Differential Effect of Adenosine on Anterograde and Retrograde Fast Pathway Conduction in Patients with Atrioventricular Nodal Reentrant Tachycardia

Adenosine and Retrograde Fast Pathway Conduction . Introduction : Several studies have shown that the fast pathway is more responsive to adenosine than the slow pathway in patients with AV nodal reentrant tachycardia. Little information is available regarding the effect of adenosine on anterograde and retrograde fast pathway conduction.
Methods and Results : The effects of adenosine on anterograde and retrograde fast pathway conduction were evaluated in 116 patients (mean age 47 ± 16 years) with typical AV nodal reentrant tachycardia. Each patient received 12 mg of adenosine during ventricular pacing at a cycle length 20 msec longer than the fast pathway VA block cycle length and during sinus rhythm or atrial pacing at 20 msec longer than the fast pathway AV block cycle length. Anterograde block occurred in 98% of patients compared with retrograde fast pathway block in 62% of patients ( P < 0.001). Unresponsiveness of the retrograde fast pathway to adenosine was associated with a shorter AV block cycle length (374 ± 78 vs 333 ± 74 msec, P < 0.01), a shorter VA block cycle length (383 ± 121 vs 307 ± 49 msec, P < 0.001), and a shorter VA interval during tachycardia (53 ± 23 vs 41 ± 17 msec, P < 0.01).
Conclusion : Although anterograde fast pathway conduction is almost always blocked by 12 mg of adenosine, retrograde fast pathway conduction is not blocked by adenosine in 38% of patients with typical AV nodal reentrant tachycardia. This indicates that the anterograde and retrograde fast pathways may be anatomically and/or functionally distinct. Unresponsiveness of VA conduction to adenosine is not a reliable indicator of an accessory pathway.     

Relationship Between Serum Potassium Concentration and Risk of Recurrent Ventricular Tachycardia or Ventricular Fibrillation

INTRODUCTION: Electrolyte abnormalities are considered a correctable cause of a life-threatening ventricular arrhythmia according to American Heart Association/American College of Cardiology Practice Guidelines, and ventricular tachycardia or ventricular fibrillation in the setting of an electrolyte abnormality is considered a class III indication for defibrillator implantation. However, there are little data to support this recommendation. The purpose of this study was to determine the risk of a recurrent sustained ventricular arrhythmia in patients with a low serum potassium concentration at the time of an initial episode of a sustained ventricular arrhythmia. METHODS AND RESULTS: One hundred sixty-nine consecutive patients who presented with a sustained ventricular arrhythmia and a serum potassium concentration determined on the day of the arrhythmia underwent defibrillator implantation. All patients had structural heart disease and left ventricular ejection fraction of 0.32+/-0.15. On the day of the index arrhythmia, 30% of the patients had a serum potassium concentration <3.5 or >5.0 mEq/L, including 7% who had a serum potassium concentration <3.0 or >6.0 mEq/L. For the entire cohort of patients, freedom from a recurrent sustained ventricular arrhythmia was 18% at 5 years and was not significantly different among patients with a serum potassium concentration <3.5 mEq/L (23%), between 3.5 and 5.0 mEq/L (16%), and >5.0 mEq/L (5%; P = 0.1). CONCLUSION: The results of the present study suggest that patients with structural heart disease and an abnormal serum potassium concentration at the time of an initial episode of sustained ventricular tachycardia or ventricular fibrillation are at high risk for a recurrent ventricular arrhythmia; therefore, implantable defibrillator therapy may be reasonable.     

