Types of ECGs

  • 12-lead ECG records electrical activity from 12 views of the heart (in most units at least once every day @ 0730 for review during morning ward round)
  • Single-lead or dual-lead monitoring provides continuous cardiac monitoring usually on every ICU patient.


12-lead ECG

  • six limb leads provide information about the heart’s frontal (vertical) plane.
  • bipolar (leads I, II, and III) require a negative and positive electrode for monitoring.
  • unipolar (leads aVR, aVL, and aVF) record information from one lead and require only one electrode.
  • the six precordial leads (leads V1 through V6) provide information about the heart’s horizontal plane.

Leads I, II, and III

  • leads I, II, and III typically produce positive deflection on ECG tracings.
  • lead I helps monitor atrial arrhythmias and hemiblocks.
  • lead II commonly aids in routine monitoring and detecting of sinus node and atrial arrhythmias.
  • lead III helps detect axis changes


Precordial leads

  • Lead V1

– biphasic

– distinguishes between right and left ventricular ectopic beats

– monitors ventricular arrhythmias, ST-segment changes, and bundle-branch blocks

  • Leads V2 and V3

– biphasic

– monitors ST-segment elevation

  • Lead V4

– produces a biphasic waveform

– monitors ST-segment and T-wave changes

  • Lead V5

– produces a positive deflection on the ECG

– monitors ST-segment or T-wave changes (when used with lead V4)

  • Lead V6

– produces a positive deflection on the ECG

– detects bundle-branch blocks


ECG strips

  • 1 small horizontal block = 0.04 second
  • 5 small horizontal blocks – 1 large block = 0.2 second
  • 5 large horizontal blocks = 1 second
  • normal strip – 30 large horizontal blocks = 6 seconds
  • 1 small vertical block = 0.1 mV
  • 1 large vertical block = 0.5 mV
  • amplitude (mV) = number of small blocks from baseline to highest or lowest point

To write much more on ECG requires extensive detailed learning and much understanding, the internet hosts many excellent university standard ‘ECG attainment, assessment and interpretation’ programs that are TOTALLY FREE.   Like “EKG Academy” in the references below or online “game style” trainers like   Do a course or download one soon!


The only EKG book you’ll ever need 6th Edition 2010 by Malcolm Thaler

The ICU Book 4th Edition 2015 by Paul L Marino   accessed 5th April 2018

More reading

Arterial Catheters & MAP

Central Venous Catheters & CVP