Afferent reinnervation of the autotransplanted heart in dogs

Renal sensory and sympathetic nerves reinnervate the kidney in a similar time-dependent fashion after renal denervation in rats

Efferent renal sympathetic nerves reinnervate the kidney after renal denervation in animals and humans. Therefore, the long-term reduction in arterial pressure following renal denervation in drug-resistant hypertensive patients has been attributed to lack of afferent renal sensory reinnervation. However, afferent sensory reinnervation of any organ, including the kidney, is an understudied question. Therefore, we analyzed the time course of sympathetic and sensory reinnervation at multiple time points (1, 4, and 5 days and 1, 2, 3, 4, 6, 9, and 12 wk) after renal denervation in normal Sprague-Dawley rats. Sympathetic and sensory innervation in the innervated and contralateral denervated kidney was determined as optical density (ImageJ) of the sympathetic and sensory nerves identified by immunohistochemistry using antibodies against markers for sympathetic nerves [neuropeptide Y (NPY) and tyrosine hydroxylase (TH)] and sensory nerves [substance P and calcitonin gene-related peptide (CGRP)]. In denervated kidneys, the optical density of NPY-immunoreactive (ir) fibers in the renal cortex and substance P-ir fibers in the pelvic wall was 6, 39, and 100% and 8, 47, and 100%, respectively, of that in the contralateral innervated kidney at 4 days, 4 wk, and 12 wk after denervation. Linear regression analysis of the optical density of the ratio of the denervated/innervated kidney versus time yielded similar intercept and slope values for NPY-ir, TH-ir, substance P-ir, and CGRP-ir fibers (all R(2) > 0.76). In conclusion, in normotensive rats, reinnervation of the renal sensory nerves occurs over the same time course as reinnervation of the renal sympathetic nerves, both being complete at 9 to 12 wk following renal denervation.

The relationship between physical activity and heart rate variability in orthotopic heart transplant recipients

AIMS AND OBJECTIVES

To investigate the relationship between physical activity and heart rate variability in orthotopic heart transplant recipients, to compare the difference in heart rate variability between patients one year after orthotopic heart transplant and healthy adults matched to the heart transplant recipients in terms of age, gender and physical activity levels.

BACKGROUND

Although physical activity affects the heart rate variability in patients with heart disease, there is a paucity of literature discussing the correlation between physical activity and heart rate variability among heart transplant recipients.

DESIGN

This was a descriptive and cross-sectional study.

METHODS

A total of 120 eligible subjects were divided into the orthotopic heart transplant recipient group (n = 60) and the healthy adult group (n = 60). The Seven-day Physical Activity Recall questionnaire was used to record the subjects' amount of physical activity per week. Heart rate variety parameters were determined by separate frequency domain components.

RESULTS

Results indicated heart transplant recipients' heart rate variety was significantly lower than that of healthy adults in terms of mean, sdr, total power (ms(2)), low frequency (ms(2)), low frequency (nu), high frequency (ms(2)) and low frequency/high frequency. Heart transplant recipients' heart rate variety including total power (ms(2)), low frequency (ms(2)) and high frequency (ms(2)) was 18·2, 2 and 7·2% of healthy controls, respectively; the amount of absolutely and relatively moderate physical activity was positively related to high frequency (ms(2)) and high frequency (nu), but was negatively related to low frequency/high frequency. High frequency (nu) increases while the total amount of weekly physical activity increases.

CONCLUSIONS

Results confirmed that the more the moderate physical activity performed, the better the patient's heart rate variability.

RELEVANCE TO CLINICAL PRACTICE

We suggest that clinical care providers have to encourage heart transplant recipients to engage in moderate physical activity.

Cardiovascular responses to incremental and sustained submaximal exercise in heart transplant recipients

The cardiovascular response to exercise in heart transplant recipients (HTR) has been compared with that of healthy individuals matched to the recipient age (RM controls). However, no study has compared HTR with donor age-matched (DM) controls. Moreover, the cardiovascular response to sustained submaximal exercise in HTR requires further evaluation. We therefore examined cardiovascular responses during incremental exercise and sustained (1 h) submaximal aerobic exercise in 9 clinically stable HTR [63 +/- 10 yr of age, 24.2 +/- 10.9 ml x kg(-1) x min(-1) peak O(2) uptake (Vo(2peak))] and 11 healthy age-matched controls (60 +/- 11 yr of age and 36.3 +/- 10.7 ml.kg(-1) x min(-1) Vo(2peak) for 6 RM controls and 35 +/- 8 yr of age and 51.1 +/- 10.4 ml x kg(-1) x min(-1) Vo(2peak) for 5 DM controls). Heart rate (HR) and left ventricular systolic and diastolic volumes (2-dimensional echocardiography) indexed to body surface area [end-systolic and end-diastolic volume indexes (EDVI and ESVI)], cardiac output (CI), ejection fraction (EF), systemic vascular resistance (SVRI), end-systolic elastance index, and arterial elastance index were determined. Although systolic function was maintained during incremental exercise, peak CI was significantly reduced (6.7 +/- 2.4 vs. 11.6 +/- 1.4 l x min(-1) x m(-2)), secondary to blunted HR, EDVI, and increased peak SVRI, in HTR compared with DM controls. The lower peak CI in HTR than in RM controls was due to blunted peak EDVI (54.1 +/- 13.2 vs. 68.6 +/- 5.7 ml/m(2)). During sustained submaximal exercise, HTR exhausted their preload reserve, a response for which changes in ESVI, HR, or EF did not fully compensate. Thus it appears that HTR are limited by impaired preload reserve, HR reserve, and vascular reserve during exercise conditions.

