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PubMed1997

Comparison of exercise electrocardiography and dobutamine echocardiography with invasively assessed myocardial fractional flow reserve in evaluation of severity of coronary arterial narrowing.

This study compares side-by-side exercise electrocardiography and dobutamine echocardiography with an invasively assessed index of myocardial flow (pressure-derived myocardial fractional flow reserve). The data show that ST-segment depression > or = 0.1 mV and the occurrence of new wall motion abnormalities during dobutamine infusion reflect a similar impairment of myocardial blood flow.

Cardiotonic Agents↗
PubMed1997

Accuracy of treadmill exercise electrocardiography in detecting restenosis following single-vessel percutaneous transluminal coronary angioplasty.

To develop an improved method for diagnosing restenosis using treadmill exercise electrocardiography (ECG) following percutaneous transluminal coronary angioplasty (PTCA), we prospectively evaluated 46 patients who underwent PTCA for the treatment of single-vessel coronary artery disease and who did not have a history of myocardial infarction. Treadmill exercise ECG and coronary angiography were performed 3 months after PTCA to determine their accuracy in diagnosing restenosis based on standard ST-segment depression criteria, the difference between the maximum ST-segment depression before and 3 months after PTCA (< or =0.5 mm: positive; >0.5 mm: negative), and the difference between sigmaST-segment depression before PTCA and 3 months after PTCA (< or = 1.5 mm: positive; > 1.5 mm: negative). The sensitivity, specificity, and diagnostic accuracy of standard ST-segment depression criteria were 65%, 66%, and 65%, respectively. The sensitivity, specificity, and accuracy for the difference in maximum ST-segment depression were 77%, 76%, and 76%, respectively, whereas the values for the difference in sigmaST-segment depression were 77%, 83%, and 80%, respectively. Based on these results, we conclude that using the difference between ST-segment depression before and after PTCA improves the accuracy of treadmill exercise ECG for diagnosing restenosis.

Aged↗
PubMed1996

Comparison of technetium-99m sestamibi-gated tomographic perfusion imaging with echocardiography and electrocardiography for determination of left ventricular mass.

Left ventricular (LV) mass estimates obtained from post-stress gated single-photon emission computed tomographic (SPECT) perfusion images were compared with 2-dimensionally targeted M-mode echocardiograms and with resting electrocardiographic voltage in 32 patients with stress perfusion scans that were either normal or only mildly abnormal. Myocardial pixel volumes were obtained from SPECT transaxial slices at end-diastole, end-systole, and summed ("ungated") static reformatted SPECT images at 2 levels of background subtraction, 37.5% and 35% of peak myocardial activity. The S-wave amplitude in lead V1 and the R-wave amplitude in V5 were summed for an electrocardiographic index of voltage. Echocardiographic LV mass was calculated using the modified Penn convention formula. SPECT myocardial mass estimates were significantly greater at diastole when compared with systolic or summed images. There was a moderated, although highly significant, correlation between echocardiographic and SPECT indexes of LV mass with the lower (35%) background threshold (r = 0.59, 0.60, and 0.53 for diastole, summed, and systole, each p < 0.001). The diastolic SPECT estimate of LV mass correlation with electrocardiographic voltage (r = 0.56) was superior to the correlation between echocardiography and electrocardiography (r = 0.30). With use of published criteria for the presence of LV hypertrophy on echocardiography, diastolic and systolic gated SPECT predicted echocardiographic results with 78% accuracy.

Cardiac Volume↗
PubMed1996

Normal values and methodologic recommendations for signal-averaged electrocardiography in children and adolescents.

Signal-averaged electrocardiography was performed in 153 normal children and adolescents (1 day to 18.3 years old) to examine the effects of age, sex, and race on different electrocardiographic variables, and to evaluate whether the current methods for analysis of the signal-averaged electrocardiogram are applicable to small children. Tracing with inaccurate automatic determination of the QRS end point or high noise levels were excluded. Filtered QRS duration, root-mean-square voltage, and low-amplitude signal duration were measured using 25, 40, and 80 Hz filters. All variables were significantly different (p <0.01) in infants compared with subjects aged >15 years. These differences gradually resolved with increasing age. Sex differences were present for some variables in adolescents only, and there was no significant race-related difference. Because of the shorter QRS duration, the terminal activities were more accurately reflected at the terminal duration of 30 ms in infants and 35 ms in children aged at least 1 year to <6 years. Normative data for filtered QRS duration, root-mean-square voltage, and low-amplitude signal duration are provided for different age groups.

