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

Decoding cardiac reinnervation from cardiac autonomic markers: A mathematical model approach

BACKGROUND

Although cardiac autonomic markers (CAMs) are commonly used to assess cardiac reinnervation in heart-transplant patients, their relationship to the degree of sympathetic and vagal cardiac reinnervation is not well understood yet. To study this relationship, we applied a mathematical model of the cardiovascular system and its autonomic control.

METHODS

By simulating varying levels of sympathetic and vagal efferent sinoatrial reinnervation, we analyzed the induced changes in CAMs including resting heart rate (HR), bradycardic and tachycardic HR response to Valsalva maneuver, root mean square of successive differences between normal heartbeats (RMSSD), low-frequency (LF), high-frequency (HF), and total spectral power (TSP).

RESULTS

For assessment of vagal cardiac reinnervation levels >20%, resting HR (ρ = 0.99, p < 0.05), RMSSD (ρ = 0.97, p < 0.05), and TSP (ρ = 0.96, p < 0.05) may be equally suitable as HF-power (ρ = 0.97, p < 0.05). To assess sympathetic reinnervation, LF/HF ratio (ρ = 0.87, p < 0.05) and tachycardic response to Valsalva maneuver (ρ = 0.9, p < 0.05) may be more suitable than LF-power (ρ = 0.77, p < 0.05).

CONCLUSIONS

Our model reports mechanistic relationships between CAMs and levels of efferent autonomic sinoatrial reinnervation. The results indicate differences in the suitability of these markers to assess vagal and sympathetic reinnervation. Although our analysis is purely conceptual, the developed model can help to gain important insights into the genesis of CAMs and their relationship to efferent sinoatrial reinnervation and, thus, provide indications for clinical study evaluation.

Neuromodulation for Atrial Fibrillation Control

Trigger and functional substrate are related to the tone of autonomic nervous system, and the role of the autonomic nerve is more significant in paroxysmal atrial fibrillation (AF) compared to non-paroxysmal AF. We have several options for neuromodulation to help to manage patients with AF. Neuromodulation targets can be divided into efferent and afferent pathways. On the efferent side, block would be an intuitive approach. However, permanent block is hard to achieve due to completeness of the procedure and reinnervation issues. Temporary block such as botulinum toxin injection into ganglionated plexi would be a possible option for post-cardiac surgery AF. Low-level subthreshold stimulation could also prevent AF, but the invasiveness of the procedure is the barrier for the general use. On the afferent side, block is also an option. Various renal denervation approaches are currently under investigation. Auditory vagus nerve stimulation is one of the representative low-level afferent stimulation methods. This technique is noninvasive and easy to apply, so it has the potential to be widely utilized if its efficacy is confirmed.

The Intrinsic Cardiac Nervous System: From Pathophysiology to Therapeutic Implications

The cardiac autonomic nervous system (CANS) plays a pivotal role in cardiac homeostasis as well as in cardiac pathology. The first level of cardiac autonomic control, the intrinsic cardiac nervous system (ICNS), is located within the epicardial fat pads and is physically organized in ganglionated plexi (GPs). The ICNS system does not only contain parasympathetic cardiac efferent neurons, as long believed, but also afferent neurons and local circuit neurons. Thanks to its high degree of connectivity, combined with neuronal plasticity and memory capacity, the ICNS allows for a beat-to-beat control of all cardiac functions and responses as well as integration with extracardiac and higher centers for longer-term cardiovascular reflexes. The present review provides a detailed overview of the current knowledge of the bidirectional connection between the ICNS and the most studied cardiac pathologies/conditions (myocardial infarction, heart failure, arrhythmias and heart transplant) and the potential therapeutic implications. Indeed, GP modulation with efferent activity inhibition, differently achieved, has been studied for atrial fibrillation and functional bradyarrhythmias, while GP modulation with efferent activity stimulation has been evaluated for myocardial infarction, heart failure and ventricular arrhythmias. Electrical therapy has the unique potential to allow for both kinds of ICNS modulation while preserving the anatomical integrity of the system.

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.

The Impact of Beta Blockers on Survival in Heart Transplant Recipients: Insights from the Zabrze HTx Registry

Introduction

The data assessing the impact of beta blocker (BB) medication on survival in patients after heart transplantation (HTx) are scarce and unequivocal; therefore, we investigated this population.

Methods

We retrospectively analyzed the HTx Zabrze Registry of 380 consecutive patients who survived the 30-day postoperative period.

Results

The percentage of patients from the entire cohort taking BBs was as follows: atenolol 24 (17%), bisoprolol 67 (49%), carvedilol 11 (8%), metoprolol 28 (20%), and nebivolol 8 (6%). The patients receiving BBs were older (56.94 ± 14.68 years vs. 52.70 ± 15.35 years, p=0.008) and experienced an onset of HTx earlier in years (11.65 ± 7.04 vs. 7.24 ± 5.78 p ≤ 0.001). They also had higher hematocrit (0.40 ± 0.05 vs. 0.39 ± 0.05, p=0.022) and red blood cells (4.63 (10⁶/μl) ± 0.71 vs. 4.45 (10⁶/μl) ± 0.68, p=0.015). Survival according to BB medication did not differ among the groups (p=0.655) (log-rank test). Univariate Cox proportional hazard regression analysis revealed that the following parameters were associated with unfavorable diagnosis: serum concentration of albumin (g/l) HR: 0.87, 95% CI (0.81–0.94), p=0.0004; fibrinogen (mg/dl) HR: 1.006, 95% CI (1.002–1.008), p=0.0017; and C-reactive protein (mg/l) HR: 1.014, 95% CI (1.004–1.023), p=0.0044.

