2 Let’s start with some basics… V1: right 4th intercostal spaceV2: left 4th intercostal spaceV3: halfway between V2 and V4V4: left 5th intercostal space, mid-clavicular lineV5: horizontal to V4, anterior axillary lineV6: horizontal to V5, mid-axillar line
3 Conduction System of the Heart Sinus node is the pacemaker of the heart, the dominant center of automaticity.Generates continuous regular depolarization stimuli at a rate of bpmThere are other potential pacemakers that can take over if SA node fails, and they have different intrinsic rates. These are in the atria, AV junction, and the ventricles.
4 EKG Paper EKG machine moves at 25 mm/sec, each small box is 1 mm Small boxes represent 0.04 secLarge boxes represent 0.2 secFive large boxes equal one second
5 EKG Waves and Intervals P wave: the sequential activation (depolarization) of the right and left atriaQRS complex: right and left ventricular depolarization (normally the ventricles are activated simultaneously)ST-T wave: ventricular repolarizationPR interval: time interval from onset of atrial depolarization (P wave) to onset of ventricular depolarization (QRS complex)QRS duration: duration of ventricular muscle depolarizationQT interval: duration of ventricular depolarization and repolarization
6 Systematic Approach to ECG Interpretation RateRhythmAxisIntervalsHypertrophyInfarct (QRST Changes)For acls only need to do rate, rhythm, and intervals on a rhythm strip
7 Determining Rate R-R interval is ventricular rate p-p interval is atrial rate. Usually the same but not alwaysSeveral ways to do this…1) Count down the number of large boxes: 300, 150, 100, 75, 60, 50, ....Ex: this one is between 150 and 100, closer to 150 so we might say ~ bpm2) Count the number of large boxes and divide by 300Ex: 300/2 = 150 but it is a little slower than that so we might say ~ bpm3) Count the number of small boxes between beats and divide into 1500Ex: 1500/11 = 136 bpmIf QRS occurs at each large box then R-R interval is 0.2 seconds, then rate is 300 bpm (5 beats/second x 60sec/min)25 small boxes/sec x 60 sec/min = 1500
8 Analyzing A Rhythm Strip Is the rhythm regular?What is the rate?Is the QRS complex narrow or wide?Are P waves present?Are P waves related to the QRS complexes?What is the PR interval ?Rhythm= mind your Ps, Qs and the 3 Rs (p waves, QRS complexes, rate, regularity, relatedness)If QRS is narrow, almost certain that the impulse is arising at or above the AV node.
9 Intervals PR interval QRS interval: QT interval From the onset of atrial depolarization to the onset of ventricular depolarizationNormal between 0.12 and 0.20 sec—so should be less than a large boxQRS interval:Time it takes for ventricular depolarization to occurNormal is 0.10 sec or less—so should be less than half of a large boxQT intervalFrom the beginning of ventricular depolarization to the end of ventricular repolarizationNormal is les than half of a R-R interval (can’t always rely on this if rate is very tachycardic)Prolonged QT interval- drugs, lytes, CNS
10 Sinus tachycardia and sinus bradycardia if all these conditions met but rate is faster or slower, respectively. May be physiologic or not.
17 Supraventricular Tachycardia (SVT) Supraventricular rhythms start by definition at or above the AV node. If the QRS is narrow in all leads, you can almost be guaranteed the rhythm is supraventricular.Sinus rhythm, atrial fibrillation, atrial flutter, junctional/nodal rhythms, and PSVTPSVT is a reentry rhythm
27 Myocardial Infarction Look for QRST changes in each leadNote each lead where Q waves are foundLook for R wave progression—transition normally occurs between V2 and V4Look at ST segments and note depression or elevationLook for T wave inversionQ waves or T wave inversion may be a normal finding in leads III, aVF, aVL, aVR, and V1Always consider clinical scenario and compare with old EKG if possible
28 Basic Lead Groupings Inferior leads: II, III, aVF Lateral (left-sided) leads: V4 to V6 and I, aVLSeptal leads: V1, V2Anterior leads: V2 to V4Right coronary artery:SA node, IV septum, inferior heart, +/- posterior heartLeft coronary artery:LAD- anterior heartLeft circumflex- lateral heart