Effects of asynchronous ventricular activation on myocardial adrenergic innervation in patients with permanent dual-chamber pacemakers; an I(123)-metaiodobenzylguanidine cardiac scintigraphic study

Aims: To evaluate myocardial sympathetic innervation abnormalities in patients with DDD pacemakers for complete heart block.

Methods: We studied 39 patients, chronically paced in DDD mode because of complete atrioventricular block. Twenty-three healthy individuals served as a control group. All patients underwent planar and single-photon emission computed tomography (SPECT) myocardial imaging 4 h after intravenous infusion of 185 MBq I(123)-MIBG. The heart to mediastinum ratio was calculated to quantify cardiac I(123)-MIBG accumulation, while the SPECT study was performed to investigate the regional distribution of adrenergic innervation. All patients underwent a SPECT thallium(201)myocardial study during the same week as the I(123)-MIBG study.

Results: The heart to mediastinum ratio was significantly smaller in paced patients than in the controls (P<0.001). 89.7% of paced patients had regional abnormalities of I(123)-MIBG uptake, mainly in the inferior (92.3%) and apical (38.5%) wall. 46.2% of paced patients had regional perfusion defects, also mainly in the inferior (46.2%) and apical (10.3%) wall. Neither the I(123)-MIBG abnormalities nor the perfusion defects were related to the duration of pacing.

Conclusions: Stimulation from the apex of the right ventricle leads to regional disturbances of the adrenergic innervation of the left ventricular myocardium, as assessed by I(123)-MIBG activity.