Exercise responses following heart transplantation: 5 year follow-up

Heart transplantation is an established treatment for end stage heart failure. In addition to increased life expectancy, heart transplant recipients report a remarkable improvement in symptoms and functional capacity. Exercise performance following heart transplantation, however, remains impaired even in the absence of exertional symptoms. We have assessed the response to exercise in 47 patients with cardiac failure prior to and then at yearly intervals to five years post transplantation. All patients performed incremental symptom limited exercise tests during which minute ventilation (V'E), oxygen consumption (V'O2) and carbon dioxide production (V'CO2) and heart rate (HR) were measured. Ventilatory response (V'E/V'CO2), anaerobic threshold (V'O2 AT %predicted) and heart rate response (HR/VO2) were calculated. The dead space to tidal volume ratio (VD/VT) and alveolar-arterial oxygen gradient (A-aO2) were computed from transcutaneous monitoring. Despite substantial improvement in subjective functional capacity, heart transplant recipients continue to have limited exercise performance [Maximal V'O2% predicted pre-transplant 41.3 (2.2); 1 year 48.6 (1.7), p <0.001: V'O2 AT% 31.5 (1.1); 1 year 35.6 (1.0); respectively p<0.05]. The maximal oxygen uptake continued to improve at two years post-transplant but, thereafter, there was no further significant change at up to 5 years post transplant [50.9 (1.5)]. At one year post-transplantation peak HR [65.2 (0.9) vs 79.1(1.4)] and the HR/VO2 response [24.0(1.8) vs 79.6(4.2)] were significantly reduced compared to pre-transplant values. The heart rate response remained lower compared to predicted at 5 years post-transplant although there was a significant increase compared to one year post-transplant (32.9 vs 24.0mls/bt). There was a weak but significant relationship between maximal VO2 and peak HR (0.39, p<0.05) and HR/VO2 (r= 0.37, p<0.05) at one year post-transplant. Prior to transplantation the ventilatory response to exercise was elevated [V'E/V'CO2 45.6 (2.5)] and decreased significantly following transplantation [1 yr 34.1 (1.3), respectively p<0.001]. In addition, despite significant improvement in VD/VT after transplantation, it remained higher than normal [Pre VD/VT at maximum exercise 0.35 (0.02); 1 yr 0.31 (0.02); p<0.05]. There was a further fall in the VE/VCO2 and VD/VT at two years post-transplantation with no further change at up to 5 years post transplantation [VE/VCO2 32.0 (1.0); VD/VT 0.29 (0.01)]. Although cardiac output is markedly improved after transplantation, due to chronotropic incompetence associated with denervation, its response remains subnormal and this may explain the residual abnormalities of ventilatory and gas exchange responses to exercise following transplantation.

Different evolutions in heart rate variability after heart transplantation: 10-year follow-up

BACKGROUND

After heart transplantation, the donor heart is extrinsically denervated. No input of sympathetic or vagal nerves can influence the heart rate, resulting in a flat power spectrum of the beat-to-beat variability. The occurrence and the significance of reinnervation remain controversial.

METHODS AND RESULTS

We monitored the evolution of heart rate variability (HRV) after heart transplantation, starting from a few weeks postoperatively up to 10 years after surgery. Twenty-four-hour Holter recordings of 216 heart-transplant patients were analyzed using time and frequency domain analysis of HRV. Analysis of all data revealed an increase in 24-hour and night-time total power starting from 2 years after transplantation. Low-frequency oscillations calculated over the total 24 hours, day- and nighttime increased significantly starting from year 4 and onward (year 4-8: P < 0.005). No evolution was found in high-frequency power. Subgroup analysis revealed a group with a clear spectral component (n = 16), a group with a small component (n = 124), and a group with a flat spectrum (n = 76). Only the first group revealed an evolution in both high- and low-frequency power.

CONCLUSION

These results indicate three different types of evolution in HRV, with reinnervating patterns present in only a minority of the patients. The vast majority of the patients show no signs of reinnervation.

