Sino-Atrial Node

Elliptical area at junction of SVC and Right atrium

Atrio-Ventricular Node

Triangular area of right atrial wall just above septal cusp of tricuspid valve

Lead positions

1. Limb leads
   • Right arm
   • Left arm
   • Left leg
2. Chest leads
   • V1: 4ICS Right sternum
   • V2: 4ICS Left sternum
   • V3: Midway between V2/4
   • V4: Apex 5ICS MCL
   • V5: 5ICS AAL
   • V6: 5ICS MAL

• P-wave: passage of current across atrium
• PR interval: time from SA node to ventricle
• QRS: Ventricular depolarisation 0.12s
• QT: Time from ventricular depolarisation to full repolarsiation (rate dependent) hence QTc = corrected for heart rate (QT/rootRR interval) = Bazett's formula
• T-wave: ventricular myocardial repolarisation
• J-wave; J-point is at junction of Swave and ST segment (may be seen in hypothermia)
• U-wave: Prominent in hypokalaemia

Sinus Tachy: exercise, pain, pyrexia, shock, hyperthyroidism, anaemia, drugs
Sinus Brady: Atheletes, hypothyroidism, (Cushing reflex), drugs - B-blockers

Supra-ventricular tachycardias

1. Atrial ectopics
2. SVTs
3. AF / Fibrillation

Bradyarrythmias

1. First degree heart block
2. Second degree heart block
   • Mobitz type I: Wenkenbach
   • Mobitz type II: 2:1 / 3:1 block
3. Third degree (complete) heart block