Arrhythmia Management After Mustard or Senning Repair
Adults who underwent a Mustard or Senning operation for transposition of the great arteries are a growing clinical population. These atrial-switch repairs redirect venous blood through baffles so the morphologic left ventricle supports the systemic circulation. With longer survival, atrial tachycardia, atrial flutter and intra-atrial reentrant tachycardia (IART) have become common reasons for hospital presentation, syncope, heart-failure symptoms and reduced quality of life. Arrhythmias can also compromise systemic ventricular function and complicate anticoagulation and device follow-up.
This review focuses on practical management of atrial arrhythmias after these repairs, from initial identification through long-term prevention. It emphasises distinguishing IART from other supraventricular rhythms, assessing systemic ventricular and baffle-related risks, and selecting rate control, rhythm control, ablation and anticoagulation for the individual. In Australia, care often begins with a GP referral and Medicare-covered public or private assessment, while complex cases are concentrated around tertiary adult congenital services in Melbourne, Sydney and Brisbane.
Why the Atria Become Vulnerable
Both operations alter atrial anatomy and conduction. Mustard uses a pericardial or synthetic baffle, while Senning forms channels from native atrial tissue. This rerouting can stretch atrial muscle, injure the sinus node and leave areas of slow conduction. Sinus node dysfunction and atrial enlargement consequently become more common with age.
Conduction bottlenecks around surgical margins, baffles and venous connections can support macroreentry. Blood may travel around the baffle, through atrial walls and back across a protected isthmus, producing IART or atypical atrial flutter. Scar-related automatic foci can also generate focal atrial tachycardia, allowing several mechanisms to coexist in one patient.
Risk rises with time after surgery, atrial dilatation, impaired ventricular function, baffle obstruction and significant venovenous collateral flow. Tachycardia may reduce cardiac filling, disrupt atrioventricular synchrony and provoke heart failure or syncope. Persistent arrhythmia also increases thromboembolic risk and makes repeated cardioversion or device-based therapy more likely.
Recognising the Arrhythmia
Patients may describe palpitations, unusual fatigue, breathlessness, reduced exercise tolerance, presyncope or syncope. Some episodes are asymptomatic and detected on a device or routine ECG. The pulse pattern can help: IART and atrial flutter may appear regular, whereas focal atrial tachycardia may have an abrupt onset and variable conduction. Baffle-related venous obstruction can also cause desaturation, making the episode feel different from ordinary palpitations.
A 12-lead ECG during the tachycardia is essential. IART often produces discrete atrial waves at a rate faster than sinus rhythm, while typical flutter may show a sawtooth pattern in standard leads. Atypical flutter and concealed atrial activity can be difficult to identify. A wide-complex rhythm must not automatically be assumed to be ventricular tachycardia; ventricular dysfunction and scar make that distinction especially important after congenital heart surgery.
Device interrogation should accompany every available rhythm recording. Pacemaker or ICD electrograms can identify atrial pacing, atrial undersensing, mode changes and the onset of an arrhythmia. Ambulatory monitoring, exercise testing and selected electrophysiology studies can establish the mechanism. The clinician should also distinguish IART from sinus tachycardia caused by heart failure, atrioventricular nodal or accessory-pathway tachycardia, and ventricular tachycardia.
Assessment and Risk Stratification
Assessment should cover arrhythmia frequency, precipitating factors, medication use, adherence to anticoagulation and any history of syncope, transient ischaemic attack or stroke. Physical examination includes systemic oxygen saturation, signs of congestion, blood pressure and ventricular rhythm. The broader congenital assessment should establish current systemic ventricular function, pulmonary pressures, residual anatomical lesions and whether the patient has a mechanical valve or other device.
Echocardiography is the baseline imaging test, while cardiac MRI can define ventricular volumes, function and fibrosis when appropriate. Assessment of baffle patency and venovenous collaterals may require additional imaging or catheterisation. Blood tests should include electrolytes, magnesium, renal and liver function, thyroid function, full blood count and brain natriuretic peptide when heart failure is suspected. Medication review should identify QT prolongation, negative inotropic effects, renal dosing issues and possible digoxin toxicity.