Innervation of ectopic endometrium in a rat model of endometriosis

Endometriosis (ENDO) is a disorder in which vascularized growths of endometrial tissue occur outside the uterus. Its symptoms include reduced fertility and severe pelvic pain. Mechanisms that maintain the ectopic growths and evoke symptoms are poorly understood. One factor not yet considered is that the ectopic growths develop their own innervation. Here, we tested the hypothesis that the growths develop both an autonomic and a sensory innervation. We used a rat model of surgically induced ENDO whose growths mimic those in women. Furthermore, similar to women with ENDO, such rats exhibit reduced fertility and increased pelvic nociception. The ENDO was induced by autotransplanting, on mesenteric cascade arteries, small pieces of uterus that formed vascularized cysts. The cysts and healthy uterus were harvested from proestrous rats and immunostained using the pan-neuronal marker PGP9.5 and specific markers for calcitonin gene-related peptide (CGRP) (sensory C and A delta fibers), substance P (SP) (sensory C and A delta fibers) and vesicular monoamine transporter (sympathetic fibers). Cysts (like the uterus) were robustly innervated, with many PGP9.5-stained neurites accompanying blood vessels and extending into nearby luminal epithelial layers. CGRP-, SP-, and vesicular monoamine transporter-immunostained neurites also were observed, with CGRP and SP neurites extending the furthest into the cyst lining. These results demonstrate that ectopic endometrial growths develop an autonomic and sensory innervation. This innervation could contribute not only to symptoms associated with ENDO but also to maintenance of the ectopic growths.

Long-term regeneration of abdominal vagus: efferents fail while afferents succeed

Vagal afferents regenerate, by 18 weeks after subdiaphragmatic transection, to reinnervate the gut and to differentiate into the two types of terminals normally found in the smooth muscle wall of the gastrointestinal (GI) tract (Phillips et al. [2000] J Comp Neurol. 421:325-346). Regeneration, however, is neither complete nor entirely accurate by 18 weeks. Moreover, the capacity of the vagal efferents to reinnervate the GI tract under comparable conditions has not been evaluated. Therefore, to determine whether a more extended postaxotomy survival interval would (1). result in more extensive reinnervation of smooth muscle, (2). facilitate correction of the inaccuracies of the regenerated axons and terminals, and (3). yield motor as well as sensory reinnervation of GI targets, Sprague-Dawley rats received either complete subdiaphragmatic vagotomies (n = 18) or sham surgeries (n = 12). Physiological endpoints that might normalize as vagal elements regenerated, including body weight, daily food intake, size of first daily meal, and metabolic efficiency, were monitored. At 45 weeks after the vagotomies, the animals were randomly assigned to afferent (wheat germ agglutinin-horseradish peroxidase) or efferent (cholera toxin subunit B-horseradish peroxidase) mapping conditions, and labeled axons and terminals in the stomach and first 8 cm of the small intestine were inventoried in whole-mounts. Afferent regeneration was more extensive at 45 weeks than previously observed at 18 weeks after surgery; however, the amount of GI innervation was still not comparable to the intact pattern of the sham rats. Furthermore, abnormal patterns of sensory organization occurred throughout the reinnervated field, with small bundles of axons forming complex tangles and some individual axons terminating in ectopic locations. The presence of growth cone profiles suggested that vagal reorganization was ongoing even 45 weeks after surgery. In contrast to this relatively extensive, albeit incomplete, sensory reinnervation of the gut, motor fibers had failed to reinnervate the GI tract. Thus, dramatic differences exist in the regenerative capacities of the sensory and motor arms of the vagus under the same surgical and maintenance conditions. Furthermore, the functional measures of disordered energy regulation did not normalize over the 45 weeks during which afferent but not efferent innervation was restored.

Long-term assessment of heart rate variability in cardiac transplant recipients

Sympathetic and parasympathetic reinnervation of the transplanted heart were evaluated by assessing time and frequency domain measurements of heart rate variability at 5 and 8 years. Continuous 24-hour ECG measurements were performed in 13 patients (57 +/- 6 months and 90 +/- 7 months) after orthotopic cardiac transplantation and in 22 healthy age and gender-matched controls, and were analyzed for heart rate variability in the time and frequency domains. Heart rate variability measures reflective of sympathetic reinnervation were sub-normal at 5 years and unchanged at 8 years: those reflective of parasympathetic reinnervation were absent.

