Advances in measurement technology and wireless signal transfer have enabled the design of new, smaller and portable—even plaster-like—electrocardiographic (ECG) measurement devices that enable patient monitoring at home or in emergency situations. The development of new, miniaturized biomedical sensors has opened up possibilities for their application, but also set new demands on signal analysis and interpretation. In particular, the new small wireless systems often utilize bipolar electrodes that have a shorter interelectrode distance (IED) and different electrode locations from those of the standard 12-lead system. This affects the quality and the information content of the signal. The general objective of this thesis was to evaluate the performance of short IED precordial bipolar ECG leads and to determine their optimal location.
This thesis adopted three methods to assess the properties of new bipolar precordial ECG leads: modeling, body surface potential map (BSPM) data, and exercise ECG data. First, two realistic, three-dimensional (3D) thorax models and lead field analysis were used to evaluate whether modeling of the measuring sensitivity of ECG leads could be used as a tool for designing new ECG leads. Second, BSPM data was used to study whether short-distance bipolar leads (IED approximately 6 cm) provide an ECG signal that is adequate for clinical utilization. Third, BSPM data was used to define where a bipolar ECG lead should be located in order to maximize the ECG signal strength within healthy subjects. Finally, the value of bipolar leads for diagnosing two major cardiac conditions—left ventricular hypertrophy (LVH) and coronary artery disease (CAD)—was assessed.
It was found that the modeled measuring sensitivity corresponds to the changes in actual ECG signal strength, so modeling can be useful, especially in cases where in vivo measurements are impossible such as in designing implantable applications. Based on ECG data from 236 healthy subjects, all studied bipolar ECG leads with a short IED (approximately 6 cm) provided a detectable signal when compared to a low noise level of 15 μV and considering the P-wave as the smallest parameter. The optimal location of the bipolar lead was diagonally near the chest electrodes of the standard precordial leads V2, V3, and V4 (to maximize QRS amplitude), or above the chest electrodes of leads V1 and V2 (to maximize P-wave amplitude). In the selected clinical applications, LVH and CAD, the performance of bipolar leads was surprisingly good. In differentiating LVH (n=305) and healthy subjects (n=236), the performance of a correctly positioned small bipolar lead was similar to that of the traditional Sokolow-Lyon method. When differentiating CAD (n=255) patients from non-CAD (n=126) or low-likelihood of CAD (n=198) subjects, the overall performance of bipolar lead CM5 corresponded to that of standard lead V5.
These results indicate that short IED bipolar leads provide a signal that is adequate for clinical use. Furthermore, the performance of these leads was shown to be similar or even superior to that of the commonly used standard leads. It can be concluded that when correctly positioned, short IED bipolar leads are useful and can give additional value for clinical diagnostics. These results provide promising information on the applicability and potential of short IED bipolar ECG leads, and demonstrate that they are worth developing further
