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Biomedical subjects

B M Horacek

Publications and source records attributed to B M Horacek.

At least 19 recordsLinked to original sources
PubMed1999

Low-frequency component of body surface potential maps identifies patients at risk for ventricular tachycardia.

AIMS: To investigate the ability of spectral features of signal-averaged body-surface potential maps in identifying post-infarction patients who are at risk of developing ventricular tachycardia. METHODS AND RESULTS: We recorded 120 lead body surface potential maps during sinus rhythm in 135 subjects (45 patients with healed myocardial infarction but no history of ventricular tachycardia, 45 patients with both healed myocardial infarction and at least one episode of sustained ventricular tachycardia, and 45 normal subjects) and analysed spectral features of body surface potential maps selected on the basis of isoharmonic maps for given bands of the frequency spectrum. We found that in the low-frequency band (1-11 Hertz), the group-mean power spectra of leads located at isoharmonic map maxima were significantly different (P<0.0001) between the two groups of myocardial infarction patients. We estimated that this single feature alone can prospectively identify myocardial infarction patients at risk for ventricular tachycardia with a predictive accuracy of 74+/-6%. CONCLUSION: Our results suggest that the bulk of diagnostic information associated with arrhythmogenicity resides in the low-frequency band of the power spectrum. This finding is at variance with the established notion that only the high-frequency component of signal-averaged electrocardiograms carries such information.

Adult↗
PubMed1993

The effects of unilateral stellate ganglion blockade on human cardiac function during rest and exercise.

INTRODUCTION: Left-sided stellate ganglion predominance has been proposed as a mechanism responsible for lethal ventricular arrhythmias, due to heterogenous ventricular repolarization. To determine the cardiovascular effects of such asymmetric sympathetic ganglion innervation in man, studies were performed in 15 patients undergoing unilateral stellate ganglion blockade for the management of chronic arm pain. METHODS AND RESULTS: Standard 12-lead ECGs, systemic blood pressure, body surface potential mapping, and radionuclide angiography were performed during rest and graded exercise before and after blockade. Successful unilateral blockade was accomplished in 13 of the patients, 11 of whom had right-sided blockade and two left-sided blockade. No significant changes due to blockade of stellate ganglia, including QT intervals, were detected during rest or graded exercise in standard ECGs. No cardiac rhythm disturbances occurred in these states. Body surface potential maps and arterial blood pressure were similar during resting supine and upright positions, as well as immediately after exercise before and after blockade. Unilateral ganglionic blockade did not modify resting or exercise cardiac ejection fractions. CONCLUSION: Unilateral stellate blockade in man does not induce untoward cardiovascular effects during rest or exercise.

Adult↗
PubMed1992

Electrocardiographic body surface mapping in patients with ventricular tachycardia. Assessment of utility in the identification of effective pharmacological therapy.

BACKGROUND: Body surface maps of net QRST deflection areas (isointegrals) reflect regional ventricular repolarization properties. Vulnerability to ventricular tachyarrhythmias is associated with maps that feature multiple islands (extrema) of positive and negative values; such maps reflect regional disparity of ventricular recovery properties. The value of body surface mapping in prediction of the efficacy of antiarrhythmic therapy for ventricular tachyarrhythmias has not been determined. METHODS AND RESULTS: Isointegral ECG body surface mapping was performed in 51 patients with inducible ventricular tachycardia having programmed stimulation studies at baseline and after oral quinidine therapy. The degree of nondipolarity of QRST isointegral distribution was expressed by the number of extrema and by the percentage contribution of nondipolar eigenvectors after Karhunen-Loeve transformation. QRST isointegral nondipolarity was greater in ventricular tachycardia patients than in 51 age- and sex-matched normal subjects expressed as mean number of extrema (4.1 +/- 2.8 versus 2.0 +/- 0.2, respectively), mean eigenvector-determined nondipolar content percentages (12.4 +/- 10.1% versus 4.5 +/- 4.9%), prevalence of abnormal numbers of extrema (63% versus 4%), or prevalence of abnormal nondipolar content percentages (33% versus 4%) (each p less than 0.01). Quinidine prevented ventricular tachycardia induction in 14 patients. Patients for whom quinidine was or was not effective had similar nondipolarity indexes at baseline. However, maps on quinidine differed as a function of antiarrhythmic efficacy. Although effective therapy produced no significant mean changes in nondipolarity, ineffective therapy increased the number of extrema compared with baseline (5.4 +/- 3.4 versus 3.8 +/- 2.5, respectively) (p = 0.002). Individually, 43% of patients on effective therapy had drug-induced decreases in numbers of extrema compared with 14% of those on ineffective therapy (p = 0.02). Furthermore, 29% of patients on effective therapy showed drug-induced increases in numbers of extrema compared with 62% of those on ineffective therapy (p = 0.03). CONCLUSIONS: QRST isointegral body surface mapping shows promise as a noninvasive measure of drug efficacy in patients with ventricular tachycardia.

