The role of the sympathetic nervous system in congestive heart failure

Non-invasive transcutaneous vagal nerve stimulation improves myocardial performance in doxorubicin-induced cardiotoxicity

AIMS

The clinical use of antitumor agent doxorubicin (DOX) is hampered by its dose-dependent cardiotoxicity. Development of highly efficient and safe adjuvant intervention for preventing DOX-induced adverse cardiac events is urgently needed. We aimed to investigate whether transcutaneous vagal nerve stimulation (tVNS) plays a cardio-protective role in DOX-induced cardiotoxicity.

METHODS AND RESULTS

Healthy male adult Sprague Dawley rats were used in the experiment and were randomly divided into four groups including control, DOX, tVNS and DOX+tVNS groups. A cumulative dose of 15 mg/kg DOX was intraperitoneally injected into rats to generate cardiotoxicity. Non-invasive tVNS was conducted for 6 weeks (30 min/day). After six-week intervention, the indices from the echocardiography revealed that tVNS significantly improved left ventricular function compared to the DOX group. The increased malondialdehyde (MDA) and Interleukin-1β (IL-1β), and decreased superoxide dismutase (SOD) were observed in the DOX group, while tVNS significantly prevented these changes. From cardiac histopathological analysis, the DOX+tVNS group showed a mild myocardial damage, and decreases in cardiac fibrosis and myocardial apoptosis compared to the DOX group. Heart rate variability (HRV) analysis showed that tVNS significantly inhibited DOX-induced sympathetic hyperactivity compared to the DOX group. Additionally, the results of RNA-sequencing analysis showed that there were 245 differentially expressed genes in the DOX group compared to the control group, among which 39 genes were downregulated by tVNS and most of these genes were involved in immune system. Moreover, tVNS significantly downregulated the relative mRNA expressions of chemokine-related genes and macrophages recruitment compared to the DOX group.

CONCLUSION

These results suggest that tVNS prevented DOX-induced cardiotoxicity by rebalancing autonomic tone, ameliorating cardiac dysfunction and remodeling. Notably, crosstalk between autonomic neuromodulation and innate immune cells macrophages mediated by chemokines might be involved in the underlying mechanisms.

A TRANSLATIONAL PERSPECTIVE

Non-invasive tVNS has been identified an effective neuromodulation strategy exerting beneficial effects on rebalancing autonomic tone and cardiac pathological conditions. The present study provided direct evidence for a beneficial role of tVNS in preventing DOX-induced autonomic dysfunction and cardiotoxicity in vivo. Additionally, recent studies revealed the importance of sympathetic nerve fibers involving in tumorigenesis and the benefits of higher vagal tone for tumor prognosis either in animal or human trials. Together, tVNS may not only become a novel, nonpharmacological adjuvant therapy for preventing doxorubicin-induced cardiotoxicity, but also may be beneficial for prognosis of cancer patients during chemotherapy. In our future study, we would investigate the effect of tVNS on both combined chemotherapy-induced cardiotoxicity and the antitumor efficacy of DOX in tumor models.

Improving Accuracy of Heart Failure Detection Using Data Refinement

Due to the wide inter- and intra-individual variability, short-term heart rate variability (HRV) analysis (usually 5 min) might lead to inaccuracy in detecting heart failure. Therefore, RR interval segmentation, which can reflect the individual heart condition, has been a key research challenge for accurate detection of heart failure. Previous studies mainly focus on analyzing the entire 24-h ECG recordings from all individuals in the database which often led to poor detection rate. In this study, we propose a set of data refinement procedures, which can automatically extract heart failure segments and yield better detection of heart failure. The procedures roughly contain three steps: (1) select fast heart rate sequences, (2) apply dynamic time warping (DTW) measure to filter out dissimilar segments, and (3) pick out individuals with large numbers of segments preserved. A physical threshold-based Sample Entropy (SampEn) was applied to distinguish congestive heart failure (CHF) subjects from normal sinus rhythm (NSR) ones, and results using the traditional threshold were also discussed. Experiment on the PhysioNet/MIT RR Interval Databases showed that in SampEn analysis (embedding dimension m = 1, tolerance threshold r = 12 ms and time series length N = 300), the accuracy value after data refinement has increased to 90.46% from 75.07%. Meanwhile, for the proposed procedures, the area under receiver operating characteristic curve (AUC) value has reached 95.73%, which outperforms the original method (i.e., without applying the proposed data refinement procedures) with AUC of 76.83%. The results have shown that our proposed data refinement procedures can significantly improve the accuracy in heart failure detection.

Spinal genesis of Mayer waves

Variability in cardiovascular spectra was first described by Stephan Hales in 1733. Traube and Hering initially noted respirophasic variation of the arterial pressure waveform in 1865 and Sigmund Mayer noted a lower frequency oscillation of the same in anesthetized rabbits in 1876. Very low frequency oscillations were noted by Barcroft and Nisimaru in 1932, likely representing vasogenic autorhythmicity. While the origins of Traube Hering and very low frequency oscillatory variability in cardiovascular spectra are well described, genesis mechanisms and functional significance of Mayer waves remain in controversy. Various theories have posited baroreflex and central supraspinal mechanisms for genesis of Mayer waves. Several studies have demonstrated the persistence of Mayer waves following high cervical transection, indicating a spinal capacity for genesis of these oscillations. We suggest a general tendency for central sympathetic neurons to oscillate at the Mayer wave frequency, the presence of multiple Mayer wave oscillators throughout the brainstem and spinal cord, and possible contemporaneous genesis by baroreflex and vasomotor mechanisms.

Low-level transcutaneous electrical stimulation of the auricular branch of vagus nerve ameliorates left ventricular remodeling and dysfunction by downregulation of matrix metalloproteinase 9 and transforming growth factor β1

Vagus nerve stimulation improves left ventricular (LV) remodeling by downregulation of matrix metalloproteinase 9 (MMP-9) and transforming growth factor β1 (TGF-β1). Our previous study found that low-level transcutaneous electrical stimulation of the auricular branch of the vagus nerve (LL-TS) could be substituted for vagus nerve stimulation to reverse cardiac remodeling. So, we hypothesize that LL-TS could ameliorate LV remodeling by regulation of MMP-9 and TGF-β1 after myocardial infarction (MI). Twenty-two beagle dogs were randomly divided into a control group (MI was induced by permanent ligation of the left coronary artery, n = 8), an LL-TS group (MI with long-term intermittent LL-TS, n = 8), and a normal group (sham ligation without stimulation, n = 6). At the end of 6 weeks follow-up, LL-TS significantly reduced LV end-systolic and end-diastolic dimensions, improved ejection fraction and ratio of early (E) to late (A) peak mitral inflow velocity. LL-TS attenuated interstitial fibrosis and collagen degradation in the noninfarcted myocardium compared with the control group. Elevated level of MMP-9 and TGF-β1 in LV tissue and peripheral plasma were diminished in the LL-TS treated dogs. LL-TS improves cardiac function and prevents cardiac remodeling in the late stages after MI by downregulation of MMP-9 and TGF-β1 expression.

Chronic intermittent low-level transcutaneous electrical stimulation of auricular branch of vagus nerve improves left ventricular remodeling in conscious dogs with healed myocardial infarction

BACKGROUND

Vagus nerve stimulation attenuates left ventricular (LV) remodeling after myocardial infarction (MI). Our previous study found a noninvasive approach to deliver vagus nerve stimulation by transcutaneous electric stimulation of auricular branch of vagus nerve. So we hypothesize that chronic intermittent low-level tragus stimulation (LL-TS) could attenuate LV remodeling in conscious dogs with healed MI.

