[Syncope and bifascicular block: who needs a pacemaker?].

Correspondence: C. W. Israel, MD, Evangelical Hospital Bielefeld, Department of Medicine, Division of Cardiology, Burgsteig 13, 33617 Bielefeld, Germany E-mail: [email protected] Infra-hisian conduction delay is a well-known phenomenon. It was studied extensively in the early seventies when invasive recording of the His potential and measurement of the interval from the His bundle to the right ventricle (HV interval) became widely available.1 Studies showed that infra-hisian conduction delay is associated with progression to trifascicular (that is, complete atrioventricular [AV]) block. On the assumption that conduction through the His bundle, unlike the AV node, follows an “all or nothing” rule, a maximum value for a normal HV interval has been suggested. By means of the measurement of the HV interval in 517 patients with bifascicular block, Dhingra et al found a value of >55 ms to be associated with an increased risk of progression to complete AV block.2 In contrast, Scheinman et al studied 313 patients with bundle branch block3 over 3 years and found a progression to complete AV block in only 2% of the patients with an HV interval <55 ms, compared to 4% for an HV interval of 55 to 69 ms and 12% when it was ≥70 ms. In these patients, syncope had occurred before the electrophysiological study in only 40%. Interestingly, progression to complete AV block was observed in 24% of the individuals with very long HV intervals (≥100 ms). Once the enthusiasm about the recording of the His potential had faded away, there has been no major study on this topic over the last 25 years. Therefore, current guidelines on the indication for permanent pacing in bifascicular block are still based on these data: pacemaker therapy is indicated if the HV interval exceeds 70 ms in syncope, or if an electrophysiologic study performed for other reasons happens to find an HV interval ≥100 ms.4 Unfortunately, these old studies2,3 had several weaknesses: