Effects of posture and respiration on body surface electrocardiogram

Reconstruction of cardiac position using body surface potentials

Electrocardiographic imaging (ECGI) is a noninvasive technique to assess the bioelectric activity of the heart which has been applied to aid in clinical diagnosis and management of cardiac dysfunction. ECGI is built on mathematical models that take into account several patient specific factors including the position of the heart within the torso. Errors in the localization of the heart within the torso, as might arise due to natural changes in heart position from respiration or changes in body position, contribute to errors in ECGI reconstructions of the cardiac activity, thereby reducing the clinical utility of ECGI. In this study we present a novel method for the reconstruction of cardiac geometry utilizing noninvasively acquired body surface potential measurements. Our geometric correction method simultaneously estimates the cardiac position over a series of heartbeats by leveraging an iterative approach which alternates between estimating the cardiac bioelectric source across all heartbeats and then estimating cardiac positions for each heartbeat. We demonstrate that our geometric correction method is able to reduce geometric error and improve ECGI accuracy in a wide range of testing scenarios. We examine the performance of our geometric correction method using different activation sequences, ranges of cardiac motion, and body surface electrode configurations. We find that after geometric correction resulting ECGI solution accuracy is improved and variability of the ECGI solutions between heartbeats is substantially reduced.

Preliminary Analysis of a Wireless and Wearable Electronic-Textile EASI-Based Electrocardiogram

Background: With cardiovascular disease continuing to be the leading cause of death and the primary reason for hospitalization worldwide, there is an increased burden on healthcare facilities. Electronic-textile (e-textile)-based cardiac monitoring offers a viable option to allow cardiac rehabilitation programs to be conducted outside of the hospital.

Objectives: This study aimed to determine whether signals produced by an e-textile ECG monitor with textile electrodes in an EASI configuration are of sufficient quality to be used for cardiac monitoring. Specific objectives were to investigate the effect of the textile electrode characteristics, placement, and condition on signal quality, and finally to compare results to a reference ECG obtained from a current clinical standard the Holter monitor.

Methods: ECGs during different body movements (yawning, deep-breathing, coughing, sideways, and up movement) and activities of daily living (sitting, sitting/standing from a chair, and climbing stairs) were collected from a baseline standard of normal healthy adult male using a novel e-textile ECG and a reference Holter monitor. Each movement or activity was recorded for 5 min with 2-min intervals between each recording. Three different textile area electrodes (40, 60, and 70 mm²) and electrode thicknesses (3, 5, and 10 mm) were considered in the experiment. The effect of electrode placement within the EASI configuration was also studied. Different signal quality parameters, including signal to noise ratio, approximate entropy, baseline power signal quality index, and QRS duration and QT intervals, were used to evaluate the accuracy and reliability of the textile-based ECG monitor.

Results: The overall signal quality from the 70 mm² textile electrodes was higher compared to the smaller area electrodes. Results showed that the ECGs from 3 and 5 mm textile electrodes showed good quality. Regarding location, placing the “A” and “I” electrodes on the left and right anterior axillary points, respectively, showed higher signal quality compared to the standard EASI electrode placement. Wet textile electrodes showed better signal quality compared to their dry counterparts. When compared to the traditional Holter monitor, there was no significant difference in signal quality, which indicated textile monitoring was as good as current clinical standards (non-inferior).

Conclusion: The e-textile EASI ECG monitor could be a viable option for real-time monitoring of cardiac activities. A clinical trial in a larger sample is recommended to validate the results in a clinical population.

R-wave amplitude changes with posture and physical activity over time in an insertable cardiac monitor

Background

Insertable cardiac monitors (ICMs) are accepted tools in cardiac arrhythmia management. Consistent R-wave amplitude (RWA) is essential for optimal detection.

Objectives

Assess RWAs with posture/activities at insertion and at 30 days.

Methods

Participants (n = 90) with Confirm Rx™ ICM had RWAs measured in different postures (supine, right-side [RS], left-side [LS], sitting, and standing) and defined physical activities (including isometric push [IPUSH] and pull) at 2 time points. ICMs were inserted in 45° to sternum and parasternal orientations.