METHODS AND RESULTS

Thirty beagle dogs were randomly divided into 3 groups, MI group (left anterior descending artery and major diagonal branches ligation to introduce MI, n=10), LL-TS group (MI plus chronic intermittent LL-TS, n=10), and control group (sham surgery without stimulation, n=10). Tragus stimulation was delivered to bilateral tragus with ear-clips connected to a custom-made stimulator. The voltage slowing sinus rate was used as the threshold for setting LL-TS at 80% below that. LL-TS group was given 4 hours stimulation at 7-9 am and 4-6 pm on conscious dogs. At the end of 90-day follow-up, LL-TS group significantly reduced LA and LV dilatation, improved LV contractile and diastolic function, reduced infarct size by ≈50% compared with MI group. LL-TS treatment alleviated cardiac fibrosis and significantly decreased protein expression level of collagen I, collagen III, transforming growth factor β1, and matrix metallopeptidase 9 in LV tissues. The plasma level of high-specific C-reactive protein, norepinephrine, N-terminal pro-B-type-natriuretic peptide in LL-TS group was significantly lower than those in MI group from the 7th day to the end of follow-up.

CONCLUSIONS

Chronic intermittent low-level transcutaneous electric stimulation of auricular branch of vagus nerve can attenuate LV remodeling in conscious dogs with healed MI.

Slow and deep respiration suppresses steady-state sympathetic nerve activity in patients with chronic heart failure: from modeling to clinical application

Influences of slow and deep respiration on steady-state sympathetic nerve activity remain controversial in humans and could vary depending on disease conditions and basal sympathetic nerve activity. To elucidate the respiratory modulation of steady-state sympathetic nerve activity, we modeled the dynamic nature of the relationship between lung inflation and muscle sympathetic nerve activity (MSNA) in 11 heart failure patients with exaggerated sympathetic outflow at rest. An autoregressive exogenous input model was utilized to simulate entire responses of MSNA to variable respiratory patterns. In another 18 patients, we determined the influence of increasing tidal volume and slowing respiratory frequency on MSNA; 10 patients underwent a 15-min device-guided slow respiration and the remaining 8 had no respiratory modification. The model predicted that a 1-liter, step increase of lung volume decreased MSNA dynamically; its nadir (−33 ± 22%) occurred at 2.4 s; and steady-state decrease (−15 ± 5%), at 6 s. Actually, in patients with the device-guided slow and deep respiration, respiratory frequency effectively fell from 16.4 ± 3.9 to 6.7 ± 2.8/min ( P < 0.0001) with a concomitant increase in tidal volume from 499 ± 206 to 1,177 ± 497 ml ( P < 0.001). Consequently, steady-state MSNA was decreased by 31% ( P < 0.005). In patients without respiratory modulation, there were no significant changes in respiratory frequency, tidal volume, and steady-state MSNA. Thus slow and deep respiration suppresses steady-state sympathetic nerve activity in patients with high levels of resting sympathetic tone as in heart failure.

Activation of central angiotensin type 2 receptors by compound 21 improves arterial baroreflex sensitivity in rats with heart failure

BACKGROUND

In a previous study we demonstrated that central administration of compound 21 (C21), a nonpeptide AT2R agonist, inhibited sympathetic tone in normal rats. In this study, we hypothesized that C21 exerts a similar effect in rats with coronary ligation-induced heart failure (HF).

METHODS

C21 was intracerebroventricularly infused for 7 days by osmotic mini pump. Blood pressure (BP) and heart rate (HR) were recorded by radiotelemetry in the conscious state to measure spontaneous arterial baroreflex sensitivity. Urine was collected for measurement of norepinephrine excretion. On the last day of C21 treatment, renal sympathetic nerve activity, BP, and HR were directly recorded under anesthesia, and the induced arterial baroreflex sensitivity was evaluated. Protein expressions of neuronal nitric oxide synthase (nNOS) and angiotensin II type 1 receptor (AT1R) in the subfornical organ, paraventricular nucleus, rostral ventrolateral medulla, and nucleus tractus solitarius were determined by Western blot analysis.

RESULTS

C21-treated HF rats displayed significantly less norepinephrine excretion (2,385.6 ± 121.1 vs. 3,677.3 ± 147.6 ng/24 hours; P < 0.05) and lower renal sympathetic nerve activity (50.2 ± 1.9% of max vs. 70.9 ± 8.2% of max; P < 0.05) than vehicle-treated HF rats. C21-treated rats also exhibited improved spontaneous arterial baroreflex sensitivity and induced arterial baroreflex sensitivity. Bolus intracerebroventricular injection of angiotensin II-evoked pressor and sympatho-excitatory responses were attenuated in the C21-treated HF rats, which displayed upregulated nNOS and downregulated AT1R expression in the subfornical organ, paraventricular nucleus, and rostral ventrolateral medulla.

CONCLUSIONS

Activation of central angiotensin II type 2 receptor AT2R by C21 suppresses sympathetic outflow in rats with HF by improving baroreflex sensitivity and may provide important benefit in the HF syndrome.

β1-Adrenergic receptor signaling activates the epithelial calcium channel, transient receptor potential vanilloid type 5 (TRPV5), via the protein kinase A pathway

Epinephrine and norepinephrine are present in the pro-urine. β-Adrenergic receptor (β-AR) blockers administered to counteract sympathetic overstimulation in patients with congestive heart failure have a negative inotropic effect, resulting in reduced cardiac contractility. Positive inotropes, β1-AR agonists, are used to improve cardiac functions. Active Ca(2+) reabsorption in the late distal convoluted and connecting tubules (DCT2/CNT) is initiated by Ca(2+) influx through the transient receptor potential vanilloid type 5 (TRPV5) Ca(2+) channel. Although it was reported that β-ARs are present in the DCT2/CNT region, their role in active Ca(2+) reabsorption remains elusive. Here we revealed that β1-AR, but not β2-AR, is localized with TRPV5 in DCT2/CNT. Subsequently, treatment of TRPV5-expressing mouse DCT2/CNT primary cell cultures with the β1-AR agonist dobutamine showed enhanced apical-to-basolateral transepithelial Ca(2+) transport. In human embryonic kidney (HEK293) cells, dobutamine was shown to stimulate cAMP production, signifying functional β1-AR expression. Fura-2 experiments demonstrated increased activity of TRPV5 in response to dobutamine, which could be prevented by the PKA inhibitor H89. Moreover, nonphosphorylable T709A-TRPV5 and phosphorylation-mimicking T709D-TRPV5 mutants were unresponsive to dobutamine. Surface biotinylation showed that dobutamine did not affect plasma membrane abundance of TRPV5. In conclusion, activation of β1-AR stimulates active Ca(2+) reabsorption in DCT2/CNT; an increase in TRPV5 activity via PKA phosphorylation of residue Thr-709 possibly plays an important role. These data explicate a calciotropic role in addition to the inotropic property of β1-AR.

Chronic vagus nerve stimulation improves autonomic control and attenuates systemic inflammation and heart failure progression in a canine high-rate pacing model

BACKGROUND

Autonomic dysfunction, characterized by sympathetic activation and vagal withdrawal, contributes to the progression of heart failure (HF). Although the therapeutic benefits of sympathetic inhibition with beta-blockers in HF are clear, the role of increased vagal tone in this setting has been less studied. We have investigated the impact of enhancing vagal tone (achieved through chronic cervical vagus nerve stimulation, [VNS]) on HF development in a canine high-rate ventricular pacing model.

