Arterial baroreflex modulation of heart rate in patients early after heart transplantation: lack of parasympathetic reinnervation

Endocardial ablation of epicardial ganglionated plexi: history, open questions and future prospects of cardioneuroablation

Neurocardiogenic syncope is the most common cause of transient loss of consciousness and considerably reduces quality of life. Pharmacological and pacing therapy may not be fully efficacious and complications related to implanted hardware must be considered. In this context, cardioneuroablation (CNA) has been proposed to attenuate the vagal reflex with elimination of cardioinhibition. It has been shown that CNA is able to eliminate recurrences of syncope in over 90% of cases and no major complications are reported in the current literature. Despite these encouraging findings, CNA is only mentioned in current guidelines as a possible alternative treatment and has no real indication class. The diversity of mapping techniques, the absence of direct denervation control, the lack of a precise endpoint, the possible placebo effect, the short follow-up, and the question of the learning curve represent the major limitations of this promising procedure. The aim of this review was to look over the existing literature, analysing the novelties, the limitations, the unresolved issues and the outcome of CNA.

Long-term heart transplant recipients: heart rate-related effects on augmented transfer function coherence during repeated squat-stand maneuvers in males

Previous research has highlighted that squat-stand maneuvers (SSMs) augment coherence values within the cerebral pressure-flow relationship to ∼0.99. However, it is not fully elucidated if mean arterial pressure (MAP) leads to this physiological entrainment independently, or if heart rate (HR) and/or the partial pressure of carbon dioxide (Pco₂) also have contributing influences. A 2:1 control-to-case model was used in the present investigation [participant number (n) = 40; n = 16 age-matched (AM); n = 16 donor control (DM); n = 8 heart transplant recipients (HTRs)]. The latter group was used to mechanistically isolate the extent to which HR influences the cerebral pressure-flow relationship. Participants completed 5 min of squat-stand maneuvers at 0.05 Hz (10 s) and 0.10 Hz (5 s). Linear transfer function analysis (TFA) examined the relationship between different physiological inputs (i.e., MAP, HR, and Pco₂) and output [cerebral blood velocity (CBV)] during SSM; and cardiac baroreceptor sensitivity (BRS). Compared with DM, cardiac BRS was reduced in AM (P < 0.001), which was further reduced in HTR (P < 0.045). In addition, during the SSM, HR was elevated in HTR compared with both control groups (P < 0.001), but all groups had near-maximal coherence metrics ≥0.98 at 0.05 Hz and ≥0.99 at 0.10 Hz (P ≥ 0.399). In contrast, the mean HR-CBV/Pco₂-CBV relationships ranged from 0.38 (HTR) to 0.81 (DM). Despite near abolishment of BRS and blunted HR following heart transplantation, long-term HTR exhibited near-maximal coherence within the MAP-CBV relationship, comparable with AM and DM. Therefore, these results show that the augmented coherence with SSM is driven by blood pressure, whereas elevations in TFA coherence as a result of HR contribution are likely correlational in nature.

Strong evidence for parasympathetic sinoatrial reinnervation after heart transplantation

BACKGROUND

Heart transplantation (HTx) surgically denervates the heart. We examined indices of sinoatrial reinnervation, with emphasis on (1) the occurrence and timing of parasympathetic reinnervation, and (2) the consequences of reinnervation for heart rate (HR) responsiveness and arterial baroreceptor sensitivity.

METHODS

Fifty HTx recipients were prospectively followed for 36 months after surgery. Hemodynamic variables and heart rate variability were continuously recorded at supine rest, 60 degrees head-up-tilt, during the Valsalva maneuver and during handgrip isometric exercise.

RESULTS

Suggesting parasympathetic reinnervation: at baseline rest, root of the mean squared differences of successive RR intervals increased from median 3.9(5.9) to 7.1(5.1) ms (p < 0.001); high-frequency power increased from 4.0(12) to 5.7(18.9) ms² (p = 0.018); and baroreceptor sensitivity increased from 0.04(0.36) to 1.3(2.4) ms/mmHg (p < 0.001). Suggesting sympathetic reinnervation: at baseline rest low-frequency power increased from 0.49(2.5) to 7.5(18.1) ms² (p < 0.001); and HR responses to sympathetic stimulation during (1) head-up tilt increased from 1.9(4.2) to 9.1(8.2) bpm (p < 0.001), (2) Valsalva increased from 1.6(1.4) to 8.3(10.8) bpm (p < 0.001) and (3) handgrip increased from 0.3(0.6) to 1.9(5.1) bpm (p < 0.001). Signs of sympathetic reinnervation emerged within 6 months, while signs of parasympathetic reinnervation emerged by 24 months.

CONCLUSIONS

Root of the mean squared differences of successive RR intervals, high-frequency and low-frequency variability, HR responsiveness and arterial baroreflex sensitivity all increased after HTx, suggesting functional parasympathetic and sympathetic sinoatrial reinnervation. Accordingly, the pathological regulatory state present in heart transplant recipients, which is responsible for a host of functional and clinical abnormalities, is being partially offset over time by restored autonomic control of the heart in many heart transplant recipients.

Early Signs of Sinoatrial Reinnervation in the Transplanted Heart

BACKGROUND

Heart transplantation (HTx) surgically transects all connections to the heart, including the autonomic nerves. We prospectively examined signs, timing and consequences of early sympathetic and parasympathetic sinoatrial reinnervation, as well as explored indirect evidence of afferent cardiopulmonary reinnervation.