Results

There were significant reductions at insertion with RS, LS, sitting, or standing vs supine (reference position) (all P < .05). At 30 days, significant changes only occurred with LS and sitting (P < .05). Sex had an effect on RWAs, with females having significant variability at insertion (supine vs RS, LS, sitting, standing, and IPUSH; all P < .05). Males showed large RWA interpatient variabilities but minimal differences between positions vs supine. At 30 days, RS, LS, and sitting positions remained significant for females (P < .05), while in males RWAs were higher than at insertion for most postures and activities. The orientation 45° to sternum had consistently higher RWAs vs parasternal orientation at both time points (P < .0001). In females, ICM orientation had no significant effect on RWAs; however, in males the 45° to sternum produced higher RWAs. ICM movement from the insertion site showed no correlation with RWA changes.

Conclusion

The mean RWAs were higher at 30 days with less interparticipant and interpostural variability; males had higher RWAs compared to females; 45° to sternum orientation had higher RWAs; and ICM migration from the insertion site did not affect RWAs.

Augmented Oscillations in QT Interval Duration Predict Mortality Post Myocardial Infarction Independent of Heart Rate

Objective

This study seeks to decompose QT variability (QTV) into physiological sources and assess their role for risk stratification in patients post myocardial infarction (MI). We hypothesize that the magnitude of QTV that cannot be explained by heart rate or respiration carries important prognostic information.

Background

Elevated beat-to-beat QTV is predictive of cardiac mortality, but the underlying mechanisms, and hence its interpretation, remain opaque.

Methods

We decomposed the QTV of 895 patients post MI into contributions by heart rate, respiration, and unexplained sources.

Results

Cox proportional hazard analysis demonstrates that augmented oscillations in QTV and their level of dissociation from heart rate are associated with a higher 5-year mortality rate (18.4% vs. 4.7%, p < 0.0001). In patients with left ventricular ejection fraction (LVEF) > 35%, a higher QTV risk score was associated with a significantly higher 5-year mortality rate (16% vs. 4%, p < 0.0001). In patients with a GRACE score ≥ 120, a higher QTV risk score was associated with a significantly higher 5-year mortality (25% vs. 11%, p < 0.001).

Conclusion

Augmented oscillations in QTV and discordance from heart rate, possibly indicative of excessive sympathetic outflow to the ventricular myocardium, predict high risk in patients post MI independent from established risk markers.

Clinical Trial Registration

www.ClinicalTrials.gov, identifier NCT00196274.

Repolarization variability independent of heart rate during sympathetic activation elicited by head-up tilt

The fraction of repolarization variability independent of RR interval variability is of clinical interest. It has been linked to direct autonomic nervous system (ANS) regulation of the ventricles in healthy subjects and seems to reflect the instability of the ventricular repolarization process in heart disease. In this study, we sought to identify repolarization measures that best reflect the sympathetic influences on the ventricles independent of the RR interval. ECG was recorded in 46 young subjects during supine and then following 45 degrees head-up tilt. RR intervals and five repolarization features (QTend, QTpeak, RTend, RTpeak, and TpTe) were extracted from the ECG recordings. Repolarization variability was separated into RR-dependent and RR-independent variability using parametric spectral analysis. Results show that LF power of TpTe is independent of RR in both supine and tilt, while the LF power of QTend and RTend independent of RR and respiration increases following tilt. We conclude that TpTe is independent of RR and is highly affected by respiration. QTend and RTend LF power might reflect the sympathetic influences on the ventricles elicited by tilt. Graphical abstract.

Valsalva Maneuver and Strain-Related ECG Changes

BACKGROUND

During the four steps of the Valsalva maneuver (VM), opposite changes can be observed in some physiologic parameters. Manifestations of the VM in the electrocardiogram (ECG) have been studied in detail, but there have been few reports comparing VM-related biochemical and hemodynamic changes with a focus on the strain phase of the VM.

OBJECTIVES

We studied strain-related ECG changes during the VM.

PATIENTS AND METHODS

This self-control descriptive study was conducted in 20 healthy male college students aged 20.12 ± 2.23 years. They were well trained to perform the standard VM: maintenance of a 15-second expiratory pressure at 40 mmHg with open glottis. An ECG was continuously recorded in the supine position at (a) rest (before the VM) and at (b) the start and (c) end of strain maintenance in the second phase of the VM. The averages of four successive beats were computed for each set of (a), (b), and (c). Means ± standard errors of the mean were used for comparison.

