How can we identify the best implantation site for an ECG event recorder?

The aim of this study was to show how to find the preferable implantation s ite for an ECG event recorder (ECG-ER). We compared the quality of bipolar ECG recordings (4-cm electrode distance, vertical position) in 65 patients at the following sites: left and right subclavicular, left and right anteri or axillary line (4(th)-5(th) interspace), left and right of the sternum (4 (th)-5(th) interspace), heart apex, and subxyphoidal. The results were comp ared to the standard ECG lead II. In 30 patients, an additional comparison between vertical and horizontal ECG registrations was done using the same s ites. ECG signals in five patients were compared positioning the electrodes towards the skin with turning them towards the muscle during ECG-ER implan tation. The best ECG quality (defined as highest QRS amplitude, best visibl e P wave and/or pacemaker spike, best measurable QRS duration, and QT inter val) and best agreement with the standard lead II was found in 68% on the l eft of the sternum, significantly less often (P < 0.001) on the right of th e sternum (14.1%), left subclavicular (6.9%), apical (5.5%) and subxyphoida l (4.2%). A significantly higher QRS amplitude tvas measured and the P wave was more often visible in the vertical electrode position than in the hori zontal position. In all five ECG-ER patients, there was a good agreement be tween the bipolar surface ECG at the implantation site and ECG-ER stored si gnals. A significant noise signal occurred in all five patients when the-EC G-ER was implanted with electrodes towards the muscle. A P wave was visible in only three of those patients, but there was an insignificantly higher Q RS amplitude than in ECG-ERs implanted with electrodes towards the skin. Fr om these results, it can be concluded that the best implantation site for a n ECG-ER is right or left of the sternum, positioning the electrodes vertic ally and towards the skin.