Experimental and laboratory report

An orthogonal lead system for clinical electrocardiography☆

Vectorcardiography is an alternative form of ECG for measuring electrical activity of the heart. It achieves higher sensitivity and provides the cardiologist additional information that can contribute to early diagnosis. This study is focused on proposal of a methodology for the processing of directly measured and transformed VCG records by using Kors regression transformation. A total 16 VCG features were extracted, while 12 features showed relevant information based on the statistical analysis and the method of maximum relevance minimum redundancy. These features served as input to the LDA and decision trees classifiers, while LDA achieved the most accurate results with accuracy 91.5%, specificity 76.3% and sensitivity 94.8% for directly measured VCG and accuracy 90.9%, specificity 76.3% and sensitivity 94.0% for transformed VCG. We conclude that this proposed methodology and the results obtained from it can be beneficial for the early diagnosis of myocardial infarction within the framework of automated detection.

Vectorcardiography (VCG) as an alternative form of 12-lead ECG is another method of measuring the electrical activity of the heart. The use of vectorcardiography in clinical practice is not common, but VCG leads can be derived from 12-lead ECG. VCG has proven to be a useful and more accurate tool for diagnosing various heart diseases within automated detection. This paper presents the application of four transformation methods namely: Kors regression, IDT, QLSV and Quasi-Orthogonal transformation to obtain a derived VCG. A total of 20 physiological and 20 records with the diagnosis of myocardial infarction were used. For physiological records, the Kors regression method achieved the best results in leads X and Y with relative deviation $<$1%, correlation and percentage similarity $>$99%. In lead Z, the QLSV method achieved the most accurate results with relative deviation $<$1%, correlation $>$98% and percentage similarity $>$99%. For pathological records, the most accurate method in all leads was Kors regression with relative deviation $<$2.2%, correlation $>$93% and percentage similarity $>$97%. From these results, there is the possibility of creating a new transformation method from the existing ones in order to obtain a more accurate transformation.

The purpose of this study was to develop optimal configuration of adhesive ECG patches placement on the torso, which would provide the best agreement with the Frank orthogonal ECGs. Ten seconds of orthogonal ECG followed by 3–5 min of ECGs using patches at 5 different locations simultaneously on the torso were recorded in 50 participants at rest in sitting position. Median beat was generated for each ECG and 3 patch ECGs that best correlate with orthogonal ECGs were selected for each participant. For agreement analysis, spatial QRS-T angle, spatial QRS and T vector characteristics, spatial ventricular gradient, roundness, thickness and planarity of vectorcardiographic (VCG) loops were measured. Key VCG parameters showed high agreement in Bland–Altman analysis (spatial QRS-T angle on 3-patch ECG vs. Frank ECG bias 0.3 (95% limits of agreement [−6.23;5.71 degrees]), Lin's concordance coefficient = 0.996). In conclusion, newly developed orthogonal 3-patch ECG can be used for long-term VCG monitoring.

In the course of time, electrocardiography has assumed several modalities with varying electrode numbers, electrode positions and lead systems. 12-lead electrocardiography and 3-lead vectorcardiography have become particularly popular. These modalities developed in parallel through the mid-twentieth century. In the same time interval, the physical concepts underlying electrocardiography were defined and worked out. In particular, the vector concept (heart vector, lead vector, volume conductor) appeared to be essential to understanding the manifestations of electrical heart activity, both in the 12-lead electrocardiogram (ECG) and in the 3-lead vectorcardiogram (VCG). Not universally appreciated in the clinic, the vectorcardiogram, and with it the vector concept, went out of use. A revival of vectorcardiography started in the 90’s, when VCGs were mathematically synthesized from standard 12-lead ECGs. This facilitated combined electrocardiography and vectorcardiography without the need for a special recording system.

This paper gives an overview of these historical developments, elaborates on the vector concept and seeks to define where VCG analysis/interpretation can add diagnostic/prognostic value to conventional 12-lead ECG analysis.

Vectorcardiography (VCG), as an alternative to standard 12-lead electrocardiography (ECG), represents the electrical activity of the heart. Previous studies on VCG document that VCG criteria for the diagnosis of, for example, myocardial infarction (MI), ventricular hypertrophy and ischemic diseases, are superior to the corresponding 12-lead ECG criteria. Its use in clinical practice is not common because it requires the placement of additional electrodes. However, VCG leads can be derived from standard ECG by using mathematical transformations.

This paper reviews the published works on transformation techniques for derivation VCG from 12-lead ECG, their historical evolution and their importance in today's clinical practice. Different kinds of criteria for evaluation accuracy of transformations are briefly described and the accuracy of individual techniques discussed.

Einthoven not only designed a high quality instrument, the string galvanometer, for recording the ECG, he also shaped the conceptual framework to understand it. He reduced the body to an equilateral triangle and the cardiac electric activity to a dipole, represented by an arrow (i.e. a vector) in the triangle's center. Up to the present day the interpretation of the ECG is based on the model of a dipole vector being projected on the various leads. The model is practical but intuitive, not physically founded. Burger analysed the relation between heart vector and leads according to the principles of physics. It then follows that an ECG lead must be treated as a vector (lead vector) and that the lead voltage is not simply proportional to the projection of the vector on the lead, but must be multiplied by the value (length) of the lead vector, the lead strength. Anatomical lead axis and electrical lead axis are different entities and the anatomical body space must be distinguished from electrical space. Appreciation of these underlying physical principles should contribute to a better understanding of the ECG. The development of these principles by Burger is described, together with some personal notes and a sketch of the personality of this pioneer of medical physics.