Surface potential contribution from discrete elements of ventricular wall: A closed chest,postmortem-documented prospective study

Isopotential distribution maps were recorded before and after infarction in five dogs with an induced lesion in the circumflex branch of the left coronary artery and in five dogs with an occlusion created in the ventral interventricular branch by a closed chest catheter technique. Maps of “lost” potential distribution, derived by subtracting time-equivalent postinfarction maps from the dog's original or base-line maps, proved to be remarkably consistent in their configuration with respect to the location of the myocardial lesion. Even when the small, discrete infarctions, documented by histochemical postmortem examination, went undetected by conventional vector and scalar cardiography, the “difference” technique not only verified the presence of the lesion, but also served to predict its location.     

Multipolar maps in patients with postinfarction heart failure

Purpose

The aim of this study was to assess the changes in body surface maps in patients with postinfarction heart failure (PIHF).

Materials and Methods

Body surface mapping was performed in 22 patients with PIHF and 20 age-matched healthy controls, using a 64-electrode vest. A card index was made for every patient and person of the control group, containing isopotential and isointegral maps. The number and absolute value of maxima and minima were assessed for every map.

Results

Only bipolar maps were recorded in the healthy control group, and multipolar maps were found in 55% of the patients with PIHF. All patients with multipolar isointegral QRST maps had also multipolar isopotential ST maps (J + 110 milliseconds); 67%, multipolar isopotential QRS peak maps; 33%, multipolar isointegral Q40 maps; 17%, multipolar isointegral QRS maps; 67%, multipolar isointegral STT maps; and 50%, multipolar isointegral ST maps. Significant differences were noticed in maxima and minima in patients with PIHF compared with healthy controls and in patients with multipolar isointegral maps (QRST and Q40) compared with those with bipolar maps. Multiple regression analysis revealed that multipolar QRST maps were significantly associated (P < .001) with maxima and minima of the isointegral maps. Isointegral multipolar QRST maps were significantly associated (P < .001) with multipolar isopotential ST maps, multipolar isointegral QRS maps, multipolar isointegral STT maps, and multipolar isointegral ST maps.

Conclusion

Postinfarction heart failure increases the prevalence of multipolar maps and significantly changes maxima and minima. Multipolar QRST isointegral maps are significantly associated with maxima and minima of the QRS, ST, STT, and QRST maps and with other types of multipolar maps: isointegral QRS, STT, ST and isopotential ST (J + 110 milliseconds), and QRS peak maps.     

Isointegral analysis of body surface maps for the assessment of location and size of myocardial infarction

To estimate the location and size of myocardial infarction (MI), an isointegral mapping technique was adopted from among various body surface electrocardiographic mapping techniques. QRS isointegral and departure maps were made in 35 patients with MI. These patients were separated into 3 groups, based on the location of MI: anterior, inferior, and anterior plus inferior. The severity and location of MI were estimated by thallium-201 myocardial perfusion imaging and the degree of scintigraphic defect was represented by a defect score.

The extent of MI was expected to be reflected on the QRS isointegral maps as a distribution of negative QRS complex time-integral values. However, the extent and the location of MI were hardly detectable by the original maps. A departure mapping technique was then devised to observe the distribution of departure index on the body surface. Particular attention was given to the area where the departure index was less than −2, and this area was expected to reflect the location and size of specific abnormality of isointegral map due to MI. There were strong correlations between departure area and defect score in the anterior and inferior MI cases (r = 0.88 and r = 0.79, respectively). However, patients with anterior MI plus inferior MI showed no such correlation.

Q-wave mapping was compared with QRS isointegral mapping, and QRS isointegral mapping was found to be more accurate in the estimation of the location and size of MI than Q wave mapping. Thus, QRS isointegral mapping, especially departure mapping, is more useful and convenient for detecting the location and size of MI than methods such as isopotential and Q wave mapping.     

