Biomedical subjects
Publications and source records attributed to L Schamroth.
This report reflects a case of bigeminal and trigeminal ventricular extrasystoles where bigeminal extrasystoles are associated with short coupling intervals, while trigeminal extrasystoles manifest long coupling intervals. The arrhythmia is interpreted as an "atypical" form of concealed bigeminy.
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Concealed extrasystolic ventricular bigeminy reflects a distributional pattern of ventricular extrasystoles where intervening sinus beats are always in odd numbers. This has been explained on bigeminal rhythm associated with exit block. This presentation reflects a modification of this concept in that the distributional pattern may be explained on the basis of complex concealed modulation of ventricular parasystole, the concealment being due to impulses falling within the refractory period rather than suffering true exit block.
Modulation of ventricular parasystole by sinus beats has been shown both in vitro and in vivo to result in a classic biphasic phase-response curve. The first clinical presentation of 3 cases of supernormal modulation of ventricular parasystole resulting in a triphasic phase response curve is reported. Supernormal modulation reflects an unexpected early enhancement expedition of the ectopic ventricular impulses. An alternative explantation for the triphasic phase-response curve is the discharge and resetting of the parasystolic focus by critically timed sinus impulses.
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This paper reflects a hitherto undescribed mechanism for alternation of conduction time during supraventricular reciprocating tachycardia. Delayed anterograde conduction through an A-V nodal pathway effectively delays conduction of the reciprocal impulse to its retrograde course and hence to its intrajunctional reciprocal point: the point where it begins anterograde conduction once again. This section of the A-V nodal pathway consequently has a longer recovery time. The ensuing anterograde conduction is therefore faster and the ensuing cycle therefore shorter. The shorter ensuing cycle, in turn, means that the returning impulse reaches its intrajunctional reciprocal point earlier. There is consequently less time for recovery for the anterograde A-V nodal pathway. Hence the ensuing delay and longer cycle. This establishes a sequel of long and short cycles due to alternation of conduction.
We report two cases of atrial extrasystolic bigeminy manifesting with alternating right and left bundle branch block aberration. The manifestation is explained on the basis of cycle-dependent variations of the bundle branch refractory period with alternate resetting of bundle branch refractoriness.
Left ventricular hypertrophy due to diastolic overload is characterized by the following in lead V6: (a) tall R wave; (b) prominent initial Q wave; (c) minimally elevated concave-upward ST segment; and (d) relatively tall symmetrical T wave. Reciprocal deep S waves are seen in lead V1. This study reflects a further evaluation of these parameters in the four main causes of left ventricular diastolic overload: mitral incompetence, aortic incompetence, patent ductus arteriosus, and ventricular septal defect. An S wave in lead V1 which is equal to or greater than the R wave in lead V6 excludes the diagnosis of mitral incompetence.
The electrocardiogram recorded from a patient with third degree A-V block reflected almost regular A-V junctional escape rhythm. Some of the R-R cycles were slightly shorter than the basic escape cycle. A QRS complex ending such a relatively short R-R interval was always preceded by a sinus P wave, and had a QRS configuration which was minimally different from that of the escape complexes. The His bundle recording demonstrated that these minimally premature complexes were associated with an H-V interval which was shorter than that of the escape complexes. This indicates that the premature QRS complex could not be a capture beat. The relationship between the slightly premature QRS complex and the preceding sinus P-waves is explained on the basis of electrotonic potentiation or modulation to due Wedensky facilitation.
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