METHODS

Fifty HTx recipients were assessed at 2.5, 6, and 12 mo after HTx. For comparison, 50 healthy controls were examined once. Continuous, noninvasive recordings of hemodynamic variables and heart rate variability indices were performed at supine rest, 0.2 Hz controlled breathing, 60° head-up-tilt, during the Valsalva maneuver and during handgrip isometric exercise.

RESULTS

In HTx recipients, supine low-frequency heart rate variability gradually increased; supine high-frequency variability did not change; heart rate variability indices during controlled breathing remained unaltered; heart rate responses during tilt and isometric exercise gradually increased; the tachycardia response during Valsalva maneuver increased, while the bradycardia response remained unchanged; and indices of baroreflex sensitivity improved. Responses remained low compared to healthy controls. A negative correlation between indices of preload and heart rate response during head-up tilt emerged at 12 mo.

CONCLUSIONS

Results suggest that sympathetic reinnervation of the sinoatrial node starts within 6 mo after HTx and strengthens during the first year. No evidence of early parasympathetic reinnervation was found. Indirect signs of afferent reinnervation of cardiopulmonary low-pressure baroreceptors emerged at 12 mo. Better sympathetic sinoatrial control improved heart rate responsiveness to orthostatic challenge and isometric exercise, as well as heart rate buffering of blood pressure fluctuations.

Heart rate kinetics during standard cardiopulmonary exercise testing in heart transplant recipients: a longitudinal study

AIMS

Heart transplantation (HTx) results in complete autonomic denervation of the donor heart, causing resting tachycardia and abnormal heart rate (HR) responses to exercise. We determined the time course of suggestive cardiac reinnervation post HTx and investigated its clinical significance.

METHODS AND RESULTS

Heart rate kinetics during standard cardiopulmonary exercise testing at 2.5-5 years after HTx was assessed in 58 patients. According to their HR increase 30 s after exercise onset, HTx recipients were classified as denervated (slow responders: <5 beats per minute [b.p.m.]) or potentially reinnervated (fast responders: ≥5 b.p.m.). Additionally, in 30 patients, longitudinal changes of maximal oxygen consumption and HR kinetics were assessed during the first 15 post-operative years. At 2.5-5 years post HTx, 38% of our study population was potentially reinnervated. Fast responders were significantly younger (41 ± 15 years) than slow responders (53 ± 13 years, P = 0.003) but did not differ with regard to donor age, immunosuppressive regime, cardiovascular risk factors, endomyocardial biopsy, or vasculopathy parameters. While HR reserve (56 ± 20 vs. 39 ± 15 b.p.m., P = 0.002) and HR recovery after 60 s (15 ± 11 vs. 5 ± 6 b.p.m., P < 0.001) were greater in fast responders, resting HR, peak HR of predicted, and peak oxygen consumption of predicted were comparable.

CONCLUSIONS

Signs of reinnervation occurred mainly in younger patients. Maximal oxygen consumption was independent of HR kinetics.

The Benefits of Oral Rehydration on Orthostatic Intolerance in Children with Postural Tachycardia Syndrome

OBJECTIVE

To evaluate whether equal volumes of oral rehydration solution (ORS) or intravenous (IV) saline provide similar improvements in cardiovascular status during controlled orthostatic challenge when administered to subjects with postural tachycardia syndrome (POTS) with orthostatic intolerance.

STUDY DESIGN

We studied the neurovascular response to fluid loading during orthostatic stress using lower body negative pressure (LBNP) in 10 subjects with POTS with orthostatic intolerance and 15 controls, and on subsequent days before and 1 hour after IV saline infusion or ingestion of ORS.

RESULTS

Subjects with POTS exhibited reduced tolerance to LBNP (P < .0001) compared with controls (Orthostatic Index of 35 715 ± 3469 vs 93 980 ± 7977, respectively). In POTS, following ORS but not saline infusion, cerebral blood flow velocity (CBF_v) was significantly higher than that with no treatment, at -45 mm Hg (P < .0005). Although fluid loading did not confer any advantage in controls, subjects with POTS experienced a significant improvement in orthostatic tolerance following both saline infusion (100 ± 9.7 vs 134.5 ± 17.4; P < .05) and ORS (100 ± 9.7 vs 155.6 ± 15.7; P < .001) when evaluated by normalized orthostatic index (P < .001, compared with untreated baseline).

CONCLUSIONS

Maintenance of CBF_v may have resulted in the improved short-term orthostatic tolerance exhibited by the subjects with POTS following ORS administration. ORS is a convenient, safe, and effective therapy for short-term relief of orthostatic intolerance.

Autonomic cardiovascular control changes in recent heart transplant recipients lead to physiological limitations in response to orthostatic challenge and isometric exercise

PURPOSE

Heart transplantation causes denervation of the donor heart, but the consequences for cardiovascular homeostasis remain to be fully understood. The present study investigated cardiovascular autonomic control at supine rest, during orthostatic challenge and during isometric exercise in heart transplant recipients (HTxR).

METHODS

A total of 50 HTxRs were investigated 7-12 weeks after transplant surgery and compared with 50 healthy control subjects. Continuous, noninvasive recordings of cardiovascular variables were carried out at supine rest, during 15 min of 60° head-up tilt and during 1 min of 30% of maximal voluntary handgrip. Plasma and urine catecholamines were assayed, and symptoms were charted.

