Bundle Branch Blocks incomplete

Use quinidine with extreme caution in incomplete AV block, because complete block and asystole may result. The drug may cause unpredictable dysrhythmias in digitalized patients. Use cautiously in patients with partial bundle branch block, severe CHF, and hypotensive states due to the depressant effects of quinidine on myocardial contractility and arterial pressure. 

A 44-year-old woman took an overdose of venlafaxine 3 g. An electrocardiogram showed sinus rhythm and incomplete right bundle branch block (32). She was monitored in an intensive care unit and 10 hours later a further electrocardiogram showed atrial fibrillation with a wide QRS complex. Both of these abnormalities resolved with sodium bicarbonate (100 ml of a 1 M solution). No further conduction disturbances were noted over the following days. 

Complete atrioventricular block occurred in a 10-year-old child with a history of hypertension, severe renal dysfunction, incomplete right bundle branch block, and a ventricular septal defect that had been repaired at birth (10). After slow induction with sevoflurane and nitrous oxide 66%, complete atrioventricular block occurred when the inspired sevoflurane concentration was 3% and reverted to sinus rhythm after withdrawal of the sevoflurane. The dysrhjrthmia recurred at the end of the procedure, possibly caused by lidocaine, which had infiltrated into the abdominal wound, and again at 24 hours in association with congestive cardiac failure following absorption of peritoneal dialysis fluid. 

A 29-year-old man with a history of depression and hypercholesterolemia took 25 g of diphenhydramine in a suicide attempt. He had a generalized tonic-clonic seizure, which resolved spontaneously. Electrocardiography showed a sinus tachycardia with incomplete right bundle branch block and a Brugada pattern. An intravenous bolus of sodium bicarbonate 150 mmol resulted in almost immediate resolution of the electrocardiographic abnormalities. 

An incomplete Bundle Branch Block has the same appearance as either a LBBB or a RBBB with the exception of the QRS duration. The QRS width does not fit the requirement for a true Bundle Branch Block but the other features are present. 

This is termed an incomplete Bundle Branch Block. 

Joubert, P. and Vorster, B. (1975) Incomplete right bundle branch block associated with diphenyl hydantoin toxicity. S. Afr. med. J., 49, 2149. 

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