Phase-invariant signature algorithm: a noninvasive technique for early detection and quantification of ouabain-induced cardiac disorders

Visualization of Complex Processes in Cardiovascular System during Electrical Auricular Vagus Nerve Stimulation

The analysis of human physiological systems from the point of view of complex systems theory remains a very ambitious task. The complexity of the problem often encourages the use of innovative mathematical methods analyzing the processes that take place in space and time. The main goal of this paper is to visualize the cardiovascular system during auricular vagus nerve stimulation (aVNS) using the matrix differences to evaluate the dynamic signal interfaces by cointegrating the initial signal data into the matrices during each case. Algebraic relationships between RR/JT and JT/QRS cardiac intervals are used not only to track the cardiovascular changes during aVNS but also to characterize individual features of the person during the transit through the therapy. This paper presents the computational techniques that can visualize the complex dynamical processes taking place in the cardiovascular system using the electrical aVNS therapy. Four healthy volunteers participated in two verum and two placebo experiments. We discovered that the body's reaction to the stimulation was very different in each of the cases, but the presented techniques opened new possibilities for a novel interpretation of the dynamics of the cardiovascular system.

Sampling rate and the estimation of ensemble variability for repetitive signals

The measurement of ensemble variability in time-aligned event signals is studied in relation to sampling rate requirements. The theoretical analysis is based on statistical modelling of time misalignment in which the time resolution is limited by the length of the sampling interval. For different signal-to-noise ratios (SNRs), the sampling rate is derived which limits the misalignment effect to less than 10% of the noise effect. Each signal is assumed to be corrupted by additive noise. Using a normal QRS complex with a high SNR (approximately equal to 30 dB), a sampling rate of approximately 3 kHz is needed for accurate ensemble variability measurements. This result is surprising since it implies that the Nyquist rate is far too low for accurate variability measurements. The theoretical results are supplemented with results obtained from an ECG database of 94 subjects for which the ensemble variability is computed at different sampling rates using signal interpolation. The ensemble variability is substantially reduced (40%) when increasing the rate from 1 to 3 kHz, thus corroborating the results suggested by the theoretical analysis.

Vectorcardiographic loop alignment and the measurement of morphologic beat-to-beat variability in noisy signals

The measurement of subtle morphologic beat-to-beat variability in the electrocardiogram (ECG)/vectorcardiogram (VCG) is complicated by the presence of noise which is caused by, e.g., respiration and muscular activity. A method was recently presented which reduces the influence of such noise by performing spatial and temporal alignment of VCG loops. The alignment is performed in terms of scaling, rotation and time synchronization of the loops. Using an ECG simulation model based on propagation of action potentials in cardiac tissue, the ability of the method to separate morphologic variability of physiological origin from respiratory activity was studied. Morphologic variability was created by introducing a random variation in action potential propagation between different compartments. The results indicate that the separation of these two activities can be done accurately at low to moderate noise levels (less than 10 microV). At high noise levels, the estimation of the rotation angles was found to break down in an abrupt manner. It was also shown that the breakdown noise level is strongly dependent on loop morphology; a planar loop corresponds to a lower breakdown noise level than does a nonplanar loop.

Beat-to-beat QRS amplitude variability in elite endurance athletes

Results from variance electrocardiography, displaying the wide-band, phase-locked electrical micro-variability during the depolarization phase, was analysed versus clinical data, echocardiographic structural and functional variables and myocardial scintigraphic findings in 174 elite orienteers compared with 37 age-matched elite endurance athletes and 50 age-matched, healthy medical students. PCA analysis identified a subgroup of five orienteers deviating from the rest of the study group and both control groups with regard to their QRS amplitude variability. No correlations were found between pathology by medical history or any of the echocardiographic and scintigraphic variables or by the variance electrocardiographic aberrations in any of the groups studied.

Vectorcardiographic loop alignment and morphologic beat-to-beat variability

The measurement of subtle morphologic beat-to-beat variations in the electrocardiogram is complicated by the presence of respiration-induced movements of the heart. A statistical signal model is developed which accounts for such movements by means of scaling, rotation, and time synchronization of vectorcardiographic loops. The maximum-likelihood estimator of the parameters describing these three transformations is presented and is extended to the case of multiple loop alignment. The performance of the method is assessed by measuring morphologic variability before and after loop alignment. It is shown that the effects of respiration on morphologic variability can be considerably reduced by the new method. Measurements on morphologic variability were typically reduced by a factor of 0.53 after loop alignment. The results show also that beat-to-beat measurements are strongly dependent on the selected sampling rate and that a rate of 1 kHz is too low.

