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Cardiac Conduction

Physiology of Cardiac Conduction

•  The excitatory & electrical conduction system of the heart is responsible for the contraction and relaxation of the heart muscle.

•  The sinoatrial node (SA node) is the pacemaker where the electrical impulse is generated.

How to Read an

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PQRST wave Deflection waves

P wave

•  Lasts 0.08 s •  Shows Atrial contraction

Deflection waves

QRS complex

•  Results due to depolarization of ventricles •  Ventricular contraction •  R waves are deflected positively and the Q and S waves

are negative

T wave •  Results due to ventricular decontraction (Relax)

Normal ECG Deflection Wave Pattern

Abnormal ECG Deflection Wave Patterns

Sinus Bradycardia

Rate = 40-59 b.p.m.

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Sinus Tachycardia

Rate = 101-160 b.p.m.

Causes

• CHF, hypoxia, pulmonary edema

• Increased temperature

• Stress or response to pain

Sinus Arrhythmia

Rate = 45-100 b.p.m.

Sinus Arrest

Causes

Myocarditis

MI

Digitalis toxicity

Atrial Flutter

Rate = 250-350 b.p.m.

Precipitates CHF

Atrial Fibrillation (afib)

Causes

COPD

CHF

AV block

Causes

• Digitalis toxicity

• Acute infection

• MI

• Degeneration of the conductive tissue.

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Ventricular Tachycardia (V-tac)

Causes • CAD • Acute MI • Digitalis toxicity • CHF

Rate = 100-220 b.p.m.

Ventricular Fibrillation (V-fib)

Causes

Acute MI

Asystole