Cardiac conduction and anomalies

Resting membrane potential isĀ  -80 to -100mv

Phases of cardiac muscle contraction

Phase 0- Na+ Influx

Phase I- Initial rapid depolarization

Transient K+efflux

Phase II- Plateau phase

Calcium efflux

Phase III and IV- K+ efflux, delayed and inward rectifying K+ channels

Apex of heart is first depolarized and base of heart last depolarized.Repolarization also proceeds in the same order.

ECG

3 limb leads and 6 Chest leads

Limb Leads

Left arm(+-),Right arm(–)and Left Leg(++)

Lead I,II and III are arranged in anti clockwise direction.

Lead I- Connects LA and RA

Lead II-Connects RA and LL

Lead III-Connects LL and LA

Chest Leads

V1- 4th Right ICS near sternum

V2-4th Left ICS near sternum

V3-Between v2 and V4

V4-at apex of heart

V5-5th ICS in anterior axillary line

v6-5th ICS in Mid Axillary line

V7,V8,V9-Extra leads

Mean electrical axis of heart -30 to +110

Except AvR all the leads are placed in direction of depolarization

His Bundle electrocardiogram

To study the conducting system of heart

A wave-Depolarization of AV node

H wave- Depolarization of bundle of his

V wave- Depolarization of purkinje fibres

PA-Beginning of Pwave to beginning of A wave, conduction time from SA to AV node

AH-Conduction time from AV node to bundle of his

HV- Ventricular depolarization

Anomalies

Atrial tachycardia- 100- 200 bets/min

Atrial flutter-SVT

Atrial fibrillation-Most common cardiac arrythmia, Absent P wave

LGL syndrome and WPW syndrome a comparison(Supraventricular tachycardias)

Lown-Ganong-Levine syndrome (LGL) -is a syndrome of pre-excitation of the ventricles due to an accessory pathway providing an abnormal electrical communication from the atria to the ventricles. It is grouped with Wolff-Parkinson-White syndrome as an atrioventricular re-entry tachycardia (AVRT).

  • Byepasses AV node but joins the bundle of His.
  • PJ interval shortens
  • A short PR is seen

Wolff-Parkinson-White syndrome (WPW) is a syndrome of pre-excitation of the ventricles of the heart due to an accessory pathway known as the bundle of Kent. This accessory pathway is an abnormal electrical communication from the atria to the ventricles.

  • Delta wave seen in WPW.
  • QRS widens and PR interval shortens.
  • PJ interval is normal

Ventricular Tachycardias

Long QT syndrome

Ventricular tachycardia

K+ Channel defect

Depolarization is delayed

Torsades De Pointes

VT

Abnormal QRS complex

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