Exercise and organ transplantation

Life-saving treatment of disease by organ transplantation has become increasingly important. Annually over 35,000 transplantations of vital organs are carried out world-wide and the demand for knowledge regarding exercise in daily life for transplant recipients is growing. The present review describes whole-body and organ reactions to both acute exercise and regular physical training in persons who have undergone heart, lung, liver, kidney, pancreas or bone marrow transplantation. In response to acute exercise, the majority of cardiovascular, hormonal and metabolic changes are maintained after transplantation. However, in heart transplant recipients organ denervation reduces the speed of heart rate increase in response to exercise. Furthermore, lack of sympathetic nerves to transplanted organs impairs the normal insulin and renin responses to exercise in pancreas and kidney transplant recipients, respectively. In contrast, surgical removal of sympathetic liver nerves does not inhibit hepatic glucose production during exercise, and denervation of the lungs does not impair the ability to increase ventilation during physical exertion. Most studies show that physical training results in an improved endurance and strength capacity in almost all groups of transplant recipients, which is of importance for their daily life. With a little precaution, organ transplant recipients can perform exercise and physical training and obtain effects comparable with those achieved in the healthy population of similar age.

Evidence for differential sympathetic and parasympathetic reinnervation after heart transplantation in humans

During heart transplantation (HTX) all neural connections are severed. In humans, signs of autonomic reinnervation have been found. In this study non-invasive tests were used to compare signs of sympathetic and parasympathetic reinnervation. Non-invasive autonomic function tests and heart rate variability parameters (HRV; 24 h electrocardiographic registration) were used to investigate signs of reinnervation. 16 HTX patients (14 males) were compared with age-and sex-matched controls. Parasympathetic heart rate changes in HTX compared to controls were attenuated during the diving test, deep breathing, the Valsalva maneuver and standing up but not during carotid sinus massage. Sympathetic heart rate increases were lower during the cold pressor test and mental stress. The blood pressure responses were comparable to the control group, but not during active standing and tilting. This finding suggests an obligatory 'blood pressure' role for the innervated heart in these two tests. All HRV parameters were lower in HTX. One or more normal parasympathetic responses were found in 13 out of 16 patients versus 4 out of 16 with normal sympathetic responses (p < 0.05). Heart rate variations were less in case of a higher donor age, and higher in case of a longer time after HTX. Parasympathetic signs of reinnervation are more common than sympathetic signs of reinnervation. A higher donor age reduces signs of reinnervation. If the sympatho-vagal balance is a prognostic factor in HTX patients as it is in other cardiac diseases these findings are clinically relevant.

Long-term sequential changes in exercise capacity and chronotropic responsiveness after cardiac transplantation

BACKGROUND

Peak exercise capacity improves early after orthotopic cardiac transplantation. However, the physiological response to exercise remains abnormal, with a reduced rate of heart rate (HR) rise and reductions in peak exercise HR and the increment in HR from rest to peak exercise. This chronotropic incompetence is due in large part to cardiac denervation. If reinnervation occurs after transplantation, it might result in an improvement in both chronotropic responsiveness and maximal exercise capacity. We therefore hypothesized that the chronotropic response to exercise and maximal exercise capacity would improve with time after transplantation.

METHODS AND RESULTS

Peak symptom-limited cardiopulmonary exercise tests performed in 57 clinically stable cardiac transplant recipients (mean age, 45 +/- 2 years) serially for up to 5 years after transplantation and in 33 control subjects without heart disease were analyzed retrospectively. Pretransplantation exercise tests were also performed in 41 patients an average of 4.7 +/- 0.6 months before transplantation. At 1 year after transplantation, peak oxygen consumption was 16.6 +/- 0.9 mL.kg-1.min-1, reflecting a 43% increase versus pretransplantation. Nevertheless, compared with control subjects, maximal exercise capacity and the HR response to exercise were subnormal in transplant recipients. There were no further increases in peak exercise capacity, peak exercise HR, or the peak increment in HR with exercise up to 5 years after transplantation.

CONCLUSIONS

One year after cardiac transplantation, peak exercise capacity and chronotropic responsiveness are subnormal. There is no further improvement in peak exercise capacity or chronotropic responsiveness as late as 5 years after transplantation. These data indicate that with regard to chronotropic responsiveness, functionally significant cardiac reinnervation does not occur between the first and fifth years after transplantation.

Induction of paradoxic bradycardia in rats by inferior vena cava occlusion during the administration of isoproterenol: the essential role of augmented sympathetic tone

INTRODUCTION

Testing human susceptibility for vasodepressor reactions involves combining venous return restriction by passive upright tilting and administering isoproterenol. While sympathetic tone is usually increased by the stimuli that incite a vasodepressor reaction, it is not known if the increased sympathetic tone is an essential or passive component of the mechanism that triggers the reaction. Given that paradoxic bradycardia is a major manifestation of vasodepressor reactions and allowing for the possible extrapolation between paradoxic bradycardia in rats and vasodepressor reactions, we examined the role of sympathetic tone in the paradoxic bradycardia reaction. Paradoxic bradycardia was induced in rats by inferior vena cava occlusion during an isoproterenol infusion. To examine the role of increased sympathetic tone on this reaction, we studied whether carotid artery perfusion (80 to 100 mmHg) during inferior vena cava occlusion, a maneuver that blunts the rise in sympathetic tone, inhibits paradoxic bradycardia.

