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Biomedical subjects

L G Horan

Publications and source records attributed to L G Horan.

At least 19 recordsLinked to original sources
PubMed1999

Right ventricular infarction: specific requirements of management.

The principal cause of right ventricular infarction is atherosclerotic proximal occlusion of the right coronary artery. Proximal occlusion of this artery leads to electrocardiographically identifiable right-heart ischemia and an increased risk of death in the presence of acute inferior infarction. Clinical recognition begins with the ventricular electrocardiographic manifestations: inferior left ventricular ischemia (ST segment elevation in leads II, III and aVF), with or without accompanying abnormal Q waves and right ventricular ischemia (ST segment elevation in right chest leads V3R through V6R and ST segment depression in anterior leads V2 through V4). Associated findings may include atrial infarction (PR segment displacement, elevation or depression in leads II, III and aVF), symptomatic sinus bradycardia, atrioventricular node block and atrial fibrillation. Hemodynamic effects of right ventricular dysfunction may include failure of the right ventricle to pump sufficient blood through the pulmonary circuit to the left ventricle, with consequent systemic hypotension. Management is directed toward recognition of right ventricular infarction, reperfusion, volume loading, rate and rhythm control, and inotropic support.

Combined Modality Therapy↗
PubMed1999

Comparative effects of sodium bicarbonate and sodium chloride on reversing cocaine-induced changes in the electrocardiogram.

Cocaine abuse is associated with a number of cardiovascular complications that include arrhythmias and sudden cardiac death. Although the mechanism(s) remain unclear, cocaine-induced block of sodium channels resulting in slowed cardiac conduction is thought to play an important role. Several reports suggest that the effects of cocaine effects on cardiac sodium channels can be reversed by administration of sodium bicarbonate. Whether the beneficial effects of sodium bicarbonate are due to sodium ions or an increase in blood pH is unknown. Therefore the purpose of this study was to compare the effects of sodium loading alone (by using sodium chloride) versus sodium loading with an associated increase in arterial pH (by using sodium bicarbonate) on reversing cocaine-induced effects on the electrocardiogram (ECG) in a canine model. Seventeen anesthetized dogs received three i.v. injections of cocaine, 5 mg/kg, with each dose separated by 15 min. Two minutes after the third cocaine dose, each dog was randomly assigned to receive 2 mEq/kg i.v. sodium bicarbonate (1 mEq/ml) or 2 mEq/kg i.v. sodium chloride (1 mEq/ml). ECG, electrophysiologic, and hemodynamic data were recorded at baseline, after each cocaine injection, and after administration of sodium bicarbonate or sodium chloride. In both groups of animals, the first cocaine injection significantly (p < 0.05) prolonged the PR, QTc, AH, and HV intervals, and QRS duration compared with baseline. All intervals continued to lengthen in a dose-dependent manner after the second and third cocaine doses. Sodium bicarbonate significantly (p < 0.05) reduced cocaine-induced prolongation of PR [(147 +/- 5-130 +/- 5 ms), AH (81 +/- 6 - 72 +/- 6 ms), and HV intervals (55 +/- 2 - 39 +/- 1 ms). and QRS duration (96 +/- 6 - 66 +/- 4 ms), peak effect after third cocaine dose versus after sodium bicarbonate, respectively]. Sodium chloride had no effect on reversing cocaine-induced effects on the ECG. Cocaine produces dose-dependent slowing of cardiac conduction that is effectively reversed by sodium bicarbonate. The lack of efficacy of sodium chloride suggests that the increase in arterial pH associated with sodium bicarbonate is responsible for reversal of the effects of cocaine on the ECG. Therefore sodium bicarbonate may be clinically useful in the treatment of cocaine-induced cardiac arrhythmias, primarily as a result of its effects on arterial pH.

Animals↗
PubMed1995

The comparative predictive accuracy of spectral turbulence analysis and time-domain analysis for sustained monomorphic ventricular tachycardia in postinfarction patients with conduction defects.

