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D M Mirvis

Publications and source records attributed to D M Mirvis.

At least 19 recordsLinked to original sources
PubMed1979

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.

Action Potentials↗
PubMed1979

Electrocardiographic QRS changes induced by acute coronary ligation in the isolated rabbit heart.

The electrical fields associated with augmented R- and decreased S-wave amplitudes during acute, severe myocardial ischemia were studied in fifteen isolated rabbit heart preparations. Hearts were suspended in a spherical tank and perfused with oxygenated electrolyte solution. Electrocardiographic signals were recorded from electrodes on the tank's surface and processed by computerized methods. Fifteen minutes after suture ligation of the left anterior descending coronary artery, records from electrodes overlying the lesion demonstrated increased R-wave amplitude and ST-segment elevation. Fitting a single moving dipole to pre- and post-ligation potentials demonstrated that the ligation increased the dipolarity of the field and shifted the terminal QRS dipole to a position topographically related to the location of the ischemic lesion. The effects of injury were further assessed by study of fields computed by subtracting control from post-ligation data. This generated a dipolar field at the instant of maximal dipole moment whose strength directly correlated (r=0.74) with the area of non-perfused epicardium, as determined by post-ligation methylene blue infusion. These results suggest that the electrical fields generated during mid to late dipolarization by coronary ligation are qualitatively similar to those generated during repolarization, and may therefore be of similar clinical and/or experimental value.

Action Potentials↗
PubMed1979

A microprocessor controlled timing device for cardiac electrical stimulation.

A microcomputer controlled device for delivering precisely timed stimuli to cardiac chambers is described. Stimulation patterns are determined by software, rather than hardware design, resulting in enhanced flexibility. Additionally, by providing timing inputs to conventional laboratory stimulators, this instrument can convert these limited use devices into ones capable of generating complex cardiac stimulation patterns at moderate cost.

Cardiac Pacing, Artificial↗
PubMed1979

A system oriented electrocardiographic amplifier.

A low noise, programmable gain amplifier has been developed for acquiring ECG data from a variety of recording environments. Features include: low noise (4muV peak-to-peak) differential inputs; digitally programmable gains (range 100 to 16000) and output DC offsets (range -3.5 to +4 V) controlled via a serial interface; externally selectable low frequency response (0.04 or 0.08 Hz); and an on-board output monitor multiplexer controlled via a second serial interface.

Amplifiers, Electronic↗
PubMed1978

Atrioventricular nodal gap conduction as a manifestation of dual nodal pathways.

Electrophysiologic studies were performed in a 76 year old patient for evaluation of sinus bradycardia. Atrial extrastimuli were induced during sinus rhythm at progressively decreasing coupling (A1-A2) intervals. At an A1-A2 interval of 420 msec, right bundle branch block developed, and at 370 msec conduction failed below the His bundle. When the interval was reduced to 320 msec, conduction resumed with a normal QRS pattern with an abrupt increase in A-H intervals from 165 to 305 msec. These findings are interpreted as type I or atrioventricular (A-V) nodal gap conduction physiologically related to conversion from a rapid to a slow A-V nodal conduction mode.

Aged↗
PubMed1978

Ventricular pre-excitation and prolonged Q-T interval syndromes in a patient with mitral valve prolapse.

A 34-year-old woman with mitral valve prolapse, frequent ventricular dysrhythmias, and chest pain was studied. Surface electrocardiograms demonstrated short PR and prolonged Q-T intervals. A-V nodal conduction times during atrial pacing were characteristic of A-V nodal bypass tract function. The case is thus interpreted to be one of overlap between three syndromes known to predispose to cardiac dysrhythmias, i.e., mitral valve prolapse, Lown-Ganong-Levine syndrome, and prolonged Q-T interval syndrome.

Adult↗
PubMed1978

Harmonic analysis of the left ventricular pressure waveform of the primate.

Most attempts to quantitate myocardial function rely on morphologic features of complex pressure waveforms to reflect the functional properties of the ventricular myocardium. Relationships between waveform components and the function of the organ generating them were examined in 38 rhesus monkeys by harmonic analysis of left ventricular pressure waveforms. In the basal state, harmonic content was closely correlated (r=0.98) with hemodynamic state, as quantitated by heart rate, systolic and diastolic pressures, left ventricular end-diastolic pressure and maximum contractile element velocity. Hemodynamic indices were expressed as significant linear functions of harmonic terms (r=0.71--0.83), in patterns consistent with the principle of superposition. In 20 animals, infusions of dextran, methoxamine, propranolol or ouabain were used to further assess this relationship. Results demonstrated (1) significant correlation between changes in hemodynamic and harmonic parameter (4= 0.99), (2) correlations between each harmonic term and the set of hemodynamic indices such that specific terms varied directly with contractility but not with loading, whereas others correlated significantly only with loading, and (3) that the patterns in these correlations were of such specificity as to permit construction of significant discriminant functions (p less than 0.0001) that accurately characterized the pharmacologically induced hemodynamic change in 85% (56/67) of trials.

