An evaluation of planarity of the spatial QRS loop by three dimensional vectorcardiography: Its emergence and loss.

AIMS: To objectively characterize and mathematically justify the observation that vectorcardiographic QRS loops in normal individuals are more planar than those from patients with ST elevation myocardial infarction (STEMI). METHODS: Vectorcardiograms (VCGs) were constructed from three simultaneously recorded quasi-orthogonal leads, I, aVF and V2 (sampled at 1000 samples/s). The planarity of these QRS loops was determined by fitting a surface to each loop. Goodness of fit was expressed in numerical terms. RESULTS: 15 healthy individuals aged 35-65years (73% male) and 15 patients aged 45-70years (80% male) with diagnosed acute STEMI were recruited. The spatial-QRS loop was found to lie in a plane in normal controls. In STEMI patients, this planarity was lost. Calculation of goodness of fit supported these visual observations. CONCLUSIONS: The degree of planarity of the VCG loop can differentiate healthy individuals from patients with STEMI. This observation is compatible with our basic understanding of the electrophysiology of the human heart.

Geometry of the Poincaré plot can segregate the two arms of autonomic nervous system - A hypothesis.

Autonomic Nervous System (ANS) operates to achieve the optimum physiological functioning and maintains homeostasis in a tonic and continuous manner. Evaluation of ANS profile is crucial in assessing autonomic dysfunction. Conventional ANS evaluation procedures fail to capture minute dynamic alterations of ANS activities. The ANS output pattern is appropriately reflected in the fine alteration of the resting heart rate (HR). HR is a non-stationary variable, results from the dynamic interplay between the multiple physiologic mechanisms. The control of cardiac rate or the chronotropic regulation of heart is considered as a coupled network of oscillators, each representing a specific facet of the cardiovascular reflex. The slower vasomotor oscillation via sympathetic system is combined with rapid respiratory oscillation by parasympathetic system to modulate the intrinsic oscillation pattern of the SA Node. Heart Rate Variability (HRV) is used to understand the autonomic influence on cardiovascular system in health and disease. Fourier decomposition of HRV offers us mainly two different frequency components. High frequency (HF) variation indicates parasympathetic variability due to respiration and Low frequency (LF) mainly implicates tonic sympathetic influence, due to slower vasomotor modulation of heart rate. However, different studies show conflicting results and direct recording of sympathetic nerve activity also failed to correlate with LF power in either healthy subjects or in patients with increased cardiac sympathetic drive. A scatter-plot where each R-R interval is plotted against the preceding R-R interval forms a distributed elliptic point cloud in two dimensional plane. The phase space realization of this plot with dimension two and delay one is referred to as Poincaré plot analysis, an emerging quantitative-visual technique where the shape of the plot is categorized into different functional classes. The plot provides summary as well as detailed beat-to-beat information of the heart. This plot can be extended to three dimensions and with multi-lag, offering more insight and information. A mathematical expression was developed by an interventional study by Toichi et al., using pharmacological blockers during different physiological variables that calculated the lengths of transverse and longitudinal axes of the Poincaré plot to derive two quantitative expressions of sympathetic and vagal influence on HRV: 'cardiac sympathetic index' (CSI)) and 'cardiac vagal index' (CVI). In the present study, we emulate Poincaré plot patterns seen in normal range of sympatho-vagal balances and also in Diabetes Mellitus (DM), known to cause autonomic dysfunction. The emerging pattern of R-R interval time series would provide valuable insight into the altered temporal dynamics and also extract crucial features embedded within. DM is a major public health crisis globally and particularly in Indian population. We hypothesize that, CSI and CVI will effectively segregate the two arms of ANS and can be utilized as an effective evaluation tool to explore the disease status in patients of Diabetes Mellitus. We also propose that, the dynamics of fluctuations in physiological rhythms that exhibit long-term correlation and memory, can also be explored and expressed quantitatively by incorporating various degrees of 'lag' in these recurrence plots.

Spatial velocity of the dynamic vectorcardiographic loop provides crucial insight in ventricular dysfunction.

