Right atrial flutter due to lower loop reentry: mechanism and anatomic substrates.

BACKGROUND: The mechanisms of an atrial flutter (AFL) that is more rapid and at times more irregular than typical AFL are unknown. METHODS AND RESULTS: Twenty-nine patients with AFL were studied. Atrial electrograms were recorded from a 20-pole catheter placed against the tricuspid annulus (TA), with its distal electrodes lateral to the isthmus between the TA and the eustachian ridge (ER), and from the His bundle and coronary sinus catheters. Atrial extrastimuli were delivered in the TA-ER isthmus during typical AFL. Episodes of a right atrial flutter rhythm that was different from typical AFL were induced in 3 patients and occurred spontaneously in 3 patients. This sustained AFL, designated as lower-loop reentry (LLR), involved the lower right atrium (RA), as manifested by early breakthrough in the lower RA, wave-front collision in the high lateral RA or septum, and conduction through the TA-ER isthmus. Linear ablation resulting in bidirectional conduction block in the TA-ER isthmus terminated spontaneous LLR in 3 patients and rendered LLR noninducible in all patients. The cycle length of LLR was shorter than that of typical AFL (217+/-32 versus 272+/-40 ms, P<0. 01). Alternating LLR and typical AFL in 1 patient resulted in cycle length oscillation. CONCLUSIONS: LLR is a subtype of right atrial flutter and depends on conduction through the TA-ER isthmus.

Sodium efflux in rabbit myocardium: relationship to sodium-calcium exchange.

1. The washout of (22)Na, (45)Ca and (58)CoEDTA(-) has been observed in arterially perfused rabbit interventricular septa both in the presence and absence of intoxicating doses of the aglycone, 3 acetylstrophanthidin (ACS).2. The washout of (22)Na from paced septa (21.0/min) was rapid with approximately 99% of the exchange occurring in 30 min.3. Septa labelled with (22)Na and washed out in the presence of 10(-5)m-ACS were quiescent, exhibited marked contracture and a slowed (22)Na exchange with 99% of the initial (22)Na leaving the tissue in approximately 200 min.4. Comparison of the washout of the extracellular marker (58)CoEDTA(-) from paced and intoxicated septa revealed no differences, suggesting that regions of the extracellular space had not become inexchangeable as a result of the contracture that these septa exhibited.5. Simultaneous measurements of the distribution of (22)Na and (58)CoEDTA(-) in the presence of 10(-5)m-ACS revealed an apparent cellular Na concentration of 54.8+/-10.4 (s.e.). This was considerably in excess of the maximum amount of Na contributing to the slowest component of Na efflux from intoxicated septa. Origins of this discrepancy are considered.6. The slowest component of (22)Na efflux from intoxicated septa could be markedly stimulated by increasing the external Ca concentration from a nominal 1.5 to 16 mm. The magnitude of stimulation was 44.3+/-7.8% (s.e.). Increases in the concentration of Mg from 1.0 to 16.0 mm were without effect on the (22)Na efflux.7. Application of 10(-5)m-ACS produced marked depolarization of the membrane to new stable levels that lay between -10 and -20 mV.8. Washout of ACS after several hours of intoxication resulted in a partial decline in contracture tension, an acceleration of Ca efflux, little change in (22)Na efflux and a repolarization of the cell membrane.9. Some of the Na and Ca movements reported in this paper have been interpreted by supposing that there is, in this preparation, a coupled exchange of three Na ions for a single Ca ion.

The prevalence of conduction defects and cardiac arrhythmias in progressive systemic sclerosis.

A prospective noninvasive electrocardiographic study was done on 50 patients with progressive systemic sclerosis. Thirty-two percent had abnormalities on the resting electrocardiogram, of which the commonest were left anterior fascicular block (16%) and first-degree heart block (8%). The 24-hour ambulatory continuous tape-recorded electrocardiograms showed serious abnormalities in 62% of the patients: supraventricular tachycardias (32%), conduction disturbances (14%), coupled ventricular extrasystoles (20%), and ventricular tachycardia (10%). Intracardiac electrophysiologic data were obtained in 20 of these patients, and functional abnormalities of the sinus node, atria, and atrioventricular node were noted in seven, nine, and 10 patients, respectively. One patient had prolonged His-Purkinje conduction time. Of the 20 patients who had electrophysiologic studies, only six had entirely normal findings. These results suggest a much higher degree of cardiac involvement in progressive systemic sclerosis than previously believed. We postulate that the first-degree heart block and supraventricular tachycardias may derive from a similar pathologic process, namely, fibrous atrophy of the proximal atrioventricular node.

