The synthesized vectorcardiogram resembles the measured vectorcardiogram in patients with dyssynchronous heart failure
Introduction
With the use of vectorcardiography (VCG), the size and direction of the electrical forces generated by the heart are recorded and displayed in three dimensions. The VCG consists of three orthonormal leads X, Y, and Z, containing phase information between these leads. This technique was first described 101 years ago by Williams [1]. The VCG technique was almost abandoned and the 12-lead electrocardiogram (ECG) became the clinical standard, because of the need for special VCG recording equipment, the lack of a standard VCG-lead system [2], [3], [4], the impracticality of a back electrode in many of these systems, and the complexity to interpret the different loop morphologies for diagnosis [5], [6]. The interest in the diagnostic value of the VCG has, however, never completely subsided and with today's computer technology the vector loops can be synthesized from the 12-lead ECG resulting in a revival of the VCG.
Several systems of three orthonormal leads have been described for recording the VCG, though the most commonly used one is the 8-electrode system according to Frank [4]. Due to limited availability of Frank-VCG recording systems, the VCG is commonly synthesized from the 12-lead ECG. This is achieved by multiplying 8 independent ECG leads (two limb leads and all six precordial leads) by a matrix. Recent studies demonstrated that the Kors-derived VCG results in the best approximation of the Frank-VCG [5], [7], [8], [9].
The matrix proposed by Kors et al. is based on a learning set from the Common Standards for Electrocardiography (CSE) multilead library, including both patients and healthy individuals, and was generated by multiple linear regression [8]. Although the Kors-VCG nicely resembles the Frank-VCG in previous studies [5], [7], [8], [9], a comparison has never been made for patients with heart failure and a left ventricular (LV) conduction delay, mostly due to left bundle branch block (LBBB). These patients are commonly treated with cardiac resynchronization therapy (CRT). CRT has been shown to improve cardiac pump function, heart failure symptoms, quality of life, and survival [10]. Although the effects of CRT in large clinical trials are impressive on a group level, the benefits in individuals vary considerably; the non-response rate to this therapy is still 30–50% [11]. To reduce the risk of complications and the unnecessary use of expensive products, patient selection should be improved. Recent studies have shown that the VCG could play an important role in the selection of patients for CRT [12], [13] or in the optimization of the CRT settings [14]. Therefore, the current study aims to compare the Frank-VCG and the Kors-VCG in patients with heart failure and LV conduction delay focusing on vectorcardiographic variables relevant to resynchronization of the ventricles.
Section snippets
Patient population
The patient population used in this study has been described previously [13]. It consisted of 138 consecutive patients with heart failure, who were scheduled for implantation of a CRT device at the Maastricht University Hospital between September 2010 and June 2012. Excluded were patients with an intrinsic QRS duration < 120 ms (n = 13) or previous RV pacing during either the VCG (n = 22) or ECG recording (n = 2). Another 9 patients were excluded due to technical disturbances, multiple ectopic beats or
Patient characteristics
The baseline characteristics of the 92 patients are shown in Table 1. Most patients were male, had NYHA class II or III and LBBB according to the Strauss [17] criteria. In addition, half of the patients had ischemic heart failure etiology and a quarter had atrial fibrillation (AF). Furthermore, the patients had a reduced left ventricular ejection fraction (LVEF). These characteristics are typical for patients receiving CRT [18].
Frank-VCG versus Kors-VCG
Examples of the Frank-VCG and Kors-VCG are presented in Fig. 1.
Discussion
This study shows a good resemblance between the recorded Frank-VCG and the Kors-VCG in patients with left ventricular conduction abnormalities. Also variables calculated from the Frank-VCG and the Kors-VCG method showed good correspondence.
Conclusions
In patients with heart failure and LV conduction delay who are candidate for CRT, the Frank-VCG and the Kors-VCG show good resemblance. Furthermore, the Kors-VCG method avoids the need for special recording equipment, while the extra information from the VCG is still obtained. The Kors-VCG enables retrospective as well as prospective VCG analysis of routinely recorded 12-lead ECGs in studies related to CRT.
Disclosures
The customized software was developed in collaboration with Ortivus AB, Danderyd, Sweden and the recording equipment was a loan from the same source. F.W.P. has received research grants from Medtronic, Biological Delivery Systems (Johnson&Johnson), EBR Systems, MSD, and Proteus Biomedical and is advisor to St. Jude Medical. K.V. consults for Medtronic and received speaker's fees of St. Jude Medical. E.B.E, S.A., C.J.M.v.D, and L.W. have nothing to disclose.
Acknowledgments
This research was performed within the framework of CTMM (Center for Translational Molecular Medicine; www.ctmm.nl), Project COHFAR (Congestive Heart Failure and Arrhythmia; Grant 01C-203), and supported by the Dutch Heart Foundation.
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