Ventricular activation time maps in health and after myocardial infarction registered in spherical system

The present paper concerns the results of the examinations on Ventricular Activation Time distribution. The registrations were performed using the 30-electrode network connected to from the diamentoid scheme giving the sphere system, in the centre of which the heart is located. The potentials for one ECG cycle were measured at every electrode. The created computer program changed the spheric recordings into the plane development which resulted in the 30 ECG recordings located under the particular electrode. Using these values the activation time was determined for every registration point. On that basis, the isochronic map for the patient is created. The ECG tracings were recorded in 48 healthy subjects, treated as the control group, and in the 96 patients with the previous myocardial infarction varying in location and extension. The obtained maps were compared both within and between the examined groups. For the normal subjects, the isochrone distributions are similar. The lines are arranged according to the physiological activity propagation through the myocardium. The quite different distribution was observed on the isochrone maps obtained from the patients with myocardial infarction, as compared with the maps from the control group. On the basis of the specific isochrone distribution, the exact location and can be identified. The patterns for the given location of the myocardial infarction are significant similarity--the possible differences concern only the foci extensions.     

Detection of posterior myocardial infarction by body surface mapping: A comparative study with 12 lead ECG and VCG

To examine the diagnostic ability of body surface mapping in posterior myocardial infarction (PMI), mapping was performed in 11 patients with PMI proven by left ventriculography and T1-201 myocardial perfusion imaging (PMI group) and in 44 normal subjects (N group). Map data was analysed by the following methods: (1) potential departure maps at 10, 20, 30, 40 and 50 msec after the onset of QRS; each map indicates the area of decreased potential out of the normal range at the time. (2) AQRS departure map which indicates the area of decreased time-integral value of QRS out of the normal range. True positive (TP) in the PMI group and false positive (FP) in the N group were calculated for each method, and were compared with those of various criteria for PMI with standard 12-lead electrocardiogram (ECG) and Frank lead vectorcardiogram (VCG). The potential departure maps and the AQRS departure map had high TP (10/11 and 8/11) and low FP (0/44 and 0/44). The diagnostic ability of mapping is considered to be higher than that of ECG and VCG. Mapping, especially the departure map technique, is a sensitive and specific method to detect posterior infarction.     

The determination of the human ventricular gradient from body surface potential map data

We have analyzed the Wilson ventricular gradient in terms of body surface potential maps and of the reduction of such surface patterns to equivalent dipoles or vectors. While the ventricular gradient traditionally was treated as first a scalar, then a vector concept, we found that the three entities (QRS area, T area, QRST area) did not reduce to vectors with a common location. However, conventional vector addition (QRST area = QRS area + T area) did precisely apply. Further we found considerable more-than-vector or extra-dipolar information remaining for all three entities after removal of the dipole effect. This suggests that maps of these entities should be considered the boundaries of complex electrical fields rather than simple surface effects of vectors.     

Experimental evaluation of the mean electrical equivalent generator of the isolated rabbit heart

Previous data have documented that the instantaneous cardiac equivalent generator is inadequately modeled as a single dipole. The properties of the mean equivalent generator during the QRS, ST-T and QRST intervals were determined in 22 isolated rabbit heart preparations suspended within a spherical volume conductor and perfused with an electrolyte solution. ECG potentials recorded from 32 surface electrodes were processed to compute instantaneous equivalent generator properties at 0.4 to 2.0 msec intervals during QRS and ST-T. QRS and ST-T areas of each electrode waveform were determined and processed to compute the parameters of the mean generator during QRS, ST-T and QRST intervals. A centric dipole fit 77.96, 71.73 and 67.48 percent of the recorded summed square (SSQ) area during these three intervals. Corresponding values for a single moving dipole model were 86.14%, 87.17% and 86.11%. A four element centric multipole series, in contrast, fit over 98% of SSQ area during each interval. Isoarea maps demonstrated multiple maxima and/or minima in 48% of the studied cases. Thus, mean cardiac forces during activation and recovery, as well as the instantaneous counterparts, are inadequately represented as single dipolar generator sources.     

Reduction of S-T segment elevation with infusion of nitroprusside in patients with acute myocardial infarction