METHODS AND RESULTS

Fifteen dogs were randomized into control (n=7) and VNS (n=8) groups. All dogs underwent 8 weeks of high-rate ventricular pacing (at 220 bpm for the first 4 weeks to develop HF and another 4 weeks at 180 bpm to maintain HF). Concomitant VNS, at an intensity reducing sinus rate approximately 20 bpm, was delivered together with the ventricular pacing in the VNS group. At 4 and 8 weeks of ventricular pacing, both left ventricular end-diastolic and -systolic volumes were lower and left ventricular ejection fraction was higher in the VNS group than in the control group. Heart rate variability and baroreflex sensitivity improved in the VNS dogs. Rises in plasma norepinephrine, angiotensin II, and C-reactive protein levels, ordinarily expected in this model, were markedly attenuated with VNS treatment.

CONCLUSIONS

Chronic VNS improves cardiac autonomic control and significantly attenuates HF development in the canine high-rate ventricular pacing model. The therapeutic benefit of VNS is associated with pronounced anti-inflammatory effects. VNS is a novel and potentially useful therapy for treating HF.

Differential control of collagen synthesis by the sympathetic and renin-angiotensin systems in the rat left ventricle

In the present study, we tested the hypothesis of the indirect (via the sympathetic nervous system (SNS)) and direct (via AT1 receptors) contributions of Angiotensin II (Ang II) on the synthesis of collagen types I and III in the left ventricle (LV) in vivo. Sympathectomy and blockade of the Ang II receptor AT1 were performed alone or in combination in normotensive rats. The mRNA and protein synthesis of collagen types I and III were examined by Q-RT-PCR and immunoblotting in the LV. Collagen types I and III mRNA were decreased respectively by 53% and 22% after sympathectomy and only collagen type I mRNA was increased by 52% after AT1 receptor blockade. mRNA was not changed for collagen type I but was decreased by 25% for collagen type III after double treatment. Only collagen protein type III was decreased after sympathectomy by 12%, but collagen proteins were increased respectively for types I and III by 145% and 52% after AT1 receptor blockade and by 45% and 60% after double treatment. Deducted interpretations from our experimental approach suggest that Ang II stimulates indirectly (via SNS) and inhibits directly (via AT1 receptors) the collagen type I at transcriptional and protein levels. For collagen type III, it stimulates indirectly the transcription and inhibited directly the protein level. Therefore, the Ang II regulates collagen synthesis differently through indirect and direct pathways.

Symbolic analysis detects alterations of cardiac autonomic modulation in congestive heart failure rats

Congestive heart failure (CHF) is associated with neurohumoral activation. Only very few studies have examined the progression of autonomic dysfunction in CHF in humans and scanty data are available in animal models of CHF. This study was performed to assess the changes in cardiac autonomic modulation during the progression of CHF in a rat model, using an innovative analysis of heart rate variability. Progression of cardiovascular autonomic dysfunction was assessed in a rat model of CHF induced by coronary artery ligation. Spectral and symbolic analyses were performed on heart period (approximated with pulse interval, PI) and systolic arterial pressure (SAP) signals, acquired ~2 and ~4 weeks after the surgical procedure. As CHF developed, symbolic analysis revealed a decrease of rhythmical physiological sympathetic modulation, as indicated by the reduction of the percentage of stable patterns. In addition, symbolic analysis revealed that runs of short-long-short and/or long-short-long PI values and high-low-high and/or low-high-low SAP values were more and more frequent as CHF progressed. On the contrary, spectral analysis of PI and SAP series was not able to detect any impairment of autonomic regulation. Indeed, low frequency and high frequency powers derived from both PI and SAP series were not significantly changed. These data indicate that the autonomic cardiovascular modulation is altered during the progression of CHF and that symbolic analysis seems to be more suitable than spectral analysis to describe alterations of heart period dynamics and of cardiovascular regulation in this animal model of CHF.

Reactive oxygen species in the paraventricular nucleus mediate the cardiac sympathetic afferent reflex in chronic heart failure rats

The aim of this study was to determine whether reactive oxygen species (ROS) in the paraventricular nucleus (PVN) mediate both the cardiac sympathetic afferent reflex (CSAR) and angiotensin II-induced CSAR enhancement in chronic heart failure (CHF) rats. CSAR was evaluated from the responses of renal sympathetic nerve activity (RSNA) to epicardial application of bradykinin. In both CHF and sham-operated rats, PVN microinjection of the superoxide anion scavengers tempol or tiron almost abolished the CSAR, but the superoxide dismutase inhibitor DETC potentiated the CSAR. PVN pretreatment with tempol or tiron abolished, whereas DETC augmented, the angiotensin II-induced CSAR enhancement. In CHF rats, superoxide anion and malondialdehyde (MDA) levels in the PVN were increased, but were normalized by the AT(1) receptor antagonist losartan. PVN microinjection of tempol decreased superoxide anion and MDA levels, but epicardial application of bradykinin or PVN microinjection of angiotensin II increased superoxide anion and MDA to higher levels in CHF rats than in sham-operated rats. These results indicate that ROS in the PVN mediates the CSAR and the effect of angiotensin II in the PVN on the CSAR in both CHF and sham-operated rats. Increased ROS in the PVN are involved in the enhanced CSAR in CHF.

Endogenous hydrogen peroxide in paraventricular nucleus mediating cardiac sympathetic afferent reflex and regulating sympathetic activity

We previously reported that reactive oxygen species (ROS) in paraventricular nucleus (PVN) mediated cardiac sympathetic afferent reflex (CSAR). The present study investigated the role of endogenous hydrogen peroxide (H(2)O(2)), a ROS, in the PVN in mediating the CSAR and regulating sympathetic activity. The CSAR was evaluated by the response of renal sympathetic nerve activity (RSNA) to epicardial application of bradykinin (BK) in rats. Bilateral microinjection of polyethylene glycol-catalase (PEG-CAT, an analogue of endogenous catalase) or polyethylene glycol-superoxide dismutase (PEG-SOD, an analogue of endogenous superoxide dismutase) into the PVN abolished the CSAR, decreased baseline RSNA and mean arterial pressure (MAP). Moreover, pretreatment with PEG-CAT or PEG-SOD blocked the enhanced CSAR and RSNA responses induced by exogenous angiotensin II (Ang II) in the PVN. Aminotriazole (ATZ, a catalase inhibitor) alone potentiated the CSAR, increased RSNA and MAP, but failed to augment the Ang II-induced CSAR enhancement responses. Pretreated with PEG-SOD, ATZ still increased baseline RSNA and MAP but inhibited the CSAR and Ang II-induced CSAR and RSNA enhancement responses. These results suggested that endogenous H(2)O(2) in the PVN mediated both the CSAR and Ang II-induced CSAR enhancement responses. H(2)O(2) in the PVN were involved in regulating sympathetic activity and arterial pressure.