Signal-averaged electrocardiograms obtained in 86 postinfarction patients with right bundle branch block (RBBB), left bundle branch block (LBBB), or intraventricular conduction defect (IVCD), underwent time-domain analysis (TDA) and spectral turbulence analysis (STA) to determine which approach provided the more effective marker for patients with sustained monomorphic ventricular tachycardia. TDA parameter included the root mean square value of the last 40 ms of the vectormagnitude complex and the duration of the low amplitude signal below 40 microV. STA utilized a summation lead (X + Y + Z) and quantitated four parameters: interslice correlation mean, interslice correlation standard deviation, low slice correlation ratio, and spectral entropy. High-pass filters of 40 Hz and 25 Hz were used to study the total patient population with noise levels > or = microV and a subset of 67 patients with noise levels < or = 0.5 microV. The techniques compared their effectiveness as measured by their positive predictive values (PPV), negative predictive values (NPV), sensitivity (Sn), and specificity (Sp). In RBBB, STA was uniformly a more powerful tool utilizing either filter at both noise levels. In LBBB, STA was consistently more powerful at both noise levels at 40 Hz and, generally, more powerful at 25 Hz with isolated exceptions. In conduction defects in which QRS was > 100 ms but < 120 ms, TDA was equal to or more effective than STA, with the exception of PPV and Sp at 40 Hz at 1-microV noise level and the Sp at 0.5 microV. The addition of ejection fraction data to STA score resulted in further overall improvement in performance, but above conclusions were unchanged.

Adult↗
PubMed1990

Relation of peri-infarction block to ventricular late potentials in patients with inferior wall myocardial infarction.

This study explores the relation of the presence of peri-infarction block to ventricular late potentials in patients with inferior wall myocardial infarction (MI). The hypothesis was that both the gross peri-infarction block pattern and subtle low-level ventricular late potentials are expressions of conduction abnormality associated with infarction. The consequent question arose whether peri-infarction block may have the same association with sustained ventricular arrhythmias that has been demonstrated in postinfarction patients with ventricular late potentials. Seventy patients with documented Q-wave MI were divided into those with (23) and those without (47) peri-infarction block. Signal-averaged electrocardiograms were obtained. Analysis of the vectormagnitude complex revealed that the total duration of that complex and the duration of terminal potential under 40 microV in the peri-infarction group exceeded that in the group without peri-infarction block (p less than 0.0001). The voltage in the last 40 ms of the vectormagnitude complex was also significantly less in the peri-infarction group (p less than 0.0005). There were 13 instances of sustained ventricular tachycardia, ventricular fibrillation or sudden death occurring subsequent to infarction not associated with the acute ischemic event, 11 of which occurred in the peri-infarction group. The significantly higher incidence of late potentials along with the significantly higher incidence of sustained ventricular arrhythmias in the peri-infarction block on the surface electrocardiogram may provide another marker for identifying persons at increased risk for these arrhythmias subsequent to MI.

Adult↗
PubMed1990

Application of beat-to-beat techniques.

The focus of this report is to describe a system for recording surface His-Purkinje and ventricular late potentials on a beat-by-beat basis outside of a shielded environment. An AC magnetic field monitoring device was designed for improved site selection, orientation, and quality control of the acquisition. His-Purkinje signals are detected utilizing spatial averaging and specific channel selection algorithms applied to discriminate random noise from signal. Beat-by-beat vectormagnitude complexes were generated from pairs of X, Y, and Z leads. Both infinite impulse response (IIR) filters, modified for beat-by-beat approaches, and finite impulse response (FIR) filters were utilized. Using the IIR filter, beat-by-beat recordings from test subjects were compared to the signal averaged electrocardiogram (SAECG). Measurement parameters from normal test subjects fell within the previously specified normal range for the SAECG. The IIR filter applied to beat-by-beat recordings exhibited sharp frequency response and a precisely defined cutoff frequency allowing maximal attenuation of the low frequency components in the ST segment. While filter ringing was eliminated, discontinuity and distortion of the filtered waveform resulted. The FIR filter with linear phase response retained the integrity and morphology of the complex but because of its flat frequency response, the ST segment was not as well attenuated and it was more difficult to isolate late potentials. A high order FIR filter should be used if the desire is to match the frequency response of the four-pole IIR filter, since the frequency response of the FIR filter is primarily determined by the order of the filter.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1990

Patterns of body surface potential and ventriculograms specific to occlusion of subdivisions of the coronary arteries.

The thoracic activation map patterns, the distribution of occlusions, and the ventriculograms obtained at cardiac catheterization were examined in 166 patients with multivessel coronary disease without conduction defects or prior coronary intervention. The mean potential and ventriculographic configurations were determined for 15 groups, each formed on the basis of significant luminal occlusion (less than or equal to 90%) of an individual coronary arterial subdivision. We mathematically extracted distinctive map and wall motion patterns specific for isolated occlusion of each of the 15 major subdivisions. For these prototypes we found the following: 1) Definitive change in electrical pattern (less than 2 SD from the normal mean) occurred frequently outside the electrode sites of the standard electrocardiogram. 2) Focal akinesis systematically followed lesion site down the arterial courses; early electrical activation patterns corresponded to identifiable anatomic loss. 3) Certain paradoxes arose, for example, similar wall motion change but quite dissimilar electrical patterns from posterior descending artery occlusion of right coronary versus left circumflex origin. This technique unmasks component surface electrical patterns and ventriculographic deformities otherwise unrecognized in multisite, multivessel disease.

