I. Introduction

The fast improvement in microelectronic systems is having a large impact in the design of novel ambulatory electrocardiogram (ECG) monitoring devices. New advances in electronics allow more complex computational algorithms working in ultra low power consumption microprocessors [1]. Novel wearable systems extend the time of continuous monitoring from the 24-hours that was standardized about a decade ago to several days or even weeks. Ambulatory monitoring of the ECG has several clinical applications. It is widely used for the diagnosis of cardiac pathologies and in the assessment of therapy [2]. In addition, low cost ECG monitoring devices lead to other new non-clinical applications in sports and lifestyle. However, ECG recorded during daily activities have higher levels of noise as compared to when measured at rest. Noise due to motion artifacts can corrupt the signal making its interpretation difficult.