Anti-Arrhythmia Agents↗
PubMed1991

Magnetocardiographic localisation and modelling.

In our magnetocardiographic (MCG) localisation studies, two modelling approaches have been applied: (a) modelling the sources with dipole and quadrupole moments in a general multipole expansion and using a homogeneous, semi-infinite volume conductor, and (b) using a single current dipole source in a homogeneous, realistically shaped torso. Both approaches have been successfully applied in localising the premature ventricular excitation site in patients suffering from the Wolff-Parkinson-White syndrome. In addition, we have participated in developing a model of propagation of electrical activation in the ventricles. Anisotropic conductivity properties and spiral arrangement of myocardial fibres are included in the model.

Heart Function Tests↗
PubMed1991

Magnetocardiographic functional localization using a current dipole in a realistic torso.

We describe a fast and numerically effective biomagnetic inverse solution using a moving dipole in a realistic homogeneous torso. We applied the localization model and high-resolution magnetocardiographic mapping to localize noninvasively the ventricular preexcitation site in ten patients suffering from Wolff-Parkinson-White syndrome. In all cases, the computed localization results were compared to the results obtained by invasive catheter technique. Using a standard-size torso model in all cases, the average 3-D distance between the computed noninvasive locations and the invasively obtained results was 2.8 +/- 1.4 cm. When the torso was rescaled to better match the true shape of the subject in five cases, the 3-D average was improved to 2.2 +/- 1.0 cm. This accuracy is very satisfactory, suggesting that the method would be clinically useful.

Adult↗
PubMed1990

Complementary nature of electrocardiographic and magnetocardiographic data in patients with ischemic heart disease.

High resolution body surface potential maps (BSPM) and magnetic field maps (MFM) for study groups consisting of 11 Q wave and 11 non Q wave myocardial infarct (MI) patients as well as 9 normal subjects, were recorded in a magnetically and electrically shielded room. A control group of 22 normal subjects provided group mean normal time integral maps for selected QRST time intervals. The difference between magnitudes of extrema in each map defined the normal mean data range R for that time interval. The root mean square sum of the differences between the time integral map of a study subject and the normal group-mean map provided an estimate of individual map variability, V. Subsequent calculation of group-mean map variability, V, and group-mean normalized variability, V/R, for specific time intervals of the cardiac cycle, were used to test the abilities of BSPM and MFM techniques to distinguish between the normal and MI study groups. Results indicate that BSPM V/R differences between MI and normal groups are most pronounced during Q wave and Q zone activity; between inferior MI's and normals (p less than 0.05) and between anterior MI's and normal (p less than 0.01). Significant differences in MFM V/R occur during repolarization; between inferior MI's and non Q wave MI's (p less than 0.05), between anterior MI's and normals (p less than 0.05), between non Q wave MI's and normals (p less than 0.05) and between all MI's and normals (p less than 0.01). It is concluded that high resolution BSPM and MFM provide complementary means of discriminating between normal subjects and MI patients.

Coronary Disease↗
PubMed1990

Exercise body surface potential mapping in single and multiple coronary artery disease.

Body surface ST integral maps were recorded in 36 coronary artery disease (CAD) patients at: rest; peak, angina-limited exercise; and, 1 and 5 min of recovery. They were compared to maps of 15 CAD patients who exercised to fatigue, without angina, and eight normal subjects. Peak exercise heart rates were similar (NS) in all groups. With exercise angina, patients with two and three vessel CAD had significantly (p less than 0.05) greater decrease in the body surface sum of ST integral values than patients with single vessel CAD. CAD patients with exercise fatigue, in the absence of angina, had decreased ST integrals similar (NS) to patients with single vessel CAD who manifested angina and the normal control subjects. There was, however, considerable overlap among individuals; some patients with single vessel CAD had as much exercise ST integral decrease as patients with three vessel CAD. All CAD patients had persistent ST integral decreases at 5 min of recovery and there was a direct correlation of the recovery and peak exercise ST changes. Exercise ST changes correlated, as well, with quantitative CAD angiographic scores, but not with thallium perfusion scores. These data suggest exercise ST integral body surface mapping allows quantitation of myocardium at ischemic risk in patients with CAD, irrespective of the presence or absence of ischemic symptoms during exercise. A major potential application of this technique is selection of CAD therapy guided by quantitative assessment of ischemic myocardial risk.

