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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