Where should an implantable ECG event recorder be placed?

Aim of our study was the comparison of bipolar ECG quality (with a 4 cm lea d distance) at different sites within the anterior thorax to find the prefe rable implantation site for an ECG event recorder (ECG-ER). In 70 patients a bipolar ECG with a short electrode distance and in the ver tical position was registered at the following sites: left and right subcla vicular, left and right parasternal (4th-5th ICR), left and right anterior axillar (4th-5th ICR), at the heart apex and subxiphoidal. Then it was comp ared to the standard lead II. In 34 patients, an additional comparison betw een vertical and horizontal ECG registration was performed at the above men tioned sites. During implantation of an ECG-ER in 5 patients, ECG signals were compared w ith electrodes placed towards the skin or towards the muscle. The best ECG quality (greatest QRS amplitude, visible P-wave and pacemaker spike, measur able QT period and bundle-branch block) and the best agreement with standar d lead II was found in 67% left parasternal, significant less often (p<0.00 1) right parasternal (14.3%), left subclavicular (7.1%), apical (5.7%), and subxiphoidal (4.3%). In a vertical electrode position a significantly higher QRS amplitude and a more often visible P wave was found in comparison to a horizontal electrod e position. In all cases, there was good agreement between bipolar surface ECG at the implantation site and ECG-ER stored signals. When the ECG-ER is positioned with electrodes towards the muscle, significant noise-signal occ urred in all 5 patients. Only in 3 patients was a P wave visible, but with a slightly greater QRS amplitude than in ECG-ERs positioned with electrodes towards the skin. From these results, it is recommended to implant ECC-ERs vertically with el ectrodes towards the skin and in the parasternal position.