Adult↗
PubMed1989

Persistent changes in the body surface electrocardiogram following successful coronary angioplasty.

One hundred twenty-lead body surface potential maps (BSPMs) were recorded immediately before and 24 hours after coronary angioplasty (PTCA) in 24 patients with symptomatic coronary artery disease (single-vessel in 21 and two-vessel in 3). All PTCAs were uncomplicated and successful. The modified Gensini score decreased in every patient and the mean score fell from 43 +/- 36 to 21 +/- 28 (p less than 0.001). Resting spatial patterns of QRS, ST-segment, and T wave integral distributions over the torso surface were unchanged from before to after PTCA. Quantitative temporal subtraction maps, however, revealed a large precordial area of decreased T wave integral values after PTCA. The sum (sigma) positive T wave integrals fell from 20,501 +/- 10,544 microV.s before PTCA to 17,647 +/- 10,310 microV.s after PTCA (p less than 0.02). In contrast, the sigma positive QRS (10,115 +/- 4,848 microV.s before PTCA vs. 9,656 +/- 4,556 microV.s after PTCA) and the sigma negative ST integrals (-2,489 +/- 1,467 microV.s before PTCA vs. -2,359 +/- 1,505 microV.s after PTCA) were unchanged (NS). Thus, successful PTCA does not produce any persistent change in depolarization or early repolarization electrocardiographic variables but is associated with a decrease in late repolarization potentials that persists for at least 24 hours after the procedure. The pathophysiology of this persistent change is speculative, but myocardial ischemia during the PTCA procedure is a likely possibility. The clinical significance, including predictive value for subsequent stenosis, and the natural history of T wave effect remain incompletely defined. These data suggest that measures to decrease myocardial ischemia during PTCA are warranted.

Adult↗
PubMed1989

Two-dimensional Fourier spectrum of QRST integral maps in classification of patients prone to ventricular arrhythmia.

Two-dimensional Fourier spectra of QRST integral maps, obtained by body surface potential mapping, were analyzed to identify subjects prone to ventricular arrhythmia, when they have not been identified by the extrema count method. The diagnostic performance (84.38 percent) of the peak value of the Fourier spectrum as a classifier for subjects prone to ventricular arrhythmia showed an improvement of 3.65 percent over the use of the extrema count method as a classifier.

Arrhythmias, Cardiac↗
PubMed1989

Cardiac function at rest and with exercise in the chronic fatigue syndrome.

To evaluate a possible cardiac pathophysiology of the chronic fatigue syndrome, we compared the resting cardiac function and exercise performance of 41 patients to those of an age-matched and sex-matched normal control group. Persistent fatigue following an acute apparently viral illness was the major complaint of all patients; none had specific cardiac symptoms nor abnormal physical findings. Electrocardiographic spatial patterns were normal in the patients, and there were no differences in the body surface sum of positive T-wave integrals between the patients (240 microV.x 10(2) +/- 107 microV.s x10(2)) and control (244 microV.x 10(2) +/- 108 microV.s x 10(2) subjects. Twenty-four hour ambulatory ECGs revealed no differences in sinus rates and incidences of ventricular dysrhythmias in the two populations. Left ventricular dimensions and systolic fractional shortening values were also similar in both groups; moreover none of the patients had segmental wall motion abnormalities. On graded exercise testing, 20 of 32 normal subjects achieved target (85 percent of age-maximum) heart rates, compared to four of 31 patients (p less than 0.001). The duration of exercise averaged 12 +/- 4 minutes for the normal subjects and 9+/- 4 minutes for the patients (p less than 0.01). The temporal profile of exercise heart rates was dissimilar in the two groups, with patients' rates consistently and progressively less than those of normal subjects. Peak heart rate averaged 152 +/- 16 beats per minute for the normal group vs 124 +/- 19 beats per minute for the patients (p less than 0.0001); in age-related terms, respectively, 82 +/- 6 percent of the maximum heart rate vs 66 +/- 10 percent (p less than 0.0001). Thus, patients with chronic fatigue syndrome have normal resting cardiac function but a markedly abbreviated exercise capacity characterized by slow acceleration of heart rate and fatigue of exercising muscles long before peak heart rate is achieved.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Body surface potential maps with low-level exercise in isolated left anterior descending coronary artery disease.