The effect of infusion of sodium nitroprusside on S-T segment elevation was evaluated in 12 patlents with acute anterior myocardial infarction. Precordial 35 lead S-T segment maps were obtained in each patient immediately before and 10 minutes after infusion of 53 μ/min (range 20 to 100 μg/min) of nitroprusside. The following measurements were made from each S-T map: ∑ST (total S-T elevation in all leads), NST (number of leads with S-T elevation greater than 1 mm) and $\text{ST}$ (average S-T elevation in leads with more than 1 mm elevation). After administration of nitroprusside, evidence of myocardial ischemic injury as assessed by S-T mapping decreased in association with reduction of the myocardial oxygen consumption index of pressure-time per minute. Group mean values diminished significantly for ∑ST (41.7 to 28.6 mm, P <0.001), NST (20.3 to 14.6, P <0.001) and $\text{ST}$ (1.6 to 1.2 mm, P <0.005). Pressure-time per minute decreased from 2,690 to 2,372 mm Hg-sec/min (P <0.001). Because there was no significant relation (P >0.05) between reductions in S-T elevation and lower indexes of myocardial oxygen consumption, it is suggested that nitroprusside may possess a separate action of augmenting regional blood flow to ischemic myocardium. Evaluation with the precordial S-T mapping technique suggested that intravenous administration of nitroprusside was associated with evidence of reduced ventricular ischemic injury in patients with acute myocardial infarction. This effect appears to be related to reduction of myocardial oxygen demand by the peripheral cardiac unloading mechanisms of nitroprusside as well as to a possible direct action of the drug in improving regional blood flow to ischemic heart muscle.     

Fine detail in body surface potential maps: accuracy of maps using a limited lead array and spatial and temporal data representation

In order to evaluate the accuracy with which a limited lead array can be used to estimate fine details of the thoracic distribution of cardiac potentials, we compared 192-lead body surface maps and those constructed using a subset of 32 leads. We also evaluated preservation of detail in body surface maps reconstructed following spatial and temporal data representation, a method proposed for quantitative comparison of maps. Maps were analyzed with respect to four previously reported normal map features recorded with extensive lead arrays. The maps constructed from 32 leads accurately reproduced all map features with 92% or greater accuracy. Maps constructed after spatial and temporal data representation had a reproduction accuracy of 93% and 98% respectively for two map features more than 100 microV in amplitude but accuracy with respect to the two map features less than 100 microV in amplitude was 86% and 59% respectively. The study demonstrates that a selected limited lead array permits accurate estimation of the body surface distribution of cardiac potentials even when potentials are low level or occur in regions not directly sampled by a recording electrode. To represent potentials of less than 100 microV, more coefficients would be required to permit accurate spatial and temporal representation.     

The relation of activation boundary size to body surface QRS potential sum

The relation of QRS amplitude sums to activation boundary size at two instants was evaluated in five normal subjects. In earch subject, QRS amplitude sums from 192 simultaneously recorded torso electrocardiograms and from 35 leads from the precordial area only were obtained 10 and 15 msec after the QRS onset. Activation boundary size at these instants was taken from published studies of ventricular excitation sequence in the human heart. The relative size of electrocardiographically effective boundaries at 10 and 15 msec and the measured QRS amplitude sum at 10 msec were used to predict expected QRS amplitude sums at 15 msec. Differences between the predicted and measured QRS amplitude sums at 15 msec constitute an estimate of error in determining cardiac source size from its expressions in the body surface electrocardiogram (ECG). Results demonstrated a more consistent relation of activation boundary size to QRS sums from the 192 than from the 35 electrode array. Indirectly the results suggest summed ST segment displacement from the larger array of electrodes would be more consistently related to the extent or severity of myocardial injury than an ST segment displacement sum based on 35 precordial leads. Finally, the findings suggested that the absolute sum of an electrocardiographic measurement such as ST segment displacement would provide a better index of lesion size than ST elevation or depression only.     

Natural course of the S-T segment and QRS complex in patients with acute anterior myocardial infarction

Sums of the S-T segment elevation from the 35 lead precordial electrocardiographic map (∑ST₃₅) and Standard 6 lead precordial electrocardiogram (∑ST₆) were obtained from 20 patients after acute anterior myocardial infarction and the calculations repeated 2, 4, 12, 24, 48, 72 and 240 hours later. Q and R wave areas were summed (∑Q₃₅, ∑Q₆, ∑R₃₅ and ∑R₆). ∑ST₃₅ and ∑ST₆ values decreased significantly in patients without pericarditis 7 to 12 hours after the onset of symptoms (P < 0.02), but increased significantly from these reduced values 25 to 48 hours after the onset of symptoms. An increase in ∑ST₃₅ and ∑ST₆ (P < 0.05) occurred 13 to 24 hours after the onset of symptoms in four patients with pericarditis before a pericardial rub was heard. No significant change in ∑Q₃₅ occurred from the initial to the final map study; a decrease in ∑R₃₅ (P < 0.02) occurred only in a group of patients studied at or before 5 hours after initial symptoms. No correlation was found between the initial level of S-T segment elevation and subsequent change in Q or R wave areas except in two patients whose initial electrocardiographic studies were performed at or within 5 hours of initial symptoms. Good correlation was found between ∑ST₃₅ and ∑ST₆ (r = +0.906, P < 0.001), ∑Q₃₅ and ∑Q₆ (r = +0.864, P < 0.001), and ∑R₃₅ and ∑R₆ (r = +0.903, P < 0.001). The course of the S-T segment and QRS complex after anterior myocardial infarction depends on the time of study after initial symptoms. The Standard 6 lead precordial electrocardiogram may offer a practical alternative to the 35 lead map for patients with anterior myocardial infarction.     

