VALUE AND LIMITATIONS OF THE BRADYCARDIA DIAGNOSTIC FUNCTION OF A VENTRICULAR PACEMAKER

The indication for permanent pacing may be confirmed by a bradycardia counter in patients without ECG or Holter recording of the causal brad ycardia. The algorithm was assessed in a multicenter register with the SORIN Theorema model. The activation of the device was programmed on a double hysteresis of 2 seconds with a programmable histogramme of de tections and sensing and pacing counters. One hundred and forty five p atients were recruited in 50 centers over 2 years : 89 men and 56 wome n aged 33 to 96 years (average 72 years), 87 of whom had no other obvi ous cardiac disease. One hundred and ten had typical syncopal episodes , 19 had atypical or minor syncopal attacks and 16 were asymptomatic, one with sinus node dysfunction and the others with pathological prolo ngation of the HV interval (greater than or equal to 70 ms) during end ocavitary electrophysiological investigation. The mechanism of the bra dycardia was considered to be infra-hisian in 62 patients who had HV i ntervals greater than or equal to 70 ms. This was also the probable me chanism in 20 others who had bundle branch block and typical syncope d espite a HV interval < 70 ms and in 6 patients with bundle branch bloc k and typical syncope who did not undergo electrophysiological investi gation before implantation. Twenty one patients had sinus node dysfunc tion during electrophysiological investigation and 8 had a carotid sin us syndrome. The remaining 28 cases had transient syncope but no ECG c hanges or abnormality on electrophysiological investigation. Permanent pacing was proposed when an extracardiac origin of the syncope was ex cluded. After an average follow-up period of 268 +/- 225 days: a brady cardia was recorded in 103 cases (71 % of the series). This confirmati on was obtained in 71 % of syncope of unknown origin, 62 % of sinus no de dysfunction and 75 % of carotid sinus syndromes. In infra-hisian co nduction defects, bradycardia was confirmed in 73 % of patients with a long HV interval, in 75 % of patients with HV intervals < 70 ms and i n 67 % of uninvestigate bundle branch block. The bradycardia counter w as activated in 71 % of asymptomatic patients with abnormal electrophy siological investigation. Fifty six patients remained symptomatic, one third of whom had no recorded episodes of bradycardia. The persistenc e of symptoms was correlated with the number of long cycles of more th an 1 500 ms, with that of cycles shorter than 400 ms and with the caro tid sinus syndrome. This type of algorithm which can confirm a pacing indication a posteriori may be useful in prospective series to validat e the criteria of implantation and follow up the evolution of conducti on defects. It requires improvement to avoid long periods of symptomat ic bradycardia above the threshold frequency. Finally, a dual-chamber mode would be useful to determine the mechanism of the bradycardia and to improve pacing in cases progressing to permanent complete atrioven tricular block.