Denervated heart physiology

Surgical approach (context: orthotopic heart transplantation)

Recipient cardiectomy on cardiopulmonary bypass (CPB), donor heart implanted with atrial and great vessel anastomoses
- Biatrial technique (older): donor atria sewn to recipient atrial cuffs → larger atria, more tricuspid regurgitation/arrhythmias
- Bicaval technique (common): separate SVC and IVC anastomoses + LA cuff → better atrial geometry, less TR/arrhythmia
Aortic and pulmonary artery anastomoses, de-airing, reperfusion, wean from CPB with inotropes/vasopressors as needed
Denervation occurs because autonomic cardiac nerves are transected during explant/implant (variable partial reinnervation over months–years)

Anaesthetic management (for heart transplant / denervated heart patient undergoing surgery)

Type of anaesthesia: General anaesthesia (cardiac surgery), for non-cardiac surgery GA or regional may be used with haemodynamic goals in mind
Airway: ETT for transplant, for minor non-cardiac surgery ETT or SGA depending on aspiration risk and procedure
Duration: transplant typically 4–8+ hours (centre/complexity dependent), non-cardiac varies
How painful: sternotomy = severe, requires multimodal analgesia (opioids ± regional fascial plane blocks where appropriate) while avoiding haemodynamic instability
- Neuraxial techniques in transplant are uncommon due to anticoagulation/CPB and haemodynamic considerations
Monitoring (transplant): invasive arterial line, CVC, often PA catheter/TOE, pacing capability, frequent ABGs, electrolytes, lactate
Key physiological principles: preload dependence, blunted HR responses, reliance on circulating catecholamines, treat hypotension with direct-acting agents

Definition and causes

Denervated heart: loss of sympathetic and parasympathetic (vagal) innervation to SA node, AV node, and myocardium
Commonest clinical model: orthotopic heart transplantation
Other contexts: surgical cardiac denervation (rare), advanced autonomic neuropathy (e.g. diabetes) causes partial functional denervation
Reinnervation: variable, often partial (sympathetic more than parasympathetic), may occur months–years post-transplant and is incomplete/heterogeneous

Baseline physiology in the denervated heart

Resting HR typically higher (often ~90–110 bpm) due to loss of vagal tone
Loss of rapid reflex control of HR and contractility (baroreceptor-mediated changes are absent at the heart)
- Baroreflex still acts on peripheral vasculature (sympathetic outflow to vessels intact) → SVR can change, but HR does not respond appropriately
Cardiac output regulation relies more on preload (Frank–Starling) and circulating catecholamines (slower onset)
Reduced HR variability, absent respiratory sinus arrhythmia
Exercise response: delayed rise in HR and contractility, peak HR lower, slower recovery after exercise

Autonomic reflexes and pharmacology: what changes?

Vagal manoeuvres (carotid sinus massage, Valsalva) have little/no effect on HR/AV conduction
Atropine/glycopyrrolate: minimal effect on HR (no vagal tone to block), may still be used for antisialagogue/other indications but not for bradycardia treatment
Indirect-acting sympathomimetics (e.g. ephedrine) may have reduced/unpredictable chronotropic effect because they rely on presynaptic noradrenaline release
Direct-acting agents work: adrenaline, noradrenaline, phenylephrine, isoprenaline, dobutamine (act at receptors on myocardium/vessels)
- Phenylephrine increases SVR, HR may not reflexly fall (no vagal reflex) → can increase BP without bradycardia
Adenosine: still acts directly on AV node, can terminate AVNRT but may cause prolonged AV block/asystole—use caution and resuscitation readiness
Neostigmine reversal: can cause bradycardia/asystole in transplant patients via non-vagal mechanisms (e.g. direct muscarinic effects on intrinsic cardiac neurons/denervation hypersensitivity), atropine may not reliably prevent/treat
- Practical: consider sugammadex for aminosteroid NMBAs where appropriate, if neostigmine used, be prepared for pacing/direct chronotropes (isoprenaline/adrenaline)
Denervation hypersensitivity: upregulation of postsynaptic receptors may increase sensitivity to catecholamines (variable, more relevant early post-transplant)

Haemodynamic implications for anaesthesia

Preload dependence: avoid hypovolaemia, excessive venodilation, and sudden reductions in venous return (e.g. high neuraxial block, rapid position changes, pneumoperitoneum)
Blunted tachycardic response to hypotension/anaemia/light anaesthesia: rely on BP trends, stroke volume, and signs other than HR to judge depth/physiology
Treat hypotension: first optimise preload, then use direct-acting vasopressors/inotropes (phenylephrine/noradrenaline/adrenaline) rather than ephedrine as first-line
Bradycardia management: atropine often ineffective → use isoprenaline/adrenaline, consider pacing (external/transvenous) depending on context
Arrhythmias: atrial arrhythmias and conduction issues can occur, transplanted hearts may have dual P waves (recipient atrial remnant + donor atrium) depending on technique

Respiratory and ventilatory considerations

Avoid hypoxia, hypercapnia, acidosis: all increase PVR and can precipitate RV failure (especially if pulmonary hypertension present pre-transplant)
Positive pressure ventilation reduces venous return, titrate PEEP carefully and monitor stroke volume/BP

Perioperative issues in transplant recipients (important FRCA add-ons)

