Changes in QRS Complex During PTCA: Comparison of Vectorcardiographic and Topographic Presentation of Orthogonal ECG

Ljuba Bacharova^a, Anton Mateasik^a, Stanislav Katina^a, Milan Horacek^b,
Henrik Engblom^c, Galen S. Wagner^d

^aInternational Laser Centre, Bratislava, Slovak Republic
^bDalhousie University, Halifax, Nova Scotia, Canada
^cLund University Hospital, Lund, Sweden
^dDuke University Medical Center, Durham, NC, USA

Correspondence: L Bacharova, International Laser Centre, Ilkovicova 3, 812 19 Bratislava, Slovak Republic.
E-mail: bacharova@ilc.sk, phone +421.2.654 21 575, fax +421.2.654 23 244

1.  Introduction

Percutaneous transluminal coronary angioplasty (PTCA) produces ischemia that is controlled and reproducible, therefore it can serve as an appropriate model to study electrocardiographic changes due to transient regional ischemia of known locations. While during repolarization both changes in morphology and duration of ST-T have been reported, during depolarization mostly changes in time intervals, i.e. changes in QTc or QRS prolongation, have been observed. The aim of this study was to compare the ability of vectorcardiographic (VCG) and topographic presentations (DECARTO - Dipolar ElectroCArdioTOpography) of orthogonal ECG to detect and visualize subtle changes in the QRS complex during the transient ischemia due to balloon inflation of elective PTCA.

2.  Material and Methods

Study population consisted of 202 ECGs registered in patients with single-vessel coronary artery disease, located in: a) left anterior descending coronary artery (LAD), n = 76; b) right coronary arthery (RCA), n = 77; c) left circumflex coronary artery (LCx), n = 49.

Frank orthogonal ECGs were extracted from body-surface potential mapping data recorded at Dalhousie University prior to and during the balloon inflation during PTCA in 93 patients [Horacek et al. 2001]. The following VCG parameters were analyzed: X, Y, Z coordinates of instantaneous QRS vectors and the QRS spatial vector magnitude (QRSmax) at 10 ms intervals from the onset of QRS complex.

Orthogonal ECGs were transformed by means of a mathematical model DECARTO [Titomir and Ruttkay-Nedecky 1987], and presented as instantaneous maps of activated areas at 10 ms intervals from the onset of QRS (decartograms) in a form of a rectangle (a matrix of 11 lines, 24 columns). For each point of this matrix the value of relative frequency (probability) of its occurrence in the activated state was calculated in three subgroups of patients according to the occlusion sites.

The matrices before and during the balloon inflation in subgroups of patients were compared using the paired modification of Kolmogorov-Smirnov goodness-of-fit test to compare cumulative distribution fraction of differences and vector of null difference, and the test for differences between population proportions for each point of the matrix. Vectorcardiographic data were tested using paired t-test.

3.  Results

No significant difference was found in VCG parameters under study before and during the peak balloon inflation. The results of statistical analysis of decartograms using the paired modification of Kolmogorov-Smirnov test showed significant differences before and during balloon inflation in all time intervals in all subgroups of patients (p<0.001). The results of statistical analyses of decartograms using the test for differences between population proportions are presented in Table 1.

Table 4.    Results of the test for differences between population proportions. Values represent ratios of nonsignificant to significant intervals (a = 0.01). LAD: left anterior descending coronary artery, LCX: left circumflex coronary artery, RCA: right coronary artery, (s): significant.

4.  Discussion

This study showed that the derived information obtained by the DECARTO model is more sensitive for the detection of subtle changes in QRS complex during PTCA as compared to the primary information of its X, Y, and Z components. However, the significant difference observed in decartograms could be also influenced by the degree of discretisation of the image surface (24 to 11 points matrix, what represented a step of 15 degrees of azimuth and elevation, respectively), and by the statistical methods used in this study.

Acknowledgements

This study was supported, in part, by the grant 1/0509/03 from The Science Grant Agency (VEGA), Slovak Republic.

References

Titomir LI, Ruttkay-Nedecky I. Chronotopocardiography: A new method for presentation of orthogonal electrocardiograms and vectorcardiograms. Int J Bio-Medical Computing, 20: 275 - 282, 1987.

Horacek M, Warren JW, Penney CJ, Macleod RS, Title LM, Gardner MJ, Feldman ChL: Optimal electrocardiographic leads for detecting acute myocardial ischemia. J Electrocardiol, 34 (Suppl.) : 97-111, 2001.