METHODS AND RESULTS

The maximum changes in R-R were measured during 60 seconds of inferior vena cava occlusion as follows: (a) in control the heart rate accelerated (delta R-R - 10.2 +/- 2.3 msec, P < 0.001); (b) during an infusion of isoproterenol, paradoxic bradycardia occurred (delta R-R + 140.6 +/- 18.2 msec, P < 0.001), and this was inhibited by common carotid artery perfusion (delta R-R - 6.6 +/- 1.5 msec, P < 0.001); and (c) following carotid sinus denervation and during an infusion of isoproterenol, paradoxic bradycardia was induced without and with carotid artery perfusion (delta R-R + 122.6 +/- 12.0 msec, P < 0.001; delta R-R + 151.8 +/- 12.7 msec, P < 0.001, respectively).

CONCLUSIONS

Since carotid artery perfusion during inferior vena cava occlusion inhibits paradoxic bradycardia only when the carotid sinus is innervated, we conclude that carotid artery perfusion blocks the reaction by increasing carotid sinus afferents, thereby limiting the increased sympathetic tone during inferior vena cava occlusion, and not as a result of cerebral perfusion. Thus, the paradoxic bradycardia resulting from inferior vena cava occlusion requires activation of sympathetic tone as a result of carotid sinus hypotension.

Circadian variations of blood pressure and heart rate early and late after heart transplantation

Cardiac reinnervation late after heart transplantation has been reported in individual patients. As a measure for reinnervation, circadian changes in arterial blood pressure and heart rate have been used but not yet systemically evaluated in cardiac transplant recipients. Ambulatory blood pressure and heart rate monitoring was performed in 62 patients for 24 hr early (<6 months, mean 26 days, range 5-90 days, n=30) and late (> or = 6 months, mean 12 months, range 7-78 months, n=32) after heart transplantation. A loss of physiological nocturnal decline in blood pressure and heart rate was noted early after transplantation, whereas late after operation an improvement in circadian changes of blood pressure and heart rate was observed. The patients late after heart transplantation had a significant higher diastolic blood pressure. A pathological circadian blood pressure and heart rate pattern was observed in patients early after heart transplantation, which was improved late after operation. This could be explained by partial reinnervation of the heart. Diastolic hypertension late after transplantation may be due to cyclosporine treatment and/or neuroendocrine hyperactivity.

Dobutamine stress-induced angina in patients with denervated cardiac transplants. Clinical and angiographic correlates

BACKGROUND

The clinical consequences of cardiac denervation include the inability of the heart transplant recipient to sense cardiac pain. This is due mainly to interruption of ventricular sympathetic afferents normally responsible for transmission of cardiac pain. Although angina has been reported in transplant recipients, to our knowledge, its temporal relationship to myocardial ischemia has not been previously demonstrated.

OBJECTIVE AND METHODS

Eighty-two patients with heart transplants were serially evaluated by dobutamine stress echocardiography (DSE). In patients who developed angina during DSE, we sought to determine if the onset of angina was related to myocardial ischemia as demonstrated by stress-induced wall motion abnormalities. Coronary angiography was performed within 48 h of DSE in 45 of 82 patients.

RESULTS

Mean patient age and time since transplant were 53.1 +/- 1.1 years and 57.7 +/- 30.4 months, respectively (mean +/- SEM). Eleven patients developed typical angina during DSE. Three of the 11 (27%) had diagnostic ECG changes. All 11 had stress-induced regional wall motion abnormalities (WMA). Nine of the 11 patients (82%) had coronary angiographic data available that demonstrated significant coronary artery disease (CAD) in 8 (89%). All coronary lesions matched the observed segmental WMA. There was no difference between the angina (n = 11) and no angina (n = 71) groups with respect to peak heart rate (HR) (141 +/- 7 vs 145 +/- 3 beats/min; p = NS), peak systolic blood pressure (SBP) (155 +/- 8 vs 149 +/- 3 mm Hg; p = NS), or rate pressure product (21,699 +/- 1,490 vs 21,646 +/- 621 mm Hg x beats/min; p = NS). However, the mean time since transplant was significantly higher in patients with DSE-induced angina (80.3 +/- 6.2 vs 57.3 +/- 3.5 months; p < 0.05).

CONCLUSIONS

These data suggest that (1) the occurrence of angina in long-term transplant recipients with CAD is directly related to myocardial ischemia despite anatomic ventricular denervation, and (2) sympathetic reinnervation in the long-term may account for the occurrence of angina in cardiac transplant recipients.

