Heart Block

Heart Block

1ST Degree


Pathology:                    Decrease in conduction ofimpulse from atria to ventricles through AV node.

                                        Manifested as a prolonged PR interval(>02s) on ECG


Aetiology:                     Drug therapy e.g. beta blockade, fibrosis ofconductive tissue, Lyme disease, acute rheumatic fever, aortic valve disease, sarcoidosis,myocarditis, MI, idiopathic


Signs:                              None


Symptoms:                  Usuallynone


Investigations:          ECG: see fig 1.8


Treatment:                  Nonerequired  


Complications:          None


Prognosis:                    Good




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Figure 1.8 1st degree heart block with PRinterval of 292ms

2ND Degree


Pathology:                    Intermittentfailure of atrial impulses to be conducted through AV node and His bundle, subdividedinto Mobitz type 1 (Wenckebach) or Mobitz type 2

Mobitz type 1: delayin AV conduction progressively increases until an impulse

is not conducted, on the ECG the PR interval getslonger and longer until there is a dropped beat

                                   Mobitz type 2: intermittentfailure of conduction of the atrial impulse to the

ventricles usually in a 2:1 ratio, the PR intervaldoes not lengthen


Aetiology:                    Mobitz type 1 can be due toincreased vagal tone and often occurs during sleep

Mobitz type 2is pathological and has a similar aetiology to 1st degree AVblock  


Symptoms:                   Can be asymptomatic, SOB,chest pain, pre-syncope/syncope


Signs:                              Bradycardia,hypotension


Investigations:          ECG:To assess rhythm; may require a Holter monitor

                                        Echo:if LV function impaired the patient may benefit from CRT


Treatment:                  Stop offending medications

A temporary pacing wire may be required

Mobitz type 2 always requires a permanent pacemaker

Complications:          Death, injuries from syncope


Prognosis:                  Both Mobitz type 1 and 2 canprogress to complete heart block                        

                                          Prognosisis good following PPM implantation














Figure 1.9 2ndDegree Heart Block – Mobitz Type I (Top) Mobitz Type II (Bottom)


3rd Degree/Complete Heart Block


Pathology:                    Complete AV dissociation, impulsesfrom atria cannot be conducted to ventricles


Aetiology:                     Drugtherapy e.g. beta blockade, fibrosis of conductive tissue, Lyme disease, acuterheumatic fever, aortic valve disease, sarcoidosis, myocarditis, MI, idiopathic


Signs:                              Bradycardia,hypotension


Symptoms:                  Canbe asymptomatic, SOB, chest pain, pre-syncope/syncope


Investigations:          ECG:No association between p-waves and ventricular conduction

                                          Echo: To assess for any structuralabnormalities


Treatment:                  Stopoffending drugs

A temporary pacing wire may be required

Long-term PPM    


Complications:          Death, injuries from syncope


Prognosis:                    Untreated at high risk ofsudden cardiac death, once treated prognosis is good






















Figure 1.10 Complete Heart Block

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