AT1 receptor in paraventricular nucleus mediates the enhanced cardiac sympathetic afferent reflex in rats with chronic heart failure

Our previous studies have shown that the cardiac sympathetic afferent reflex (CSAR) was enhanced in the chronic heart failure in dogs and rats. Exogenous angiotensin II (Ang II) in the paraventricular nucleus (PVN) potentiated this reflex which was mediated by AT1 receptor. The aim of the present study was to determine if the abnormal endogenous Ang II and AT1 receptor in the PVN were responsible for the enhanced CSAR in rats with coronary ligation-induced chronic heart failure (CHF). Under urethane and alpha-chloralose anesthesia, mean arterial pressure, heart rate and renal sympathetic nerve activity (RSNA) were recorded in sino-aortic denervated and cervical vagotomized CHF and sham-operated rats. The effects of bilateral microinjection of AT1 receptor antagonist losartan and angiotensin converting enzyme inhibitor captopril on the CSAR evoked by epicardial application of bradykinin (BK, 0.04 and 0.4 microg) were determined respectively. Both AT1 receptor mRNA and AT1 receptor protein in the PVN were measured. Bilateral microinjection of either captopril (10 nmol) or losartan (50 nmol) into the PVN inhibited the enhanced CSAR evoked by BK in rats with CHF, but had no significant effects in sham-operated rats. AT1 receptor protein in the PVN significantly increased in CHF rats compared with sham-operated rats. These results indicated that either decrease of Ang II or blockage of AT1 receptor in the PVN normalized the enhanced CSAR evoked by epicardial application of BK in rats with CHF, and that increased expression of AT1 receptor in the PVN contributed to the enhanced CSAR in the CHF state.

Mechanisms of neurohormonal activation in chronic congestive heart failure: pathophysiology and therapeutic implications

Patients with chronic congestive heart failure have a sequential and incessant activation of those neurohormonal systems, which control body fluids, cardiac output and systemic blood pressure. Neurohormonal activation is initially selective and regional. Generalized activation is a late event in the natural history of congestive heart failure. Although the ultimate stimulus responsible for the activation of these neurohormonal systems is unknown, a decreased cardiac output and diminished effective blood volume have been proposed as the responsible mechanisms. However, extensive clinical and experimental research suggest that cardiac remodeling and loading of low-pressure cardiac receptors with sympathetic afferents could be the triggering events followed by unloading of high-pressure carotid receptors by decreased cardiac output and diminished effective blood volume.

ANG II in the paraventricular nucleus potentiates the cardiac sympathetic afferent reflex in rats with heart failure

Chronic heart failure (CHF) is characterized by sympathoexcitation, and the cardiac sympathetic afferent reflex (CSAR) is a sympathoexcitatory reflex. Our previous studies have shown that the CSAR was enhanced in CHF. In addition, central angiotensin II (ANG II) is an important modulator of this reflex. This study was performed to determine whether the CSAR evoked by stimulation of cardiac sympathetic afferent nerves (CSAN) in rats with coronary ligation-induced CHF is enhanced by ANG II in the paraventricular nucleus (PVN). Under alpha-chloralose and urethane anesthesia, renal sympathetic nerve activity (RSNA) was recorded. The RSNA responses to electrical stimulation (5, 10, 20, and 30 Hz) of the CSAN were evaluated. Bilateral microinjection of the AT1-receptor antagonist losartan (50 nmol) into the PVN had no significant effects in the sham group, but it abolished the enhanced RSNA response to stimulation in the CHF group. Unilateral microinjection of three doses of ANG II (0.03, 0.3, and 3 nmol) into the PVN resulted in dose-related increases in the RSNA responses to stimulation. Although ANG II also potentiated the RSNA response to electrical stimulation in sham rats, the RSNA responses to stimulation after ANG II into the PVN in rats with CHF were much greater than in sham rats. The effects of ANG II were prevented by pretreatment with losartan into the PVN in CHF rats. These results suggest that the central gain of the CSAR is enhanced in rats with coronary ligation-induced CHF and that ANG II in the PVN augments the CSAR evoked by CSAN, which is mediated by the central angiotensin AT1 receptors in rats with CHF.

Attenuated respiratory modulation of chemoreflex-mediated sympathoexcitation in patients with chronic heart failure

BACKGROUND

Enhanced hypercapnic chemoreflex in chronic heart failure could modulate sympathetic nerve activity in a different manner depending on the severity of heart failure. This study was designed to evaluate the dynamic aspects of sympathoexcitation caused by central hypercapnic chemoreflex in patients with chronic heart failure.

METHODS AND RESULTS

In 21 patients with chronic heart failure, wavelet analysis was applied to elucidate the spectral components of muscle sympathetic nerve activity (MSNA) and instantaneous ventilation during hypercapnic chemoreceptor stimulation. Hypercapnia increased MSNA (83+/-8 versus 29+/-9 %, P<.01) and ventilation (209+/-27 versus 190+/-21%, P<.05) more in 12 symptomatic patients than in 9 asymptomatic patients. This hypercapnic chemoreflex exerted a greater influence on the sympathetic limb than on the ventilatory limb in the symptomatic patients. The wavelet analysis revealed that the within-breath sympathoinhibition in the symptomatic patients was attenuated as compared with that in the asymptomatic patients (0.33+/-0.03 vs. 0.44+/-0.04, P<.05).

CONCLUSIONS

The enhanced chemoreflex sympathetic drive and relative attenuation of ventilatory sympathoinhibition could contribute to exaggerated sympathoexcitation in patients with heart failure when they are exposed to carbon dioxide during exercise or sleep apnea.

AT1 receptor mRNA antisense normalizes enhanced cardiac sympathetic afferent reflex in rats with chronic heart failure

Previous studies showed that the cardiac sympathetic afferent reflex (CSAR) is enhanced in dogs and rats with chronic heart failure (CHF) and that central ANG II type 1 receptors (AT(1)R) are involved in this augmented reflex. The aim of this study was to determine whether intracerebroventricular administration and microinjection of antisense oligodeoxynucleotides targeted to AT(1)R mRNA would attenuate the enhanced CSAR and decrease resting renal sympathetic nerve activity (RSNA) in rats with coronary ligation-induced CHF. The CSAR was elicited by application of bradykinin to the epicardial surface of the left ventricle. Reflex responses to epicardial administration of bradykinin were enhanced in rats with CHF. The response to bradykinin was determined every 50 min after intracerebroventricular administration (lateral ventricle) or microinjection (into paraventricular nucleus) of antisense or scrambled oligonucleotides to AT(1)R mRNA. AT(1)R mRNA and protein levels in the paraventricular nucleus were significantly reduced 5 h after administration of antisense. Antisense significantly decreased resting RSNA and normalized the enhanced CSAR responses to bradykinin in rats with CHF. Scrambled oligonucleotides did not alter resting RSNA or the enhanced responses to bradykinin in rats with CHF. No significant effects were found in sham-operated rats after administration of either antisense or scrambled oligonucleotides. These results strongly suggest that central AT(1)R mRNA antisense reduces expression of AT(1)R protein and normalizes the augmentation of this excitatory sympathetic reflex and that genetic manipulation of protein expression can be used to normalize the sympathetic enhancement in CHF.

