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Mobitz type 1 second-degree atrioventricular (AV) block (Wenckebach)

Etiology: 1) increased vagal tone 2) antiarrhythmic agents 3) electrolyte abnormalities 4) myocardial ischemia or infarction (inferior wall) 5) conduction system disease Pathology: - progressive delay in AV conduction prior to a conduction block - in the setting of a normal-appearing QRS complex, type 1 2nd degree AV block is a benign arrhythmia - rarely progresses to 3rd degree AV block (complete heart block) Clinical manifestations: 1) usually asymptomatic 2) may be transient 3) dizziness, presyncope, syncope Laboratory: - electrocardiogram: 1) gradual PR elongation preceding a non-conducted p-wave b) QRS complexes appear in regular groupings, i.e. as in bigeminy, trigeminy c) shortest PR interval occurs with first p-wave following a blocked p-wave d) RR interval shortens prior to a blocked p-wave Management: - symptomatic patients 1) atropine 0.5-2.0 mg IV 2) transcutaneous pacemaker in patients resistent to atropine 3) bradycardia refractory to atropine & transcutaneous pacemaker not available a) dopamine 5-20 ug/kg/min b) epinephrine 2-20 ug/min c) isoproterenol 2-10 ug/min - treat underlying disorder (i.e. acute coronary syndrome) [3]

Related

HV interval

General

second-degree atrioventricular (AV) block

Figures/Diagrams

EKG: Wenckebach

References

  1. Manual of Medical Therapeutics, 28th ed, Ewald & McKenzie (eds), Little, Brown & Co, Boston, 1995, pg 139
  2. Saunders Manual of Medical Practice, Rakel (ed), WB Saunders, Philadelphia, 1996, pg 271
  3. Medical Knowledge Self Assessment Program (MKSAP) 14, 17 American College of Physicians, Philadelphia 2006, 2015