RESULTS

Following the VM, the RR and PR intervals, corrected QT interval (QTc), P wave duration and amplitude, T wave amplitude, and the ratio of T/R amplitudes showed significant changes. The QRS duration and R wave amplitude did not show significant changes.

CONCLUSIONS

The VM caused time and voltage changes in some ECG waves during the strain phase. Alterations in heart or lung volume, electrode-related alterations, and autonomic tone may cause these changes.

Valsalva Maneuver and Strain-Related ECG Changes

BACKGROUND

During the four steps of the Valsalva maneuver (VM), opposite changes can be observed in some physiologic parameters. Manifestations of the VM in the electrocardiogram (ECG) have been studied in detail, but there have been few reports comparing VM-related biochemical and hemodynamic changes with a focus on the strain phase of the VM.

OBJECTIVES

We studied strain-related ECG changes during the VM.

PATIENTS AND METHODS

This self-control descriptive study was conducted in 20 healthy male college students aged 20.12 ± 2.23 years. They were well trained to perform the standard VM: maintenance of a 15-second expiratory pressure at 40 mmHg with open glottis. An ECG was continuously recorded in the supine position at (a) rest (before the VM) and at (b) the start and (c) end of strain maintenance in the second phase of the VM. The averages of four successive beats were computed for each set of (a), (b), and (c). Means ± standard errors of the mean were used for comparison.

RESULTS

Following the VM, the RR and PR intervals, corrected QT interval (QTc), P wave duration and amplitude, T wave amplitude, and the ratio of T/R amplitudes showed significant changes. The QRS duration and R wave amplitude did not show significant changes.

CONCLUSIONS

The VM caused time and voltage changes in some ECG waves during the strain phase. Alterations in heart or lung volume, electrode-related alterations, and autonomic tone may cause these changes.

Improving sensing and detection performance in subcutaneous monitors

Implantable loop recorders (ILRs) are used for continuous assessment of patients at risk for syncope and arrhythmia. Device accuracy depends on appropriate sensing of the patient's electrocardiogram (ECG) signal. However, current methods for sensing cardiac electrical activity rely on simple threshold detectors that are computationally efficient but nonspecific. We test the hypothesis that better ILR implant positions will increase detection accuracy. Ten healthy subjects were studied as they assumed 12 different postures. Body surface potential map (BSM) recordings were used to estimate bipolar R-wave amplitudes for 64 potential implant sites at 360 orientations per site. Optimal sites were identified as the combination of position and orientation that consistently gave the largest signal and the lowest variability during posture changes. Results showed that posture impacts the R-wave amplitude in both BSM and derived bipolar ECGs in healthy subjects. Specific postures are associated with significant drops in R-wave signal amplitude that could cause loss of signal detection in ILRs, especially in positions likely to displace the diaphragm. R-wave changes occurred abruptly as posture was changed. Optimal implant locations cluster near the center of the chest, aligned with the cardiac axis, consistent with the steeper isoelectric gradients known to be associated with these positions.

Effects of Cardiac Resynchronization Therapy on Ventricular Repolarization in Patients with Congestive Heart Failure

INTRODUCTION

Biventricular pacing has been shown to improve the clinical status of patients with congestive heart failure, but little is known about its influence on ventricular repolarization. The aim of our study was to evaluate the effect of biventricular pacing on ECG markers of ventricular repolarization in patients with congestive heart failure.

METHODS AND RESULTS

Twenty-five patients with congestive heart failure, sinus rhythm (SR), and complete LBBB (6 females; age 61 +/- 8 years; NYHA class II-III; echocardiographic ejection fraction 21 +/- 5%; QRS > or = 130 ms) underwent permanent biventricular DDDR pacemaker implantation. A high-resolution 65-lead body-surface ECG recording was performed at baseline and during right-, left-, and biventricular pacing, and the total 65-lead root mean square curve of the QRST complex and the interlead QT dispersion were assessed. The QRS duration was increased during right (RV)- and left ventricular (LV) pacing (127 +/- 26% and 117 +/- 40%; P < 0.05), as compared to SR (100%) and biventricular pacing (93 +/- 16%; ns). The QTc interval was increased during RV and LV pacing (112 +/- 12% and 114 +/- 14%; P < 0.05) as compared to SR (100%) or biventricular pacing (99 +/- 12%). There was no effect on JT interval during all pacing modes. The T(peak-end) interval was increased during right (120 +/- 34%; P < 0.01) and LV pacing (113 +/- 29%; P < 0.05) but decreased during biventricular pacing (81 +/- 19%; P < 0.01). A similar effect was found for the T(peak-end) integral and the T(peak) amplitude. QT dispersion was increased during right ventricular (129 +/- 16 ms; P < 0.05) and decreased during biventricular pacing (90 +/- 12 ms; P < 0.01), as compared to SR (114 +/- 22 ms).

