Endocardial stimulation of efferent parasympathetic nerves to the atrioventricular node in humans: optimal stimulation sites and the effects of digoxin

Exosomes derived from cardiac parasympathetic ganglionic neurons inhibit apoptosis in hyperglycemic cardiomyoblasts

Diabetic cardiomyopathy is known to involve two forms of cardiac cell death: apoptosis and necrosis. However, it remains unknown whether hyperglycemia-induced apoptosis in the H9c2 cell culture system is inhibited by parasympathetic ganglionic neurons (PGN) derived exosomes (exos). We isolated PGN and sympathetic ganglionic neurons (SGN) from the right stellate ganglion in rats, and derived exos from these sources. H9c2 cells were divided into 4 groups: (1) Control, (2) H9c2 + Glucose (100 mmol/L), (3) H9c2 + Glucose + PGN-exos, and (4) H9c2 + Glucose + SGN-exos. We determined cell proliferation and viability with an MTT assay kit, and assessed apoptotic cell death with TUNEL staining and ELISA. Data were further confirmed by analyzing the presence of pro-apoptotic proteins Caspase-3 and Bax, and anti-apoptotic protein Bcl-2. Glucose exposed H9c2 cells significantly reduced cell viability, which was improved by PGN-exos, but not by SGN-exos. Furthermore, increased apoptosis in hyperglycemia in H9c2 cells was confirmed with TUNEL staining and cell death ELISA which demonstrated significantly (p < 0.05) reduction with PGN-exos treatment, but not with SGN-exos. Moreover, high expression of pro-apoptotic proteins Caspase-3 and Bax was reduced following treatment with PGN-exos; however, SGN-exos were unable to reduce the expression. Significantly reduced anti-apoptotic protein Bcl-2 following glucose treatment was improved with PGN-exos. Therefore, our data suggest that hyperglycemia induces apoptosis in H9c2 cells and decreases cell viability, and that PGN-exos are able to inhibit apoptosis, improve cell viability, and restore levels of anti-apoptotic protein Bcl-2.

Post-operative atrial fibrillation management by selective epicardial vagal fat pad stimulation

PURPOSE

Post-operative atrial fibrillation (POAF) is a common complication after cardiac surgery and often leads to poorly tolerated fast ventricular rates. Negative dromotropic drugs are not always effective and may not be well tolerated in heart failure patients. Aim of this study is to verify if high-frequency stimulation of the right inferior fat pad (RIFPS) allows an effective decrease in ventricular rate (VR) during POAF.

METHODS

We enrolled 32 consecutive patients submitted to bypass; during surgery, a temporary heart wire was implanted in a site where RIFPS evoked a functional AV block. During POAF, RIFPS was delivered from the heart wire to decrease VR.

RESULTS

Intra-operative RIFPS evoked complete AV block in 29 patients (91%). Fourteen patients (44%) developed POAF (mean VR 127 +/- 12 bpm). In these patients, RIFPS achieved a 25% reduction of VR and complete AV block with 6.0 +/- 1.9 and 7.5 +/- 1.8 V (duration 0.2 ms, frequency 50 Hz), respectively.

CONCLUSION

Epicardial RIFPS represents an effective and feasible technique to decrease VR during POAF.

Electrical and hemodynamic function produced by stimulation of atropine sensitive right ventricular nerves in humans

In mammalian ventricles including humans, it is recognized that parasympathetic ganglia innervate the heart. Little is known about the location and function of right ventricular parasympathetic nerves in humans. We hypothesized that in humans: (1) there are parasympathetic ganglia that supply the right ventricle that can be stimulated via an endocardial catheter and (2) stimulation of these fibers will alter the electrical and hemodynamic function of the right ventricle. Parasympathetic nerve stimulation was performed via an endocardial catheter placed along several sites of the right ventricle, superior vena cava, and right internal jugular area in humans. The spatial extent of parasympathetic innervation was mapped in 1-cm zones across the right ventricle. Cardiac output, heart rate, and atrioventricular conduction were monitored to provide independent assessment of parasympathetic innervation. In all 22 patients, ventricular refractoriness shortened from 12 +/- 3 to 3 +/- 1 ms during parasympathetic nerve stimulation, and the greatest shortening of refractoriness was observed at the base of the right ventricle (p = 0.01). No significant shortening in ventricular refractoriness occurred in areas beyond 2 cm from the right ventricular base. These results were compared by using T table test. The parasympathetic nerve stimulation protocol decreased cardiac output, reaffirming the principle effect of parasympathetic ganglia. Atropine was administered in seven patients. All effects from nerve stimulation were abolished after atropine administration. These results were also compared by using T table test. These data provide the first demonstration of the electrical and hemodynamic function by stimulation of atropine sensitive nerves of the human right ventricle. Greater understanding of parasympathetic innervation may lead to novel therapies for arrhythmias.

Ventricular rate control during atrial fibrillation and AV node modifications: past, present, and future

Atrial fibrillation (AF) is the most common arrhythmia. Currently there are two broad strategic treatment options for AF: rhythm control and rate control. For rhythm control, the treatment is directed toward restoring and maintaining the sinus rhythm. For rate control, the intention is to slow ventricular rate while allowing AF to continue. In both cases anticoagulation therapy is recommended. The results of currently available clinical trials demonstrated clearly that rate control is not inferior to rhythm control. Thus, rate control is an acceptable primary therapy for many AF patients. The rate control can be achieved essentially by depressing or modifying the filtering properties of the atrioventricular (AV) node. This can be attained by medications that depress the impulse transmission within the AV node, by anatomic modification of the AV communications, as well as by autonomic manipulations that produce AV node negative dromotropic effect. We are reviewing current clinical and newer experimental modalities aimed at enhancing the lifesaving function of this remarkable nodal structure.