100 QUESTIONS IN CARDIOLOGY

77 Should the patient with trifascicular disease

be routinely paced? If not, why not?

Simon Sporton

Normal activation of the ventricles below the bundle of His occurs

by way of three “fascicles” – the right bundle branch and the

anterosuperior and posteroinferior divisions of the left bundle

branch. Conduction block in two of the three fascicles is bi-

fascicular block. Additional prolongation of the PR interval

results in “trifascicular block” implying abnormal conduction

through or above the remaining fascicle. The concern is that

conduction will fail in the remaining fascicle, i.e. complete heart

block will develop with a slow and unreliable ventricular escape

rhythm. Potential consequences include syncope and death.

There have been no randomised trials of pacing vs no pacing in

patients with chronic bi- or trifascicular block. Clinicians must

therefore be guided by knowledge of the natural history of the

condition without pacing, and expert consensus guidelines.

The largest prospective study of patients with bi- and tri-

fascicular block followed 554 asymptomatic patients for a mean of

42 months. The five year mortality from an event that may

conceivably have been a bradyarrhythmia was just 6%, a figure

that must inevitably include some non-bradyarrhythmic deaths.

The five year incidence of complete heart block was also low at

5%. A prolonged PR interval was associated with a higher

incidence of potentially bradyarrhythmic deaths but not with the

development of complete heart block. An important finding of

this study was a five year all cause mortality of 35% reflecting the

high incidence of underlying coronary heart disease and

congestive cardiac failure.

The available evidence would suggest that asymptomatic

patients with trifascicular block should not be paced routinely. A

history of syncope should prompt thorough investigation for both

brady- and tachyarrhythmic causes. If intermittent second or

third degree block is documented permanent pacing is indicated.

If tachyarrhythmias are implicated then therapy is likely to

include antiarrhythmic drugs, which may exacerbate AV block

and prophylactic permanent pacing would seem wise. Bi- and

trifascicular block are associated with a high incidence of under-

lying coronary heart disease and heart failure. Attention should