ECG EKG

Electrocardiography is a transthoracic interpretation of the electrical activity of the heart over time captured and externally recorded by skin electrodes.It is a noninvasive recording produced by an electrocardiographic device.The ECG works mostly by detecting and amplifying the tiny electrical changes on the skin that are caused when the heart muscle “depolarises” during each heart beat. At rest, each heart muscle cell has a charge across its outer wall, or cell membrane. Reducing this charge towards zero is called de-polarisation, which activates the mechanisms in the cell that cause it to contract. During each heartbeat a healthy heart will have an orderly progression of a wave of depolarisation that is triggered by the cells in the sinoatrial node, spreads out through the atrium, passes through “intrinsic conduction pathways” and then spreads all over the ventricles. This is detected as tiny rises and falls in the voltage between two electrodes placed either side of the heart which is displayed as a wavy line either on a screen or on paper. This display indicates the overall rhythm of the heart and weaknesses in different parts of the heart muscle.

Normal P waves 
Height less than 2.5 mm in lead II 
Width less than 0.11 s in lead II 
Abnormal P waves see in right atrial hypertrophy, left atrial hypertrophy, atrial premature beat, hyperkalaemia

Normal PR interval 
0.12 to 0.20 s (3 – 5 small squares) 
Short PR segment consider Wolff-Parkinson-White syndrome or Lown-Ganong-Levine syndrome (other causes – Duchenne muscular dystrophy, type II glycogen storage disease (Pompe’s), HOCM) 
Long PR interval see first degree heart block and ‘trifasicular’ block

Normal QRS complex 
Less than 0.12 s duration (3 small squares) 
for abnormally wide QRS consider right or left bundle branch block, ventricular rhythm, hyperkalaemia, etc. 
no pathological Q waves

Normal QT interval 
Calculate the corrected QT interval (QTc) by dividing the QT interval by the square root of the preceeding R – R interval. Normal = 0.42 s. 
Causes of long QT interval 
Myocardial infarction, myocarditis, diffuse myocardial disease 
Hypocalcaemia, hypothyrodism 
Subarachnoid haemorrhage, intracerebral haemorrhage 
Drugs (e.g. sotalol, amiodarone) 
Hereditary – Romano Ward syndrome (autosomal dominant) ,Jervill + Lange Nielson syndrome (autosomal recessive) associated with sensorineural deafness

Normal ST segment  – no elevation or depression 
Causes of elevation include acute MI (e.g. anterior, inferior), left bundle branch block, normal variants (e.g. athletic heart, Edeiken pattern, high-take off), acute pericarditis 
cCauses of depression include myocardial ischaemia, digoxin effect, ventricular hypertrophy, acute posterior MI, pulmonary embolus, left bundle branch block

Normal T wave 
Causes of tall T waves include hyperkalaemia, hyperacute myocardial infarction and left bundle branch block 
Causes of small, flattened or inverted T waves are numerous and include ischaemia, age, race, hyperventilation, anxiety, drinking iced water, LVH, drugs (e.g. digoxin), pericarditis, PE, intraventricular conduction delay (e.g. RBBB)and electrolyte disturbance.

1. Long PR interval (of over 200 ms) may indicate a first degree heart block.
2. Prolongation can be associated with hyperkalemia or acute rheumatic fever.
3. Short PR interval may indicate a pre-excitation syndrome via an accessory pathway that leads to early activation of the ventricles, such as seen in Wolff-Parkinson-White syndrome.
4. Variable PR interval may indicate other types of heart block

Premature atrial contractions are a type of heart arrhythmia that are extremely common, with many people experiencing premature atrial contractions at some point in their lives. In some cases, the condition is benign, while in other cases, the PACs can indicate that the patient is at risk for a more serious problem, and it may be necessary to take steps to manage the heart rhythm. People with heart conditions who experience premature atrial contractions are a cause for special concern.
Premature atrial contractions occurs when the atria beat before they are supposed to. Many people never even notice that a premature atrial contraction is occurring, although some people feel the contraction as a faint flutter or palpitation, as though the heart has skipped a beat. Cutting down on caffeine often eliminates or greatly reduces the incidence of premature atrial contractions.