RESULTS

At supine rest, heart rate, blood pressures and total peripheral resistance were higher, and stroke volume and end diastolic volume were lower in the HTxR group. During tilt, heart rate, blood pressures and total peripheral resistance increased less, and stroke volume and end diastolic volume decreased less. During handgrip, heart rate and cardiac output increased less, and stroke volume and end diastolic volume decreased less. Orthostatic symptoms were similar across the groups, but the HTxRs complained more of pale and cold hands.

CONCLUSION

HTxRs are characterized by elevated blood pressures and total peripheral resistance at supine rest as well as attenuated blood pressures and total peripheral resistance responses during orthostatic challenge, possibly caused by low-pressure cardiopulmonary baroreceptor denervation. In addition, HTxRs show attenuated cardiac output response during isometric exercise due to efferent sympathetic denervation. These physiological limitations might have negative functional consequences.

Postural Heart Rate Changes in Young Patients With Vasovagal Syncope

BACKGROUND AND OBJECTIVES

Recurrent postural vasovagal syncope (VVS) is caused by transient cerebral hypoperfusion from episodic hypotension and bradycardia; diagnosis is made by medical history. VVS contrasts with postural tachycardia syndrome (POTS), defined by chronic daily symptoms of orthostatic intolerance with excessive upright tachycardia without hypotension. POTS has recently been conflated with VVS when excessive tachycardia is succeeded by hypotension during tilt testing. We hypothesize that excessive tachycardia preceding hypotension and bradycardia is part of the vasovagal response during tilt testing of patients with VVS.

METHODS

We prospectively performed head-up tilt (HUT) testing on patients with recurrent VVS (n = 47, 17.9 ± 1.1 y), who fainted at least 3 times within the last year, and control subjects (n = 15, 17.1 ± 1.0 y), from age and BMI-matched volunteers and measured blood pressure, heart rate (HR), cardiac output, total peripheral resistance, and end tidal carbon dioxide.

RESULTS

Baseline parameters were the same in both groups. HR (supine versus 5 and 10 minutes HUT) significantly increased in control (65 ± 2.6 vs 83 ± 3.6 vs 85 ± 3.7, P < .001) and patients with VVS (69 ± 1.6 vs 103 ± 2.3 vs 109 ± 2.4, P < .001). HUT in controls maximally increased HR by 20.3 ± 2.9 beats per minute; the increase in patients with VVS of 39.8 ± 2.1 beats per minute was significantly greater (P < .001). An increase in HR of ≥40 beats per minute by 5 and 10 minutes or before faint with HUT, occurred in 26% and 44% of patients with VVS, respectively, but not in controls.

CONCLUSIONS

Orthostasis in VVS is accompanied by large increases in HR that should not be construed as POTS.

Orthostatic Circulatory Disorders: From Nosology to Nuts and Bolts

When patients complain of altered consciousness or discomfort in the upright posture, either relieved by recumbency or culminating in syncope, physicians may find themselves baffled. There is a wide variety of disorders that cause abnormal regulation of blood pressure and pulse rate in the upright posture. The aim of this focused review is 3-fold. First, to offer a classification (nosology) of these disorders; second, to illuminate the mechanisms that underlie them; and third, to assist the physician in the practical aspects of diagnosis of adult orthostatic hypotension, by extending clinical skills with readily available office technology.

Comparison of Causes of Death After Heart Transplantation in Patients With Left Ventricular Ejection Fractions ≤35% Versus >35

Sudden cardiac death (SCD) is a common cause of death in the general population, occurring in 300,000 to 350,000 people in the United States alone. Currently, there are no data supporting implantable cardioverter-defibrillator therapy in patients who underwent orthotopic heart transplant (OHT) with low left ventricular ejection fraction (LVEF). In this retrospective study, we included all patients who underwent primary OHT at our institution from 2007 to 2013. We compared the cause of death in patients who underwent OHT and evaluated the correlation of the cause of death and the patients' LVEF. Our objectives were to determine whether patients who underwent OHT with LVEF <35% are at increased risk for SCD compared with those who underwent OHT with normal LVEF. To summarize our results, a total of 345 patients were included in our study (mean age 50 ± 14 years, 68% men). The mean follow-up was 1,260 ± 698 days. Forty patients (11.5%) died >6 months after OHT. Surviving patients had higher LVEF compared with deceased patients (64 ± 7% and 50 ± 24%, respectively, p ≤0.001). In all, 10 (25%) of the deceased patients died suddenly, 9 (23%) from sepsis, and 8 (20%) from malignancy. Of the 11 deceased patients with LVEF ≤35%, 2 patients (18%) died suddenly compared with 9 SCDs among the 29 deceased patients (31%) with LVEF >35% (p = 0.54). In conclusion, patients who underwent OHT who died were more likely to have LVEF <35%, and a quarter of the deceased patients who underwent OHT died suddenly. A reduced LVEF was not associated with an increased risk of SCD.