Microinjection of ANG II into paraventricular nucleus enhances cardiac sympathetic afferent reflex in rats

The aims of present study were to determine whether angiotensin II (ANG II) in the paraventricular nucleus (PVN) is involved in the central integration of the cardiac sympathetic afferent reflex and whether this effect is mediated by the ANG type 1 (AT(1)) receptor. While the animals were under alpha-chloralose and urethane anesthesia, mean arterial pressure, heart rate, and renal sympathetic nerve activity (RSNA) were recorded in sinoaortic-denervated and cervical-vagotomized rats. A cannula was inserted into the left PVN for microinjection of ANG II. The cardiac sympathetic afferent reflex was tested by electrical stimulation (5, 10, 20, and 30 Hz in 10 V and 1 ms) of the afferent cardiac sympathetic nerves or epicardial application of bradykinin (BK) (0.04 and 0.4 microg in 2 microl). Microinjection of ANG II (0.03, 0.3, and 3 nmol) into the PVN resulted in dose-related increases in the RSNA responses to electrical stimulation. The percent change of RSNA response to 20- and 30-Hz stimulation increased significantly at the highest dose of ANG II (3 nmol). The effects of ANG II were prevented by pretreatment with losartan (50 nmol) into the PVN. Microinjection of ANG II (0.3 nmol) into the PVN significantly enhanced the RSNA responses to epicardial application of BK, which was abolished by pretreatment with losartan (50 nmol) into the PVN. These results suggest that exogenous ANG II in the PVN augments the cardiac sympathetic afferent reflex evoked by both electrical stimulation of cardiac sympathetic afferent nerves and epicardial application of BK. These central effects of ANG II are mediated by AT(1) receptors.

Effects of endoscopic transthoracic sympathicotomy on hemodynamic and neurohumoral responses to exercise in humans

Endoscopic transthoracic sympathicotomy (ETS) is a minimal invasive procedure of thoracic sympathetic block and has been used successfully in the treatment of primary palmar hyperhidrosis. To examine the effect of Th 2-3 ETS on hemodynamic responses to submaximal upright treadmill exercise in humans, cardiac output, plasma noradrenaline and adrenaline at rest and during the last 40s of stage 2 in a modified Bruce protocol were measured before and after ETS in 21 patients with primary palmar hyperhidrosis. Heart rate, mean arterial pressure, rate-pressure product, and noradrenaline decreased at rest and at submaximal exercise after ETS. Cardiac index at rest did not change either before or after ETS, but decreased (8.9 +/- 0.6 vs 6.8 +/- 0.4L x min(-1) m-2; p<0.01, mean +/- SEM) at submaximal exercise after ETS. Stroke index and systemic vascular resistance were similar both at rest and at submaximal exercise before and after ETS. Thus, ETS reduces myocardial oxygen demand and plasma noradrenaline levels both at rest and during exercise without significantly depressing cardiac function in terms of stroke volume.

Correlation of Lorenz scatterplots with frequency-domain heart rate variability

Heart rate (HR) variability is important with respect to disease prognosis and the effects of drugs. Lorenz scatterplots provide a simple way to evaluate HR variability visually. The relation of Lorenz scatterplots to frequency-domain HR variability was examined in 75 Holter recordings and in simulated HR trends. The length of Lorenz scatterplots was double-exponentially correlated with total frequency and very-low frequency powers, with correlation coefficients (r) of 0.88. The width of Lorenz scatterplots was highly correlated with the high frequency power (r=0.98). The sum of the width and length of Lorenz scatterplots was highly correlated with the total frequency power (r=0.92). Identical results were obtained when simulated HR trends were used. In conclusion, Lorenz scatterplots provide a simple way to estimate the frequency-domain HR variability.

Emerging excitatory role of cardiovascular sympathetic afferents in pathophysiological conditions

There is sound experimental evidence that cardiovascular sympathetic afferent fibers mediate cardiovascular reflexes largely excitatory in nature with positive-feedback characteristics. This afferent neural channel is likely to normally participate in the neural regulation of cardiovascular function. The hypothesis, which is the core of this article, is that in some pathophysiological conditions, sympathetic overactivity may be partly due to an emerging excitatory reflex action of cardiovascular sympathetic afferents. In fact, the early phase of congestive heart failure can be characterized by an increase in arterial pressure and heart rate and/or by a diastolic dysfunction, leaving unchanged the cardiac output; in these conditions, in which no baroreceptor deactivation should occur, it is possible that cardiovascular sympathetic afferents with sensory endings in the thoracic low-pressure areas, highly responsive to volume loading, are responsible for mediating the reflex sympathetic excitation. Similarly, during acute myocardial infarction, ventricular sympathetic afferents are likely to mediate a reflex sympathetic overactivity, which is known to facilitate sudden death. Finally, numerous reports have described in essential arterial hypertension an increased sympathetic activity that may be due, at least in part, to the reinforcing action of sympathosympathetic reflexes. Thus, in pathophysiological conditions, cardiovascular sympathetic afferents would mediate a reflex sympathetic overactivity independently of baroreceptive mechanisms, and such an absence of a homeostatic purpose would provide a better rationale for some beneficial effects of therapeutic correction.

Respiratory modulation of muscle sympathetic nerve activity in patients with chronic heart failure

BACKGROUND

Sympathoexcitation and respiratory instability are closely related to worsening of chronic heart failure. To elucidate the dynamic nature of respiratory modulation of sympathetic activity in patients with heart failure, we studied within-breath variation of muscle sympathetic nerve activity (MSNA) under various ventilatory volumes.

METHODS AND RESULTS

MSNA, blood pressure, and respiratory flow were recorded in 23 patients with left ventricular ejection fraction </=45%. Within-breath suppression of MSNA (neural silence) was found in 11 patients (MSNA bursts: 71+/-10/100 heartbeats) but not in the remaining 12 patients (MSNA bursts: 88+/-8/100 heartbeats). Patients without neural silence had a smaller tidal volume (391+/-70 versus 267+/-75 mL/m(2), P<0.01) and a higher respiratory rate (15+/-2 versus 19+/-4 breaths/min, P<0.01) during spontaneous respiration than those with neural silence. The relationship between tidal volume and minimal amplitude of MSNA bursts in each breath was obtained during random-interval breathing and fitted by an exponential function. The curve of patients without neural silence was shifted to the right and upward, which suggests that a greater tidal volume was required to suppress MSNA (227+/-70 versus 437+/-195 mL/m(2), P<0.01).

CONCLUSIONS

Sympathoexcitation in patients with chronic heart failure is closely related to both a decrease in resting tidal volume and an attenuated sympathoinhibitory effect of lung inflation reflex.

Heart rate variability in chronic heart failure

The analysis of heart rate variability (HRV) provides information about autonomic cardiovascular control in healthy subjects. In the past 15 years, several articles have been published regarding HRV and chronic heart failure (CHF). The results of these papers substantially demonstrated that HRV is significantly different in CHF patients compared to controls. Moreover, some variables derived from HRV analysis showed significant independent prognostic capacity. In particular, the reduction of variance (expressed as SDNN) and low-frequency spectral component of HRV (ranging from 0.03 to 0.15 Hz) seem related to an increased mortality in CHF. Nevertheless, these variables are not yet considered in clinical practice. A better understanding of the physiopathological basis of the reported alterations of HRV in CHF patients is required in order to permit its use as a clinical tool for prognosis and tailored therapy in individual CHF patients.

Different baseline sympathovagal balance and cardiac autonomic responsiveness in ischemic and non-ischemic congestive heart failure

BACKGROUND

A profound autonomic unbalance is present in heart failure: its correlation with the etiology of the disease has never been investigated.

AIMS

We characterized the sympatho-vagal balance and autonomic responsiveness of 42 patients (21 with ischemic heart failure, 21 with idiopathic dilated cardiomyopathy). Patients had comparable NYHA class, ejection fraction, exercise pVO(2), exercise ventilatory response, incidence of beta-blocking treatment. None showed periodic breathing or nocturnal arterial desaturation.

METHODS

Heart rate variability was assessed in the time and frequency domain during: (1) 10 min of quiet supine resting and free breathing; (2) 10 min of regular breathing at a frequency of 20 acts/min (=parasympathetic stimulus); and (3) 10 min of active standing (=sympathetic stimulus). The ratio of the low- to high-frequency components of each autospectrum obtained in the frequency domain (LF/HF) was used as an index of sympathovagal balance.

