20-03-2012, 04:50 PM
Electrocardiogram
Electrocardiography.ppt (Size: 4.28 MB / Downloads: 344)
ECG – What it Detects
Heart chamber enlargement
Eccentric hypertrophy
Dilation and growth
Due to volume overload
Concentric hypertrophy
Wall thickening
Due to pressure overload
ECG – Helpful Hints
Always in right lateral recumbency
Patient on a towel or rubber mat
Metal tables are more problematic
Limbs perpendicular to body
Place leads at the elbow and knee
No one moves while the ECG is being recorded
Enhance lead contact with gel or alcohol
ECG – Rhythm
Normal Sinus rhythm
Regular heart rate
QRS and T waves in each complex
Respiratory Sinus Arrhythmia
heart rate regularly irregular
QRS and T waves in each complex
Variable P wave – wandering pacemaker
Heart rate less than 200
ECG – Mean Electrical Axis (MEA)
when a wavefront spreads toward an electrode, the largest possible deflection will occur
When a wavefront spreads perpendicular to a lead, the smallest or no deflection occurs
ECG shows the sum of all wavefronts relative to the lead being used to measure (MEA)
Physiology - Cardiac Pacemakers
Automatic cells in the heart
Depolarize on their own during phase 4 of the cardiac cycle
Rate of depolarization affected by autonomic nervous system
SA node (60-180 beats/min dog) (100-240 cat)
AV node (40-60 beats/min dog) (80-130 cat)
Purkinje fibers (20-40 beats/min)
Bundle of HIS (20-40 beats/min)
Escape rhythm – pacemaker other than SA node, because it fails to fire