An integrated mathematical model of the human cardiopulmonary system: model validation under hypercapnia and hypoxia

A novel integrated physiological model of the interactions between the cardiovascular and respiratory systems has been in development for the past few years. The model has hundreds of parameters and variables representing the physical and physiological properties of the human cardiopulmonary system. It can simulate many dynamic states and scenarios. The description of the model and the results in normal resting conditions were presented in a companion paper (Albanese A, Cheng L, Ursino M, Chbat NW. Am J Physiol Heart Circ Physiol 310: 2016; doi:10.1152/ajpheart.00230.2014), where model predictions were compared against average population data from literature. However, it is also essential to test the model in abnormal or pathological conditions to prove its consistency. Hence, in this paper, we concentrate on testing the cardiopulmonary model under hypercapnic and hypoxic conditions, by comparing model's outputs to population-averaged cardiorespiratory data reported in the literature. The utility of this comprehensive model is demonstrated by testing the internal consistency of the simulated responses of a significant number of cardiovascular variables (heart rate, arterial pressure, and cardiac output) and respiratory variables (tidal volume, respiratory rate, minute ventilation, alveolar O2 and CO2 partial pressures) over a wide range of perturbations and conditions; namely, hypercapnia at 3–7% CO2 levels and hypoxia at 7–9% O2 levels with controlled CO2 (isocapnic hypoxia) and without controlled CO2 (hypocapnic hypoxia). Finally, a sensitivity analysis is performed to analyze the role of the main cardiorespiratory control mechanisms triggered by hypercapnia and hypoxia.

Early Parasympathetic Reinnervation Is Not Related to Reconnection of Major Branches of the Vagus Nerve after Heart Transplantation

Background and Objectives

Bicaval heart transplantation (HTx) may promote parasympathetic reinnervation. However, the prevalence and timing of reinnervation have not been fully investigated. Heart rate variability (HRV) and direct vagal stimulation were used to evaluate the presence of parasympathetic reinnervation after bicaval HTx.

Subjects and Methods

A total of 21 patients (time after HTx 0.52-4.41 years, mean 1.8±1.2 years) who received a bicaval HTx was enrolled. Reinnervation was evaluated using HRV values from 24-hour Holter recordings. A cross-sectional analysis of the HRV at 0.5-1, 1-2, and >2 years after HTx was performed. We also applied high-frequency electrical stimulation (16.7 Hz, 1 msec pulse width, ≤10 V) to the cardiac branches of the vagus nerve at the level of the superior vena cava in eight patients at 6 and 12 months after HTx.

Results

The degree of parasympathetic reinnervation corresponded to the time after HTx. The HRV analysis revealed that the root mean square of the successive differences between consecutive RR-intervals (RMSSD) and high-frequency power were significantly higher during the late period (>2 years) compared with the early period (0.5-1 year) after HTx. None of the eight patients who underwent direct vagal stimulation responded during the stimulation at 6 and 12 months, whereas incremental trends in HRV parameters were observed, which indicated that parasympathetic reinnervation began within 1 year after HTx.

Conclusion

Parasympathetic reinnervation seemed to begin in the early period (<1 year) after bicaval HTx. Reconnection of major branches of the vagus nerve may not be related to early reinnervation.

Relationship Between Cerebral Blood Flow and Blood Pressure in Long-Term Heart Transplant Recipients

Heart transplant recipients are at an increased risk for cerebral hemorrhage and ischemic stroke; yet, the exact mechanism for this derangement remains unclear. We hypothesized that alterations in cerebrovascular regulation is principally involved. To test this hypothesis, we studied cerebral pressure-flow dynamics in 8 clinically stable male heart transplant recipients (62±8 years of age and 9±7 years post transplant, mean±SD), 9 male age-matched controls (63±8 years), and 10 male donor controls (27±5 years). To increase blood pressure variability and improve assessment of the pressure-flow dynamics, subjects performed squat–stand maneuvers at 0.05 and 0.10 Hz. Beat-to-beat blood pressure, middle cerebral artery velocity, and end-tidal carbon dioxide were continuously measured during 5 minutes of seated rest and throughout the squat–stand maneuvers. Cardiac baroreceptor sensitivity gain and cerebral pressure-flow responses were assessed with linear transfer function analysis. Heart transplant recipients had reductions in R-R interval power and baroreceptor sensitivity low frequency gain ( P <0.01) compared with both control groups; however, these changes were unrelated to transfer function metrics. Thus, in contrast to our hypothesis, the increased risk of cerebrovascular complication after heart transplantation does not seem to be related to alterations in cerebral pressure-flow dynamics. Future research is, therefore, warranted.

Update on the theory and management of orthostatic intolerance and related syndromes in adolescents and children

Orthostasis means standing upright. One speaks of orthostatic intolerance (OI) when signs, such as hypotension, and symptoms, such as lightheadedness, occur when upright and are relieved by recumbence. The experience of transient mild OI is part of daily life. 'Initial orthostatic hypotension' on rapid standing is a normal form of OI. However, other people experience OI that seriously interferes with quality of life. These include episodic acute OI, in the form of postural vasovagal syncope, and chronic OI, in the form of postural tachycardia syndrome. Less common is neurogenic orthostatic hypotension, which is an aspect of autonomic failure. Normal orthostatic physiology and potential mechanisms for OI are discussed, including forms of sympathetic hypofunction, forms of sympathetic hyperfunction and OI that results from regional blood volume redistribution. General and specific treatment options are proposed.

