement P-mitrale: : broad, notched P waves in II and AVF (>( 2.5 millimeters wide or 100 milliseconds duration) with a negative component in V1 or V2 (that exceeds one millimeter by one millimeter, - associated with mitral regurgitation, congestive heart failure or any clinical condition that elevates LV filling pressure. It can even be transient with the occurrence of CHF.

QRS Complex Composition of 2 or more waves Q, R, and S represents ventricular depolarization much variability Duration usually < 0.12 sec 0.04 0.09 sec is considered normal for a supraventricular rhythm 0.10 0.12 sec with hemiblock (look at leads Ifor axis deviation) >0.12 sec with bundle branch block or a ventricular rhythm

Q Wave First negative deflection after P wave Depolarization of septum May by physiologic or pathologic Not always seen May be seen with idiopathic hypertrophic subaortic stenosis (IHSS) If seen, will be in conjunction with LVH

Q Wave Pathologic or Physiologic Q Wave Considered pathologic if: Greater than 0.04 sec or 1 small box Greater in depth than 1/3 the height of the QRS Form in leads where septal depolarization should be positive Develop where there is permanent, complete occlusion of a coronary artery with resultant transmural infarct of the myocardium

Q Wave

R Wave First positive deflection following P or Q waves Subsequent positive deflections are R, R, R etc

S Wave Negative deflection following R wave Subsequent negative deflections are S, S, S etc May be part of QS complex absent R wave in aberrant conduction

ECG Components T Wave repolarization of ventricles concurrent with end of ventricular systole Should be upright in most leads Upslope is normally longer than downslope (ratio is 2/3 1/3). Inverted T waves with equal downslope considered abnormal. Called arrowhead Ts, usually indicates ischemia Tall, peaked, narrow T waves can indicate hyperkalemia or early ischemia

ECG Components U Wave Etiology is uncertain Believed to be associated with electrolyte imbalances and the over repolarization of the ventricle due to the sudden burst of K + into the cell by the Na + /K + pump. Normal and expected finding in children May form with hypokalemia May form as part of the digitalis effect May be seen with myocardial injury or infarction

Osborn (J) wave ECG Components Occurs in cases of severe hypothermia due to: Environmental exposure Addison s s disease Sepsis Hypothyroidism

ECG Segments QT Segment ST Seg. Q PRI.12 -.20 s R S <.12 s

PR Interval Time impulse takes to move through atria and AV node From beginning of P wave to next deflection on baseline (beginning of QRS complex) Normally 0.12-0.20 sec May be shorter with faster rates

J Point Point where QRS complex returns to isoelectric line Beginning of ST segment Critical in measuring ST segment elevation

S-T T Segment Early repolarization of ventricles Measured from J point to onset of T wave Elevation or depression may indicate abnormality Elevation indicates an injury pattern Depression indicates ischemia Sagging or cupping may be due to medications like digitalis

S-T T Segment Locate the J point, then look for S-T segment elevation or depression

Q-T T Interval (QTc( QTc) Represents all events of ventricular systole Prolonged QT intervals may lead to arrythmias including Torsades de Pointes Should be shorter than ½ of the preceding R-R R interval Normal values are between 0.30 and 0.44 seconds c stands for corrected for heart rate.

Q-T T Interval (QTc( QTc) Causes of a prolonged Q-T Q T interval: Genetics. Some people are predisposed. Hypothyroidism Phenothiazines Tricyclic Antidepressants Class 1A Antiarrhythmics like Amiodarone Electrolyte imbalance; hypokalemia, hypocalcemia,, or hypomagnesemia Stroke, seizures, intracerebral or brainstem bleeds

R-R R Interval Used to measure the distance between identical points Regular rhythms are those with consistent R-R R intervals

ECG Interpretation

Rate Rhythm/Regularity ECG Interpretation Regular Regularly irregular Irregularly irregular QRS Complex, look at duration, configuration, and relationship to P waves P Waves, presence or absense,, configuration, relationship to QRS. (Is there a P wave for every QRS and a QRS for every P wave?) Relationships, intervals, and measurements

ECG Interpretation Ventricular Rate Triplicate method 300-150 150-100-75-60-50 R-R R method divide 300 by # of large squares between consecutive R waves 6 Second method multiply # of R waves in a 6 second strip by 10 Rate meter may be unreliable!!!

Rhythm Measure R-R R R intervals across strip Should find regular distance between R waves Classification Regular Irregular ECG Interpretation Regularly irregular Irregularly irregular

QRS Complex Narrow < 0.12 seconds (3 small boxes) is normal 0.04 0.09 indicates supraventricular origin (AV node or above) as location of the pacemaker with normal conduction of the impulse. 0.10 0.12 seconds, look for axis deviation and the possibility of a hemiblock. Wide ECG Interpretation > 0.12 seconds is wide indicates ventricular, paced ventricular, or supraventricular with aberrant conduction or a conduction defect, i.e. Bundle Branch Block.

P Waves ECG Interpretation Present? Do they all look alike? Regular interval Upright or inverted in Lead II? Upright = atria depolarized from top to bottom Inverted = atria depolarized from bottom to top

ECG Interpretation Relationships/Measurements PR Interval Is it constant? Less than 0.20 seconds P to QRS Relationship P wave before, during or after QRS? 1 P wave for each 1 QRS? Regular relationship?

ECG Interpretation A monitoring lead can tell you: How often the myocardium is depolarizing How regular the depolarization is How long conduction takes in various areas of the heart The origin of the impulses that are depolarizing the myocardium

ECG Interpretation A monitoring lead cannot tell you: Presence or absence of a myocardial infarction Axis deviation Chamber enlargement Right vs. Left bundle branch blocks Quality of pumping action If the heart is contracting!!!

ECG Interpretation An ECG is a diagnostic tool, NOT a treatment No one was ever cured by an ECG! Treat the PATIENT not the Monitor!!!

ECG Interpretation In the following sections we will look at Sinus Rhythms Atrial, Junctional,, and Supraventricular Rhythms Ventricular Rhythms AV Blocks and Paced Rhythms The 12-Lead ECG

Questions?