PubMed · 458294
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J Tenczer, L Littman. 1979. Concealed atrial rhythms.. https://doi.org/10.1016/s0022-0736(79)80035-7
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Premature ventricular complexes (PVCs) can provide clues to the physical or electrocardiographic diagnosis through the associated compensatory pause, the break in the regularity of the rhythm, or the morphology of the PVC itself. A PVC may allow visualization of the P wave or of atrial flutter waves that would otherwise be obscured in the electrocardiogram. It can also be useful in distinguishing an S3 gallop from an S4 gallop. The compensatory pause that follows a PVC may allow normal conduction of the next QRS complex in a patient with a rate-dependent intraventricular conduction defect, and this normalized QRS complex may contain important diagnostic findings. A PVC can also reveal a myocardial infarct pattern when the sinus complex fails to do so. Although the need to treat PVCs is currently being de-emphasized, their diagnostic utility should not be overlooked.
A novel method has been developed to map activation in the triangle of Koch during surgery for cardiac arrhythmias and relate the map to anatomic landmarks. It uses a hand-held electrode mounted in a freely moving linkage that has three degrees of mechanical freedom. The movements of the linkage are sensed by a computer that continuously calculates the coordinates of the electrode. The surgeon clamps the device over the triangle of Koch after the right atrium has been opened and uses the electrode to trace the anatomic landmarks of the region that are displayed on the computer screen. The position of the electrode is displayed continuously relative to these landmarks and electrograms are recorded at known positions to generate a map. The activation sequences during sinus rhythm, atrioventricular node reentrant tachycardia, "common" and "uncommon" atrial flutter, long RP' tachycardia and retrograde conduction through paranodal pathways are presented. It is concluded that 1) the high spatial resolution reveals physiologically important areas in the maps that are 8 mm long and 3 mm wide and that these areas can be related to specific anatomic landmarks; 2) there are complex electrograms in the region that may reflect the activation of different myocardial layers; and 3) there are marked changes in conduction velocity and direction within the region.
The clinical electrophysiologic approaches to atrial flutter (F) have been activation mapping and the observation of changes induced by programmed stimulation. Sequential endocardial activation mapping has recently yielded information indicating that common F is produced by a large right atrial (RA) reentry circuit, with counterclockwise rotation in the frontal plane, including the inferior vena cava in its center. Functional block in the crista terminalis and conduction slowing in the approaches to the atrioventricular node seem to be important to support reentry. F inscribing positive deflections in the inferior leads usually follows the same path, but in a clockwise direction. Atypical F may be produced by left atrial circuits. Atrial stimulation during F entrains the circuit, resetting it with each stimulus. Collision between antidromic and orthodromic activation during entrainment produces fusion that can be identified in the surface electrocardiogram. The last paced activation restarts F, unless circuit penetration has been enough to modify it by block or disorganization. Entrainment may result in F acceleration, with changes in activation sequence, suggesting a different type of reentry, possibly based on functional factors.