CONCLUSIONS

Using a high-resolution surface ECG, biventricular pacing resulted in a significant reduction of ECG markers of ventricular dispersion of repolarization.

Effects of heart position on the body-surface electrocardiogram

Previous studies have examined the influence of body position, respiration, and habitus on body surface potentials. However, the authors could only estimate the sources of the effects they documented. Among the proposed origin of changes in body surface potentials from those studies were the position of the heart, alterations in autonomic tone, differences in ventricular blood volume, and variations in torso resistivity. The goal of this study was to investigate specifically the role of geometric factors in altering body surface potentials and the electrocardiogram. For this, we used experiments with an isolated, perfused dog heart suspended in a realistically shaped electrolytic torso tank. The experimental preparation allowed us to measure epicardial and tank surface potentials simultaneously, and then reconstruct the geometry of both surfaces. Our results mimicked some of the features described by previous investigators. However, our results also showed differences that included considerably larger changes in the peak QRS and T-wave amplitudes with heart movement than those reported in human studies. We detected smaller values of root-mean-squared variability from heart movements than those reported in a human study comparing body surface potentials during change in inspiration and body position. There was better agreement with relative variability, which in these studies ranged from 0.11 to 0.42, agreeing well with an estimate from human studies of 0.40. Our results suggest that the isolated heart/torso tank preparation is a valuable tool for investigating the effects of geometric variation. Furthermore, the geometric position of the heart appears to be a large source of variation in body surface potentials. The size of these variations easily exceeded thresholds used to distinguish pathologic conditions and thus such variations could have important implications on the interpretation of the standard electrocardiogram.

Positional changes of spatial QRS- and ST-segment variables in normal subjects: implications for continuous vectorcardiography monitoring during myocardial ischemia

Electrocardiographic QRS- and ST-segment changes are to be expected during changes in body posture. We prospectively analyzed the influence of changes in body position on continuous vectorcardiography monitoring of QRS-vector difference (QRS-VD) and ST change-vector magnitude (STC-VM) according to the currently used criteria of myocardial ischemia in 21 normal subjects. Fifteen (71%) and 6 (29%) subjects had significant positional QRS-VD and STC-VM changes, respectively. Vectorcardiography changes were most frequent and pronounced in the left lateral position. An alternative to the existing criterion of ischemia is proposed to improve the specificity of STC-VM. Subjects with positional QRS-VD changes had higher mean STC-VM values as compared with those without such changes. Otherwise no characteristics among those with positional vectorcardiography changes could be identified. There was no statistically significant association between positional QRS-VD and STC-VM changes (R = .13, P = .57). We conclude that the clinical use of QRS-VD in its present form for continuous vectorcardiography monitoring of myocardial ischemia seems to be of limited practical value, because of the presence of frequent "pseudo-ischemic" changes. STC-VM seems to have a significant potential of continuous vectorcardiography monitoring. However, an indicator of body position change or even an algorithm enabling on-line correction for positional vectorcardiography changes seems to be essential to improve the accuracy of this technique in identifying myocardial ischemia.

Temporal and positional variability of the ST segment during continuous vectorcardiography monitoring in healthy subjects

Continuous vectorcardiography ST-segment monitoring (cVST) is a well-established method in the diagnosis and risk evaluation of patients with acute myocardial ischemia. Previous investigations have demonstrated that electrocardiographic ST-segment changes are to be expected, during both repeated measurements and changes in body position. We prospectively analyzed the influence of spontaneous temporal variation (technical and biological noise) and changes in body position on the ST segment (ST-vector magnitude [ST-VM]) during cVST of 21 healthy human subjects. The 95% expectancy range of the spontaneous intraindividual ST-VM variation was found to be +/-8 microV for the error of measurement, and +/-14 and +/-24 microV during 24-hour and day-to-day cVST measurements, respectively. Positional ST-segment changes in the orthogonal leads were frequent, especially in leads X and Z, and in the left lateral position. Positional orthogonal ST-segment changes resulted in significant ST-VM changes in two of seven subjects. It is concluded that the low spontaneous temporal ST-VM variation must be considered as good reproducibility. Moreover, the present findings support currently used ST-VM ischemia criteria. However, the impact of positional changes on ST-VM seems to be of importance (with the possibility of false-positive results) and should be taken into account during cVST.

