Susceptibility for ventricular tachycardia and the correlation between depolarization and orthogonal components of repolarization.ABSTRACT
Objective: There is a continuing need of methods to identify subgroups of patients at high risk of ventricular arrhythmias, in particular after myocardial infarction myocardial infarction: see under infarction. (MI).
Methods: We performed a singular value decomposition In linear algebra, the singular value decomposition (SVD) is an important factorization of a rectangular real or complex matrix, with several applications in signal processing and statistics. of repolarization repolarization /re·po·lar·iza·tion/ (re-po?ler-i-za´shun) the reestablishment of polarity, especially the return of cell membrane potential to resting potential after depolarization. potentials in individual recordings in 134 healthy males, in 203 males with old MI and without documented sustained ventricular tachycardia (VT) and in 104 MI males with documented VT. We considered the absolute correlation coefficient between the first orthogonal component, constructed by matrix multiplication of the first left and right singular vectors and the QRS QRS
A pattern seen in an electrocardiogram that indicates the pulses in a heart beat and their duration. Variations from a normal QRS pattern indicate heart disease.
Mentioned in: Bundle Branch Block integral (RT1) and a similar index for the second component (RT2).
Results: Abnormally high (more than two standard deviations above the mean) value of the RT1 had a 89% specificity for VT in MI patients. Abnormally low RT2 had specificity of 87%. Both indices combined had a 97% specificity. However, sensitivity of the combined indices was only 13%.
Conclusion: Abnormalities in the correlation of orthogonal components of repolarization with depolarization depolarization /de·po·lar·iza·tion/ (de-po?lahr-i-za´shun)
1. the process or act of neutralizing polarity.
2. in electrophysiology, reversal of the resting potential in excitable cell membranes when stimulated. are highly specific for a small group of patients with old myocardial infarction at high risk of ventricular tachycardia. (Anadolu Kardiyol Derg 2007: 7 Suppl 1; 139-41)
Key words: ventricular tachycardia, repolarization, depolarization, orthogonal component of repolarization
The implantable cardioverter defibrillator defibrillator, device that delivers an electrical shock to the heart in order to stop certain forms of rapid heart rhythm disturbances (arrhythmias). The shock changes a fibrillation to an organized rhythm or changes a very rapid and ineffective cardiac rhythm to a (ICD ICD International Classification of Diseases (of the World Health Organization); intrauterine contraceptive device.
abbr. ) trials have highlighted the need for methods with better specificity for patients at the highest risk of ventricular arrhythmias, who would mostly benefit from an ICD (1).
Even specific arrhythmias, such as ventricular tachycardia (VT) can be produced through a variety of mechanisms (2), thus most arrhythmogenic markers may only select a small fraction of the patients at risk. Progress in this field may turn out to consist of numerous markers, obtained with a variety of investigational methods, each of them specific for a limited subgroup of patients.
A pathological substrate associated with arrhythmogenicity is abnormally heterogenous (spelling) heterogenous - It's spelled heterogeneous. ventricular repolarization. As the relative distribution of potentials on the body surface during repolarization is largely constant in time, changing mostly in the general amplitude, subtle abnormalities of repolarization, as deviations from this normal feature (7), have been described using a singular value decomposition of the series of instantaneous repolarization potentials over the ST-T interval in a single cardiac cycle.
In normal subjects, the first component corresponds to the general repolarization pattern. An abnormal reduction in its contribution to repolarization potentials, measured by the magnitude of the first singular value relative to the sum of singular values, has been associated with arrhythmogenicity in a variety of pathological contexts (3-5).
However, even when a major component is present, it might reflect a different electrophysiological phenomenon in different individuals. This might lead to a reduction of specificity.
We are trying to better understand this phenomenon and perhaps find ways to avoid the loss of specificity in indices based on singular value decomposition of repolarization potentials in individual recording. To this end, we reconstructed individual components by multiplying the left, right singular vector and the singular value of each component. Thus, we obtained orthogonal components, the sum of which, lead by lead and sample by sample correspond to the original electrocardiogram electrocardiogram /elec·tro·car·dio·gram/ (-kahr´de-o-gram?) a graphic tracing of the variations in electrical potential caused by the excitation of the heart muscle and detected at the body surface. (ECG ECG electrocardiogram.
