Heart Block - Arrhythmias

Heart Block

·        Atrioventricular block/Heart Block: Delay or interruption in conduction between atrium and ventricle

o   First degree (partial block): PR interval prolonged beyond 0.2 secs (5 small squares). Often seen in normal people. ?Acute MI or Rheumatic Fever. No urgent action needed.

o   Second degree AV block (partial block): some impulses are conducted and some not. Þ Heart disease. Often seen in acute MI:

§  Mobitz type 1 (Wenckebach): progressive prolongation of PR interval before an impulse is completely blocked – then sequence starts over. Usually transient and prognosis is good

§  Mobitz type 2: PR interval does not lengthen but some beats are not conducted. May lead to bundle branch block (® wide QRS), transvenous pacing may be required

§  2:1 block (every second beat gets through). Also 3:1 block. May need pacing if ventricular rate too slow.

o   Third degree (complete heart block): no conduction – either at AV, bundle of His or bundle branch level. More often fibrosis than ischaemia:

§  At level of AV node: junctional escape pacemaker will fire at 40 – 60 bpm with normal QRS. Prognosis favourable. Due to ­parasympathetic tone from inferior MI or drug effect

§  At infranodal level: Implies extensive disease of both bundles. Associated with anterior MI. Distal escape rhythm, slow rate (<40) plus wide QRS, possibly asystole. Management: transvenous or transthoracic pacing, dopamine or adrenaline, pacemaker