Body surface mapping during pacing at multiple sites in the human atrium: P-wave morphology of ectopic right atrial activation

BACKGROUND

The morphology and polarity of the P wave on 12-lead ECG are of limited clinical value in localizing ectopic atrial rhythms. It was the aim of this study to assess the spatial resolution of body surface P-wave integral mapping in identifying the site of origin of ectopic right atrial (RA) impulse formation in patients without structural atrial disease.

METHODS AND RESULTS

Sixty-two-lead ECG recordings were obtained during RA pacing at 86 distinct endocardial sites in nine patients with normal biatrial anatomy. After P-wave integral maps were generated for each paced activation sequence, 17 groups with nearly identical map features were visually selected, and a mean P-wave integral map was computed for each group. Supportive statistical analysis to corroborate qualitative group selection was performed by assessment of (1) intragroup pattern uniformity by use of jackknife correlation coefficient analysis of the integral maps contained in each group and (2) intergroup pattern variability by use of the calculation of cross correlations between the 17 mean integral maps. The spatial resolution of paced P-wave body surface mapping in the right atrium was obtained by estimating the area size of endocardial segments with nearly identical P-wave integral maps by use of a biplane fluoroscopic method to compute the three-dimensional position of each pacing site. The latter approach yielded a mean endocardial segment size of 3.5+/-2.9 cm2 (range, 0.79 to 10.75 cm2).

CONCLUSIONS

Use of the P-wave morphology on the 62-lead surface ECG in patients with normal biatrial anatomy allows separation of the origin of ectopic RA impulse formation into one of 17 different endocardial segments with an approximated area size of 3.5 cm2. This database of paced P-wave integral maps provides a versatile clinical tool to perform detailed noninvasive localization of right-sided atrial tachycardia before radiofrequency catheter ablation.

Vectorcardiographic changes during laparoscopic cholecystectomy may mimic signs of myocardial ischaemia

BACKGROUND

Laparoscopic surgery involves the use of intra-abdominal carbon dioxide insufflation (pneumoperitoneum). The increased intra-abdominal pressure causes marked haemodynamic changes, which may influence electrocardiographic monitoring. The aim of the present study was to elucidate the influence of pneumoperitoneum on vectorcardiographic recordings.

METHODS

Vectorcardiographic changes (QRS vector difference = QRS-VD, QRS loop area, QRS magnitude, ST vector magnitude, spatial ST vector change) were recorded continuously applying computerized vectorcardiography in 12 anaesthetised cardiovascularly healthy patients, scheduled for laparoscopic cholecystectomy. Measurements were made before and during pneumoperitoneum in three different body positions (supine, Trendelenburg and reversed Trendelenburg), also employing transesophageal echocardiography and invasive blood pressure monitoring.

RESULTS

Pneumoperitoneum significantly increased QRS-VD, in parallel with an enlargement in loop area and magnitude. The magnitude was significantly increased in the transversal and frontal planes and there was a tendency to increase the magnitude in the sagittal plane. The increase in QRS-VD reached levels previously associated with the development of myocardial ischaemia in patients with coronary artery disease. The ST-variables were not changed by the pneumoperitoneum. The positional changes also influenced QRS-VD significantly.

CONCLUSIONS

When computerized vectorcardiography is used for ischaemia monitoring during pneumoperitoneum, the ST-variables seem reliable. However, vectorcardiographic QRS-changes should be interpreted with caution, as the QRS alterations found during pneumoperitoneum mimic the changes seen during myocardial ischaemia.