ADRENAL AND GONADAL STEROIDS IN GIRLS DURING SEXUAL MATURATION

The peripheral venous plasma concentrations of gonadotrophins (LH and FSH), prolactin (Prl), cortisol, dehydroepiandrosterone (DHA), dehydroepiandrosterone-sulphate (DHA-S), pregnenolone (Δ₅P), progesterone (P), 17-hydroxyprogesterone (17P), androstenedione (A), testosterone (T), dihydrotestosterone (DHT) and oestradiol (E₂) were measured in girls at different stages of sexual development (from P1 to P4–5 according to Tanner, 1962). Both gonadotrophins increase progressively during sexual maturation, to reach the highest concentrations in P4–5. However, the FSH values were significantly lower in these P4–5 pre-menarchal girls than those found in adult women in the early follicular phase. No significant changes were found in plasma Prl, cortisol and 17P levels during pubertal development; in contrast, plasma concentrations of DHA tripled from P1 to P4–5, reaching adult levels. A progressive rise was also found in DHA-S plasma levels. A significant, but less evident increase was found in Δ₅P and P plasma concentrations, from group P1 to P4–5. A, T and DHT levels rose progressively and significantly from P1–2 to the end of sexual maturation. In the case of E₂, only a moderate increase was found during pubertal development. All these data indicate that during pubertal development, there is a progressive reduction in the sensitivity towards oestrogen of the hypothalamic centres controlling gonadotrophin secretion. Prl does not seem to be involved in human sexual maturation, while important changes have been found in adrenal androgens. The constant levels of 17P and cortisol, in comparison with the behaviour of DHA, DHA-S, T and A, seem to indicate that during this period of life, the adrenal gland is stimulated by unknown factors other than ACTH, acting on the adrenal androgen-producing cells and responsible for the reported rises in plasma adrenal androgens.     

Long-Term Evaluation of the Ventricular Defibrillation Energy Requirement

Defibrillation Energy Requirements. Introduction : Defibrillation energy requirements in patients with nonthoracotomy defibrillators may increase within several months after implantation. However, the stability of the defibrillation energy requirement beyond 1 year has not been reported. The purpose of this study was to characterize the defibrillation energy requirement during 2 years of clinical follow-up.
Methods and Results : Thirty-one consecutive patients with a biphasic nonthoracotomy defibrillation system underwent defibrillation energy requirement testing using a step-down technique (20, 15, 12, 10, 8, 6, 5, 4, 3, 2, and 1 J) during defibrillator implantation, and then 24 hours, 2 months, 1 year, and 2 years after implantation. The mean defibrillation energy requirement during these evaluations was 10.9 ± 5.5 J, 12.3 ± 7.3 J, 11.7 ± 5.6 J, 10.2 ± 4.0 J, and 11.7 ± 7.4 J, respectively ( P = 0.4). The defibrillation energy requirement was noted to have increased by 10 J or more after 2 years of follow-up in five patients. In one of these patients, the defibrillation energy requirement was no longer associated with an adequate safety margin, necessitating revision of the defibrillation system. There were no identifiable clinical characteristics that distinguished patients who did and did not develop a 10-J or more increase in the defibrillation energy requirement.
Conclusion : The mean defibrillation energy requirement does not change significantly after 2 years of biphasic nonthoracotomy defibrillator system implantation. However, approximately 15% of patients develop a 10-J or greater elevation in the defibrillation energy requirement, and 3% may require a defibrillation system revision. Therefore, a yearly evaluation of the defibrillation energy requirement may he appropriate.     

Prevalence of Fever in Patients Undergoing Left Atrial Ablation of Atrial Fibrillation Guided by Barium Esophagraphy

Background: Real-time esophageal imaging is critical in avoiding esophageal injury. However, the safety of esophageal imaging with barium has not been specifically explored.
Methods: Three hundred seventy consecutive patients underwent left atrial (LA) ablation of atrial fibrillation (AF) under conscious sedation. One hundred eighty-five patients (50%) underwent the ablation procedure with, and 185 patients (50%) underwent the procedure without administration of barium. Fever, as a surrogate for aspiration, was defined as a maximal temperature ≥100°F within the first 24 hours following the ablation procedure.
Results: Thirty of the 370 patients (8%) developed fever within 24 hours after LA ablation. The prevalence of fever was 9% (17/185) among patients who received barium and 7% (13/185) among those who did not receive barium (P = 0.6). Evaluation revealed the following causes of fever in 14 of the 30 patients (47%) with no difference in prevalence between the 2 groups: pericarditis, venous thromboembolism, hematoma, and infiltrate on chest radiography. Multivariate analysis failed to reveal any factors associated with development of fever. None of the patients experienced serious complications such as respiratory failure or atrioesophageal fistula.
Conclusions: Fever may occur in approximately 10% of patients undergoing LA ablation of AF. Administration of barium is not associated with fever or other complications such as aspiration pneumonia. Real-time imaging of the esophagus with barium administration in conjunction with conscious sedation appears to be safe.