Adolescent↗
PubMed1999

Comparison of treatment plans for lower extremity arterial occlusive disease made with electrocardiography-triggered two-dimensional time-of-flight magnetic resonance angiography and digital subtraction angiography.

BACKGROUND: The purpose of the study was to determine whether preoperative treatment plans for patients with lower extremity ischemia can be made with electrocardiography (EKG)-triggered two-dimensional (2D) time-of-flight (TOF) magnetic resonance angiography (MRA) as accurately as digital subtraction angiography (DSA). METHODS: Forty patients were prospectively evaluated with the combination of EKG-triggered 2D TOF MRA, DSA, and pulse volume recordings. Blinded reviewers graded arterial segments for disease severity. Accuracy of separate MRA- and DSA-based treatment plans was compared with the procedures performed based on all available information. RESULTS: There was an 86% exact match between MRA- and DSA-based plans (92% MRA and 94% DSA accuracy). The MRA-based plan accurately predicted 90% of suprainguinal and 95% of infrainguinal procedures, whereas the DSA-based plan accurately predicted 100% of suprainguinal and 85% of infrainguinal procedures. Two-year primary patency was 83% for all procedures. Radiologists' review of disease severity resulted in a mean exact correlation between studies of 81% (kappa = 0.64). The agreement between radiologists interpreting the MRA was 84% (kappa = 0.7) compared with 82% (kappa = 0.66) for the DSA. CONCLUSIONS: MRA- and DSA-based preoperative management plans were of comparable efficacy. Significant interobserver variability was seen with the interpretations of both preoperative studies. EKG-triggered 2D TOF MRA can be used to plan arterial reconstructions; however, all patients require arterial pressure measurements prior to suprainguinal repair and confirmatory intraoperative angiography during infrainguinal revascularization.

Aged↗
PubMed1979

Electrocardiography in myocardial infarction.

Electrocardiography is an evolving clinical diagnostic modality for detection of acute myocardial infarction. Animal studies and electrocardiographic-clinical-pathological correlations have provided experience currently used for detection and rough localization of myocardial infarcts. Additions to the conventional 12 electrocardiographic leads have been utilized to increase the diagnostic sensitivity of the ECG in the setting of myocardial infarction. Mapping of ST-segment elevation an QRS complex from several chest wall loci have been employed for purposes of quantitating serially myocardial ischemic injury and eventual necrosis. These multiple lead electrocardiographic systems have also been utilized in assessing therapeutic interventions in the Coronary Care Unit. Usefulness of standard and multiple-lead recording systems is enhanced by awareness of their limitations when applied to patients with acute myocardial infarction.

Action Potentials↗
PubMed1983

Circadian rhythms in dynamic electrocardiography.

A group of ten healthy subjects aged 32-58 years was studied by dynamic electrocardiography. An electrocardiogram (ECG) was recorded on CM 5 lead for 14 seconds every 15 minutes during the 24 hours. All the subjects were under a similar nyctohemeral schedule, sleeping between 23.30 and 06.45, and all followed their spontaneous diet without any restriction. "Mean Cosinor" analysis of the data revealed statistically significant circadian rhythms of heart rate (HR), R and T-wave voltages, duration of the QT interval and ST segment displacement, but not of the duration of the corrected QT (QTc).

Adult↗
PubMed1986

High frequency electrocardiography using an advanced method of signal averaging for non-invasive detection of coronary artery disease in patients with normal conventional electrocardiogram.