RESULTS

Patients with ischemic heart failure had a greater baseline sympathetic activation (higher LF/HF) than those with idiopathic dilated cardiomyopathy, maintaining some parasympathetic responsiveness as well (reduced LF/HF with regular breathing).

CONCLUSIONS

There is a distinct autonomic control according to the etiology of heart failure, a finding that may help understanding its pathophysiology, and could be useful in the clinical management of patients.

Effects of spinal section and of positive-feedback excitatory reflex on sympathetic and heart rate variability

The sympathetic outflow appears to be capable of displaying a rhythmicity synchronous with cardiovascular Mayer's waves even after spinal section. To test the hypothesis that spinal sympathetic low frequency (LF) oscillation can be enhanced during sympathetic excitation, we recorded cardiac sympathetic nerve activity (SNA), R-R interval, arterial pressure, and ventilation in 9 unanesthetized decerebrate-vagotomized cats before and after C1 spinal section. LF and high frequency (HF) components were detected in the variability of SNA, R-R interval, and systolic arterial pressure both before and after spinal section. In this latter condition, a significant coherence between LF(SNA) and LF(R-R) was present in 5 animals, whereas HF(SNA) and HF(R-R) were correlated in 4 animals. During an excitatory sympathetic spinal reflex elicited by aortic constriction, the efferent sympathetic firing was markedly enhanced (from 7+/-2 to 33+/-7 spikes/s); concomitantly, the powers of both LF(SNA) and HF(SNA) were also increased. Coherence between LF(SNA) and LF(R-R) became significant in all cases, whereas HF(SNA) and HF(R-R) became correlated in 6 animals. In 3 animals, the reflex sympathetic excitation was no longer elicitable after interrupting a vast contingent of sympathetic afferents by means of thoracic dorsal root section. We report for the first time that LF and HF oscillations are detectable in SNA, R-R interval, and systolic arterial pressure variabilities of decerebrate-vagotomized spinal cats and that an excitatory spinal reflex is capable of increasing the power of both SNA spectral components.

Cardiorespiratory interactions during periodic breathing in awake chronic heart failure patients

We applied spectral techniques to the analysis of cardiorespiratory signals [instantaneous lung volume (ILV), instantaneous tidal volume (ITV), arterial O(2) saturation (Sa(O(2))) at the ear, heart rate (HR), systolic (SAP), and diastolic (DAP) arterial pressure] during nonapneic periodic breathing (PB) in 29 awake chronic heart failure (CHF) patients and estimated the timing relationships between respiratory and slow cardiovascular (<0.04 Hz) oscillations. Our aim was 1) to elucidate major mechanisms involved in cardiorespiratory interactions during PB and 2) to test the hypothesis of a central vasomotor origin of PB. All cardiovascular signals were characterized by a dominant (>/=84% of total power) oscillation at the frequency of PB (mean +/- SE: 0.022 +/- 0.0008 Hz), highly coherent (>/=0.89), and delayed with respect to ITV (ITV-HR, 2.4 +/- 0.72 s; ITV-SAP, 6.7 +/- 0.65 s; ITV-DAP, 3.2 +/- 0.61 s; P < 0.01). Sa(O(2)) was highly coherent with (coherence function = 0.96 +/- 0. 009) and almost opposite in phase to ITV. These findings demonstrate the existence of a generalized cardiorespiratory rhythm led by the ventilatory oscillation and suggest that 1) the cyclic increase in inspiratory drive and cardiopulmonary reflexes and 2) mechanical effects of PB-induced changes in intrathoracic pressure are the more likely sources of the HR and blood pressure oscillations, respectively. The timing relationship between ITV and blood pressure signals excludes the possibility that PB represents the effect of a central vasomotor rhythm.

Cardiac afferents and neurohormonal activation in congestive heart failure

Cardiac chambers have afferent connections to the brainstem and to the spinal cord. Vagal afferents mediate depressor responses and become activated by volume expansion, increased myocardial contractility and atrial natriuretic factor. Sympathetic afferents, on the contrary, are activated by metabolic mediators, myocardial ischemia and cardiac enlargement. These opposite behaviors may lead to activation or suppression of the sympathetic nervous system and of the renin-angiotensin-aldosterone system. As cardiac diseases progress, the heart dilates, plasma norepinephrine increases, atrial natriuretic factor is released and the renin-angiotensin-aldosterone system is suppressed to maintain water and sodium excretion. This dissociation of the neurohormonal profile of cardiac patients, may be explained by coactivation of sympathetic afferents, by cardiac dilatation, and of vagal afferents by atrial natriuretic factor. In more advanced stages, atrial natriuretic factor suppression of the renin-angiotensin-aldosterone system is overridden by overt sympathetic activation and sodium and water retention ensues. Digitalis, angiotensin-converting enzyme inhibitors and beta-blockers selectively decrease cardiac adrenergic drive. A common mechanism of action, to all three groups of drugs, would be attenuation of sympathetic afferents and partial normalization of vagal afferents. Consequently, heart size and cardiac afferents emerge as the key factors to understand the pathophysiology and treatment of the syndrome of congestive heart failure.

Chronic central infusion of ANG II potentiates cardiac sympathetic afferent reflex in dogs

The aims of this study were to determine whether ANG II is involved in the central integration of the cardiac sympathetic afferent reflex (CSAR), and if this central effect of ANG II is mediated by the AT(1) receptor. Experiments were undertaken in dogs that were anesthetized with alpha-chloralose, sinoaortic denervated, and vagotomized. The renal sympathetic nerve activity (RSNA) responses to varying frequency and voltage stimulation of cardiac sympathetic afferent nerves were used to evaluate the central sensitivity of the CSAR. In two groups of dogs, two doses (50 and 100 ng/min icv) of ANG II were acutely infused. In a third group of dogs, ANG II was chronically infused for 3 days (100 ng/min, 1 microliter/h icv). We found that acute infusion into the cerebroventricle of two doses of ANG II did not affect the central sensitivity of the CSAR or the baseline hemodynamics, but the baseline RSNA increased significantly during the infusion of the higher dose of ANG II. However, chronic intracerebroventricular infusion of ANG II enhanced the central sensitivity of the CSAR significantly. In addition, chronic intracerebrovetricular infusion of ANG II elicited a significant increase in water intake and in arterial pressure from the first and second day of infusion, respectively. In the group that received chronic intracerebroventricular infusion of ANG II, the administration of an AT(1)-receptor antagonist losartan (0.125 mg/kg icv) abolished ANG II-induced augmentation of the CSAR. These results suggest that chronic elevation of central ANG II can sensitize the CSAR via central AT(1) receptors.

Sympathetic rhythmicity in cardiac transplant recipients

BACKGROUND

Variability of R-R interval and muscle sympathetic nerve activity (MSNA) occurs predominantly at a low frequency (LF, +/-0.1 Hz) and a high frequency (HF, +/-0.25 Hz) in normal humans. Increased sympathetic drive in normal humans is associated with an increased LF component of the R-R interval and MSNA. Patients with severe heart failure have high sympathetic activity but decreased or absent LF power of both R-R and MSNA. We tested the hypothesis that this dysfunction in autonomic modulation in heart failure can be reversed by heart transplantation.