Common syndromes of orthostatic intolerance

The autonomic nervous system, adequate blood volume, and intact skeletal and respiratory muscle pumps are essential components for rapid cardiovascular adjustments to upright posture (orthostasis). Patients lacking sufficient blood volume or having defective sympathetic adrenergic vasoconstriction develop orthostatic hypotension (OH), prohibiting effective upright activities. OH is one form of orthostatic intolerance (OI) defined by signs, such as hypotension, and symptoms, such as lightheadedness, that occur when upright and are relieved by recumbence. Mild OI is commonly experienced during intercurrent illnesses and when standing up rapidly. The latter is denoted "initial OH" and represents a normal cardiovascular adjustment to the blood volume shifts during standing. Some people experience episodic acute OI, such as postural vasovagal syncope (fainting), or chronic OI, such as postural tachycardia syndrome, which can significantly reduce quality of life. The lifetime incidence of ≥1 fainting episodes is ∼40%. For the most part, these episodes are benign and self-limited, although frequent syncope episodes can be debilitating, and injury may occur from sudden falls. In this article, mechanisms for OI having components of adrenergic hypofunction, adrenergic hyperfunction, hyperpnea, and regional blood volume redistribution are discussed. Therapeutic strategies to cope with OI are proposed.

Hypertension after heart and heart/lung transplantation in childhood--study on the evolution of short-term blood pressure regulation

Arterial hypertension complicates the follow-up of heart- and heart/lung-transplanted children. We investigated the evolution of BRS as short-time BP regulation mechanism and BP after heart and heart/lung transplantation. Twenty patients (15 males; mean age 15.1 ± 4.3 yr) were studied twice at intervals of 2.96 ± 0.87 yr. BRS was calculated using non-invasive beat-to-beat BP measurement system. HRV was calculated (LF, sympathetic influence; HF, parasympathetic influence). BRS increased in 10 patients (3.67 ± 1.43 ms/mmHg vs. 7.59 ± 3.40 mmHg, p = 0.005) (group 1). Six of 10 patients received antihypertensive medication. BRS decreased or remained unchanged in 10 patients (8.93 ± 7.9 ms/mmHg vs. 5.32 ± 6.6 ms/mmHg, p = 0.008) (group 2) with 9/10 patients necessitating antihypertensive medication. Group 1 showed LF/HF increase (LF/HF 1.03 ± 0.9 vs. 4.36 ± 2.32, p = 0.03); group 2 showed LF/HF decrease (LF/HF 3.7 ± 2.1 vs. 1.84 ± 1.1, p = 0.023). Evolution of BRS after heart and heart/lung transplantation in childhood seems to influence the necessity of antihypertensive medication. With time, increasing short-time BP regulation involving sympathetic reinnervation may improve BP.

Anatomy of the cardiac nervous system with clinical and comparative morphological implications

Unlike autonomic nervous preservation in other surgeries for improving patient quality of life, autonomic cardiac nervous system (ACNS) preservation has been neglected in cardiovascular surgery because of technical difficulties and other unsolved issues. Because such ACNS preservation in cardiovascular surgery is anticipated in the future, detailed anatomical investigation of the human ACNS is required. Therefore, we have conducted morphological studies of the ACNS from macroscopic, clinical, and evolutionary anatomical viewpoints. In this study, I review detailed anatomical studies of the human ACNS together with their clinical implications. In addition, the evolutionary comparative anatomical significance of primate ACNS is also summarized to help understand and translate the findings of functional experiments to humans. These integrated findings will be the subject of a future study unifying molecular embryological and anatomical findings to clarify cardiac functions based on functional animal experiments, clinical applications such as improving surgery techniques and individual order-made surgery in cardiac surgery, and for future evaluation in regenerative medicine.

Motor and sensory re-innervation of the lung and heart after re-anastomosis of the cervical vagus nerve in rats

There is no study in the literature dealing with re-innervation of the cardiopulmonary vagus nerve after its transection followed by re-anastomosis. In the present study, we explored the bronchomotor, heart rate and respiratory responses in rats at 2, 3 and 6 months after re-anastomosis of one cervical vagus trunk. The conduction velocity of A, B and C waves was calculated in the compound vagal action potential. We searched for afferent vagal activities in phase with pulmonary inflation to assess the persistence of pulmonary stretch receptor (PSR) discharge in re-innervated lungs. In each animal, data from the stimulation or recording of one re-anastomosed vagus nerve were compared with those obtained in the contra-lateral intact one. Two and three months after surgery, the conduction velocities of A and B waves decreased, but recovery of conduction velocity was complete at 6 months. By contrast, the conduction velocity of the C wave did not change until 6 months, when it was doubled. The PSR activity was present in 50% of re-anastomosed vagus nerves at 2 and 3 months and in 75% at 6 months. Respiratory inhibition evoked by vagal stimulation was significantly weaker from the re-anastomosed than intact nerve at 2 but not 3 months. Vagal stimulation did not elicit cardiac slowing or bronchoconstriction 6 months after re-anastomosis. Our study demonstrates the capacity of pulmonary vagal sensory neurones to regenerate after axotomy followed by re-anastomosis, and the failure of the vagal efferents to re-innervate both the lungs and heart.