Adult↗
PubMed1989

Relation between the ventriculographic silhouette and topography of thoracic potential in coronary artery disease.

The body surface potential map obtained within 30 days of cardiac catheterization was examined in 180 patients with coronary artery disease. Radii to the systolic and diastolic boundaries of the right anterior oblique ventriculogram were measured at 18 degrees intervals; isointegral voltages were tabulated for early and late halves of the QRS complex at 35 definitive electrode sites. Multivariate analysis showed all ray lengths depended on all 70 voltage values. Linear transformation matrices to predict ray length from voltage distribution were calculated for a training set which was successively expanded from 80 to 160 at increments of 20 patients. Training set expansion led to a progressive decrease in the error of reproduction of the ray lengths for patients outside the training set. There is a strong relation between ventriculographic contours in patients with coronary artery disease and body surface potential values during early and late QRS complexes. Even in simplified linear formulation, the relation is detectable throughout a large population despite interindividual variations in anatomic geometry.

Adult↗
PubMed1989

Recurrent resemblance in potential topography at different instants during ventricular depolarization and repolarization. Normal conduction contrasted with left bundle branch block and paced beats.

During ventricular activation and recovery, potential distribution may be exquisitely reproduced on instantaneous maps separated in time by many milliseconds. The timing and duration of these periods of strong resemblance (absolute r = 0.80 over 142 thoracic reference sites) may provide useful insight into the underlying patterns of the spread of activation and resumption of the repolarized state. This study examined 80 normal volunteers, 35 patients with left bundle branch block (LBBB), and 41 patients with permanent pacemakers. Normal subjects showed three basic patterns of recurrent surface map resemblance: (1) positive correlation between maps in early QRS and those throughout ST-T, but with greatest focus in late ST-T; (2) negative correlation between maps in early QRS and late QRS; and (3) negative correlation between maps in late QRS and early ST-T. These findings may be hypothetically attributed to the retention or recreation of similar relationships between the anatomic distributions of resting versus active or plateau versus repolarizing cells on the endocardial and epicardial surfaces, respectively. On the other hand, patients with LBBB and pacemakers were distinctly different in the timing and frequency of sustained resemblances. In these two states, there was sustained or continuing resemblance (positive correlation) between successive maps throughout QRS and again between successive maps through ST-T. In addition, the surface map pattern found throughout ST-T consistently appeared as the negative correlate of the preceding pattern that had dominated QRS.

Bundle-Branch Block↗
PubMed1989

Anatomic localization of a single electrical source within the boundary of the human torso.

A closed prolate ellipsoid was used to approximate the surface of the Rush torso model to permit recovery of the site and orientation of known dipoles in 15 cardiac locations. Localization was found to be reasonably close, usually within 2 cm. When body surface potential maps of 37 subjects with right ventricular pacemakers were similarly treated, the discrepancy between known pacemaker site and the site of earliest activation was relatively large (mean, greater than 4 cm) and rapidly increased within the ensuing millisecond. The discrepancy not only emphasizes the wide variation in body shape and tissue distribution in living subjects, but also points to probable physical separation between stimulus site and earliest detectable activation site because of ischemia, infarction, or myocardial response to variation in current strength of the stimulus.

Cardiac Pacing, Artificial↗
PubMed1989

Use of body surface maps to identify vessel site of coronary occlusion.

Body surface mapping is more sensitive than conventional electrocardiography for various cardiac regions. In this pilot study, the authors used isoarea maps of early (the first 40 msec), late (the next 40 msec), and total (early and late, or 80 msec) QRS complex to determine the site of coronary occlusion in patients with known coronary artery disease. In the absence of conduction abnormalities or axis deviation in the 12-lead electrocardiogram, isoarea body surface map data of single-vessel disease were unremarkable; however, isoarea departure maps (ie, the average isoarea map of normal population extracted from the study group) were characteristic. Early departure isoarea maps were revealing in all three coronary artery disease groups, with a large negative potential noted over the anterior thorax, midline for the right coronary artery, left anterior in the left anterior descending artery, and further laterally for the left circumflex artery groups. The late isoarea departure map was distinct in the left circumflex artery group with positive potentials leftward, anterolaterally. Discriminant function analysis revealed a high predictive accuracy for the left anterior descending artery group. Thus, isoarea departure maps hold promise for predicting the site of coronary occlusion in this training set of patients.

