Effects of PRES baroreceptor stimulation on thermal and mechanical pain threshold in borderline hypertensives and normotensives

Prior studies have noted a pain relieving effect of baroreceptor stimulation and of higher tonic blood pressure in animals and humans. The present study used a new technique for the controlled, noninvasive stimulation of human carotid baroreceptors (PRES). PRES baroreceptor manipulation was delivered to both normotensive subjects (n= 11) and medication-free labile hypertensive subjects (n= 10) during both thermal and mechanical pain. Consistent with prior research, hypertensives had a higher threshold for thermal pain than did normotensives. PRES baroreceptor manipulation had no significant effect on thermal pain threshold for either group. For the mechanical pain model, the opposite results were obtained; group pain threshold did not differ, but there was a significant PRES baroreceptor stimulation effect of increasing pain threshold for both groups. Results are discussed in terms of specific features of the stimuli, dampening of pain in hypertensives, and adaptation to pain.     

Critical Atrial Site for Ablation of Pacing-Induced Atrial Fibrillation in the Normal Dog Heart

Site for Ablation of AF in Dogs. Introduction: Radiofrequency catheter ablation (RFA) has been used recently to treat atrial fibrillation (AF). The purpose of this study was to investigate a new approach to preventing AF by RFA.
Methods and Results: In open chest, anesthetized dogs, AF (lasting > 30 sec) was induced after burst stimulation, and electrophysiologic parameters were recorded before and after RFA. In group 1 (9 dogs) we performed selective and combined slow and fast pathway RFA, whereas in group 2(11 dogs) RFA was applied as a linear lesion at the mid-atrial septum between the inferior vena cava and the fossa ovalis. After ablation, the Wenckebach cycle length was significantly prolonged only in group 1 (194 ± 23 vs 282 ± 35 msec, P = 0.002). whereas the interval between the stimulus (S) artifact applied at the high right atrium to the His hundle (H) (SH interval) prolonged to the same extent in both groups (162 ± 14 vs 146 ± 45 msec. P = NS); group 1 due to an A-H prolongation whereas in group 2 it was due to an intra-atrial conduction delay. In group 1 AF still remained inducible, although with a longer mean R-R interval (215 ± 16 vs 433 ± 88 msec, P < 0.05). No instance of complete AV block developed. In group 2, sustained AF was noninducible in 10 dogs and its duration was markedly shorter in the remaining one (8 sec). Gross anatomy and histology did not reveal any damage inside of Koch's triangle, and particularly to the compact AV node.
Conclusion: These findings suggest that RFA at the mid-atrial septum prevents AF in the normal dog heart. This approach might also be successful in those clinical settings in which the atrial septum plays a critical role in the maintenance of sustained AF.     

The effect of respiratory and metabolic acid-base changes on ionized calcium concentration: in vivo and in vitro experiments in man and rat

Abstract. Correlation of ionized calcium concentration, [Ca²⁺] and blood pH has long been recognized. So far no distinction of the acid-base changes, i.e. respiratory changes or metabolic changes seemed necessary. The present study, with the use of a recently developed system for in vivo analysis of [Ca²⁺], and with in vitro experiments reinvestigates this question.
In a first series respiratory and metabolic changes were induced in rats. Changes of [Ca²⁺] (Δ[Ca²⁺]) and of plasma pH (ΔpH) were recorded continuously in vivo , plasma bicarbonate, [HCO^-₃] was measured in vitro . In a second series respiratory and metabolic changes were induced in sixteen volunteers and, separately, in vitro in plasma and modified Ringer solution, and the same parameters were determined.
In all experiments Δ[Ca²⁺] correlates negatively with ΔpH. However, the correlation in respiratory changes was significantly less as compared to that in metabolic changes. As expected, Δ[HCO^-₃] correlates positively with pH in metabolic and negatively in respiratory changes. We conclude from these experiments that in metabolic changes the effects of calciumalbumin interaction and calcium complexation with bicarbonate are additive, whereas both effects oppose each other in respiratory changes. This might explain the blunted effect of pH changes on [Ca²⁺] in respiratory changes.     

No Cardioprotective Benefit of Ischemic Postconditioning in Patients With ST‐Segment Elevation Myocardial Infarction

Background

Postconditioning is a potential cardioprotective strategy that has demonstrated conflicting and variable reductions in infarct size in human trials.

Objectives

To determine whether postconditioning could increase the extent of myocardial salvage in patients with acute ST‐segment elevation myocardial infarction undergoing primary percutaneous coronary intervention (PPCI).

Methods

One hundred two patients (aged 57 ± 11 years; 88% male) were randomly assigned to a postconditioning or standard protocol. Cardiovascular magnetic resonance imaging was performed 3 days after PPCI to measure the volumetric extent of myocardial necrosis and the area at risk.

Results

With similar time‐to‐reperfusion (170 ± 84 minutes in the postconditioning group vs. 150 ± 70 minutes in the standard group, P = 0.22), the myocardial salvage index was not significantly different between the postconditioned group and the control group, averaging 42 ± 22% vs. 33 ± 21%, respectively (P = 0.08). Furthermore, postconditioning was not associated with a smaller infarct size compared to controls (13 ± 7 g/m² vs. 15 ± 8 g/m², respectively, P = 0.18).

Conclusions

Postconditioning does not significantly increase myocardial salvage or reduce infarct size in patients with STEMI undergoing PPCI. However, the possibility of a more modest impact of postconditioning cannot be excluded with our sample size. (J Interven Cardiol 2013;26:482‐490)

     

Combination of Antitachycardia Pacemaker and Automatic Implantable Cardioverter/Defibrillator for Ventricular Tachycardia

Antitachycardia pacing for ventricular tachycardia (VT) is associated with the possibility of fibrillating the heart; on the other hand, the frequency of VT and patient discomfort can limit treatment with the automatic implantable cardioverter/defibrillator (AICD). To contribute to the further development of a universal pacemaker, we evaluated the combined use of the antitachycardia pacemaker ("tachylog") and the AICD in five patients with recurrent VT. In the automatic mode, the "tachylog" worked as a bipolar VVI pacemaker. For antitachycardia pacing, a burst of rapid ventricular pacing was delivered at about 80% of the cycle length. During a follow-up period of 5 +/- 2 months (range, 3 to 8) two to 291 successful interventions of antitachycardia pacing were counted from diagnostic data which had been collected by the pulse generator during the course of treatment. When the antitachycardia pacemaker failed to terminate VT, the AICD was activated. In the individual case, between 0 and 41 discharges of the AICD were delivered. The high pulse energy of the AICD did not damage the antitachycardia pacemaker; no interference of the two devices was observed. Future antitachycardia systems should be more flexible with regard to detection and termination modes, combining antitachycardia pacing with back-up defibrillation.