Immunosuppression: infection risk, strict asepsis, consider perioperative antimicrobial prophylaxis as per local protocol
Drug interactions: calcineurin inhibitors (tacrolimus/ciclosporin) interact with macrolides/azole antifungals, nephrotoxicity affects fluid/NSAID choices
Coronary allograft vasculopathy: can cause silent ischaemia (denervation) → ischaemia may present as heart failure/arrhythmia rather than angina
Rejection: may present with reduced exercise tolerance, arrhythmias, heart failure, perioperative decompensation risk

Key drug response summary (high-yield table in words)

Reduced/absent effect: atropine, glycopyrrolate (chronotropy), vagal manoeuvres, ephedrine (variable/reduced chronotropy)
Preserved effect: adrenaline, noradrenaline, phenylephrine, isoprenaline, dobutamine, adenosine (AV node), amiodarone (antiarrhythmic)
Potentially exaggerated/unpredictable: catecholamines (denervation hypersensitivity), neostigmine (bradycardia/asystole risk)

Test yourself…

Explain the physiological consequences of cardiac denervation after heart transplantation.

Structure your answer: baseline HR, reflexes, CO control, exercise response.

Loss of parasympathetic and sympathetic cardiac nerves → loss of rapid autonomic control of SA/AV node and myocardium
Resting HR higher due to loss of vagal tone, reduced HR variability
No reflex tachycardia/bradycardia in response to BP changes, baroreflex effects on vessels remain
CO becomes more preload dependent, stress/exercise HR rise is delayed and mediated by circulating catecholamines

A transplant patient becomes hypotensive after induction. HR is unchanged. Why, and how do you treat it?

Examiner wants: mechanism + practical, drug-specific management.

HR unchanged because cardiac autonomic reflexes are absent, hypotension from vasodilation/reduced preload will not trigger reflex tachycardia
Treat causes: reduce anaesthetic depth if appropriate, optimise preload (fluids, leg raise), address bleeding
Use direct-acting vasopressors/inotropes: phenylephrine or noradrenaline for vasodilation, adrenaline/dobutamine if low contractility
Ephedrine may be less effective/unpredictable (indirect action)

Why is atropine often ineffective for bradycardia in a denervated heart, and what are your alternatives?

Core pharmacology viva.

Atropine blocks muscarinic receptors to remove vagal tone, in a denervated heart there is little/no vagal input to block
Alternatives: direct chronotropes (isoprenaline, adrenaline) and pacing (transcutaneous/transvenous) depending on severity
Correct reversible causes: hypoxia, hyperkalaemia, myocardial ischaemia, drug effects

Discuss the response of a denervated heart to ephedrine vs phenylephrine vs adrenaline.

Focus on indirect vs direct sympathomimetics and reflexes.

Ephedrine: mixed but largely indirect (noradrenaline release) → reduced/unpredictable chronotropy/inotropy in denervated heart
Phenylephrine: direct α1 agonist → increases SVR and BP, no reflex bradycardia expected
Adrenaline: direct β1/β2/α effects → reliable chronotropy/inotropy (dose dependent) and vasopressor effect at higher doses

A heart transplant recipient needs neuromuscular blockade reversal. What are the issues with neostigmine and what would you do?

This has appeared repeatedly as an FRCA-style viva topic (denervated heart + reversal).

Neostigmine can cause profound bradycardia/asystole in transplant recipients, atropine may not reliably prevent or treat it
Prefer sugammadex for rocuronium/vecuronium where suitable (renal function, availability, anaphylaxis risk considered)
If neostigmine used: ensure monitoring, have direct chronotrope ready (isoprenaline/adrenaline) and pacing capability

How does a denervated heart respond to exercise and why?

Mechanism-based explanation required.

Initial increase in CO mainly via increased venous return and stroke volume (Frank–Starling)
HR rise is delayed because it depends on circulating catecholamines rather than direct sympathetic nerves
Lower peak HR and slower recovery after exercise

What ECG features might you see after heart transplantation and why can there be two P waves?

Links surgical technique to physiology.

Depending on anastomotic technique, residual recipient atrial tissue can remain electrically active but disconnected from donor atrium/AV node
This can produce dual P waves (one from recipient atrium, one from donor SA node) with only donor atrial activity conducting to ventricles
Atrial arrhythmias and conduction abnormalities may occur, particularly with biatrial technique

Adenosine for SVT in a transplant patient: does it work and what are the risks?

Direct AV nodal action is preserved, safety considerations are key.

Adenosine acts directly on AV node receptors → can terminate AV node–dependent SVT
Risk of prolonged AV block/asystole, have resuscitation drugs and pacing/defib available, consider lower initial dose and senior support per local policy

Why might myocardial ischaemia be clinically silent in a transplanted (denervated) heart, and what are the implications for perioperative monitoring?

Classic FRCA concept: denervation abolishes angina.

Afferent pain fibres are interrupted → angina may be absent despite ischaemia
Ischaemia may present as heart failure, arrhythmias, hypotension, or ECG changes rather than pain
Implications: vigilant ECG monitoring, haemodynamic monitoring, low threshold for troponin/echo if unstable, optimise oxygen delivery

Outline key anaesthetic goals for non-cardiac surgery in a stable heart transplant recipient.

A common FRCA-style long viva: physiology + practical management.

Maintain preload and avoid sudden vasodilation, treat hypotension with direct-acting vasopressors
Do not rely on HR as a marker of pain/light anaesthesia, use BP, stroke volume surrogates, ET agent concentration, clinical signs
Plan for bradycardia: atropine may fail, have isoprenaline/adrenaline and pacing access available for higher-risk cases
Infection prevention and immunosuppression considerations, avoid nephrotoxins if renal impairment from calcineurin inhibitors