Potential of carotid ultrasonography in the diagnosis of coronary artery disease: a comparison with exercise test and variance ECG

BACKGROUND AND PURPOSE

Carotid artery atherosclerosis has been shown to correlate with coronary artery disease (CAD). This study evaluates the capacity of duplex ultrasonography of the carotid arteries as a tool in the diagnosis of CAD in comparison with exercise stress test and variance ECG.

METHODS

Carotid ultrasonography, exercise stress test, and variance ECG were performed in 184 symptomatic patients evaluated with coronary angiography. The diagnostic capacity of the studied noninvasive methods was assessed by use of receiver operating characteristic (ROC) curves constructed by successive consideration of several cut points, such as (1) the presence of unilateral/bilateral plaques and (2) cross-sectional common carotid artery (CCA) intima-media (IM) area from 10 to 30 mm2 for ultrasonography; (1) ST depression > or =0.1 mV and > or =0.2 mV with and (2) without chest pain for exercise test; and electrical variability index from 50 to 100 for variance ECG.

RESULTS

Coronary angiography revealed the presence of CAD (> or =50% luminal stenosis in 1 or more major epicardial arteries) in 147 patients (80%). Identification of carotid plaques on one or both sides and calculation of the left-sided (but not right-sided) CCA IM area provided a significant discrimination (P<.001 and P<.01, respectively) of patients with CAD. The discriminating capacity of the ultrasound procedures was equal to that of variance ECG and exercise test with ST depression criterion only but somewhat lower than that of exercise test with the combined chest pain and ST depression criterion (P<.05). However, at the chosen cut points, carotid plaque identification offered higher sensitivity than exercise test with either criterion (P<.01 and P<.001, respectively).

CONCLUSIONS

Carotid ultrasonography is a useful diagnostic method that is comparable to exercise test and variance ECG for detection of CAD in a high-prevalence population.

Variance ECG detection of coronary artery disease--a comparison with exercise stress test and myocardial scintigraphy

Variance electrocardiogram (ECG) is a newly developed method by which resting ECG is registered with 24 leads during 220 beats. The temporal beat-to-beat QRS microamplitude variability is computed and a nondimensional diagnostic variance ECG coronary artery disease (CAD) index is derived from it. Consecutive outpatients (n = 160) were referred to myocardial scintigraphy (SPECT) investigation for the evaluation of angina pectoris. The variance ECG CAD index was compared with a symptom-limited exercise stress test and SPECT during and after the exercise test and with coronary angiography (n = 67). Discriminant accuracy was tested with receiver-operating characteristics (ROC). Relative to angiographic coronary pathology (prevalence 0.85), diagnostic information for the variance ECG CAD index and for SPECT were both p < 0.001, while the outcome of the exercise stress test was non-contributory. Prevalence of persistent or transient perfusion defects at SPECT was 0.59. The exercise stress test had a diagnostic capacity of p < 0.01 for transient perfusion defects and variance ECG CAD index showed a high diagnostic performance (p < 0.001) for persistent perfusion defects. Overall pathology at SPECT was better (p < 0.05) identified by variance ECG CAD index than by symptom-limited exercise stress test. It was concluded that in this high prevalence population the variance ECG CAD index has a diagnostic capacity at least as good as that of SPECT and better than that of the exercise stress test. The variance ECG CAD index was strongly diagnostic for persistent perfusion defects while exercise stress test was slightly diagnostic for transient perfusion defects. Therefore, the two tests provide complementary diagnostic information.