Effects of omega-3 fatty acids on heart rate in cardiac transplant recipients

Omega-3 fatty acid (n-3 FA) consumption has been linked to reductions in the risk of death from coronary heart disease and, recently, to lower heart rates (HRs). The investigators previously observed a reduction of 5 beats/min in HR in patients with coronary heart disease given n-3 FAs (eicosapentaenoic acid and docosahexaenoic acid) for 4 months. Reductions in HR may be explained by enhanced vagal tone, influences on cardiac voltage-gated ion channels, or both. The hypothesis that n-3 FAs would affect HR independent of vagal input was investigated by studying the effects of n-3 FA supplementation on HR in patients with denervated hearts after orthotopic heart transplantation. Electrocardiographic data obtained in 2 prospective trials in which 18 heart transplant recipients received n-3 FA supplementation (1 to 3.4 g/day) for 4 to 6 months were collected. Patients were studied 4.4 +/- 2.6 years after transplantation. HR, QRS complex, and QTc duration were determined before and after treatment. Pretreatment HR was reduced from 88 +/- 14 to 83 +/- 13 beats/min after n-3 FA treatment (p = 0.016). QRS duration increased from 107 +/- 24 to 117 +/- 25 ms (p = 0.001). QTc duration remained unchanged from baseline (427 +/- 34 ms) to study end (424 +/- 39 ms). In conclusion, n-3 FA supplementation reduced HR and prolonged QRS duration in heart transplant recipients who were presumably devoid of vagal innervation. These findings suggest that n-3 FAs may modify electrophysiologic properties of the myocardium itself.

Reinnervation after heart transplantation in children: results of short-time heart rate variability testing

AIMS

To detect impairment in short-term heart rate variability (HRV) in children after heart and heart-lung transplantation (TX) as reported in adults. To assess vagal and sympathetic influence on the donor heart rate using frequency domain analysis of HRV.

METHODS AND RESULTS

Measurement of short-term HRV was performed in 17 patients (age 16.9+/-3.6, 6.1+/-3.7 yr after TX) and 12 healthy controls (age 14.8+/-3.0 yr). Testing consisted of a resting phase of 15 minutes followed by a tilt phase of 45 min. All HRV parameters were significantly impaired in transplanted patients: RR interval (RRI) 717.2+/-122.5 m/s (controls 827+/-139.7, p<0.05), standard deviation of RR interval (RRI-SD) 20.1+/-15.5 (89.9+/-38.4, p<0.001), RRI at tilt 607.9+/-79.7 (654.0+/-104.7, NS), RRI-SD at tilt 21.1+/-20.0 (60.4+/-31.4, p<0.001). Low-frequency (LF)/High-frequency (HF) ratio of HRV showed prominent sympathetic influence in TX-patients (3.38+/-5.60 vs. 1.18+/-0.86, NS) increasing during tilting (5.91+/-8.36 vs. 4.74+/-5.27, NS). In subgroup analysis, 4 yr after TX an increasing sympathetic control of heart rate was observed.

CONCLUSION

Short-term HRV is severely impaired in children after TX. If changes are observed, they are time-related and show increasing sympathetic influence starting from 4 yr after TX.

Efficacy of Atropine as a Chronotropic Agent in Heart Transplant Patients Undergoing Dobutamine Stress Echocardiography

BACKGROUND

After heart transplant (HTX), the heart is completely denervated. While sympathetic reinnervation is likely to occur, there is conflicting evidence regarding parasympathetic reinnervation. Accordingly, it is unclear if atropine is efficacious as a chronotropic agent in HTX patients undergoing dobutamine stress echocardiography (DSE), since cholinergic cardiac stimulation is required for atropine to exert its effect. The purpose of this study was to demonstrate that atropine can sufficiently increase the heart rate (HR) in HTX patients undergoing DSE.

METHODS

A retrospective review was performed on 68 HTX patients who underwent DSE as part of their routine annual HTX follow-ups. Dobutamine was administered in the standard fashion of 10, 20, 30, 40, 50 mcg/kg per minute with blood pressure and electrocardiographic monitoring. If target HR was not attained, atropine was administered to aid in achieving 85% of maximum age-predicted HR.

RESULTS

Mean patient age was 58 +/- 10 years. Mean period since transplant was 9 +/- 4 years. Forty-seven (69%) patients received dobutamine only, and 21 (31%) required additional atropine to reach target HR. Of the 21 patients who received atropine, 10 (48%) reached target HR. Neither time from transplant, age, gender, resting HR, medications, nor atherosclerotic risk factors predicted responsiveness to atropine. Those responding to dobutamine had a significantly greater resting HR than those receiving additional atropine.

CONCLUSIONS

The adjunctive use of atropine in HTX patients during DSE aids in reaching 85% of maximum predicted HR in some patients. Furthermore, resting HR may predict the additional need of atropine during DSE.

Hypertension in Heart and Heart-Lung Transplanted Children: Does Impaired Baroreceptor Function Play a Role?

BACKGROUND

Baroreceptor control of beat-to-beat blood pressure in heart and heart-lung-transplanted children is impaired. Time-related trends of baroreceptor function recovery are studied and a possible correlation of baroreflex impairment and systolic hypertension may give evidence for supplemental medical treatment of hypertension.

METHODS

Seventeen patients (six female) 6.1 +/- 3.7 years (range 0.8-13.0 years) after heart (n = 14) and heart-lung (n = 3) transplantation (TX) were studied. Twelve healthy children and 10 children after liver and bone marrow TX taking cyclosporine A (CyA) served as control groups 1 and 2, respectively. Baroreceptor sensitivity (BRS) was calculated from noninvasive systolic beat-to-beat blood pressure (sBP) measurement during a resting phase and a tilt-table test.