Animals↗
PubMed1977

Symptomatic swallowing-induced paroxysmal supraventricular tachycardia.

A 55 year old woman with palpitations during ingestion of food or drink was evaluated with surface, esophageal and dynamic electrocardiographic techniques. Recordings documented the consistent induction of supraventricular tachycardia by swallowing; no definable gastrointestinal or other cardiac abnormality was present. Nine previously reported cases are reviewed, with special reference to the role of vagovagal reflexes in the pathogenesis of this unusual clinical syndrome.

Deglutition↗
PubMed1977

The electrocardiographic image surface revisited.

An image torso may be viewed as a one-to-one transform of a physical volume conductor to a geometric form which defines both the axis and sensitivity of any electrocardiographic connection. In this report, the image surfaces of laminar, spherical, rectangular and humanoid physical torsos are explored theoretically and experimentally. All proved to be rounded or spherical in form despite the marked differences in the configuration of the physical conductor. Moderate degrees of dipole eccentricity induced only small departures from this basic circular pattern. Introduction of phase inhomogeneity, however, resulted in more striking deviations from roundness.

Animals↗
PubMed1977

Left precordial isopotential mapping during supine exercise.

Junctional depression is often observed during physical exercise in overtly normal subjects. To explore its pathogenesis, 15 normal volunteers were studied during supine, bicycle ergometer, submaximal stress tests. Electrocardiograms were simultaneously recorded from 42 electrodes on the left anterior precordium at two minute intervals at rest and during exercise. Data were used to construct isopotential maps throughout the P-QRS-T intervals. At rest, maps throughout the ST segment were dominated by a single maximum along the upper left sternal border. During exercise, all subjects developed junctional depression that was maximal along the lower left sternal border. Exercise maps during the early to mid-ST segment showed an intense minimum along the lower left sternal border that was continuous with terminal QRS forces in both intensity and location. Later in ST, this minimum decreased in strength and was replaced by a maximum located in the same area as that observed at rest. These observations suggest that junctional depression is the result of competition between two effects, one being normal repolarization which is obscured in the early ST segment by the second, possibly representing delayed terminal depolarization forces.

Action Potentials↗
PubMed1977

Relative dipolar behavior of the equivalent T wave generator: quantitative comparison with ventricular excitation in the rabbit heart.

We studied the relative dipolar and nondipolar content of signal energy throughout ventricular excitation and recovery in 34 isolated, perfused rabbit hearts, suspended in an electrolyte-filled spherical chamber. Computer-processed signals were derived from 20 evenly spaced tank-surface electrodes, and a single, moving, equivalent cardiac dipole generator was optimally fitted to the recorded potentials for each 1-msec sampling interval. Superimposed, time-based plots of signal energy for the 34 preparations showed ventricular excitation to be strikingly more nondipolar than was recovery. In terms of the summed square ratio of nondipolar residual energies, overall nondipolarity of QRS exceed that of ST-T by 41%. Furthermore, the maximum instantaneous ratio during QRS was considerably greater than during the ST-T. Evaluation of paired differences, comparing nondipolar behavior throughout QRS with all of ST-T, proved highly significant (P less than .005). We also found that in contrast to the considerable mobility exhibited by the equivalent QRS dipole, the ST-T dipole locus remained nearly stationary during most of ventricular recovery. Presumably because repolarization is temporally and spatially a relatively diffuse process, it may generate electrical fields which are notably more dipolar than those caused by depolarization.

Animals↗
PubMed1977

Detection and localization of multiple epicardial electrical generators by a two-dipole ranging technique.

The ability of a numerical procedure to detect and to localize two experimentally induced, epicardial dipolar generators was tested in 24 isolated, perfused rabbit heart preparations, suspended in an electrolyte-filled spherical tank. Electrocardiograms were recorded from 32 electrodes on the surface of the test chamber before and after placement of each of two epicardial burns. The second lesion was located either 180 degrees, 90 degrees, or 45 degrees from the first. Signals were processed by iterative routines that computed the location of one or two independent dipoles that best reconstruced the observed surface potentials. The computed single dipole acounting for 99.68% of root mean sequare (RMS) surface potential recorded after the first burn was located 0.26 +/- 0.10 cm from the centroid of the lesion. Potentials recorded after the second lesions were fit with two dipoles that accounted for 99.36 +/- 1.51% of RMS surface potentials and that were located 0.42 +/- 0.26 cm and 0.57 +/- 0.49 cm from the centers of the corresponding burn. Seventy-one percent of computed dipoles were located within the visible perimeter of the burn. Thus, two simultaneously active dipolar sources can be detected and accurately localized by rigorous study of the generated electrical field.

Animals↗