Claude Monet: French Impressionist “Japanese Bridge”

Cardiac Electrophysiology ECG in Diagnosis Wagner: Chapter 1:3-23

What is an ECG? Recording: (“gram”) Electrical Activity: (“electro”) Generated by heart cells: (“cardio”) That reach the body surface ECG ElectroCardioGram

What Does an ECG Measure? Voltage: Vertical axis Summation of electrical activity of the total number of cardiac cells Higher voltage ~ more mass 12-Leads give 3-D “image” Time: Horizontal axis Heart Rate and Rhythm Lead II or V5-V6 usually

I aVFV1 II III aVL aVR II V2 V3 V4 V5 V6 *Limb Leads: I, II, III, aVF, aVL, aVR *Chest Leads: V1 – V6

What Can ECG Diagnose? Electrical impulse formation and conduction problems Cardiac Hypertrophy Myocardial Ischemia/Infarct Metabolic Problems: Potassium, calcium and drug toxicity

ECG and CAD Ischemic Cascade: 1. Hypoxia = Anaerobic ATP and lactic acidosis 2. Ventricles “stiffen” diastolic fill 3. Reduced SV and EF ( CO) 4. ECG Waveform Changes 5. Potentially Lethal Arrhythmias

Electrophysiology Review

Myocardial Action Potential mV ECG AP

AP ECG AP ECG Measured in the Cardiac Cell Resting Potential = -90mV Depolarization = Phase 0 Repolarization = Phase 3 Measured at the Skin Surface Resting Potential = Isoelectric Line Depolarization = +/- deflection Repolarization = “T-Wave”

Myocardial Action Potential mV ECG AP

ECG Basics ECG graphs: 1 mm squares 5 mm squares Paper Speed: 25 mm/sec standard Voltage Calibration: 10 mm/mV standard

ECG Paper: ECG Paper: Dimensions 5 mm 1 mm 0.1 mV 0.04 sec 0.2 sec Speed = rate Voltage ~Mass

Cardiac Cycle Cardiac Cycle: ECG WAVES Normal ECG formation / conduction : P Wave: Atrial depolarization/contraction QRS Waves: Ventricular depolarization/contraction T Wave: Ventricular Repolarization

ECG: Cardiac Cycle

Cardiac Cycle Basics: Begins with SA Node depolarization P – P = 1 Cycle Heart rate (pulse) is determined by ventricle depolarization/contraction R – R = 1 heart beat

Calculating Heart Rates from ECG’s: Step One Sinus Rhythm: Each QRS complex is preceded by P wave NSR: Within the intrinsic rate of the SA Node: bpm Tachycardia: >100 bpm Bradycardia: < 60 bpm

Step Two: Count the number of small squares between R – R waves (X): Divide 1500 by X: Rate = 1500 / X Example: X = / 20 =75 Rate = 75 bpm

Why “1500 / X”? Paper Speed: 25 mm/ sec 60 seconds / minute 60 X 25 = 1500 mm / minute

Activity 1: Cardiac Cycle Identification and Rates Draw and Label ECG representing one cardiac cycle (see page 18) Identify the Mechanical Events coinciding with the ECG Wave forms and intervals Calculate the heart rates for the sample rhythm strips