pathophysiology of heart blocks and ventricular preexcitation prof. hanáček
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Pathophysiology of heart blocksand ventricular preexcitation
Prof. Hanáček
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Left bundle branch block
Dominant S wave in V1 with broad, notched (‘M’-shaped) R wave in V6
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Left bundle branch block
• Aortic stenosis• Ischaemic heart disease• Hypertension• Dilated cardiomyopathy• Anterior MI• Primary degenerative disease (fibrosis) of the conducting system (Lenegre disease)• Hyperkalaemia• Digoxin toxicity
Causes
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Right bundle branch block
Tall R' wave in V1 ("M" pattern) with wide, slurred S wave in V6 ("W" pattern)
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Right bundle branch block
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• In RBBB, activation of the right ventricle is delayed as depolarization has to spread across the septum from the left ventricle.
• The left ventricle is activated normally, meaning that the early part of the QRS complex is unchanged.
• The delayed right ventricular activation produces a secondary R wave (R’) in the right precordial leads (V1-3) and a wide, slurred S wave in the lateral leads.
• Delayed activation of the right ventricle also gives rise to secondary repolarization abnormalities, with ST depression and T wave inversion in the right precordial leads.
• In isolated RBBB the cardiac axis is unchanged, as left ventricular activation proceeds normally via the left bundle branch.
Mechanism of development
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Causes of RBBB• Right ventricular hypertrophy / cor pulmonale• Pulmonary embolus• Ischaemic heart disease• Rheumatic heart disease• Myocarditis or cardiomyopathy• Degenerative disease of the conduction
system• Congenital heart disease (e.g. atrial septal
defect)
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Louis Wolff, Sir John Parkinson and Paul Dudley White, who discovered the phenomenon that later would be called the WPW syndrome
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Ventricular preexcitation - scheme
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Re-entry circuit during AVRT (retrograde conduction via Bundle of Kent)
Kent bundle
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Wolf – Parkinson – White syndrome
The features of pre-excitation may be subtle, or present only intermittently. Pre-excitation may be more pronounced with increased vagal tone e.g. during Valsalva manoeuvres, or with AV blockade, e.g. drug therapy
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