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.     

Approach to the estimation of myocardial infarct size by analysis of precordial S-T segment and R wave maps

To assess the correlation of S-T segment elevations and the height of R waves of the precordial electrocardiogram with myocardial infarct size, we performed 35 lead precordial electrocardiograms (maps) in 24 patients with uncomplicated acute anterior transmural myocardial infarction. The initial analysis was carried out in 14 patients. Infarct size was estimated from the integration, from normal baseline to baseline, of serial serum creatine kinase (CK) values obtained at 2 to 4 hour intervals and expressed as IU/liter·hours. The first electrocardiographic maps were recorded 12 hours or less after the onset of symptoms. All S-T segment elevations and R waves were summed for each map (∑S-T and ∑R). There were positive correlations between the ultimate CK infarct size and the initially recorded ∑S-T (r = 0.69), the initially recorded log ∑R (r = ? 0.70) and the initial early decline in log ∑R per hour [(Δlog ∑R/Δhour)·10³, r = 0.88]. Therefore, these variables were combined in a multiple regression analysis; CK infarct size = 0.23 ∑S-T + 0.20 [(Δlog ∑R/Δhour)·10³]? 14.9 log ∑R + 36.8 (r = 0.97). In addition, on the basis of previous studies the initially recorded ∑S-T and log ∑R values were normalized with respect to time by calculating the expected ∑S-T value at 12 hours after the onset of symptoms (∑S-T₁₂) and the 12 hour interpolated values for ∑R (∑R₁₂). These values also showed a good correlation with infarct size: CK infarct size = 0.37 ∑S-T₁₂ + 0.16 [(Δlog ∑R/Δhour)·10³]^t- 18.2 log ∑R₁₂ + 40.4 (r = 0.97).To validate this approach, 10 additional patients were studied prospectively. Correlations between CK infarct size and the various measurements from the serial precordial maps were similar to those in the first study group, and CK infarct size correlated well with the electrocardiographic infarct estimates (r = 0.90 and r = 0.95, respectively). It is concluded that in selected patients CK infarct size can be directly related to the initial height of S-T segment elevations and the early rate of R wave decline and inversely related to later ∑R values, thereby providing a general approach for use in studies on the estimation of myocardial infarct size from precordial electrocardiographic maps.     

Impact of tissue heterogeneity on noninvasive near-infrared glucose measurements in interstitial fluid of rat skin

Background

Movement of the optical interface used to collect noninvasive near-infrared spectra is known to dramatically increase prediction errors for glucose concentration measurements within the interstitial fluid of living rat skin. Prediction errors increase by more than 2.5-fold when the interface is moved before each non-invasive measurement compared to measurements where the interface position is constant throughout. Chemical heterogeneity of the skin matrix is examined as a possible mechanism for the strong sensitivity to the interface placement during noninvasive measurements conducted from transmission near-infrared absorption spectroscopy.

Method

Microspectroscopy was performed over a region of the near-infrared spectrum (4000–5000 cm⁻¹) to map the concentrations of water, collagen protein, fat, and keratin protein within the skin tissue matrix through which noninvasive spectra are collected. Maps were created for multiple samples of skin excised from male and female animals. Sets of near-infrared spectra were constructed to simulate noninvasive spectra in accord with the basic tissue composition found from the microspectroscopic maps with added information corresponding to a span of glucose concentrations ranging from 5 to 35 mM and Gaussian-distributed noise.