The ability to detect coronary artery disease (CAD) in patients with normal, conventional electrocardiograms (ECG) was studied using high frequency electrocardiography and an advanced method of signal averaging in three groups of subjects. Group A consisted of ten healthy subjects under the age of 30; Group B of 15 patients with chest pains and normal coronary arteries; and Group C of 20 patients with chest pains and CAD. Four hundred ECG waveforms from leads V3, V4 and V5 were recorded, and the recorded analog data were digitized. The digitized waveforms were averaged using a cross-correlation function which operates in the frequency domain (fast-Fourier transform algorithm). The signals were filtered with a digital band pass filter with 150 and 250 Hz low and high cut-off frequencies, respectively. Zones of reduced amplitude in the envelope of the filtered QRS complex of at least two precordial leads were found more significantly in patients with CAD (75%) than in patients without CAD (12% for Groups A and B, p less than 0.00003). However, no significant difference was found between the voltage over the high frequency QRS complex and that of its envelope between the three groups. It is concluded that the morphology of the high frequency QRS complex as determined by this advanced method of analysis of the signal averaged ECG may be a useful indicator for the presence of CAD in patients with normal conventional ECG's.

Adult↗
PubMed1987

Myocardial infarction size and location: a comparative study of epicardial isopotential mapping, thallium-201 scintigraphy, electrocardiography and vectorcardiography.

Based on epicardial isopotential mapping (the Ep Map), which was calculated from body surface isopotential mapping (the Body Map) with Yamashita's method, using the finite element technique, we predicted the location and size of the abnormal depolarized area (the infarcted area) in 19 clinical cases of anterior and 18 cases of inferoposterior infarction. The prediction was done using Toyama's diagnostic method, previously reported. The accuracy of the prediction by the Ep Map was assessed by comparing it with findings from thallium-201 scintigraphy (SCG), electrocardiography (ECG) and vectorcardiography (VCG). In all cases of anterior infarction, the location of the abnormal depolarized areas determined on the Ep Map, which was localized at the anterior wall along the anterior intraventricular septum, agreed with the location of the abnormal findings obtained by SCG, ECG and VCG. For all inferoposterior infarction cases, the abnormal depolarized areas were localized at the posterior wall and the location also coincided with that of the abnormal findings obtained by SCG, ECG and VCG. Furthermore, we ranked and ordered the size of the abnormal depolarized areas, which were predicted by the Ep Map for both anterior and inferoposterior infarction cases. In the cases of anterior infarction, the order of the size of the abnormal depolarized area by the Ep Map was correlated to the size of the abnormal findings by SCG, as well as to the results from Selvester's QRS scoring system in ECG and to the angle of the maximum QRS vector in the horizontal plane in VCG.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrocardiography↗
PubMed1996

Variability of precordial electrode placement during routine electrocardiography.

Placement of precordial electrodes by 30 experienced technicians during routine electrocardiography was compared with anatomically ascertained sites marked by ink visible only under ultraviolet "black light" in three men and five women. The distance and direction from each marked site to the center of the applied electrode was measured to allow calculation of both the linear magnitude of difference (derived from the square root of the sum of the squares of rise and run) and also the direction of difference (in quadrants) between the anatomically established location and the electrode at each precordial site. The average difference from the applied electrodes to the corresponding marked sites was 1.14 inches, ranging from a mean of 1.31 inches at lead V1 to 0.98 inches at lead V4. Overall, 64% of precordial electrodes were placed within a radius of 1.25 inch, ranging from 56% for lead V6 to 74% for lead V4, and 27% of precordial electrodes were placed within a radius of 0.625 inch. There was superior quadrant displacement of more than 0.625 inch in more than 50% of routine applications of leads V1 and V2, indicating that these electrodes are commonly placed both high and wide of their anatomically defined precordial sites. Similarly, there was an inferior and left-ward displacement of more than 0.625 inch in 30-50% leads of routine applications of V4 through V6, indicating that these lateral precordial electrodes are commonly placed both low and wide of their respective anatomic sites.

Body Constitution↗
PubMed2003

Age and anesthetic effects on murine electrocardiography.

Murine models offer potential insights regarding human cardiac disease, but efficient and reliable methods for phenotype evaluation are necessary. We employed non-invasive electrocardiography (ECG) in mice, investigating statistical reliability of these parameters with respect to anesthetic and animal age. Mice (C57BL/6, 8 or 48 weeks) were anesthetized by ketamine/xylazine (K/X, 80/10 mg/kg ip) or by inhalation anesthetic (halothane, HAL; sevoflurane, SEV) and 6 lead ECGs were recorded. P wave duration and QT interval was significantly prolonged with K/X compared to HAL and SEV, indicating slowed atrial and ventricular conduction. P-R interval (atrio-ventricular conduction) was significantly increased in aged mice under all anesthetics. Heart rate was inversely correlated to QT interval and P wave duration. We also detected significant age effects with respect to optimal approaches for QT interval corrections. Power analysis showed 4-fold higher number of mice/group, were required for K/X, to achieve identical statistical sensitivity. These data demonstrate the importance of anesthetic selection for relevant and reliable ECG analysis in mice and illustrate the selective influences of anesthetics and age on cardiac conductance in this species.