Electrocardiogram signal variance analysis in the diagnosis of coronary artery disease--a comparison with exercise stress test in an angiographically documented high prevalence population

Variance electrocardiography (variance ECG) is a new resting procedure for detection of coronary artery disease (CAD). The method measures variability in the electrical expression of the depolarization phase induced by this disease. The time-domain analysis is performed on 220 cardiac cycles using high-fidelity ECG signals from 24 leads, and the phase-locked temporal electrical heterogeneity is expressed as a nondimensional CAD index (CAD-I) with the values of 0-150. This study compares the diagnostic efficiency of variance ECG and exercise stress test in a high prevalence population. A total of 199 symptomatic patients evaluated with coronary angiography was subjected to variance ECG and exercise test on a bicycle ergometer as a continuous ramp. The discriminant accuracy of the two methods was assessed employing the receiver operating characteristic curves constructed by successive consideration of several CAD-I cutpoint values and various threshold criteria based on ST-segment depression exclusively or in combination with exertional chest pain. Of these patients, 175 with CAD (> or = 50% luminal stenosis in 1 + major epicardial arteries) presented a mean CAD-I of 88 +/- 22, compared with 70 +/- 21 in 24 nonaffected patients (p < 0.01). Variance ECG provided a stochastically significant discrimination (p < 0.01) which was matched by exercise test only when chest pain variable was added to ST-segment depression as a discriminating criterion. Even then, the exercise test diagnosed single-vessel disease with a significantly lower sensitivity. At a cutpoint of CAD-I > or = 70, compared with ST-segment depression > or = 1 mm combined with exertional chest pain, the overall sensitivity of variance ECG was significantly higher (p < 0.01) than that of exercise test (79 vs. 48%). When combined, the two methods identified 93% of coronary angiography positive cases. Variance ECG is an efficient diagnostic method which compares favorably with exercise test for detection of CAD in high prevalence population.

Accuracy of 22-lead ECG analysis for diagnosis of acute myocardial infarction and coronary artery disease in the emergency department: a comparison with 12-lead ECG

STUDY OBJECTIVES

To compare a new 22-lead ECG with the 12-lead ECG for diagnosis of acute myocardial infarction (AMI).

DESIGN

Prospective study of all consenting patients presenting to the emergency department with chest pain.

SETTING

Urban hospital ED.

TYPE OF PARTICIPANTS

163 patients admitted with a cardiac-related diagnosis and complete data sets of 22- and 12-lead ECG results and creatine kinase-MB analysis.

INTERVENTIONS

Patient care and existing protocols were unaltered, with the exception of including the new 22-lead ECG.

MEASUREMENTS AND MAIN RESULTS

Forty-one of 163 patients had an AMI as defined by creatine kinase-MB analysis. The 22-lead ECG provided a statistically significant improvement in sensitivity (83%) for AMI diagnosis over the 12-lead ECG (51%) with specificities of 76% and 99%, respectively.

CONCLUSION

When combined with clinical judgment, the 22-lead ECG could provide a 97.6% sensitivity for AMI diagnosis while reducing unnecessary admissions for "rule-out MI" by 69%.

PISA: a noninvasive method in detection and quantification of acid-induced myocardial infarction in dogs

Phase invariant signature algorithm (PISA), a new noninvasive technique, was used in the detection and quantification of acid-induced myocardial damage in anesthetized dogs. The diagnostic capabilities of this method were compared with those of conventional electrocardiogram and biochemical markers, MB-creatine phosphokinase (MB-CPK) and lactic dehydrogenase (LDH1). Myocardial damage of varying degree was induced by injecting diluted sulphuric acid (0.01 to 0.10 ml) into the free wall of the left ventricle. Conventional ECG, wideband ECG for PISA analysis, blood samples for LDH1, and MB-CPK were taken before and after 15, 30, 60, and 90 min of acid injection. The heart was removed at the end of 90 min for estimation of myocardial damage. PISA Index increased within 10-15 min of acid injection and remained elevated for the duration of the experiment (90 min). The increase in the PISA index was directly related to the extent of myocardial damage and the amount of acid injected. Although the conventional electrocardiogram detected large myocardial damage, it was unable to detect small myocardial damage. Also, most of initial change in conventional ECG with large myocardial damage disappeared within 90 min, while the PISA index was still elevated to the maximum level. The MB-CPK was not detected before or after myocardial damage. There was no significant change in the LDH1 at any time after myocardial infarction. These results suggest that the PISA technique is superior to the conventional ECG and the biochemical markers and would be a valuable diagnostic tool in the detection and quantification of incipient as well as advanced myocardial infarction.