Results

Microspectroscopic maps of rat skin reveal similar patterns of heterogeneity for major chemical components of skin samples excised from both male and female animals. These maps demonstrate concentration domains with dimensions similar to the size of the fiber interface used to collect noninvasive spectra. Partial least squares calibration models generated from sets of simulated spectra demonstrate increases in prediction errors for glucose when the spectral matrix is changed in accord with the degree of chemical heterogeneity displayed in the skin maps. Prediction errors typically increase between 100 and 1000% when comparing errors generated from spectra that represent a single tissue composition versus spectra that represent a varied skin composition in accord with the distribution displayed in the skin maps.

Conclusions

The distribution of the major components of skin is not uniform, but establishes domains within the skin matrix that strongly impact prediction errors for the noninvasive spectroscopic measurement of glucose within the interstitial fluid of rat dermis tissue. The observed increase in prediction error (>2.5-fold) determined from actual noninvasive measurements is within the lower range of prediction error increases demonstrated by this simulation study. These findings implicate that chemical heterogeneity within the tissue matrix is a major factor in the sensitivity of the location of the fiber interface used to collect noninvasive spectral data.     

Suppression of a ventricular-inhibited bipolar pacemaker by skeletal muscle activity

A patient is described in whom isometric movements of the right pectoralis muscle group totally suppressed pulse generator discharge of a ventricular inhibited pacemaker. Converting the pulse generator to the continuously discharging mode, by applying a magnet externally, prevented this inhibition. At surgery, the proximal electrode terminal was found to be improperly seated in the pulse generator and fluid had leaked into the connector boot. Two possibilities may explain the observed skeletal muscle-induced pulse generator inhibition: conversion of the bipolar demand system to a unipolar demand system by the fluid leak with subsequent sensing of myopotentials or the generation of false (make-break) electrical signals from repetitive interruption of the electrical circuit caused by pectoralis muscle activity.     

Body surface mapping during percutaneous transluminal coronary angioplasty. QRS changes indicating regional myocardial conduction delay

Using a radiotransparent electrode array, body surface maps (BSMs) were constructed based on simultaneous recordings from 62 leads on the entire thorax before, during, and after balloon inflation during percutaneous transluminal coronary angioplasty (PTCA). Twenty-five patients were studied, and 30 angioplasties were performed; 20 patients had one-vessel disease, and five patients had two-vessel disease. In total, 15 dilations in the left anterior descending artery (LAD), seven in the right coronary artery (RCA), and eight in the left circumflex artery (LCx) were studied. For each patient, the BSM and the QRS integral map before, during, and after the inflation was compared by subtraction of recordings "during-minus-before" inflation and "before-minus-after" inflation. The subtraction was performed on the results of the QRS integral maps. The conclusions derived from the inspection of the BSMs and the difference maps show specific changes in the QRS complex during ischemia related to the corresponding ischemic segment in 21 of 25 patients in the three groups. An area of positive potentials remained present on the BSM during dilation, indicating a depolarization wave front. For the LAD group, positive potentials were seen on the anterior thorax and, for the RCA group, on the lower part of the thorax. By subtraction analysis, these changes were extracted and presented as difference maps. For the LCx group, the BSM revealed no changes in pattern but the difference map showed a difference vector pointing in a anteroposterior direction. A regional myocardial conduction delay was hypothesized as the most likely cause for the results.     

Dissociation between coronary sinus and left atrial conduction in patients with atrial fibrillation and flutter

INTRODUCTION: Coronary sinus (CS) recordings are routinely used during electrophysiologic studies for various supraventricular and ventricular arrhythmias with the understanding that they represent left atrial (LA) activity. However, the behavior of CS electrical activity during atrial arrhythmias has not drawn any special attention beyond standard considerations. METHODS AND RESULTS: The study population consisted of 9 patients (3 women; mean age 59 +/- 11 years) with atrial fibrillation (AF) and atrial flutter (AFL) who developed dissociation of conduction between the CS and posterior LA during spontaneous AF and AFL. In all patients, the LA and the CS were mapped using a 64-electrode basket catheter and a multipolar electrode catheter, respectively. The right atrium (RA) was mapped simultaneously using a 24-polar electrode catheter (7 patients) or a 64-electrode basket catheter (2 patients). Eight patients showed stable double potentials in CS recordings during AF (9 episodes) and AFL (3 episodes). During ongoing arrhythmias, the first row of potentials maintained a constant relationship with the RA activity, whereas the second row of potentials was discordant with the posterior wall of the LA in 7 patients and concordant in 2 patients. In 1 patient with counterclockwise AFL, CS activation was isolated from the posterior wall of the RA until it reached the distal portion of the CS, after which it entered the lateral region of the LA. In 1 patient, a macroreentrant LA tachycardia involving CS muscle was observed. Rapid atrial pacing from the proximal CS and extrastimuli produced longitudinal dissociation of CS activation in all patients. CONCLUSION: Conduction between the CS and posterior LA can be dissociated during spontaneous atrial arrhythmias and provocative proximal CS pacing.     