Aging↗
PubMed1997

The inverse problem of electrocardiography: a solution in terms of single- and double-layer sources of the epicardial surface.

An approach to the inverse problem of electrocardiography that involves an estimation of the electric potentials (double-layer equivalent sources) on the heart's epicardial surface from the electrocardiographic potentials that are measurable on the body surface has received considerable attention. This report deals with a heretofore unexplored extension of this approach, one that yields, in addition to the electric potentials on the epicardial surface, the normal components of their gradients (single-layer equivalent sources). We show that this formulation has at least three advantages over the formulation in term of epicardial potentials alone: (1) single-layer equivalent sources, which reflect the flow of current across the epicardial surface, are well suited for the imaging of regional ischemia and infarction; (2) the transfer matrix linking the epicardial and body-surface potentials for this formulation is less ill conditioned than that for the formulation in terms of potentials alone; (3) the input vector for inverse calculations consists of spatially filtered (rather that directly measured and therefore noise) body-surface potentials. To establish the feasibility of this new formulation of the inverse problem and to compare it with the formulation in terms of potentials alone, we used a realistically shaped boundary-element model of human torso. By calculating singular values less ill conditioned. We then directly calculated epicardial and body-surface potentials for a single dipole located centrally and for three simultaneously active dipoles located eccentrically in the torso's heart region and used these results to test three methods that are prerequisites of a successful inverse solution: Tikhonov regularization, linearly constrained least squares, and an L-curve method. The feasibility of the new formulation was demonstrated by the fact that the method based on the linearly constrained least squares improved on overregularized Tikhonov solutions over a wide range of regularization parameters, and it yielded solutions that were more accurate than the best-possible Tikhonov solutions. Moreover, the L-curve solution procedure, which requires no a priori information about the solution, yielded slightly underregularized, but accurate, estimates for the optimal regularization parameter and the corresponding best-possible Tikhonov solution. Our results also showed that replacing--in the interest computational economy--quadrature formulas for the planar triangles with various approximate formulas for the nodes of the model reduces the accuracy of the inverse solution.

Electrocardiography↗
PubMed1988

Signal-averaged electrocardiography: a new noninvasive test to identify patients at risk for ventricular arrhythmias.

Signal-averaged electrocardiography (ECG) is a new noninvasive test for identifying patients at risk for ventricular arrhythmias. This computerized method of analyzing standard ECGs identifies particular microvolt-level signals called late potentials. Late potentials have been correlated with clinical ventricular tachycardia, are predictive of ventricular tachycardia inducibility at the time of electrophysiologic testing, and are predictive of arrhythmic events after myocardial infarction. In this review, we describe late potentials, the method of obtaining and processing the signal-averaged ECG, and clinical studies in various patient groups that have assessed the predictive value of the signal-averaged ECG for identification of patients at risk for subsequent ventricular arrhythmias.

Death, Sudden↗
PubMed1984

Cyclical variation of the heart rate in sleep apnoea syndrome. Mechanisms, and usefulness of 24 h electrocardiography as a screening technique.

400 sleep-apnoeic patients with an intact autonomic nervous system underwent twenty-four-hour electrocardiography with simultaneous polygraphy recording at night. At onset of sleep apnoea all showed progressive bradycardia, followed by abrupt tachycardia on resumption of breathing. The electrocardiographic pattern, which is identifiable by computer analysis, can be used as a screening tool for sleep apnoea; it was not seen in controls without sleep apnoea syndrome. A subgroup of patients with sleep apnoea and impairment of autonomic nervous control of the heart (heart transplants, autonomic neuropathy, Shy-Drager syndrome) did not show the cyclical heart rate pattern. In obstructive sleep apnoeic patients with normal autonomic nervous function, atropine sulphate blocked the pattern by eliminating the bradycardia component, while 100% oxygen, even at high rates of administration, caused only moderate blunting of the heart rate variation. The electrocardiographic changes observed in sleep apnoea syndrome are therefore mediated by the autonomic nervous system; hypoxia is not the only factor involved.