One hundred and twenty-lead body surface potential maps (BSPMs) were recorded at rest, at immediate cessation of exercise and after 1 (early) and 5 minutes (late) of recovery in 14 patients with isolated, critical, left anterior descending (LAD) coronary artery stenosis. Exercise endpoints, at an average peak rate of 98 +/- 13, were usual pain worsening in 13 LAD patients, and diagnostic ST depression in lead V5 in 1 patient. Twelve patients also had positive thallium scans. BSPMs were also recorded in 8 normal subjects who exercised to peak heart rates similar to those of the LAD subjects. Spatially, there were similar exercise changes in QRS and ST-segment integral patterns over the precordium and inferior torso in both groups. These were transient in the control group but persisted to late recovery in the LAD group, particularly for ST integral. Quantitatively, multivariate analysis revealed significant temporal differences between the 2 groups. However, the only independent BSPM variable was the sum of ST integral decrease, averaging --2,323 +/- 1,809 microV.s for normal patients between rest and immediate cessation of exercise, compared with -3,828 +/- 2,329 microV.s for the LAD patients (p less than 0.05). Late recovery minus rest difference averaged -1,264 +/- 1,080 microV.s for normal subjects and -2,575 +/- 1,844 microV.s for LAD patients (p less than 0.01). To control for the physiologic changes of exercise, the ST integral temporal differential maps of the normal subjects were subtracted from those of the LAD patients and the sum of negative intergroup differences was assumed to reflect only ischemia. Correlation of ST integral ischemia values at immediate cessation of exercise and late recovery was high (r = 0.88); however, intertechnique correlations of the BSPM variables with quantitative angiographic scores and thallium perfusion scan scores revealed generally low r values (range 0 to 0.52). These data demonstrate that ischemic repolarization changes are detectable and quantifiable by BSPM at low levels of cardiac stress in patients with 1-vessel disease when the usual electrocardiographic criteria of myocardial ischemia are frequently absent. The data further suggest that ST integral changes reflective of myocardial ischemia persist well after the exercise recovery period and that they are complementary to, rather than substitutionary for, other indirect measures of myocardial ischemia.

Adult↗
PubMed1988

Cardiac effects of common viral illnesses.

We compared the clinical, electrocardiographic and echocardiographic findings of 32 patients during the acute and recuperative phases of viral illness with similar data from a healthy age- and sex-matched normal control group. During the acute phase, no patient had cardiac symptoms and none had clinical evidence of left ventricular or valvular dysfunction, nor pericarditis. Electrocardiograms revealed no differences in mean sinus rate or ectopic dysrhythm between the two groups. Spatial 12- and 120-lead body surface electrocardiographic patterns were normal in 30 patients; two others had nonspecific T wave abnormalities. There were no differences in echo-determined left ventricular cavity size or systolic shortening fraction between the two groups. Three patients had segmental ventricular hypokinesis; 17 patients had small pericardial effusions. Data herein suggest effects on myocardial electrical and mechanical function in patients with viral illness. It may be prudent for such patients to minimize cardiac stress during illness.

Acute Disease↗
PubMed1987

The effect of torso geometry on magnetocardiographic isofield maps.

Using a computer model of a realistically shaped human torso with lungs and intraventricular blood masses, we have assessed how torso geometry and composition affect the extracorporal magnetic field produced by a current dipole in the centre of the ventricular mass. The magnetic induction vector B arising from the dipole has been calculated at points of a precordial measuring grid and the influence of boundaries has been assessed qualitatively, by comparing contour maps of the B component normal to the torso's frontal plane. We found that the maps reflected relatively faithfully the underlying dipolar source for the homogeneous torso and even for the torso with lungs. However, the intraventricular blood masses caused a noticeable rotation of the maps' extrema. Both lungs and blood masses tended to swing the distribution towards the distribution that would have been caused by a dipole oriented along the anatomical axis of the heart.

Computer Simulation↗
PubMed1986

Non-Q-wave acute myocardial infarction: body surface potential map and ventriculographic patterns.