Vectorcardiogram (VCG) represents the trajectory of the tip of cardiac vectors in three dimensional space with varying time. It is a recurring, near-periodic pattern of cardiac dynamics that is constructed by drawing the instantaneous vectors from a zero reference point according to direction, magnitude and polarity in the space. Being a three dimensional entity, it is more informative and more sensitive than conventional ECG as an evaluation tool of the physiology of cardiac dynamics, because of its extra degree of freedom. Accordingly, it is possible to find out even a minute and early electrophysiological alteration in diseases. Each cardiac cycle primarily consists of three loops in VCG corresponding to P, QRS, and T wave activities. The morphological assessment of the QRS loop was carried out in three dimensional space in order to analyze the spatial vectors of the ventricles and their patho-physiological correlation in various cardiac diseases. Spatial Velocity (SV) is a virtual velocity that represents the rate of movement of the tip of the cardiac vector through space, coordinated by three orthogonal leads, and can be estimated by using simple mathematical formula. It is the rate of change in amplitude and the directionality of instantaneous vectors in seriatim in the three dimensional space to quantify their the temporo-spatial characteristic pattern. We propose to evaluate this novel VCG descriptor SV, in normal individuals and patients of ventricular dysfunction. The possible mechanisms consistent with the patho-physiological basis of ventricular dysfunction or heart failure with altered SV would enrich the current understanding of the disease. Heart failure is the final common pathway of multitude of cardiac pathologies. Despite etiological heterogeneity, there are common mechanisms involved in the complex electrophysiological alteration of the failing myocardium. The changes observed as a consequence of ventricular dysfunction involve ion channel remodeling, intercellular uncoupling, myocardial ischemia, alterations in calcium handling, remodeling of the extracellular matrix, the presence of scars, activation of the sympathetic & the renin-angiotensin-aldosterone system, dilatation as well as stretch of viscous etc. The source modulation of the depolarization wave and its propagation in the heart and body fluid volume conductor also influence the visual pattern of cardiac vectors. In addition, patients with heart failure receive pharmacological or non-pharmacological therapies that also influence the electrophysiological changes. We hypothesize that the spatial velocity of ventricular depolarization and repolarization vectors of the VCG loop alters with a characteristic pattern in the patients with ventricular dysfunction and can differentiate healthy individuals from patients with ventricular dysfunction and also differentiate various categories, gradations and severity stratifications of the patients with ventricular dysfunction.

Planarity of the spatial QRS loop of vectorcardiogram is a crucial diagnostic and prognostic parameter in acute myocardial infarction.

Vectorcardiogram (VCG) is a recurring, near-periodic pattern of cardiac dynamics that graphically represents the trajectory of the tip of cardiac vectors in three dimensional space with varying time. VCG is constructed by drawing the instantaneous vectors from a zero reference point according to direction, magnitude and polarity in the space. It is more informative and sensitive than conventional ECG as an evaluation tool of the physiology of cardiac dynamics. Each heart cycle consists of three loops corresponding to P, QRS, and T wave activities in VCG. The morphological assessment of the QRS loop was carried out in order to analyze the spatial vectors of the ventricles and their patho-physiological correlation in various cardiac diseases. It was found that, the three dimensional QRS loop in healthy individuals lies in a plane. It is rather surprising that the normal spatial QRS loop lies in a single plane, considering the complex structure of the ventricular musculature together with the numerous possible pathways along which the depolarization impulse passes. The highly curious phenomenon of planarity of the spatial QRS loop was explained by uniform double layer (UDL) theory, which postulates the phenomenon of activation wave-fronts that propagate with a constant & uniform rate throughout the myocardium. Acute myocardial infarction results in loss of structural and functional integrity of the different layers of heart, perturbation of the uniformity in wave propagation due to the disturbance in directional symmetry, development of nonlinear relationships among the concerned variables, loss of homogeneity and complete loss of planarity of the 3D-QRS loop. The planarity of the 3D-QRS loop is a highly restricted and sensitive parameter and a characteristic feature of normal heart and can be utilized as a test for diagnostic screening of cardiac normalcy and the loss of planarity may be a conspicuous feature of AMI. It will be reasonable to study the morphology of the spatial QRS loop in patients of AMI throughout the course of disease and also in a regular interval through the long-term follow up period. It is expected that with the reperfusion, recovery and salvage of the diseased myocardium; the homogeneity and the intensity of the line density of the membrane current of the UDL would gradually recover with retrieval of the planarity of the spatial QRS loop. The temporal pattern of characteristics alteration of the QRS loop planarity with the natural course of the disease requires intensive evaluation. We propose that, the planarity of the spatial QRS loop, its loss, involution and reversal is a temporal series of events in AMI and also a crucial diagnostic and prognostic parameter.