ECG Basics-1Dr.Rathnakar U.P. Willem Einthoven [1860-1924] •Weighed in at about 600 pounds •5 people to make it work •water required cooling in order to work.. ECG Importance Immediately Non-invasive Highly Uses Detecting available versatile Inexpensive arrhythmias Conduction disturbances MI Metabolic disturbances Increased susceptibility to sudden cardiac death (e.g., QT prolongation syndromes). Gold standard-PTCA & Fibrinolysis Screening 12 Leads = 12 Video cameras 1 2 3 •All cameras record same activity as do all 12 leads •Run out is more authentic in square leg camera! •II,III,aVF tell better story about inferior wall! 12 Lead ECG 6 Limb Leads [3 Standard and 3 Augmented] 6 Precordial or Chest Leads. 12 Lead ECG Basics Limb Leads: Lead I Lead II Lead III Vertical Plane aVR aVL aVF Hexa-axial lead system aV R -ve RA LI Einthoven’s +ve LA -ve VL a LII +ve LIII LF -ve Machine ECG aVF +ve Frontal-Vertical-Coronal Plane Transverse Orientation of Leads H or iz on ta l Normal Impulse Conduction SA node AV node Bundle of His L & R Branches Purkinje fibers If the impulse moves towards the +ve pole of a lead-+ve deflection ECG & Spread of impulse Sinoatrial node AV node Bundle of His Bundle Branches Purkinje fibers If the impulse moves parallel to a lead-maximum deflection P-QRS-T • QRS - Ventricular depolarization • T wave - Ventricular Repolarization The PR Interval Beginning of P wave to beginning of QRS Atrial depolarization + Delay in AV junction (AV node/Bundle of His) (delay allows time for the atria to contract before the ventricles contract) Pacemakers of the Heart SA AV Node - Dominant pacemaker - intrinsic rate of 60 - 100 BPM. Node - Back-up pacemaker -rate of 40 - 60 BPM cells - Back-up pacemaker with an intrinsic rate of 20 - 45 BPM. Ventricular ECG Paper Speed=25mm/sec Horizontally ◦ 1 small square=1mm= 0.04 s ◦ 1 large square=5mm= 0.20 s ◦ 15 large squares=150mm=3.0 sec Vertically-One large box - 0.5 mV The ECG Paper (cont) Every 3 seconds (15 large boxes) is marked by a vertical line. 3 sec 3 sec Calculate Rate-Method 1 3 sec 3 sec ◦ Count the No. of R waves in a 6 second rhythm strip, then multiply by 10. ◦ 9 x 10 = 90 bpm Calculate Rate- Method 2 R waves ◦ Count the no. of large boxes between 2 R waves. ◦ Divide 300 by this no.=Eg.300/1=300 ◦ Or count small squares- Divide 1500/This No. =1500/5=300 Step 2: Determine regularity R R Look at the R-R intervals Regular or irregular Interpretation? Regular Step 3: Assess the P waves Are there P waves?[Sinus rhythm] Do the P waves all look alike? Do the P waves occur at a regular rate? Is there one P wave before each QRS? Interpretation? Normal P waves with 1 P wave for every QRS Step 4: Determine PR interval Normal: 0.12 - 0.20 seconds. (3 - 5 boxes) Step 5: QRS duration Normal: 0.04 - 0.12 seconds. (1 - 3 small squares) Summary Rate Regularity P waves PR interval QRS duration Normal 90-95 bpm regular normal 0.12 s 0.08 s Sinus Rhythm