3. 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

4. Mechanism of alternating bundle branch block  ECG pattern of LBBB occurS  H-V INTERVAL reflects conduction time in distal His bundle and RBB

5. 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

6. 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

7. 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

8. 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

9. 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