By Robert M A van der Boon
With its 10-year anniversary and exceeding 50,000 implantations worldwide, transcatheter aortic valve implantation (TAVI) has proven to be a viable and safe treatment strategy for patients with severe aortic stenosis and high operative risk. However, with the prospect of treating younger or less sick patients, a number of vexing issues remain.
The frequent occurrence of new-onset left bundle branch block (LBBB), high degree atrioventricular block (HDAVB; second [AV2B] and third degree [AV3B]) and subsequent permanent pacemaker implantation (PPI) have been demonstrated in several observational studies, especially following the implantation of the Medtronic CoreValve system. The radial force of this self-expandable bioprosthesis, exerted on the surrounding tissue of the left ventricular outflow tract may provoke conduction abnormalities after TAVI. Various patient- and procedure-related factors have been associated with these conduction abnormalities such as depth of implantation and pre-existing conduction defects. Although prior studies focused on assessing the possible predictors of conduction abnormalities, recent data suggest that conduction abnormalities may resolve over time. The possibility that conduction abnormalities may resolve early or late after TAVI puts the clinical implications of permanent pacemaker implantation after TAVI in a different perspective.
Between November 2005 and February 2011, 167 with symptomatic aortic valve stenosis and no previous permanent pacemaker implantation underwent TAVI with the CoreValve system in the Erasmus Medical Center, Rotterdam, The Netherlands. During the index hospitalisation, 36 patients (21.6%) underwent permanent pacemaker implantation of which the indications were HDAVB in 30 patients, bradycardia in five patients and non-sustained ventricular tachycardia (AICD) in one patient. Pacemaker dependency at follow-up was prospectively documented in all patients who underwent a permanent pacemaker implantation during the index hospitalisation by comprehensive pacemaker interrogation (median follow-up of 11.5 months) at the outpatient clinic visit. In case of a paced rhythm, the pacemaker was temporarily switched off or programmed to a slow rate VVI modus to assess underlying electrical activity. Patients were considered pacemaker dependent if a HDAVB or a slow (<30bpm) or absent ventricular escape rhythm was observed. Of the 30 patients who received a pacemaker because of a HDAVB, 11 had a complete resolution of the conduction abnormality whereas five had a partial resolution (first degree atrioventricular block [AV1B] at follow-up) while the remaining 14 patients still had an AV3B and were pacemaker dependent. Overall, 20 out of the 36 patients (55.6%) who received a new pacemaker following TAVI were pacemaker independent at their follow-up visit. Despite being from a single center observational study, with a restrictive use of new permanent pacemaker implantation and the assessment of pacemaker dependency at one single point during follow-up, these findings suggest recovery of high degree conduction abnormalities in a significant number of patients.
If true, patients with a transient conduction abnormality should be carefully distinguished from those with a permanent defect. Larger dedicated studies are needed to obtain more information on the true frequency and degree of recovery of the conduction abnormalities, at what time after TAVI it occurs and whether it is permanent or transient. Elucidation of these factors could help in the decision whether a patient with a new conduction abnormality after TAVI should undergo permanent pacemaker implantation. For now, it seems more reasonable to adjust permanent pacemaker algorithms to stimulate intrinsic conduction and ventricular activation. This may require more intense pacemaker follow up and more liberal and patient tailored adjustments.
Robert M A van der Boon is with the Erasmus Medical Center, Rotterdam, The Netherlands. His mentor is Peter P T de Jaegere