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Biomedical subjects

D A Brody

Publications and source records attributed to D A Brody.

11 recordsLinked to original sources
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

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

Rate-dependent variation in the duration of the QRS complex with left anterior fascicular block.

The case of a 67-year-old man with combined ischemic and valvular heart disease is presented. Electrocardiographic abnormalities included left anterior fascicular block with a variable duration of the QRS complex. The width of the QRS complex was dependent on the length of the cycle, being broader with short than with long preceding R-R intervals. This is interpreted as a tachycardia-dependent focal block coexisting with a fixed delay in fascicular conduction.

Aged↗
PubMed1976

Wenckebach-type exit block from an ectopic focus as a cause of variable coupling.

Intermittent bigeminal and trigeminal ventricular premature beats were recorded in an otherwise healthy 14 year old male. Coupling intervals progressively lengthened until an ectopic beat was dropped. Odd numbers of sinus beats occurred between bigeminal runs. This rhythm is interpreted as being due to Wenckebach-type block in an exit pathway from the ectopic focus, resulting in concealment of the persistently active extrasystolic mechanism.

Adolescent↗
PubMed1976

Effects of chronic anemia on the coronary and coronary collateral vasculature in dogs.

We compared coronary resistances and collateral (retrograde) flows for a group of normal dogs (hematocrit 40) to values for a group of dogs with severe chronic anemia (hematocrit 17). We used an isolated heart preparation in which the vessels were maximally dilated by dipyridamole. All data were compared for a hematocrit of 40. The results showed a significant decrease in coronary resistances with anemia; average resistances (+/-SE) of the anterior descending, circumflex, and right coronary arteries of the control dogs were 1.04 +/- 0.09,0.74 +/- 0.01, and 2.63 +/- 0.17 mm Hg/[(ml/min)/100 g], respectively, and 0.6 +/- 0.04,0.41 +/- 0.05,and 1.17 +/- 0.15 for the anemic dogs. Average coronary collateral flows increased in anemia but statistical significance could not be shown. We conclude that increased vascularity is a long-term regulatory mechanism in response to a hypoxic stimulus.

Anemia↗
PubMed1975

Microelectrode study of high grade block in canine Purkinje fibers.

Previous reports from this laboratory described an electrotonic mechanism for simple impulse transmission through blocked segments of canine Purkinje tissue with slow diastolic depolarization assuming a vital role in second degree block. Utilizing an electrical blocking current, a blocked segment of canine Purkinje tissue was produced. Transmembrane events were recorded from blocked segments during higher grades of block (3:1 to complete) to delineate further mechanisms responsible for a periodic distal boundary response. Our results confirm that slow diastolic depolarization is an important determinant in sustaining periodic impulse conduction. Its importance is related to (1) progressive decrease of the resting membrane potential toward threshold at the distal block boundary, and (2) augmentation of the transmitted electrotonic potential in accordance with voltage dependent changes in membrane resistance. These data further lend definition to the distinction between electrotonic, partially active, and active transmembrane potentials. Impulse transmission through a segment of inactivated tissue is electrotonic and slow diastolic depolarization plays an important role in the maintenance of periodic impulse transmission.

Action Potentials↗
PubMed1975

Localization of heart vectors produced by epicardial burns and ectopic stimuli; validation of a dipole ranging method.

Location of the equivalent cardiac dipole has been estimated but not fully verified in several laboratories. To test the accuracy of such a procedure, injury vectors were produced in 14 isolated, perfused rabbit hearts by epicardial searing. Strongly dipolar excitation fronts were produced in 6 additional hearts by left ventricular pacing. Twenty computer-processed signals, derived from surface electrodes on a spherical electrolyte-filled tank containing the test preparation, were optimally fitted with a locatable cardiac dipole that accounted for over 99% of the root-mean-square surface potential. For the 14 burns (mean radius 5.0 mm), the S-T injury dipole was located 3.4 plus or minus 0.7 (SD) mm from the burn center. For the 6 paced hearts, the dipole early in the ectopic beat was located 3.7 mm (range 2.6 to 4.6 mm) from the stimulating electrode. Phase inhomogeneities within the chamber appeared to have a small but predictable effect on dipole site determination. The study demonstrates that equivalent dipole location can be determined with acceptable accuracy from potential measurements of the external cardiac field.

Animals↗