Posterior fascicular block versus posteroinferior myocardial infarction in left posterior excitation disturbances.

To delineate electrocardiographic similarities and differences in ventricular depolarization between left posterior fascicular block and posteroinferior myocardial infarction, these lesions were produced in two and three stage experiments in dogs and baboons. The observed QRS changes of left posterior fascicular block were found to be immediate, little influenced by healing of the acute lesion, and partially correctable by pacing viable myocardium distal to the block. In contrast, the QRS changes of posteroinferior myocardial infarction occurred later with cicatrization and were essentially unaffected by pacing. The intrinsic deflection in direct posterior epicardial leads was more delayed by left posterior fascicular block than by posteroinferior myocardial infarction. Both lesions accounted for Q waves in leads II, III and aVF. However, R amplitude in these same leads was increased after left posterior fascicular block but decreased after posteroinferior myocardial infarction. The mean QRS axis in the frontal plane was shifted toward the vertical in left posterior fascicular block but little changed or shifted slightly away from the vertical in posteroinferior myocardial infarction. When left posterior fascicular block and posteroinferior myocardial infarction coexist, there may be masking, imitation or enhancement of the effects of one lesion by the presence of the other. To assist in recognition, distinguishing features are described.

A new microcomputer-based ECG analysis system.

A new automated ECG system using advances in microprocessor technology and computerized electrocardiography is described. This microcomputer-based system is self-contained and mobile. It acquires both the 12-lead and orthogonal lead (Frank) electrocardiograms and analyzes the latter within minutes. Software includes the program developed in the Veterans Administration which uses advanced statistical classification techniques and a large well-documented patient data base. Diagnostic probabilities are computed using a Bayesian approach. Diagnostic performance has been tested using independent clinical criteria and found to be quite accurate. This system enables the clinician to immediately review the computer's identifications, measurements, and diagnostic classifications and quickly use these results in clinical decision making. Serial comparisons are readily made since all previous recordings are stored on floppy diskettes. The use of microprocessors in this system makes it economically feasible for practicing physicians.

Restriction-endonuclease analysis of DNA from 15 Giardia isolates obtained from humans and animals.

The DNA banding pattern of 11 human and four animal isolates (two beaver, one cat, and one guinea pig) of Giardia were compared by using two related techniques. Patterns were compared after endonuclease restriction of DNA followed by agarose gel electrophoresis and ethidium bromide staining and after Southern blot analysis using recombinant plasmids containing Giardia DNA as probes. Two major groups could be distinguished with ethidium bromide staining of eight isolates. Southern blot analysis, however, could distinguish nine different patterns among the 15 isolates studied. One common banding pattern was seen in six isolates (two animal and four human); the remainder of the isolates were unique, with the exception of two identical isolates from sisters. Three isolates (one from a beaver and two from humans) were markedly different from Giardia with the common banding pattern, whereas the other six unique isolates varied moderately. Beavers and other mammals do not seem to possess their own species of Giardia. This methodology introduces a way of distinguishing one species of Giardia isolate from another and promises to be helpful in epidemiological investigations.