Validation of QwikStar Catheter for left ventricular electromechanical mapping with NOGA XP system

Left ventricular electromechanical mapping (LVEM) is a method for mapping the left ventricular cavity in 3 dimensions by use of a catheter that samples points on the endocardial surface. These points provide data on unipolar voltage and linear local shortening, which can then be used to evaluate myocardial ischemia and viability. The new QwikStar multi-electrode catheter, which acquires data from multiple points simultaneously, potentially improves map quality and decreases mapping time in comparison with the single-point NogaStar catheter. Our study sought to validate the QwikStar catheter's LVEM capabilities in a porcine model of chronic ischemia.Eight pigs underwent ameroid placement over the proximal left circumflex artery, to induce chronic ischemia. In 60 days, LVEM was performed on each animal with the NogaStar and QwikStar catheters. Unipolar voltage and linear local shortening results were displayed in 9-segment polar maps. The unipolar voltage data from both maps were then correlated by means of linear regression.There were no adverse events during LVEM. Mapping time was similar for both groups (QwikStar, 44.6 +/- 25.62 min; NogaStar, 65.75 +/- 25.33 min; P = 0.13). Results of mean unipolar voltage maps acquired with the 2 catheters showed a moderate correlation (r =0.59, P <0.001). Selecting segments with more than 6 point samples increased the Pearson coefficient to 0.69 (P <0.001).Our findings show that the QwikStar catheter enables the reproducible performance of LVEM by sampling fewer points, which shortens procedure time, decreases manipulation of the left ventricular cavity, and might increase procedural safety.     

Failure of ST segment elevation to predict severity of acute myocardial infarction.

Praecordial ST segment elevation was measured at 35 electrode positions in each of 40 patients admitted to a coronary care unit after acute transmural anterior myocardial infarction. Serial praecordial electrocardiographic maps were recorded to determine (a) the time course as well as reproducibility of measurements of ST segment alterations, and (b) the degree of correlation between the magnitude of ST segment elevation and the severity of infarction, as assessed clinically or by sequential estimations of serum creatine kinase activity. Large variations in ST segment elevation were found in different patients with a comparable degree of myocardial damage, and at intervals of as little as four hours in the same patient. These variations were greater than could be explained by technical factors, and were not related to apparent changes in the patients' clinical status. The patterns of release of myocardial creatine kinase showed that the time course of ST segment elevation was longer than the period of myocardial necrosis. No correlation was found between the myocardial infarct size as determined by enzyme release and the highest levels of ST segment elevation recorded. The findings suggest that ST segment elevation as measured by praecordial electrocardiographic mapping does not constitute a reliable index of the size or severity of myocardial infarcts in man.     

Application of body surface mapping to exercise testing: S-T80 isoarea maps in patients with coronary artery disease

Body surface electrocardiographic maps were recorded before and after exercise in 25 men with angiographically documented coronary disease. Torso potential distributions at 192 locations were derived from a 32 lead electrode array using methods previously described in our laboratory. The S-T segment was characterized by the spatial distribution of the integral of S-T segment voltage over 80 ms (S-T₈₀). Body surface regions where the S-T₈₀ areas were —8 mV·ms or greater were identified in 18 of 25 patients. The most negative S-T₈₀ site on the map was called the “S-T₈₀ minimum.” The S-T₈₀ minima were located 1 or 2 electrode rows away from the standard V₄–V₆ electrode positions in 6 of 10 patients who developed S-T₈₀ areas of —8 mV·ms or greater. Our data suggest that standard electrocardiographic leads may not be optimal for identifying S-T segment depression in all patients with coronary disease. Furthermore, body surface mapping during exercise provides a more quantitative and qualitative method for characterizing the ischémic response to exercise.