RESULTS

BRS was significantly impaired in the study group at rest and during tilting; mean sBP was slightly elevated. Significant difference between patients on CyA and healthy controls was not observed. Discrete recovery of BRS occurred after 4 years postTX with decreased sBP (n = 12 pts, BRS 6.78 +/- 7.44 msec/mmHg, sBP 116.2 +/- 12.4 mmHg) when compared to a postTX time course of less than 4 years (n = 5 pts, BRS 4.02 +/- 4.21 msec/mmHg, sBP 122.0 +/- 6.7 mmHg, P = NS).

CONCLUSION

BRS is disturbed after TX in children; four years postTX, a minimal recovery of BRS and a discrete reduction of sBP seem to occur. Those patients with a persistent low BRS and elevated sBP may profit from pharmacological influence in sympathovagal imbalance.

"Cardioneuroablation"--new treatment for neurocardiogenic syncope, functional AV block and sinus dysfunction using catheter RF-ablation

Cardiac neuroablation is a new technique for management of patients with dominantly adverse parasympathetic autonomic influence. The technique is based on radiofrequency (RF) ablation of autonomic connections in the three main ganglia around the heart. Their connections are identified by Fast-Fourier Transforms (FFTs) of endocardial signals: sites of autonomic nervous connections show fractionated signals with FFTs shifted to the right. In contrast, normal myocardium without these connections does not show these features. RF-ablation is thought to inflict permanent damage on the parasympathetic autonomic influence because its cells are adjacent to the heart whereas sympathetic cells are remote. Twenty-one patients with a mean age of 48 years, neurally mediated reflex syncope in six, functional high grade atrioventricular block in seven and sinus node dysfunction in 13 (there is overlap between the second and third groups) were treated. Follow-up for a mean of 9.2 months demonstrated success in all cases with relief of symptoms. No complications occurred.

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.

Decreased heart rate and blood pressure in a recent cardiac transplant patient after spinal anesthesia

PURPOSE

To describe the cardiovascular effects of neuraxial blockade in a heart transplant patient.

CLINICAL FEATURES

A 69-yr-old 70-kg male underwent orthotopic heart transplant (bicaval anastomosis technique) for ischemic cardiomyopathy. Five months after transplantation, the patient underwent a transurethral bladder tumour resection under spinal anesthesia. Two millilitres of bupivacaine 0.75% (15 mg) were injected intrathecally at L(3-4) and the patient remained seated for approximately 20 sec prior to assuming the lithotomy position. Subsequently, both blood pressure (BP) and heart rate (HR) diminished gradually (BP and HR immediately pre-spinal: 113 mmHg (mean arterial pressure) and 92 beats x min(-1), respectively; nadir BP and HR: 94 mmHg (16.8% decrease) 30 min postspinal and 73 beats x min(-1) (20.7% decrease) 40 min postspinal, respectively). HR and mean BP were highly correlated (r = 0.9410, P < 0.0001, R(2) = 0.8854). The dermatome level of neuraxial anesthesia, determined by sensitivity to pin prick, was T(8) (five minutes) and T(6) (ten minutes) postinjection of spinal anesthetic. Control patients (n = 10) undergoing elective urological procedures with identical anesthesia management demonstrated very similar cardiovascular responses.

CONCLUSIONS

Although cardiac transplant patients may tolerate neuraxial anesthesia admirably, a fall in HR may ensue which theoretically could have important physiological consequences. It is argued that the change in HR in the transplanted patient was mediated by mechanisms intrinsic to the transplanted heart and/or by reduced catecholamine secretion from the adrenal medulla. It is emphasized that HR changes observed in cardiac transplant patients do not necessarily imply reinnervation of the transplanted organ.

Baroreceptor-related dysrhythmias in piglets with selective autonomic denervation of the heart

This study was carried out to determine whether selective cardiac autonomic denervation performed on neonatal swine would evoke dysrhythmias later in development. Piglets (n = 27; 5-10 days old) underwent unilateral stellate ganglion ablation, or right cardiac vagotomy, or sham surgery. Fifty to sixty days after denervation, acute experiments were performed to evaluate responses to baroreceptor activation. Of all animals who exhibited prolonged R-R intervals, only those with right stellate ganglion ablation had prolonged corrected QT intervals. Despite findings suggesting an arrhythmogenic state (predominance of left-sided cardiac innervation), dysrhythmias occurred in all animals with stellate ganglion ablation, regardless of laterality, but in few vagotomized or control animals. Our results suggest that partial sympathetic innervation may alter cardiac function so that dysrhythmias are more likely to occur during baroreceptor activation.

Elevated blood pressure is not related to saliva flow in patients with Sjögren's syndrome

OBJECTIVE

The purpose of this study was to determine whether systolic and diastolic blood pressures are associated with salivary flow, dry mouth, or dry eye symptoms in patients with primary Sjögren's syndrome as compared with xerostomic control subjects.

STUDY DESIGN

One hundred forty consecutive patients seen at the Sjögren's Syndrome Clinic were categorized retrospectively with various classification schemes: (1) subjective dry mouth; (2) subjective dry eye; (3) European criteria; and (4) international criteria. Data collection included age, gender, systolic blood pressure, diastolic blood pressure, salivary flow rate, focus score, Schirmer's test, and laboratory findings, including antinuclear antibodies, anti-SSA, anti-SSB, IgG, IgA, IgM, erythrocyte sedimentation rate, and rheumatoid factor.