Activity Cycles↗
PubMed1988

Right atrial electrocardiography in placement of central venous catheters.

Right atrial electrocardiography has been used both for the positioning of ventriculoatrial shunts and for the detection and treatment of air embolism during neurosurgical procedures. Its use for the precise placement of central venous catheters for parenteral nutrition is described here. 50 lines were placed in 48 patients. The lines were satisfactorily sited in 48 cases. No false-negative or false-positive traces were obtained. The technique is extremely accurate; failure to obtain the characteristic traces indicates malposition of the catheter tip. The need for on-table radiography is virtually eliminated.

Atrial Function↗
PubMed1997

The specificity of exercise electrocardiography in women grouped by estrogen status.

We compared the specificity of exercise electrocardiography in 1880 men and 1818 women with women grouped by menopausal and estrogen replacement status. Specificity for > or = 1 mm horizontal or downsloping ST-segment depression was determined using angiography in 781 patients and using two other nonangiography-based methods (a pretest probability-based method and a predictive accuracy-based method) in all patients. Using angiography, the specificities+/-SE were 84 +/- 2 for men, 79 +/- 3 for women, 81 +/- 5 for premenopausal women, 81 +/- 4 for postmenopausal women without estrogen replacement, and 77 +/- 5 for women on estrogen replacement. None of these were significantly different. For all patients, the respective specificities using the probability and predictive accuracy-based methods were 97 +/- 1 and 94 +/- 1 for men, 90 +/- 1 and 88 +/- 1 for women, 97 +/- 1 and 92 +/- 2 for premenopausal women, 92 +/- 4 and 88 +/- 3 for postmenopausal women without estrogen replacement, and 85 +/- 4 and 81 +/- 3 for women on estrogen replacement. (Men vs. all women groups except premenopausal women-P < 0.05). Therefore, the premenopausal women had significantly greater specificity than women on estrogen replacement (P < 0.001) and no difference in specificity with men. Women on estrogen replacement had a significantly lower specificity than postmenopausal women not on estrogen replacement (P < 0.05). These results suggest that estrogen replacement therapy and not naturally occurring estrogen has a role in producing false positive exercise electrocardiograms in women.

Adult↗
PubMed1999

Prediction of atrial fibrillation recurrence after cardioversion by P wave signal-averaged electrocardiography.

The purpose of this report was to determine prospectively whether P wave signal-averaged electrocardiography (ECG) is useful for the prediction of recurrences of atrial fibrillation after cardioversion. The P wave signal-averaged ECG was recorded in 73 patients after successful cardioversion. Duration of the filtered P wave and the root mean square voltages for the last 20 ms of the P wave were calculated. In addition to signal-averaged ECG P wave analysis, all patients were evaluated by echocardiography. During 6 months follow-up period recurrence of atrial fibrillation was observed in 31 (42.5%) patients and in 42 (57.5%) patients sinus rhythm was maintained. There was no difference in gender, age, presence of organic heart disease, left atrial diameter, left ventricular ejection fraction, use of antiarrhythmic drug, and duration of atrial fibrillation (P>0.05). The filtered P-wave duration was longer and the root mean square voltages for the last 20 ms of the P wave was lower in patients with recurrence of atrial fibrillation than in patients who maintained sinus rhythm (138.3+/-12.5 ms vs. 112.4+/-11.8 ms, P = 0.001; 1.9+/-0.7 microV vs. 2.5+/-0.6 microV, P = 0.001). A filtered P-wave duration > or =128 ms associated with a root mean square voltage for the last 20 ms of the P wave < or =2.1 microV had a sensitivity of 70% and specificity of 76% for the detection of patients with recurrence of atrial fibrillation after successful cardioversion of atrial fibrillation. We found that the likelihood of recurrence of atrial fibrillation after cardioversion was increased 4.31-fold (95% confidence interval 2.08-9.83) if these parameters were used. These results suggest that P wave signal-averaged ECG could be useful to identify patients at risk for recurrence of atrial fibrillation after cardioversion.

Adult↗