Day 5 body surface map and radionuclide angiographic patterns were compared among 56 patients with first non-Q-wave or Q-wave acute myocardial infarction (AMI). Three radionuclide angiographic patterns were recognized in patients with non-Q infarction: no wall motion abnormalities (n = 8), single-segment wall motion abnormalities (n = 10) and multiple-segment wall motion abnormalities (n = 9). In contrast, only 2 radionuclide angiographic patterns were identified in patients with Q-wave infarction: multiple-segment wall motion abnormalities (n = 25) and single-segment wall motion abnormalities (n = 4). The Q-wave distributions of 14 of 18 patients with non-Q infarction with 0 or 1 wall motion abnormalities were normal; 2 patients had "missed" anterior; 1 patient had inferior; and 1 had posterior AMI patterns. Of 9 patients with non-Q infarction who had multiple-segment wall motion abnormalities, 8 had infarct Q waves on the posterior torso. Q-wave patterns in patients with anterior (n = 17) and inferior (n = 12) Q-wave infarctions were typical and homogeneous for each group. Quantitative analysis of minimum Q-zone integral, sigma Q-wave integrals, ST-integral maximum, wall motion abnormality score and ejection fraction revealed no differences between patients with non-Q-wave and those with inferior Q-wave infarction. In contrast, patients with anterior AMI had significantly more abnormal values of all variables than either of the other groups. Overall, the data support the concept of non-Q-wave AMI as a distinct, if heterogeneous, pathophysiologic entity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

Electrocardiographic and ventriculographic recovery patterns in Q wave myocardial infarction.

To further define the capacity for recovery after acute phase electrical and mechanical injury in patients with Q wave myocardial infarction who were treated with standard measures, 120 lead body surface potential maps and radionuclide angiograms were recorded at day 5 before discharge and month 6 after infarction in 23 patients with a first infarction (12 anterior and 11 inferior by standard 12 lead electrocardiographic criteria). In addition to assessment of spatial changes in electrocardiographic and wall motion patterns, five quantitative variables were evaluated: minimal Q zone integral, sigma Q wave integral, maximal ST integral, left ventricular ejection fraction and left ventricular wall motion abnormality score. From day 5 to month 6 after infarction, the only change in the inferior infarction group was a gain in sigma Q wave (-91 +/- 40 mu V X s X 10(2) to -68 +/- 24 mu V X s X 10(2); p less than 0.05). In contrast, all variables improved over the same time period in the anterior infarction group: Q zone minimum, -34 +/- 20 to -24 +/- 13 mu V X s (p less than 0.05); sigma Q wave, -160 +/- 122 X 10(2) to -120 +/- 90 mu V X s X 10(2) (p less than 0.05); ST maximum, 44 +/- 19 to 18 +/- 9 mu V X s (p less than 0.01); ejection fraction, 54 +/- 7 to 63 +/- 17% (p less than 0.05); and wall motion score, 6 +/- 3 to 3 +/- 3 (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Antagonists↗
PubMed1986

Vulnerability to ventricular arrhythmia: assessment by mapping of body surface potential.

It is now well established that the vulnerability of the ventricular myocardium to repetitive dysrhythm increases in the presence of greater than normal disparity local recovery times. Local recovery is reflected in the electrocardiographic waveform as an area of the ventricular deflection (QRST time integral), and thus disparate ventricular recovery may be manifested in the body surface distribution of this quality. To assess this possibility, we obtained simultaneous 120-lead electrocardiograms from both the anterior and posterior torso in 140 subjects (ages 8 to 75) grouped as follows: group A, 97 normal subjects; group B, 16 patients resuscitated from ventricular fibrillation or sustained ventricular tachycardia; and group C, 27 patients 6 to 12 months after myocardial infarction but without clinically significant arrhythmia. In each subject, the QRST integral was evaluated for each lead and isointegral contour maps were plotted. A score was assigned to each map, based on the number of extrema; each maximum or minimum scored one point, with the exception of simultaneously occurring anterior and posterior minima on the right shoulder (frequently occurring in normal subjects), which scored together only one point. All but one group A subject had dipolar QRST integral maps (mean +/- SD score 2.11 +/- 0.2). Conversely, 10 of 16 (62.5%) group B patients had scores of 3 or more (mean 3.16 +/- 1.08; p less than .01 vs group A). Group C patients had intermediate values, with eight of 27 (29.6%) scoring 3 or more (mean 2.46 +/- 83); this was less than in group B (p less than .01), but more (p less than .05) than in group A.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