Evidence against reinnervation of cardiac vagal afferents after human orthotopic cardiac transplantation

BACKGROUND

Orthotopic cardiac transplantation results in total cardiac denervation. Recent studies in humans suggest that reinnervation of cardiac sympathetic nerves (cardiac efferents) may occur after cardiac transplantation. We hypothesized that reinnervation of cardiac afferents may occur as well. To test this hypothesis, we investigated reflex responses produced by stimulation of ventricular chemosensory endings subserved by vagal afferents (cardiac depressor reflex).

METHODS AND RESULTS

Two cardiac transplant groups were studied: an "early" group (n = 18, < 24 months after transplant) and a "late" group (n = 18, > 43 months after transplant); these groups were compared with a control group with intact innervation (n = 18). The reflex response of the recipient sinus node (RSN) in the remnant right atrium, which remains innervated after transplantation, was observed during selective right coronary artery (RCA) and left coronary artery (LCA) injection of the radiographic contrast agent meglumine diatrizoate, which is known to stimulate ventricular chemosensory endings. A decrease in the rate of the RSN was expected if reinnervation of chemosensory endings had occurred and the afferent limb of the cardiac depressor reflex was intact. With injection, the RSN rate of both transplant groups did not decrease but increased (early: LCA, 7.2 +/- 1.4 beats per minute; RCA, 6.3 +/- 1.3 beats per minute; late: LCA, 5.9 +/- 1.0 beats per minute; RCA, 6.0 +/- 0.9 beats per minute) compared with the expected decrease in control patients (LCA, -20.8 +/- 2.5 beats per minute; RCA, -18.0 +/- 4.0 beats per minute; P < .001 versus transplants). Decreases in mean arterial pressure in the transplant groups (early: LCA, -11.3 +/- 1.4 mm Hg; RCA, -10.0 +/- 1.6 mm Hg; late: LCA, -13.0 +/- 1.6 mm Hg; RCA, -9.1 +/- 1.5 mm Hg) were less than those observed in the control group (LCA, -19.8 +/- 2.2 mm Hg; RCA, -18.7 +/- 4.0 mm Hg; P < .05 versus transplants).

CONCLUSIONS

The results suggest that reinnervation of ventricular chemosensory endings subserved by vagal afferents in cardiac transplant patients does not occur up to 74 months after transplantation.

Functional and neurochemical evidence for partial cardiac sympathetic reinnervation after cardiac transplantation in humans

BACKGROUND

The presence of cardiac reinnervation in humans after cardiac transplantation has been widely debated, based on the application of differing methods for the assessment of neuronal function. Some of these techniques have been rather indirect; consequently, the time course and extent of cardiac reinnervation remains uncertain.

METHODS AND RESULTS

To test for the presence of cardiac reinnervation after transplantation, we examined neurochemical (radiolabeled norepinephrine [NE] kinetics) and functional markers (power spectral analysis, heart rate response to exercise) of cardiac sympathetic nerve integrity in 15 cardiac transplantation recipients and 25 healthy control subjects of similar age. Cardiac transplantation subjects were studied 9 weeks to 8 years after cardiac transplantation (10 "early" patients < 18 months and 5 "late" patients > 2 years after cardiac transplantation). At rest, cardiac NE spillover was markedly attenuated early after transplantation (11.2 +/- 18.3 pmol/min) compared with subjects late after transplantation (105 +/- 11 pmol/min, P < .01) or in healthy control subjects (103 +/- 15 pmol/min, P < .01). Heart rate variability (measured by total spectral power) was significantly reduced in cardiac transplantation recipients compared with control subjects (59.4 +/- 30 vs 1673 +/- 516 milliseconds squared; P < .05), with evidence of a trend toward increasing spectral power late after transplantation. During exercise, the cardiac NE spillover was significantly lower in early cardiac transplantation recipients when compared with control subjects (163 +/- 50 vs 1876 +/- 418 pmol/min, P < .01). Late cardiac transplantation subjects showed a response intermediate (1080 +/- 254 pmol/min) between that of the early cardiac transplantation and control groups. However, measurements of the neuronal reuptake process for NE (assessed by the fractional extraction of plasma labeled NE across the heart and tritiated dihydroxyphenylglycol release) were significantly depressed in both early and late cardiac transplantation subjects.

CONCLUSIONS

The present study demonstrates a partial restoration of cardiac sympathetic nerve function in humans up to 8 years after heart transplantation.