Analysis of PTCA-induced ischemia using an ECG inverse solution or the wavelet transform

In patients without significant collaterals, percutaneous transluminal coronary angioplasty (PTCA) produces acute transient ischemia that is detectable in both standard electrocardiograms (ECG) and body surface potential maps (BSPMs). Control recordings made before or between inflations provide personalized baselines, which isolate the effects of ischemia from interpatient differences, such as torso shape and electrode location. In this study, two methods of evaluating PTCA-induced ischemia from BSPM recordings are presented. In the first method, an ECG inverse solution that estimates epicardial potentials from body surface signals using a realistic model of torso geometry is applied. The strength of this method lies in its potential ability to localize areas of cardiac ischemia on the epicardial surface. In the second approach, wavelet transforms were used to perform a multiresolution decomposition of the BSPM data into different frequency bands. The basis functions of the wavelet transform are time-limited and narrow band and hence can be expected to be sensitive to features of the BSPM that originate in discrete electrophysiologic events, such as intrusion of the activation front onto regions of ischemia or arrhythmias due to local conduction abnormalities. The method also offers a means of temporal and frequency localization of cardiac events related to the initiation of injury currents and abnormal conduction due to PTCA-induced ischemia. The inverse solution and the wavelet transform each offer new views of the spatial and temporal courses of acute ischemia potentially leading to new diagnostic insights in ECG patient examination.

Ischaemic heart disease and the changes in the QRS and ST segments during exercise: a pilot study with a novel vectorcardiographic system

In order to find new ischaemic parameters, the spatial changes of the Frank vectorcardiogram were continuously analysed with a new, highly precise vectorcardiographic method during, and immediately after a maximal exercise test. This was done in 18 young healthy males, and 18 patients with scintigraphic reversible ischaemia. During exercise, different patterns between the groups were noted for the changes in the mean QRS magnitude in the Y-lead (P less than 0.005), the QRS-integral (P less than 0.05), and the QRS-duration (P less than 0.05). Immediately after exercise, several QRS parameters in the normal group continued to change according to the same pattern as during exercise (P less than 0.05), which was in contrast with the patterns of the ischaemic group (P less than 0.01). The spatial ST difference at J+20 ms discriminated well between the groups, especially when corrected for QRS-magnitudes at rest and heart rate (P less than 0.0005). In short, this pilot study supports previous findings in that changes in amplitude and duration of the QRS complex during exercise discriminated between healthy young males and patients with ischaemic heart disease. Moreover, rapid discriminating changes were seen in the QRS segment during cessation of exercise. These changes deserve attention since they may be of importance for the conflicting results on the diagnostic value of QRS changes during exercise.

Comparison of electrocardiographic data (P waves): test of a shape-based approach

We tested a method for comparing ECG signals (P waves), in a sample of 10 normal males. In each subject, sets of 219 body surface ECGs were simultaneously recorded during tidal respiration. Only beats at end expiration and peak inspiration were considered. The beats of each group were subdivided into two subgroups of the same size (about 30 beats) and separately averaged. The two averaged beats at end expiration, assumed to be equal, were compared in order to estimate the noise variance (sigma2), i.e., the lowest value of variance at which the beats were statistically similar (P less than 0.05). At the same value of sigma2, the beat at end expiration significantly differed from that at peak inspiration. By considering the individual leads, significant differences were found in more than 50% of the 219 ECGs, in specific thoracic areas. The data indicated that the method can reveal differences between P waves occurring during tidal respiration and provide information on the topographical distribution of the differences.

Instrumentation and practice standards for electrocardiographic monitoring in special care units. A report for health professionals by a Task Force of the Council on Clinical Cardiology, American Heart Association

The proposed recommendations for continuous electrocardiographic monitoring systems represent goals for future development. Description of a technique in the report does not constitute an endorsement of its clinical use. Lead systems for ECG monitoring must adequately sense the cardiac electrical field and the leads should be standardized. Future monitors should be capable of simultaneously displaying and analyzing multiple leads. Recommendations for electrode placement and position of patient are made. Important parameters in each category of standards for instrumentation published in 1983 in the American National Standard for Cardiac Monitors, Heart Rate Meters, and Alarms are listed. Selected procedures proposed by the Association for the Advancement of Medical Instrumentation to inform users of minimally acceptable accuracy of computerized systems in a standardized manner are presented. Emphasis is placed on the importance of nursing and medical staff capabilities. Personnel qualifications and training as well as systems to assure and maintain quality of immediate ECG diagnosis are highlighted.

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.