Nodoventricular accessory atrioventricular connection associated with dual atrioventricular pathways: a case report and review of the literature.

A case is presented of a patient free from tachyarrhythmias or prior evidence of pre-excitation syndrome, in whom electrophysiologic study revealed evidence of dual AV nodal pathways associated with a nodoventricular bypass tract. Programmed atrial extrastimuli testing revealed that conduction through the fast AV nodal pathway was associated with a normal HV interval and normal QRS morphology. Conduction through the slow AV nodal pathway was always associated with a short HV interval and ventricular pre-excitation. No tachyarrhythmias could be induced with atrial extrastimuli or rapid atrial pacing. Previously reported cases of this pre-excitation variant (all of whom were symptomatic from tachyarrhythmias) are reviewed and the features summarized. This pre-excitation syndrome can occur in individuals without clinical evidence of tachyarrhythmias or overt pre-excitation and as such may be more common than previously suspected.

Atrioventricular nodal function in progressive systemic sclerosis: electrophysiological and morphological findings.

Electrophysiological data consistent with atrioventricular nodal dysfunction were obtained in 10 out of 19 patients with progressive systemic sclerosis (scleroderma). Conducting system studies were carried out in a further seven patients with progressive systemic sclerosis. In each the proximal portion of the atrioventricular node was consistently found to be smaller and more slender. It is postulated that there is a relation between proximal atrioventricular nodal structural alterations and impaired atrioventricular nodal function.

Left axis deviation: a reassessment.

This report deals with the ramifications of the concept of left axis deviation. In early life, the leftward shift of the frontal plane QRS axis is determined chiefly, if not solely, by the relative weights of the ventricles. Once adult ventricular weight ratios are reached, there is a long period of axis stability, then a gradual leftward drift of the QRS, governed principally by left anterior fascicular conduction. Thus, the normal QRS axis is age-dependent, and left axis deviation must be considered accordingly.

Mitral valve prolapse and conduction defects in Ehlers-Danlos syndrome.

A case of type 3 Ehlers-Danlos syndrome with associated mitral valve prolapse, right bundle-branch block, and left anterior fascicular block was studied, including His bundle electrocardiography and echocardiography. Mitral valve prolapse and HV prolongation were reported. The present study suggests that the basic underlying collagen defect in this syndrome is responsible for these findings, and that the association may be more widespread in the syndrome than currently acknowledged. The possibility also is considered that the connective tissue abnormalities of Ehlers-Danlos syndrome involving the heart may be the cause of some cases of idiopathic conduction system disease or valvular insufficiency.

Myocardial imaging with 123I-hexadecenoic acid.

123I-hexadecenoic acid is a terminally iodinated, 17-carbon fatty acid analog which is rapidly degraded in the myocardium. By determining regional myocardial distribution patterns and clearance rates, it may become useful as a single agent for estimating regional myocardial perfusion and for distinguished viable ischemic tissue from infarcted tissue. The high count rates obtainable with the iodine label permit acquisition of qualitative multiprojection images in only 3 min. per view, or quantifiable single projection high count images in 10 min. Ischemic defects may be observed in anginal patients without subjecting them to stress.

The inside-out electrocardiographic stress test: a view from the left ventricular cavity.

A new method is described for measuring the unipolar left ventricular cavitary electrogram by means of a standard pigtail ventriculography catheter. Experiences with this technique in 30 patients are described with particular reference to changes in the S-T segment of the cavitary electrogram during cardiac stress by atrial pacing. This method allows convenient recording of His bundle potentials from the left ventricular outflow tract in most patients.