PubMed · 6205382
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P A Levine. 1984. Pseudo-endless loop tachycardia.. https://doi.org/10.1111/j.1540-8159.1984.tb05609.x
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Sinus pause with atrioventricular asystole can be caused by an excessive vagal response. This case report describes a patient in whom this phenomenon developed after hiccups.
OBJECTIVE: To compare the hemodynamic effects, pharmacokinetic profiles, and the need for vasoactive agents between a low (20 micrograms/kg during 15 minutes [group 1; n = 10]) and a high (40 micrograms/kg during 15 minutes [group 2; n = 10]) loading dose of milrinone. DESIGN: Prospective, randomized, double-blind. SETTING: University hospital. PARTICIPANTS: Twenty patients scheduled for elective coronary artery surgery. INTERVENTIONS: Weaning from CPB was achieved using a strict protocol. After atrioventricular pacing at 90 beats per minute and preload optimalization, a first weaning attempt was started with only calcium and nitroglycerin as support. If this attempt was unsuccessful (cardiac index < 2L/min/m2), CPB was reinitiated and weaning level 2 was prepared, consisting of inotropic support with milrinone. Patients received either the low (group 1) or the high (group 2) loading dose of milrinone. After the end of the loading dose, a continuous infusion of milrinone of 0.5 micrograms/kg/min was started in both groups. MEASUREMENTS AND MAIN RESULTS: Both groups were comparable regarding preoperative and intraoperative data. Hemodynamic data were comparable in both groups at each time of measurement (p = 0.941). The need for vasoactive medication (norepinephrine [NE]) in order to keep mean arterial pressure > or = 50 mm Hg was significantly higher in group 2 (p = 0.004). Need for NE during the loading infusion was 9.6 +/- 4.9 micrograms (mean +/- SEM) in group 1 and 41.6 +/- 7.6 micrograms in group 2 (p = 0.004). Need for NE during the immediate post-CPB period was also higher in group 2 (16.0 +/- 10.4 micrograms in group 1 and 232.5 +/- 82.8 micrograms in group 2 (p = 0.002)). Plasma clearance of milrinone after CPB was less in both groups than in healthy volunteers. However, clearance of milrinone was significantly higher in group 2 (p = 0.006), and consequently, half-life of milrinone was significantly less in group 2 (p = 0.007). CONCLUSIONS: The present results demonstrate that when milrinone is used during weaning from CPB, a loading dose of 20 micrograms/kg provided to similar hemodynamic support a loading dose of 40 micrograms/kg. The need for vasoconstrictive medication was significantly less in the group with the low loading dose.
The success of radiofrequency catheter ablation in the treatment of atrioventricular junctional, or atrioventricular nodal, reentrant tachycardia has rekindled interest in the electrophysiological and anatomical characteristics of the reentrant circuit. We conclude that there is no evidence that within the atrioventricular nodal area, which contains both the compact node and transitional cells, there are anatomically delineated dual or multiple pathways. Rather, the two main atrial inputs into the atrioventricular nodal area (posterior and anterior) seem to be the anatomically relevant structures for "slow" and "fast" pathways. Two other inputs (sinus septum and left atrial) may be the cause for multiple pathways in some individuals. Nonuniform anisotropic properties of the zone of transitional cells may account for slow or fast conduction in the same area, depending on directional differences of wavefronts. We prefer the term atrioventricular junctional reentrant tachycardia rather than atrioventricular nodal reentrant tachycardia because of mounting evidence that perinodal tissue is involved in the reentrant circuit. Finally, the role and origin of double extracellular electrograms is discussed. Further research is required to establish whether an anatomical or an electrogram-guided approach for catheter ablation is preferred.