Abstract

Objective: To investigate ventricular sympathetic innervation in patients with sick sinus syndrome and to detect regional deterioration of adrenergic innervation caused by asynchronous ventricular activation from right ventricular pacing.

Design: Prospective controlled study.

Setting: Tertiary cardiac referral centre.

Patients: 22 patients with sick sinus syndrome and indications for permanent dual chamber pacing; 20 healthy individuals as controls.

Interventions: All patients underwent myocardial imaging with planar and single photon emission computed tomography (SPECT) after an intravenous infusion of 5 mCi ¹²³I-meta-iodobenzylguanidine (¹²³I-MIBG) before and after pacemaker implantation. A SPECT thallium²⁰¹ myocardial study was done during the same week as the ¹²³I-MIBG study in all patients.

Main outcome measures: The heart to mediastinum (H/M) ratio and washout rate were calculated during the ¹²³I-MIBG study to assess the global cardiac sympathetic activity; the aim of the SPECT study was to investigate the regional distribution of adrenergic innervation.

Results: The H/M ratio was significantly smaller in the patients with sick sinus syndrome than in the controls (p < 0.001). In sick sinus syndrome there were regional adrenergic innervation defects, mostly in the inferior and apical walls. After a medium term pacing period, a redistribution of ¹²³I-MIBG uptake was detected, with deterioration of adrenergic innervation in the inferior, apical, and posterior walls. The thallium²⁰¹ myocardial perfusion study showed no change after three months of permanent pacing.

Conclusions: Patients with sick sinus syndrome have global and regional disturbances of the adrenergic innervation of the left ventricular myocardium. These seem to deteriorate as a result of asynchronous electrical activation. The clinical significance of this finding requires further investigation.