Also called an electrocardiogram, it records the electrical activity of the heart. ). Orthogonal components have each a strictly constant relative distribution of body surface potentials, that only changes in amplitude over the STT STT State Street Corporation (stock symbol)
STT Suomen Tietotoimisto (Finnish National News Agency)
STT Secure Transaction Technology
STT Surface Tension Transfer (welding) , and the relative distributions of any two components are orthogonal.
We then examined these signals, and in particular their relationship with depolarization potentials. We found that even in normal subjects there is considerable variability, for example in some subjects the second component being almost identical to depolarization pattern, while in others the first component is more like depolarization. There is a continuous spectrum of cases between the two and there is also a substantial proportion of cases (20%) that is outside of this spectrum (6).
In this study, we attempted to further explore the relationship of depolarization to orthogonal components of repolarization in patients with previous MI, with and without recent history of sustained ventricular tachycardia on Holter recordings.
We used ECG body surface map recordings, obtained at the Dalhousie University, in 134 healthy males and in 307 males with MI, of whom 104 had a recent history of sustained VT and electrophysiological study of inducibility of VT. We used a single cardiac cycle, averaged from 15-second recordings.
After singular value decomposition of the leads x time matrix of ST-T potentials in each recording we multiplied the set of the first left and right vectors and singular value to obtain the first orthogonal component (OC) T1, and the second set for T2. Orthogonal components are leads x time matrices of volt values like the ECG.
We noted as RT1 and RT2 the absolute values of the correlation coefficients between the QRS integral and T1 and T2 respectively.
The first orthogonal component of repolarization was in general more closely correlated with depolarization potentials in MI patients with VT compared with MI patients without VT (Table 1). The correlation of the second component with the QRS was significantly lower in VT patients compared with the non-VT group.
Recordings in MI patients were mostly concentrated in an arc in the RT1/RT2 plane, that extended at a distance from 0.8 to 1.0 from the origin (Fig. 1), a feature shared with the distribution of recordings in healthy subjects, as we have shown in a previous study (6). Despite the significant differences mentioned above, there was a substantial overlap of the distribution of recordings of MI+VT, MI-VT patients and the healthy, except for the region of abnormally high RT1 and low RT2 (lower right corner on the Figure 1) where some MI+VT cases appear concentrated.
[FIGURE 1 OMITTED]
In order to estimate the diagnostic power of these abnormalities we chose the lowest 2.5 centile Noun 1. centile - (statistics) any of the 99 numbered points that divide an ordered set of scores into 100 parts each of which contains one-hundredth of the total
percentile of RT2 (0.17) and highest 2.5 centile of RT1 (0.86) from the healthy males group as normal limits and used them as cutoff values. Either or both identified arrhythmia arrhythmia (ārĭth`mēə), disturbance in the rate or rhythm of the heartbeat. Various arrhythmias can be symptoms of serious heart disorders; however, they are usually of no medical significance except in the presence of susceptibility with a high specificity (Table 2).
In this study we found that there is a substantial proportion of the post-MI patients with recent VT history for whom the first orthogonal component of repolarization potentials is highly correlated with the QRS integral while the second orthogonal component is uncorrelated.
Our MI+VT and MI-VT samples have been separately drawn from their respective populations. Application of these indices in other populations will result in different predictive values, depending on the a priori prevalence of the MI+VT cases. A lower prevalence (8) would result in lower positive and higher negative predictive value The negative predictive value is the proportion of patients with negative test results who are correctly diagnosed. Worked example
(as determined by "Gold standard")
True False . Thus, there is substantial scope for supplementary reduction of false negatives. Further elucidation of the mechanism underlying the normal and pathological variability of the orthogonal components will be necessary for this purpose.
A limitation of our study is the lack of assessment of the independence of these indices from other indices of arrhythmogenic risk (such as heart rate variability Heart rate variability (HRV) is a measure of variations in the heart rate. It is usually calculated by analysing the time series of beat-to-beat intervals from ECG or arterial pressure tracings. or ejection fraction of the left ventricle) which was due to lack of data.
Abnormalities in the correlation of orthogonal components of repolarization with depolarization are highly specific for a small group of patients with old myocardial infarction at high risk of ventricular tachycardia.
(1.) ACC/AHA/ESC 2006 Guidelines for management of patients with ventricular arrhythmias and prevention of sudden cardiac death-executive summary. Eur Heart J 2006; 27: 2099-140.
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hibernating myocardium see myocardial hibernation, under . In: Zipes DP, Jalife J, editors. Cardiac Electrophysiology. From Cell to Bedside. 3rd ed. Philadelphia: W.B. Saunders Co; 2000. p. 405-14.
