Alternating bundle branch block

Alternating bundle branch block is diagnosed when conducted periods of RBBB and LBBB were noted in a patient on the same or different electrocardiograms

Electrocardiographic diagnosis suggesting the presence of bilateral bundle branch disease

Poor prognosis associated with complete heart block,syncope and sudden cardiac death

Mechanism of alternating bundle branch block

ECG pattern of LBBB occurS

H-V INTERVAL reflects conduction time in distal His bundle and RBB

Rate dependent block

RBBB occurs( rate dependent)

H-V interval reflects conduction time of distal His bundle and left bundle

Length equivalent to delay in left bundle

Maintenance of RBBB once initiated, depend upon the retrograde concealed conduction to the right bundle branch

If right bundle recovery occurs is rapid despite concealed conduction , beat to beat alternation in BBB

Rate dependent block

If cycle length of spontaneous sinus rhythm is close to the refractory period of right bundle ---prolonged periods of left and right bundle branch pattern can be seen

Non rate dependent block

Incomplete left bundle branch block with intermittent non rate dependent RBBB

H-V interval again reflects distal His bundle and left bundle and lengthened by conduction in left bundle

Narrow QRS

DESTRUCTIVE LESION involving the distal His bundle AND PROXIMAL BUNDLE BRANCH

FIGURE B –intermittent LBBB

FIGURE C- intermittent RBBB

FIGURE D- intermittent block in both bundles and manifestation of paroxysomal heart block

Clinical significance

Alternating BBB – WITH SYNCOPE –permanent pacing

Alternating BBB- WITHOUT SYMPTOMS ,WITHOUT NARROW QRS – CLOSE FOLLOW UP

Alternating BBB –NARROW QRS- PERMANENT PACEMAKERS

Alternating BBB- ACUTE MYOCARDIAL INFARCTION-TEMPRORY PACEMAKER SHOULD BE INSERTED regardless of mechanism and H-V interval