Respiration and the ECG: a study using body surface potential maps

Body surface potential maps and an eccentric spheres model of the heart were used to investigate some of the factors that cause the surface ECG to change with respiration. Although the pattern of the surface maps shifted inferiorly with inspiration, the pattern itself did not change significantly, even with deep respiratory movements. However, the temporal ECGs at specific electrodes changed dramatically. The model simulations show that the contribution to the change in amplitude of the surface potential due to lung conductivity and ventricular volume changes is small. It is suggested that the major cause of the surface potential changes with inspiration is due to the change in heart position.

Labile T-wave changes caused by respiratory variation in a patient with unstable angina

We describe an unusual case of asymptomatic T-wave inversion induced by respiration in a patient with coronary artery disease.

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)

Indirect measurement of infarct size. Correlative variability of enzyme, radionuclear angiographic, and body-surface-map variables in 34 patients during the acute phase of first myocardial infarction

To gain a correlative perspective of indirect indications of the size of a myocardial infarct, we measured several body-surface electrocardiographic variables and several enzyme and radionuclear angiographic indicators of an infarct's size in 34 patients during the acute phase of first infarction. We found that bivariate correlations ranged widely, from an r value of 0.05 to an r value of 0.92, but were significantly (p less than 0.001) higher when variables from the same technique were correlated (mean r, 0.60 +/- 0.27), as opposed to correlations of variables from different techniques (mean r, 0.27 +/- 0.18). Trivariate comparisons among techniques produced significantly (p less than 0.001) higher r values, but the highest, an r value of 0.76 (total wall motion abnormality score; peak lactic dehydrogenase level; ST-segment integral maximum), indicated that even in this best case, only about 60 percent of the variation of one variable was dependent on or due to the two other variables. These data demonstrate that multiple indirect quantitative indicators of myocardial injury can vary widely in their correlations within the same population of infarcts, and much remains unknown in their relationships during the acute phase. Caution should be exercised, therefore, in their clinical application to predict an infarct's size in individual patients with acute myocardial infarction.

Exercise electrocardiographic mapping in normal subjects

To investigate the spectrum of change in multiple-lead exercise electrocardiograms, 120-lead body surface potential maps (BSPM) in normal adult subjects during upright, graded, submaximal exercise testing were recorded. Results showed that in the normal group, exercise was associated with substantial electrocardiographic changes on the body surface, many of which persisted during early recovery. The QRS waveform was minimally altered during exercise. Despite, however, no change in QRS duration, there was significant reduction in QRS potential range with consequent reduction QRS integral value. The ST waveforms changed markedly with exercise, showing abbreviated duration and increased slope. This was reflected by significantly increased ST potential range from rest to immediate cessation of exercise, which returned towards resting value during recovery. The effect of the altered ST-segment waveform was also reflected in torso potential distributions at two time instants during the ST-segment. When a spatially-fixed position on the ST-T waveform was evaluated (ST-segment offset), exercise resulted in small potential changes, especially over the torso area occupied by the standard V1 to V6 chest leads. However, when a temporally-fixed point (80 ms after QRS offset) was evaluated, there were large increases in potential over the precordium with exercise. Isointegral ST-segment maps, which reflect both spatial and temporal ST properties, showed that exercise was associated with substantial decreases in values over the precordium and inferior torso, and although diminished, they tended to persist through five minutes of recovery. Thus, electrocardiographic repolarization parameters are particularly affected by physiological exercise and, although the underlying causes of these changes remain undefined, they should be taken into account when evaluating the population at risk.

The response of the surface electrocardiogram to inspiration

The waveshape of the electrocardiogram (ECG), as is well known, varies with respiration. This effect was noted from the early days of clinical electrocardiography (1) and has generally been ascribed to changes in the position of the heart. Although it has mostly been regarded as "noise", it is generated by a process and may contain information on the process. This paper presents two hypotheses: firstly that the change of the ECG with a held-inspiration can be separated into a step and a transient component and secondly that the transient component reflects the time course of changes of the right and left ventricular end-diastolic volumes during the maneuver.

