Heart Block

1^ST 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

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

2^ND 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 1^st 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 2^ndDegree Heart Block – Mobitz Type I (Top) Mobitz Type II (Bottom)

3^rd 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