METHODS AND RESULTS

We performed spectral analysis of resting MSNA, R-R interval, and respiration in 9 patients with heart transplants, 9 chronic heart failure patients, and 9 normal control subjects, all closely matched for age, sex, and body mass index. MSNA (bursts per minute) was higher in patients with heart transplants (74+/-3) than either patients with heart failure (56+/-6) or normal subjects (40+/-4) (P<0.001). LF variability in the R-R interval was reduced in both heart transplant recipients and heart failure patients compared with the control subjects (P<0.01). The LF variability in MSNA was also nearly absent in the heart failure patients (P<0.01). However, the LF and HF oscillations in MSNA in patients with heart transplants were comparable to those evident in the control subjects.

CONCLUSIONS

Cardiac transplantation does not reduce MSNA. However, LF oscillations in sympathetic activity are restored after transplantation such that the MSNA oscillatory profile is similar to that observed in normal subjects.

Central gain of the cardiac sympathetic afferent reflex in dogs with heart failure

Previous studies from our laboratory have shown that the cardiac sympathetic afferent reflex is enhanced in dogs with experimental heart failure. The aim of the present study was to determine if the central gain of the cardiac sympathetic afferent reflex was also enhanced in dogs with heart failure. Fifteen dogs with pacing-induced heart failure were used in this study. Seventeen sham-operated dogs served as control. At the time of the acute experiment the dogs were anesthetized with alpha-chloralose. Arterial blood pressure, heart rate, and renal sympathetic nerve activity were recorded. After sinoaortic denervation and cervical vagotomy, a thoracotomy was performed in the second intercostal space. The left stellate ganglion was identified, and the left cardiac sympathetic nerves were cut. The central end of the left cardiac sympathetic nerves was placed on bipolar stimulating electrodes. The renal sympathetic nerve activity responses to electrical stimulation (30 Hz, 1 ms with varying voltages from 1 to 10 V; or 10 V, 1 ms with varying frequencies from 1 to 30 Hz) of the afferent cardiac sympathetic nerves were compared between sham and heart failure groups. Reflex renal sympathetic nerve activity responses to stimulation of the cardiac sympathetic nerves were significantly greater in the heart failure group compared with that in the sham group (21.4 +/- 3.2 vs. 9.8 +/- 2.9% at 10 V, 30 Hz and 27.7 +/- 4.5 vs. 9.9 +/- 3.4% at 30 Hz, 10 V, heart failure vs. sham group, respectively; for both relationships, P < 0.05). This enhanced central gain of the cardiac sympathetic afferent reflex in the heart failure group was significantly attenuated after intravenous and cerebroventricular injection of the angiotensin II receptor antagonist losartan (5 mg/kg i.v. and 0.125 mg/kg in 0.1 ml i.c.v.). These data suggest that the central gain of the cardiac sympathetic afferent reflex is enhanced in dogs with heart failure and central angiotensin II plays an important role in this enhanced response.

Plasma norepinephrine, myocardial damage and left ventricular systolic function in Chagas' heart disease

The functional status of the sympathetic nervous system in Chagas' heart disease is still the subject of intense controversy. To determine the nature of the abnormalities of the sympathetic nervous system, we measured the plasma norepinephrine concentration of chagasic patients with varying degrees of myocardial damage. Thirty-six patients with positive serology for Chagas' disease were studied. Twenty patients were in Functional Class I (New York Heart Association), 10 were in Functional Class II and six were in Functional Classes III-IV. Cardiac catheterization was performed in 24 patients. The asymptomatic patients had a plasma norepinephrine concentration (121 +/- 37 pg/ml, mean +/- S.D.) not different from normal controls (103 +/- 59 pg/ml). The symptomatic patients, however, had a significantly elevated plasma norepinephrine concentration (665 +/- 354 pg/ml, P < 0.001). The baseline heart rate of the asymptomatic and symptomatic patients directly correlated with the plasma norepinephrine concentration (r = 0.69, P < 0.0001). The symptomatic patients had larger ventricular volumes, higher left ventricular end-diastolic pressures and lower ejection fractions than the asymptomatic patients and normal controls. The plasma norepinephrine concentration correlated linearly with the left ventricular end-diastolic volume (r = 0.77, P < 0.0001), and non-linearly with the ejection fraction (r = -0.70, P < 0.0001) and the left ventricular end-diastolic pressure (r = 0.53, P < 0.007). These results indicate that, in Chagas' heart disease as in most other cardiac diseases, sympathetic nervous system activation is a late and compensatory phenomenon. In other words, sympathetic activation is very likely related to the progressive impairment of left ventricular function.

Control of pulmonary vasomotility in congestive heart failure

Although enhanced sympathetic tone is a well-known component of the autonomic imbalance of heart failure, its influence on pulmonary vasomotility is undefined. We investigated the pulmonary circulation in 12 patients with congestive heart failure in NYHA functional class III and in a control group of 10 normal subjects. Sympathetic influence on pulmonary vessels was studied through adrenergic activation by the arithmetic test and the cold pressor test. A rubber balloon was distended in the inferior vena cava to reduce transpulmonary flow and its influence on vascular tone. In normal individuals the arithmetic test caused pulmonary vasodilation, probably because of the mechanical effect of a largely enhanced flow: in fact, caval obstruction unmasked a neurogenic vasoconstrictor response to the arithmetic test by simply reducing the amount of cardiac output increase. In patients with heart failure, cardiac output and pulmonary arteriolar resistance remained steady during the arithmetic test, no matter what the condition of the venous return was. The cold pressor test was always a vasoconstrictor stimulus, but only in normal subjects was vasoconstriction potentiated by reducing, with caval obstruction, transpulmonary flow and its vasodilatory influence. From these data an attenuation of the sympathetic influence on pulmonary vessels in congestive heart failure seems to be likely. This might be explained as the result of modifications of pulmonary vessels rather than of reduced sympathetic excitability since circulating catecholamine levels varied to similar extents in the two groups during the tests. In congestive heart failure interstitial edema and vascular wall imbibition might increase pulmonary vessel tone and decrease vascular receptor availability. Lower reactivity to sympathetic stimuli, particularly to the vasoconstrictor ones, would ensue.

Cardiac autonomic control mechanisms in Chagas' heart disease. Therapeutic implications

According to the neurogenic theory of Chagas' heart disease, the cardiac parasympathetic abnormalities of chagasic cardiac patients are due to a selective destruction of the cardiac parasympathetic neurons. Trypanosoma cruzi would selectively destroy the cardiac vagal neurons, during the acute stage of the disease. However, these cardiac parasympathetic abnormalities are found mainly in chagasic patients who are in very advanced stages of the disease. Furthermore, the extent of cardiac parasympathetic involvement correlates with the degree of left ventricular dilation. Cardiac parasympathetic abnormalities, and a reciprocal sympathetic hyperactivity are also present in non-chagasic cardiac patients. Modern medical treatment, with sympatholytic drugs, prevents ventricular dilatation and prolongs life in these non-chagasic cardiac patients. Consequently, if chagasic cardiac patients have ventricular dilatation-related parasympathetic abnormalities; it is of the utmost importance to ask: first, do they also have a progressive activation of their neurohumoral systems?; and second, would they benefit from sympatholytic drugs?.

Control of sympathetic nerve activity by vagal mechanoreflexes is blunted in heart failure

BACKGROUND

Previous studies have documented abnormalities of arterial baroreflexes in animals and patients with congestive heart failure. This study determined whether cardiopulmonary reflex control of sympathetic nerve activity was abnormal in a canine model of low-output heart failure induced by rapid ventricular pacing.