Transient myocardial ischemia with minimal electrocardiographic changes: an echocardiographic study in patients with Prinzmetal's angina

Kn patients with Prinzmetal's angina, episodes of transient T wave abnormalities (T abn) are often documented in addition to the typical episodes of ST segment elevation (ST). As the interpretation of these minor ECG changes is still uncertain, we investigated if transient T abn are associated with reversible ventricular asynergies, similar to episodes with ST. For this purpose an ECG lead and a two-dimensional echocardiographic projection, which showed clear-cut changes during previous episodes of ST, were simultaneously monitored in five patients with Prinzmetal's angina for a total of 13 hours and 20 minutes. In all patients, the 30 episodes of ST recorded were all accompanied by reversible ventricular asynergies. Furthermore, in four of these patients, 14 episodes of T abn (peaking, flattening, or the appearance of a diphasic T wave) were recorded. All T abn were associated with reversible asynergies, as detected by three independent observers. The mechanical impairment occurred in the same ventricular wall both during ST and during T abn. During T abn the degree of mechanical impairment appeared less severe (hypokinesia in 12 and akinesia in two episodes) than during ST (hypokinesia in one, akinesia in 25, and dyskinesia in four episodes) (p less than 0.001). The duration of asynergies was less during T abn (107 +/- 76 seconds) than during ST (169 +/- 83 seconds) (p less than 0.05). Chest pain was reported in 5 of 14 episodes of T abn (36%) and in 20 of 30 (66%) episodes of ST (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Temporal evolution of body surface map patterns following acute inferior myocardial infarction

We studied the evolution of body-surface potential map (BSPM) patterns in 32 patients following first acute inferior myocardial infarction. Initial BSPMs were obtained at a mean of 79 hours post-infarction; follow-up BSPMs, a mean of eight months post-infarction. Temporal area-of-difference maps, constructed by subtracting initial from follow-up group-mean BSPMs, revealed reciprocal changes over the superior and inferior torso for both Q-zone and ST-segment time-integral distributions. The temporal changes in Q-zone patterns were small but definite: over the inferior torso there was a relative gain in Q-zone values and, over the superior torso, a relative decrease. In contrast, there were marked spatial and quantitative changes of ST-segment distributions during the follow-up period. Over the superior torso, particularly anteriorly, there was a gain in ST-segment values; over the inferior torso, a decrease. With the small temporal changes in Q-zone time-integral distributions, individual Q-zone maps continued to reflect a pattern of inferior myocardial infarction at follow-up. In contrast, the marked temporal changes in ST-segment time-integral distributions resulted in individual map patterns at follow-up that were nearly indistinguishable from normal ST-segment maps. The relatively small changes in depolarization time-integral patterns during the early post-infarction period suggest that the Q-zone patterns of the acute phase of myocardial infarction reflect near-irreversible or completed myocardial damage. The marked normalization of repolarization time-integral patterns during the recovery phase suggests, however, that there are also considerable areas of myocardium-at-risk during the early phase of the infarction process which stabilize with time.

Cardiac rhythm, rate and ventricular repolarization properties in infants at risk for sudden infant death syndrome: comparison with age- and sex-matched control infants

Using 24-hour ambulatory electrocardiographic recordings and 120-lead body surface potential maps, prevailing cardiac rate and rhythm, incidence and frequency of dysrhythm and rate and pattern of ventricular repolarization at the body surface were compared in 17 infants at risk for sudden infant death syndrome (SIDS) and 17 age- and sex-matched control subjects. Sinus rhythm was the prevailing rhythm in both study groups and there were no intergroup differences in average overall awake or asleep sinus rates, nor in temporal variability of sinus rate. Atrial and ventricular ectopic activity were equally uncommon in both study groups. Although there were smooth and bipolar body surface distributions of ST-T and QRST time integrals in both study groups, the average rate of ventricular repolarization (QTc), measured from the 12-lead electrocardiogram, 120-lead body surface potential maps and 24-hour electrocardiography, was consistently shorter in the at-risk group than in the control group. However, temporal variability of QTc was not different between the 2 groups. Thus, significant cardiac dysrhythm and QT prolongation are not found in infants at increased risk for SIDS. Rather, there is an abbreviated ventricular repolarization interval in at-risk infants. In combination with the findings of intergroup similarity of average sinus rate and temporal variability of sinus rate and ventricular repolarization rate, the data suggest a subtle, constant difference in cardiac autonomic activity, most likely an increase in sympathetic tone, in at-risk subjects. The role of this altered cardiac autonomic activity in the causation of SIDS remains undetermined.