Download Heart Block

Other arrhythmias
Sinus Bradycardia
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Extrinsic causes
o Hypothermia, hypothyroidism, cholestatic jaundice and raised ICP
o Drug therapy with beta blockers, anti-arrhythmic drugs
o Neurally mediated syndromes – e.g. carotid sinus syndrome, neurocardiogenic
(vasovagal) syndrome, etc
Intrinsic causes
o Acute ischaemia and infarction of the sinus node
o Chronic degenerative changes such as fibrosis of the atrium and sinus node (sick
sinus syndrome)
Heart Block
AV Block
 First degree AV block
o Prolongation of the PR interval
 Second degree AV block
o Occurs when some P waves conduct and others do not
o Can be caused by AMI
o Type 1 (aka Mobitz 1, Wenkebach): Progressive prolongation of PR interval with
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dropped beats
Type 2: a dropped QRS complex is not preceded by progressive PR elongation
2:1 or 3:1 block occurs when every second or third P wave conducts to the ventricles.
This is neither Type 1 or 2 but is still a second degree block.
Third degree AV block
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Complete heart block occurs when all atrial activity fails to conduct to the ventricles
No association between P waves and QRS complexes
Can be caused by congenital problems, idiopathic fibrosis, ischaemic heart disease,
non-ischaemic heart disease, cardiac surgery, iatrogenic, drug-induced, infections,
connective tissue diseases, neuromuscular diseases
Life is maintained by a spontaneous escape rhythm
Bundle Branch Block
 Generally shown by a widening of the QRS complex
 Right bundle branch block
o Can occur due to an isolated congenital heart disese, myocardial disease (e.g. AMI),
pulmonary disease causing cor pulmonale
o Produces deep S waves in leads 1 and V6 and as tall late R wave in lead V1
 Left bundle branch block
o Can occur due to left ventricular outflow obstruction, coronary artery disease
o Produces deep S wave in lead 1 and tall late R wave in leads 1 and V6
o Also produces abnormal Q waves
ECGs