(3.) De Ambroggi L, Negroni
(4.) De Ambroggi L, Aime, E, Ceriotti C, Rovida M, Negroni S. Mapping of ventricular repolarization potentials in patients with arrhythmogenic right ventricular dysplasia arrhythmogenic right ventricular dysplasia Right ventricular dysplasia, see there . Principal component analysis of the ST-T waves. Circulation 1997; 96: 4314-8.
(5.) Corlan AD, Horacek BM, De Ambroggi L. Prognostic value for ventricular tachycardia of indices of ventricular repolarization in patients with and without myocardial infarction. Folia fo·li·a
Plural of folium. cardiologica 2005; 12 (Suppl D): 209-11.
(6.) Corlan AD, De Ambroggi L. Orthogonal components of the body surface repolarization map and the depolarization pattern (Abstract). In: Proceedings 33rd International Congress on Electrocardiology; 2006 June 28-July 1; Cologne, Germany; Dusseldorf, Koln: German Medical Science; 2007. Available at: URL URL
in full Uniform Resource Locator
Address of a resource on the Internet. The resource can be any type of file stored on a server, such as a Web page, a text file, a graphics file, or an application program. :http://www.egms.de/en/ meetings/ice2006/06ice104.shtml
(7.) Corlan AD, De Ambroggi L. New quantitative methods of ventricular repolarization analysis in patients with left ventricular hypertrophy left ventricular hypertrophy Cardiology Enlargement of the left ventricle often linked to the prolonged hemodynamic stress of CHF, characterized by myocardial cell hypertrophy, ↑ left ventricular wall thickness, ↓ ventricular compliance, ↑ . Ital Ital Italian (linguistics)
ITAL Instituto de Tecnologia de Alimentos (Food Technology Institute; Brazil)
ITAL Information Technology And Libraries Heart J 2000; 1: 542-8.
(8.) Mukharji J, Rude RE, Poole WK, Gustafson N, Thomas LJ Jr, Strauss HW, et al. Risk factors for sudden death after acute myocardial infarction acute myocardial infarction (·kyōōtˑ mī·ō·karˑ·dē· : two-year follow-up. Am J Cardiol 1984; 54: 31-6.
Alexandru Dan Corlan, Milan Horacek*, Luigi De Ambroggi ** University Emergency Hospital of Bucharest, Romania
* Dalhousie University, Halifax, Nova Scotia For other uses, see Halifax.
Halifax, Nova Scotia may refer to any of the following:
** IRCCS IRCCS Istituto Di Ricovero e Cura a Carattere Scientifico (Italian Research Hospital) Policlinico San Donato, University of Milan The university is a member of the League of European Research Universities.
Throughout Milan, the University is normally known as Statale to avoid confusion with other academic institutions in the city. , Italy
Address for Correspodence: Alexandru-Dan Corlan, MD, Phd, Cardiology Research Unit, University Hospital of Bucharest, 169 Spl. Independentei, 0600698 Bucharest 6 E-mail: firstname.lastname@example.org-Web: http://ecardio.puncht.info
Table 1. Absolute correlation coefficients, lead by lead, between integrals of each of the first two orthogonal components of repolarization (T1, T2) and the QRS integral Healthy MI+VT N 134 104 RT1 0.40 [+ or -] 0.23 0.61 [+ or -] 0.29 RT2 0.72 [+ or -] 0.20 0.39 [+ or -] 0.27 p MI-VT (MI+VT vs MI-VT) N 203 -- RT1 0.47 [+ or -] 0.28 <0.0001 RT2 0.53 [+ or -] 0.27 <0.0001 Data are presented as Mean [+ or -] standard deviation MI--myocardial infarction, RT--orthogonal component of repolarization and the QRS integral, VT--ventricular tachycardia Table 2. Specificity, sensitivity, positive and negative predictive values of RT1 and RT2 beyond normal 95% confidence interval limits, for associated sustained ventricular tachycardia in males with old myocardial infarction Specificity Sensitivity PPV NPV RT1>0.86 MI +VT vs VT 89% 28% 57% 71% RT2<0.17 MI +VT vs -VT 87% 25% 49% 69% RT1>0.86 and RT2<0.17 97% 13% 68% 65% MI--myocardial infarction, NPV--negative predictive value, PPV--positive predictive value, RT--orthogonal component of repolarization and the QRS integral, VT--ventricular tachycardia