RESULTS

No meaningful associations of salivary flow rates with systolic or diastolic blood pressures were found in patients with Sjögren's syndrome or in xerostomic control subjects. An inverse correlation was seen between salivary flow and elevated diastolic blood pressure in xerostomic control subjects only.

CONCLUSION

Elevated blood pressure was not related to saliva flow in patients with Sjögren's syndrome.

Association between restoration of autonomic modulation in the native sinus node and hemodynamic improvement after cardiac transplantation

BACKGROUND

Little is known about the autonomic control of the native sinus node (NSN) after heart transplantation because its electrical activity is difficult to detect with skin electrodes.

METHODS AND RESULTS

The intracardiac electrogram of the NSN and the donor heart electrocardiogram were measured simultaneously. A total of 351 recordings of 107 heart transplant patients (age 53.6+/-12.3 years) were obtained up to 1 year after transplantation. In a subgroup of 41 patients, consecutive recordings were made. Eleven recordings of heart failure patients (age 56.2+/-6.5 years) awaiting cardiac transplantation were used as controls. To examine a relationship between autonomic indices of the NSN and hemodynamics of the donor heart, intracardiac pressures and cardiac output were recorded in the same session. Heart rate variability (HRV) parameters in time and frequency domain of the NSN showed a significant increase starting at 6 months after transplantation, whereas heart rate of the NSN tended to decrease. Heart rate and HRV parameters remained constant over the first year in the donor heart. Higher values of low-frequency and high-frequency powers in the NSN were associated with lower values of right ventricular, pulmonary artery, and mean atrial pressure and cardiac output. Recordings of patients with rejection could not be distinguished from those without rejection based on the spectral content of HRV of either the NSN or the donor heart.

CONCLUSIONS

These data suggest a restoration of autonomic modulation of the NSN. This restoration is associated with hemodynamic improvement of the donor heart.

Impact of heart transplantation on the safety and feasibility of the dobutamine stress test

BACKGROUND

Dobutamine myocardial perfusion imaging is a useful method for evaluation of coronary artery disease. However, this technique does not allow for ischemia monitoring, which may have an impact on the safety of the test in heart transplant recipients due to cardiac sensory denervation. The aim of this study was to assess the impact of heart transplantation on the feasibility and complications of the dobutamine stress test.

METHODS

We studied 225 heart transplant recipients (mean age 57 +/- 7 years) and a control group of 225 patients without previous transplant matched for age and gender by dobutamine (up to 40 microg/kg per minute) stress myocardial perfusion imaging.

RESULTS

During the test, transplant recipients had a lower prevalence of premature ventricular contractions (23% vs. 37%, p < 0.001) and ventricular tachycardia (0.04% vs 7.5%, p < 0.0001) compared with control patients. By multivariate analysis, heart transplantation was a powerful independent variable associated with a reduced risk of ventricular arrhythmias (chi(2) = 20.8, p < 0.0001) and minor side effects (nausea, dizziness, anxiety, flushing, chills) (chi(2) = 20, p < 0.0001) during dobutamine stress. The target heart rate was reached in 82% of transplant recipients and in 77% of the control group. Overall feasibility (achievement of the target heart rate and/or an ischemic end-point) was 87% in the transplant and 86% in the control group.

CONCLUSIONS

Dobutamine stress myocardial perfusion imaging is a safe and feasible method for evaluation of coronary artery disease in heart transplant recipients. The prevalence of arrhythmias and minor complications using the dobutamine stress test is lower in heart transplant recipients compared with control patients. The independent association between heart transplantation and reduced risk of arrhythmias and minor side effects of the dobutamine stress test indicates that cardiac sensory and autonomic nerve function plays a major role in the induction of these complications during the test.

Vagal reinnervation in the long term after orthotopic heart transplantation

BACKGROUND

Sympathetic reinnervation after orthotopic heart transplantation (HTx) has become an accepted phenomenon, particularly in long-term transplanted patients. Parasympathetic reinnervation, however, still remains questionable.

METHODS

In 38 HTx recipients, mean age of 51.6 +/- 9.7 years (range, 29 to 70 years), with a time span after HTx of 4.6 +/- 2.8 years (0.5 to 10.5 years), we stimulated carotid baroreceptors using periodic neck suction at low (0.1 Hz) and high (0.2 Hz) frequencies to test sympathetic and vagal responses, respectively. Respiratory rate was fixed at 0.25 Hz. We simultaneously recorded surface electrocardiogram, finger blood pressure, respiration and neck pressure signals while patients rested in the supine position. Time series of RR intervals, respiration, and neck and blood pressures were generated and subjected to spectral analysis.

RESULTS

All patients demonstrated a 0.25-Hz peak in RR-interval spectrum, caused by non-autonomic respiratory sinus arrhythmia. Thirteen patients (5. 2 +/- 3.5 years after HTx; range, 0.9 to 10.2 years) showed a baroreflex-induced sharp peak at 0.1 Hz in RR-interval power spectrum during 0.1-Hz neck suction, indicating sympathetic reinnervation. However at 0.2-Hz neck suction, 4 of the 13 sympathetically reinnervated patients displayed a baroreflex-induced 0.2-Hz peak, which could be suppressed with atropine administration-strong evidence for vagal reinnervation.

CONCLUSIONS

Non-invasive carotid baroreflex stimulation is an appropriate tool to prove restoration of autonomic control after orthotopic HTx. Sympathetic reinnervation parallels parasympathetic reinnervation in long-term transplanted patients.