Refer to the discussion on the the heart’s conduction system.

From the ECG Learning Center
Dr. Alan Lindsay. Excellent site for learning to read ECGs.

P Wave:

• Normally upright in Lead I, II, V4-6 and AVF
• Normally inverted in AVR
• Variable in Lead III, AVL and other chest leads
• Amplitude should not exceed 2 -3 mm in any lead
• Normal conture gently rounded rather than pointed and notched

P Wave  Abnormalities

• Inversion when shouldbe upright (ectopic atrial or junctional)
• Increased amplitude: atrial hypertrophy or dilation, valve disease, HTN, cor  pulmonale
• Increased width: Left atrial enlargement P< 0.11
• Diphasic LAE (Lead III, or V1)
• Notching P. mitrale I.  III signifcant when peak distance > 0.04
• Peaking P-Pulmonale III>I
• Absence of P waves

Tp Wave (Ta)

• Represents atrial recovery
• Opposite direction of P wave

P – R Interval

• 0.12 – 0.20 seconds
• Varies with heart rate
• If conduction system is diseased or affected by digitalis, P-R may lengthen as if conducting system as the rate increases.

Prolonged PR Interval

• AV block due to coronary disease, rheumatic disease,
• In some cases of Hyperthyroidism
• As a normal varriation (1.3%)

Shortened PR Interval

• AV junctional and low atrial rhythms
• WPW
• Normal variation
• Glycogen storage issue
• Pheochromocytoma
• Some hypertensive patients
• Fabry’s disease

PR Segment

• Normally isoelectric
• May be displaced in atrial infarction and acute pericarditis 

This entry was posted on Saturday, November 7th, 2009 at 22:56 and is filed under ECG. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.