Heart rate variability in patients with orthotopic heart transplantation: long-term follow-up

To evaluate heart rate variability (expressed as the standard deviation of RR intervals) within 5 years of follow-up, we studied 20 patients (14 males, 6 females, mean age 44 +/- 12 years) who underwent orthotopic heart transplantation. Six measurements were taken: one in the first 3 weeks after transplantation, and the others once annually, for 5 years. Twenty healthy subjects (mean age 44 +/- 7 years) constituted the control group. Heart rate variability increased significantly in the first 3 years of follow-up (7.2 +/- 1 vs. 11.1 +/- 4, p < 0.001; 11.1 +/- 4 vs. 15.2 +/- 4, p < 0.01; 15.2 +/- 4 vs. 18.9 +/- 5, p < 0.05); in the following years this trend slackened and values did not reach a statistically significant difference (18.9 +/- 5 vs. 21.4 +/- 5; 21.4 +/- 5 vs. 22.5 +/- 5). The mean standard deviation was invariably greater in the control group (63.6 +/- 12). These findings show that sinus rhythm variability in the denervated heart progressively increased over 5 years of follow-up. The absence of presynaptic uptake, which is responsible for adrenergic hypersensitivity to circulating catecholamines and intrinsic cardiac reflexes, does not appear to cause this phenomenon, since these mechanisms are not able to evolve in time after cardiac transplantation. Therefore, an enhanced beta-adrenergic receptors density or affinity to circulating catecholamines or a limited sympathetic reinnervation may be the more probable underlying mechanism.

Beat-to-beat variation of heart rate in diabetic patients with autonomic neuropathy and in completely cardiac denervated patients following orthotopic heart transplantation

Dysfunction of the vagal nerve, an early symptom in the development of autonomic neuropathy, can be assessed reliably by the beat-to-beat variation in heart rate. Patients after a cardiac transplantation are a unique model to investigate the beat-to-beat variation of a completely denervated heart. Heart rate and the beat-to-beat variation during normal and deep respiration were investigated in diabetic subjects with an autonomic neuropathy (n = 10), age and sex matched healthy controls (n = 10) and cardiac transplanted patients (n = 10). Further studies during pharmacological blockade of the parasympathetic nervous system with atropine were performed. In the denervated heart the coefficient of variation of the beat-to-beat interval was 0.38 +/- 0.02% during normal respiration, compared to 1.32 +/- 0.13% (P less than 0.0001) and 2.56 +/- 0.13% (P less than 0.0001) in the diabetic and control subjects, respectively. Administration of atropine (2 mg intravenously) decreased the coefficient of variation of the RR-interval to 0.73 +/- 0.09% in the diabetic patients (P less than 0.0005) and to 0.67 +/- 0.07% in the controls (P less than 0.0001), whereas the coefficient of variation remained unaffected in the cardiac denervated patients (0.39 +/- 0.02%). In the three groups an almost parallel increase of the RR-variation was observed during deep respiration at a rate of 6 breaths/min (from 0.38 +/- 0.02% to 1.99 +/- 0.38% in cardiac transplanted patients, P less than 0.0025; from 1.32 +/- 0.13% to 3.10 +/- 0.43% in diabetic patients, P less than 0.0025; from 2.56 +/- 0.13% to 5.42 +/- 0.94% in healthy controls, P less than 0.005). We conclude that a beat-to-beat variation of heart rate is present in the completely denervated heart. This RR-variation can not be influenced by a pharmacological blockade of the parasympathetic nervous system with atropine. The beat-to-beat variation increases during deep respiration not only in healthy controls but also in diabetic patients with autonomic neuropathy (partially denervated hearts) and cardiac transplanted patients (completely denervated hearts). This indicates an intracardiac mechanism in the modulation of heart rate.

Cardiac parasympathetic innervation in Chagas' heart disease

Trypanosoma cruzi is thought to selectively destroy the postganglionic cardiac vagal neurons of chagasic cardiac patients. This theory is based on morphologic and functional evidences obtained from chagasic individuals who were in very advanced stages of the disease. We have studied chagasic patients who were in both the early and late stages of the disease. Our findings and the review of the available literature suggest that myocardial damage and mild left ventricular dilatation precede the cardiac parasympathetic abnormalities. Furthermore, we have found a strong correlation between the degree of left ventricular dilatation and the extent of cardiac parasympathetic impairment. Consequently, we propose that the cardiac parasympathetic abnormalities arise as a compensating mechanism for the progressive left ventricular dilatation.

Subnormal parasympathetic activity after cardiac transplantation

Heart period variability (standard deviation of 120 consecutive RR or PP intervals) was used to assess baseline parasympathetic activity in 18 patients with congestive heart failure before and after orthotopic cardiac transplantation, and was compared to that of 16 age-matched control subjects. Mean heart period variability (+/- standard error of the mean) was significantly greater (p less than 0.05) in control subjects (58 +/- 5 ms) than in the patients at any time before or after transplantation. Heart period variability of innervated recipient atria did not change significantly early (1 to 4 weeks) after transplantation (16 +/- 2 to 24 +/- 5 ms; p = 0.11), but increased significantly between weeks 15 and 37 after transplantation (30 +/- 5 ms, p less than 0.002 versus before transplantation). A stepwise regression model (R2 = 0.35; p = 0.01) showed that heart period variability was directly related to time after transplantation and inversely related to systolic arterial pressure after transplantation and degree of rejection. Heart period variability of the denervated donor atria did not change from early to late periods after transplantation, suggesting that vagal reinnervation of the donor heart had not occurred. These data indicate that baseline parasympathetic activity does not increase significantly during the first month after transplantation but increases significantly between months 3 and 6.

