Congenital Intermittent Atrio-Ventricular Dissociation in Tetralogy of Fallot (A Case Report) Karande SC, Sheth SS, Dalvi BV*, Lahiri K, Shah MD Department of Pediatrics and *Cardiology, King Edward Memorial Hospital and Seth GS Medical College, Parel, Mumbai 400 012, India. Abstract A case of tetralogy of fallot with congenital intermittent atrio-ventricular dissociation is reported. A review of standard postgraduate books of cardiology fails to describe this condition, thus showing its extreme rarity. The therapeutic dilemma in treating such a case is also discussed. (J Postgrad Med 1991; 37(1):58B, 59-61) Congenital heart disease occurs in 0.8% of all five births. Tetralogy of Fallot (TOF) accounts for 10% of all forms of congenital heart disease and is the most common cardiac malformation responsible for cyano- sis after one year of age 3 . Frequency of congenital com- plete heart block is about 4 per 10,000 births 8 . This case report describes an unusual association of TOF with atrio-ventricular (AV) dissociation. Case Report A 7-year-old girl was brought with complaints of cyanosis since the age of 1 year, and repeated squat- ting episodes for the last 3 years. She had no syncopeal attacks or symptoms suggestive of congestive cardiac failure. There was no history of recent mumps, diph- theria or rheumatic fever. She was on no medication at the time of presentation. Her birth history and mile- stones were normal. On examination, her pulse was found to be irregu- lar with a rate of 52/min. Her other vital parameters were normal. She had central cyanosis and grade III clubbing. Jugular venous pulse showed intermittent cannon waves. Cardiovascular examination revealed a left para-sternal bulge, a well felt apex beat in the 4 th left intercostal space in the mid-clavicular line and a grade 4/6 ejection systolic murmur in the pulmonary area with a single second heart sound. Hematological and biochemical investigations were normal. Anti- streptolysin O titre was not significant. X-ray chest showed a cardiothoracic ratio of 60% with a right aortic arch and pulmonary oligemia. ECG showed varying P-P and R-R intervals suggestive of intermittent sinus arrests with transient A-V dissocia- tion. At other times, normally conducted sinus beats were seen. P wave axis was +45°, QRS. axis was +110°, with evidence of right ventricular hypertrophy and QRS transition in lead V2. The duration of the QRS. complex was less than 80 msec (See Figs. 1 and 2). Fig 1: Intermittent sinus arrest with A-V dissociation, with normally conducted sinus bears in lead a VF. Fig 2: A-V dissociation in leads V 5 and V 6 Two dimensional echocardiogram revealed a large subaortic ventricular septal defect with 50% aortic over- ride and Mitral aortic continuity. There was evidence of subvalvular and valvular pulmonary stenosis with good sized main pulmonary artery and its branches. Cardiac Catheterization confirmed the 2 echo findings. The child was not given propranolol in view of the A-V dissociation. She was advised early complete sur- gical repair of TOF with pacemaker implantation. Discussion TOF with congential A-V dissociation has not been reported. The ventricular septal defect (VSD) in TOF is large, about the size of the aortic orifice and it lies beneath the aortic valve, more anteriorly than the usual VSD 5 . The pathway of the bundle of His in tetralogy patients has been reported in detail by Feldt et al 2 The main bundle is closely related to the poster- inferior margin of the defect. It runs along its inferior margin, on the left side of the summit of the ventricular septum. Hence, conduction disturbances both transient and per- manent, including complete A-V block, can occur af- ter corrective surgery 4 . Permanent complete heart block following surgery is treated by implanting a pacemaker. Congenital A-V block is probably the result of de- fect in the main stem of the bundle of His 1 . Seventy per cent cases have no other evidence of heart dis- ease. Associated cardiac malformations include “cor-