Adult↗
PubMed1989

A basis for determining body surface potential patterns attributable to single-site coronary arterial occlusion.

The authors focus on computational separation of the individual patterns of occlusion of the major segments of the right coronary artery. The raw patterns of occlusion throughout 15 standard subdivisions of the coronary arterial tree and body surface isoarea maps for 8 consecutive 10-msec intervals of QRS were examined in 200 patients with known coronary artery disease. Mean patterns of occlusion and of potential distribution were formed into 15 groups according to which patients showed greater than or equal to 90% occlusion of the respective segments. By diagonalization of the occlusion matrix, individual potential map patterns were obtained to represent the effect of isolated occlusion of each segment. While these patterns appeared consistent with the known anatomy of ventricular myocardial perfusion, further correlative study will be needed. The authors suggest that the use of such prototypical patterns of single-site obstruction may be helpful in forming and assessing recognition patterns in the clinical setting of multiple-site, multiple-vessel disease.

Coronary Disease↗
PubMed1988

Variation in the precordial QRS transition zone in normal subjects.

From body surface potential map data for 51 normal young men (with QRS axis between 0 and 90 degrees) both the spatial QRS area vector and the isoarea map of the QRS were obtained. Acting on Grant's assumption that the transition zone defined a plane perpendicular to the spatial QRS vector, we determined the angular shift in altitude and azimuth required to move the spatial vector of each individual to the position of the group mean. We then shifted the precordial map of the transition zone of each individual with the same angular correction. These resulting transition zone boundaries clustered much closer to each other, but did not move into absolute coincidence. We interpreted the nearness-to-fit to be an estimate of the degree to which the precordial QRS configurations conformed to a common simple vector or dipolar pattern.

Adult↗
PubMed1987

Manifest orientation: the theoretical link between the anatomy of the heart and the clinical electrocardiogram.

Einthoven related the apparent direction of the heart's electrical activity to the potential differences manifest in the limb leads and the axes of their orientation. From this beginning the linked concepts of heart vector and lead vector, equivalent dipole and lead field, complex heart source and complex volume conductor have continued the electrocardiographer's search for deeper insight into cardiac function from examination of the surface expression. However, this conceptual evolution has been uneven and has littered practical interpretation with diagnostic criteria that depend on assumptions of uneven validity. The good news is that some of the criteria are surprisingly helpful and that the shattering and reassembling of the conceptual framework relating the heart to the electrocardiogram may facilitate the construction of a more comprehensive and effective diagnostic approach.

Animals↗
PubMed1985

The degree to which myocardial infarct site and size determine the electrocardiographic axis. Analysis of correlative data by computational modeling.

The spatial electrical QRS axis was determined for 428 twelve-lead electrocardiograms from patients subsequently shown by postmortem dissection to have ventricular myocardial fibrosis or necrosis. Four 16-segment ventricular models of the heart were used to "predict" the spatial electrical QRS axis from known ventricular mass and deficit. The raw model I in ideal anatomic position and vectors perpendicularly outward for each muscle segment showed a mean correlation value of -0.494; model II was rotated in the chest to produce best fit with a correlation of 0.638, but the anatomic orientation was not reasonable; model III maintained original position and orientation but the vectors were scaled (correlation 0.780); and model IV, with nonperpendicular vectors, yielded a mean correlation of 0.793. The exceptions to good predictability formed a distinct subset largely composed of electrocardiograms with some form of variant intraventricular conduction (slight QRS widening, fascicular block patterns and "indeterminate frontal-plane axis").

Electrocardiography↗
PubMed1985

Effect of various regimens of chronic and acute nicotine exposure on myocardial infarct size in the dog.

Smoking is a risk factor for atherosclerotic coronary heart disease, and the risk increases with increasing numbers of cigarettes smoked. The effect of cigarette smoking on the size of acute myocardial infarction (AMI) has not been evaluated. This study describes the effect of 1 component of tobacco smoke, nicotine, on the size of experimentally induced AMI in closed-chest dogs. Daily exposure to nicotine before AMI increased the volume of infarcted tissue (p less than 0.0001). Acute exposure to nicotine (with prior chronic exposure) resulted in a larger volume of infarcted tissue (p less than 0.0001). Thus, chronic, acute and post-AMI exposure to nicotine has an adverse effect on the volume of subsequent infarcted tissue, and continued exposure after AMI further enlarges infarct size.

Animals↗