Effects of exogenous adenosine in a patient with transplanted heart. Evidence for adenosine as a messenger in angina pectoris

In this pilot study some cardiac effects of exogenous adenosine on the denervated heart were studied in a patient with transplanted heart since 3 years. He was instrumented with catheters into the left coronary artery, the coronary sinus and the right ventricle. Adenosine was given in increasing doses intracoronarily, into the aorta at the diaphragmal level and into a peripheral vein. When given into the aorta pain was provoked dose-dependently and not different from a reference group. When given intracoronarily no pain was provoked except at the highest dose when a slight discomfort of the chest was provoked. After intravenous injection no pain was provoked in the chest or in adjacent structures. Coronary sinus flow increased dose-dependently and not different from the reference group. No increased heart rate response occurred after intravenous or intracoronary injections. Extensive degrees of sinus and AV nodal blockade occurred. In conclusion, the results are in keeping with a role for adenosine as a messenger between myocardial ischaemia and angina pectoris and cardiac sympathetic pressure response. The importance of innervation for proper sinus and AV nodal function was also illustrated.

Spectral analysis of heart rate variability following human heart transplantation: evidence for functional reinnervation

To determine the status of innervation in long-term human donor allografts, the power spectrum of heart rate variability was analysed in 9 post-transplant patients and 7 healthy control subjects. The mean post-transplant follow-up was 17.8 months (range: 2-37 months). Continuous ECG signals were recorded throughout a 15-min rest period. An R-R interval tachogram was generated and an autoregressive model using linear predictive coding, was applied to the heart rate variability data. In 8 transplant patients the frequency oscillations were irregular, broad based and widely dispersed from 0 to 1 Hz. The patterns resembled white noise and were consistent with dissociation of the donor allograft from the recipient's central nervous system. In contrast, one patient displayed a heart rate variability spectrum indistinguishable from that of control subjects. This pattern contained two distinct spectral bands; one corresponding to the patient's respiratory rate at 0.2 Hz and a low frequency Mayer wave at 0.1 Hz. Atropine abolished the respiratory (vagal) peak. Except for this patient's post-transplant time (33 months compared to the group mean of 17.6 months), there were no clinical characteristics which distinguished this patient from the others. While the mean heart rate for the remaining 8 allografts was significantly higher than controls (95.3 vs 64.5 bt/min; P less than 0.001) the standard deviation of heart rate variability for the 8 patients was significantly narrower than controls (0.7 vs 4.86; P less than 0.01). The variance of heart rate for the patient with the normal power spectrum was fourfold greater than the mean SD of the other transplant patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial norepinephrine, epinephrine and dopamine concentrations after cardiac autotransplantation in dogs

Myocardial norepinephrine is markedly reduced after cardiac transplantation because of interruption of postganglionic cardiac sympathetic nerves. There are also substantial stores of dopamine in the myocardium, but the influence of cardiac denervation on dopamine remains unknown. The effect of cardiac transplantation was determined and, thus, the effect of denervation on myocardial norepinephrine, dopamine and epinephrine. Myocardial catecholamines were measured with high-performance liquid chromatography with electrochemical detection in five dogs 6 to 8 weeks and in four dogs 8 to 12 years after cardiac autotransplantation and in six sham-operated dogs with intact cardiac innervation. Norepinephrine, dopamine and epinephrine levels were determined from samples obtained from the right and left atria and ventricles. Samples from the left ventricular apex and base were analyzed separately. There was a striking depletion of norepinephrine in all cardiac chambers after short-term autotransplantation. The norepinephrine content of the left atrium in sham-operated dogs (1,659 +/- 219 ng/g) was significantly higher than that of dogs with long-term autotransplanted hearts (754 +/- 372 ng/g). Sham-operated dogs and dogs with long-term autotransplanted hearts had statistically significant (p less than 0.05) differences in norepinephrine content in the left ventricular apex (480 +/- 197 versus 294 +/- 198 ng/g), left ventricular base (876 +/- 2204 versus 654 +/- 156 ng/g) and right ventricle (766 +/- 133 versus 247 +/- 29 ng/g). In contrast to norepinephrine, dopamine concentrations were relatively preserved in the short-term group despite the virtual depletion of myocardial norepinephrine.(ABSTRACT TRUNCATED AT 250 WORDS)