Conclusions

The use of BBs in our cohort of patients after HTx was not associated with survival benefits.

Evaluation of Cardiac Autonomic Modulation Using Symbolic Dynamics After Cardiac Transplantation

Objective

To characterize the behavior of cardiac autonomic modulation in individuals with different times after orthotopic heart transplantation (HTx) using symbolic dynamics analysis.

Methods

Sixty patients were evaluated after HTx. We recorded their instantaneous R-R intervals (RRi) by cardiac monitor Polar® RS800CX™ (Polar Electro Oy, Kempele, Finland) for 10 minutes. The same sequence of RRi with 256 consecutive beats was used to perform spectral analysis and symbolic dynamics analysis. We used hierarchical clustering to form groups. One-way analysis of variance (ANOVA) (with Holm-Sidak method) or one-way Kruskal-Wallis test (with Dunn´s post-hoc test) was used to analyze the difference between groups. Linear correlation analysis between variables was performed using Pearson’s or Spearman’s tests. P-value < 0.05 was considered statistically significant.

Results

The 0V% index increased, the 2UV% index and the normalized complexity index decreased with an increase of HTx postoperative time. There were a negative correlation between complexity indexes and 0V% and a positive correlation between complexity indexes and 2UV%.

Conclusion

Symbolic dynamics indexes were able to show a specific cardiac autonomic modulation pattern for HTx recipients with different postoperative times.

Persistent but reversible advanced atrio-ventricular block in a heart transplant man induced by dobutamine stress echocardiography

Dobutamine when used for stress echocardiography (DSE), it rarely causes transient atrio-ventricular (AV) block. We report a heart transplant patient with high cardiovascular risk who developed symptomatic advanced AV block during DSE which persisted after termination of dobutamine administration, necessitating pacemaker implantation. To our knowledge, this is the first published case of persistent high grade AV block in a heart transplant patient induced by DSE.

Measures of and changes in heart rate variability in pediatric heart transplant recipients

Heart rate variability is primarily regulated by the autonomic nervous system. Heart transplant recipients undergo surgical denervation of the graft, which results in interruption of autonomic innervation with resultant diminished heart rate variability although some degree of autonomic control may return. This study aimed to characterize heart rate variability in this population. We report a retrospective review of Holter monitor data from transplanted patients between 2005 and 2013. Studies with significant atrial or ventricular arrhythmias were excluded. We evaluated changes over time and compared standard time domain measures to published pediatric normal values. Data were reviewed from 582 monitors in 152 patients. We found that pediatric heart transplant recipients have lower heart rate variability than age-matched controls and higher average heart rate in recipients older than 3 years. There is an increase in measures of variability through the first 3 years post-transplant with plateau after that time. Surgical technique in regard to interruption of the vagus nerve does not affect variability, nor does underlying congenital vs acquired heart disease.

Effect of Heart Rate and Use of Beta Blockers on Mortality After Heart Transplantation

Heart transplantation (HT) recipients may have tachycardia secondary to cardiac denervation. As higher heart rate predicts worse outcomes in cardiovascular disease, we hypothesized that tachycardia and nonuse of β blockers are associated with increased mortality after HT. All patients who underwent HT at our institution from 1987 to 2010 were included. The association of heart rate 3 months after HT and β-blocker use during follow-up to mortality was assessed using Kaplan-Meier and multivariate Cox proportional hazards regression analyses adjusting for clinically relevant baseline variables. From 1987 to 2010, there were 493 HT. After excluding 29 who died within 3 months and 3 with follow-up <3 months, 461 HT recipients (50 ± 2 years; 20% women) were included. Over a follow-up of 12 ± 7 years, selected important univariate predictors of post-HT mortality were older age, male gender, higher body mass index, ischemic cardiomyopathy, longer post-HT intensive care unit stay, and hospitalization and at 3 months, increased mean pulmonary artery pressure, right atrial pressure and pulmonary capillary occlusion pressure, higher heart rate, and nonuse of β blockers during follow-up. In multivariate analysis, older ager, longer hospitalization, higher mean pulmonary artery pressure, higher heart rate at 3 months (hazard ratio 1.02 per beat, 95% confidence interval 1.008 to 1.035, p = 0.02) and nonuse of β blockers (hazard ratio 1.43, 95% confidence interval 1.002 to 2.031, p <0.05) were associated with mortality. In conclusion, in a large single-center cohort of HT recipients, higher heart rate and nonuse of β blockers were independently associated with higher mortality.