Claude Monet: French Impressionist“Japanese Bridge”

Cardiac Cardiac ElectrophysiologyElectrophysiology

ECG in DiagnosisECG in DiagnosisWagner:

Chapter 1:3-23

What is an ECG?What is an ECG?Recording: (“gram”)Electrical Activity: (“electro”)Generated by heart cells:

(“cardio”)That reach the body surface

EElectroCCardioGGram

What Does an ECG What Does an ECG Measure?Measure?Voltage: Vertical axis

Summation of electrical activity of the total number of cardiac cells

Higher voltage ~ more mass12-Leads give 3-D “image”

Time: Horizontal axisHeart Rate and RhythmLead II or V5-V6 usually

I aVF V1

II

III

aVL

aVR

II

V2

V3

V4

V5

V6

**Limb LeadsLimb Leads: I, II, III, aVF, aVL, aVR: I, II, III, aVF, aVL, aVR

**Chest Leads: Chest Leads: V1 – V6V1 – V6

What Can ECG Diagnose?What Can ECG Diagnose?Electrical impulse formation

and conduction problemsCardiac HypertrophyMyocardial Ischemia/InfarctMetabolic Problems:

Potassium, calcium and drug toxicity

ECG and CADECG and CAD Ischemic Cascade:1. Hypoxia = Anaerobic ATP

and lactic acidosis2. Ventricles “stiffen” diastolic fill3. Reduced SV and EF ( CO)4.4. ECG Waveform ChangesECG Waveform Changes5.5. Potentially Lethal Potentially Lethal

ArrhythmiasArrhythmias

Electrophysiology Electrophysiology ReviewReview

Myocardial Action PotentialMyocardial Action Potential

mV

-100

+40

0

4

0

1 2

3

4

ECG

AP

AP AP ECG 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 PotentialMyocardial Action Potential

mV

-100

+40

0

4

0

1 2

3

4

ECG

AP

ECG BasicsECG BasicsECG graphs:

1 mm squares5 mm squares

Paper Speed:25 mm/sec standard

Voltage Calibration: 10 mm/mV standard

ECG Paper: ECG Paper: Dimensions5 mm

1 mm

0.1 mV

0.04 sec0.2 sec

Speed = rate

Voltage ~Mass

Cardiac CycleCardiac Cycle: ECG WAVESNormal ECG formation / conduction:

P Wave: Atrial depolarization/contraction

QRS Waves: Ventricular depolarization/contraction

T Wave: Ventricular Repolarization

ECG: Cardiac CycleECG: Cardiac Cycle

Cardiac Cycle Basics:Cardiac Cycle Basics:Begins with SA Node

depolarizationP – P = 1 CycleHeart rate (pulse) is determined

by ventricle depolarization/contraction

R – R = 1 heart beat

Calculating Heart Rates from ECG’s: Step OneSinus Rhythm: Each QRS

complex is preceded by P waveNSR: Within the intrinsic rate of

the SA Node: 60-100 bpmTachycardia: >100 bpmBradycardia: < 60 bpm

Step Two: Step Two: Count the number of small

squares between R – R waves (X):

Divide 1500 by X:Rate = 1500 / X

Example: X = 20 1500 / 20 =75 Rate = 75 bpm

Why “1500 / X”?Why “1500 / X”?Paper Speed: 25 mm/ sec60 seconds / minute60 X 25 = 1500 mm / minute

Activity 1: Cardiac Cycle Activity 1: Cardiac Cycle Identification and RatesIdentification and RatesDraw 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