METHODS AND RESULTS

We stimulated mechanoreceptors throughout the cardiopulmonary region by volume expansion and left atrial mechanoreceptors selectively by inflating small balloons at the junctions of the pulmonary veins and left atrium. Responses of renal sympathetic nerve activity and left atrial and systemic arterial pressures were recorded. In the control group, 15% volume expansion raised left atrial pressure 3.5 +/- 0.8 mm Hg and resulted in a 70 +/- 8% reduction in renal nerve activity. In the heart failure group, 15% volume expansion resulted in a 6.8 +/- 3.0 mm Hg rise in left atrial pressure with only a 16 +/- 20% reduction in renal nerve activity (p < 0.01). When volume expansion was performed after pretreatment with hemorrhage to lower left atrial pressure to the normal range in the heart failure group, the markedly attenuated response in the heart failure group persisted. After vagotomy, volume expansion elicited no change in renal nerve activity. Inflation of the atrial balloons caused a 28 +/- 9% reduction in renal sympathetic nerve activity and a 13 +/- 4 mm Hg decrease in arterial pressure in the control group. Renal nerve activity (-5 +/- 3%) and mean arterial pressure (-1 +/- 1 mm Hg) did not change with balloon inflation in the heart failure group.

CONCLUSIONS

We conclude that dogs with low-output heart failure exhibit marked attenuation of cardiopulmonary mechanoreflex control of sympathetic nerve activity. This attenuated response is mediated via cardiac vagal afferent fibers and is due to either abnormalities in cardiopulmonary baroreceptors or abnormalities in the central nervous system.

Baroreceptor-mediated release of vasopressin in patients with chronic congestive heart failure and defective sympathetic responsiveness

In patients with congestive heart failure (CHF), overactivity of the sympathetic nervous system may be accompanied by an impairment of the baroreflex control mechanism. To evaluate the reflex responses of the sympathetic nervous system, the renin-angiotensin system and vasopressin release to baroreceptor unloading, 38 patients with left ventricular dysfunction were studied. Hemodynamic data, and plasma norepinephrine, renin activity and vasopressin concentrations were measured before and 60 minutes after administration of high-dose hydralazine (0.4 mg/kg intravenously). On the basis of blood pressure response to vasodilator administration, patients were divided arbitrarily into those with a decrease in mean arterial blood pressure greater than or equal to 15 mm Hg (group A; n = 12) and those with a decrease less than 15 mm Hg (group B; n = 26) compared with control values. In response to hydralazine, heart rate decreased in group A from 100 to 92 beats/min (p less than 0.001) and increased in group B from 90 to 96 beats/min (p less than 0.05). In group A, hemodynamic changes induced by hydralazine were accompanied by a decrease in plasma norepinephrine from 822 to 518 pg/ml (p less than 0.01) and an increase in plasma vasopressin from 8.4 to 45.2 pg/ml (p less than 0.001). In group B, plasma norepinephrine and vasopressin did not change significantly (407 vs 447, and 8.4 vs 8.3 pg/ml, respectively). Plasma renin activity remained unchanged in group A and increased in group B (p less than 0.001). The data show that baroreceptor-mediated release of vasopressin is not impaired in patients with CHF and a defective sympathetic reflex control mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular neural regulation explored in the frequency domain

A consistent link appears to exist between predominance of vagal or sympathetic activity and predominance of HF or LF oscillations, respectively: RR variability contains both of these rhythms, and their relative powers appear to subserve a reciprocal relation like that commonly found in sympathovagal balance. In this respect, it is our opinion that rhythms and neural components always interact, just like flexor and extensor tones or excitatory and inhibitory cardiovascular reflexes, and that it is misleading to separately consider vagal and sympathetic modulations of heart rate. In humans and experimental animals, functional states likely to be accompanied by an increased sympathetic activity are characterized by a shift of the LF-HF balance in favor of the LF component; the opposite occurs during presumed increases in vagal activity. In addition, LF oscillation evaluated from SAP variability appears to be a convenient marker of the sympathetic modulation of vasomotor activity. Although based on indirect markers, the exploration in the frequency domain of cardiovascular neural regulation might disclose a unitary vision hard to reach through the assemblage of more specific but fragmented pieces of information.

Comparative effects of angiotensin converting enzyme inhibition (perindopril) or diuretic therapy on cardiac hypertrophy and sympathetic activity following myocardial infarction in rats

The long-term effects of perindopril or chlorothiazide therapy were studied in rats after the induction of myocardial infarction by coronary artery ligation. Rats with infarction developed marked cardiomegaly, indicating the presence of chronic left ventricular dysfunction. The ratio of the norepinephrine metabolite, 3,4-dihydroxyphenylethylene glycol (DHPG) to norepinephrine (NE) was elevated in the right ventricle of rats with infarction, suggesting a chronic increase in cardiac sympathetic activity. Perindopril therapy commenced either immediately following infarction or 4 weeks following infarction reduced DHPG/NE ratios toward normal levels, and prevented or reversed cardiac hypertrophy. In contrast, chlorothiazide therapy significantly reduced DHPG/NE ratios but did not decrease cardiac hypertrophy. Perindopril reverses or prevents cardiac hypertrophy and chronic cardiac sympathetic hyperactivity following myocardial infarction, while chlorothiazide reduces cardiac sympathetic activity without influencing cardiomegaly.

Cardiac 3,4-dihydroxyphenylethylene glycol (DHPG) and catecholamine levels during perindopril therapy of chronic left ventricular failure in rats

1. Left ventricular myocardial infarction was induced in female Wistar rats by ligation of the left anterior descending coronary artery. 2. One month following operation, rats with infarcts developed marked cardiomegaly compared to sham operated rats, indicating the presence of chronic left ventricular failure. 3. The ratio of the noradrenaline metabolite 3,4-dihydroxyphenylethylene glycol (DHPG) to noradrenaline (NA) was elevated in the right ventricle of rats with heart failure one month following infarction, suggesting a chronic increase in cardiac sympathetic activity. 4. Perindopril therapy for one month commenced 4 weeks after infarction returned cardiac weights to normal and significantly reduced right ventricular DHPG/NA ratios. 5. The results suggest that ACE inhibition with perindopril reduces elevated levels of cardiac sympathetic activity in rats with chronic left ventricular failure and leads to regression of cardiomegaly.

The management of heart failure and the scope for new therapies: what role for xamoterol?

1. Current therapy of heart failure leaves much to be desired. Not all patients respond, and many agents lose their effects with time. 2. Newer agents may be effective but toxic, and some which have a beneficial action when given intravenously have proved disappointing when used orally. 3. The value of digoxin in patients in sinus rhythm is open to debate, and diuretics, although useful acutely in reducing fluid overload, do not appear to improve prognosis. 4. Vasodilators increase effort capacity and reduce symptoms, possibly conferring some long-term benefit, and angiotensin converting enzyme (ACE) inhibitors improve symptoms and decrease mortality in a wide range of patients. 5. Positive inotropes may be effective in the short term, but they increase myocardial oxygen demand and show tachyphylaxis with no prognostic benefit. 6. Xamoterol (Corwin, Carwin, Corwil, Xamtol, ICI 118,587) is a partial sympathetic agonist with approximately 50% of the activity of a pure agonist, which provides inotropic support at rest, and protection against excess sympathetic activity on exercise. 7. It is compatible with other therapies and has shown no serious toxicity. 8. It should be considered at present as an adjunct to diuretic and/or ACE inhibitor therapy, although it may be useful alone; its role will become clearer as its effects on mortality are established.