Stroke prevention requires more than applying a standard atrial fibrillation score mechanically. CHA₂DS₂-VASc remains a useful minimum estimate, but congenital anatomy, prior thromboembolism, atrial substrate and other risk factors may influence the decision. Cardioversion, ablation and long-term anticoagulation should be planned together. Clinicians can use the journal’s themed collections to locate relevant congenital heart disease and electrophysiology reviews for background evidence.
Acute Stabilisation
An unstable episode requires immediate synchronised cardioversion. Instability includes ongoing syncope, shock, ischaemic chest pain, acute pulmonary oedema or severe hypoxaemia. In Australia, emergency activation is through 000. Monitoring, intravenous access and oxygen should be established while preparing defibrillation, with attention to the possibility of an atrial thrombus when cardioversion duration is uncertain.
In a stable patient, treatment depends on the mechanism and systemic ventricular function. A beta-blocker may slow atrial conduction and improve ventricular rate. Diltiazem or verapamil may be considered when ventricular function and blood pressure permit, but they should not be used in decompensated ventricular failure. Adenosine can help diagnose a regular narrow-complex atrioventricular node-dependent tachycardia, yet it does not reliably terminate IART and may cause hypotension. Digoxin can assist in selected cases, although it is less effective during exertion and requires careful renal dosing.
Electrolyte abnormalities, infection, thyroid dysfunction, dehydration, anaemia and worsening heart failure should be corrected. Persistent symptomatic arrhythmia may require specialist rhythm control, cardioversion or ablation rather than repeated short-term treatment. If atrial flutter or IART has been present for an uncertain period, peri-cardioversion anticoagulation should be considered according to thromboembolic risk, while recognising that the evidence specific to IART is less extensive than for atrial fibrillation.
Long-Term Rhythm and Stroke Control
Long-term rate control commonly starts with a beta-blocker, adjusted to symptoms, blood pressure and ventricular function. Diltiazem or verapamil are alternatives in patients without significant ventricular dysfunction. Digoxin is less useful during active exertion and may be unsuitable in renal impairment or drug interactions. The goal is not simply a lower heart rate: atrioventricular synchrony, systemic output and symptom control must also be assessed.
Rhythm control may be considered for recurrent, symptomatic or poorly tolerated episodes. Amiodarone is often effective, but cumulative exposure makes long-term toxicity a major concern in younger adults. Sotalol may be considered with renal and QT monitoring. Flecainide and propafenone should not be used in significant structural heart disease or ventricular dysfunction. Drug selection must account for pregnancy plans, comorbidities, QT interval, renal function and interactions.
Anticoagulation decisions should distinguish atrial fibrillation, flutter and IART while considering the patient’s total thromboembolic and bleeding risk. A direct oral anticoagulant may be suitable when there is no mechanical valve and renal function permits; mechanical prostheses require warfarin. Many direct oral anticoagulants are PBS-listed in Australia, although prescribing rules, dosing and ongoing dispensing should be confirmed with a specialist and pharmacist.
Long-term care is well suited to shared management. Regional cardiologists and congenital nurses can review symptoms, anticoagulation and ECG recordings, while an adult congenital electrophysiologist coordinates rhythm strategy. Telehealth reduces travel for patients in rural or remote Australia, although device interrogation, imaging and medication changes may still require attendance at a tertiary centre. Remote monitoring can shorten the interval between symptoms and specialist review.
Ablation, Devices and Special Considerations
Catheter ablation is an important option for symptomatic recurrent IART or atrial flutter, particularly when medication control is ineffective. Three-dimensional electroanatomical mapping identifies macroreentrant circuits around the baffle and surgical channels. Outcomes vary because multiple protected isthmi and venous connections may sustain the arrhythmia. Baffle injury, vascular access difficulties and the need for repeat procedures require careful planning at an experienced centre.
Ablation may be combined with pacing or, in selected refractory cases, a hybrid surgical and endocardial approach. Atrial or ventricular pacing can suppress some atrial tachycardias, but lead position and atrioventricular synchrony are particularly important when the systemic ventricle already has impaired function. An implantable cardioverter-defibrillator may be indicated for independent ventricular risk, but atrial arrhythmia alone does not justify one. Pre-existing leads, venous anatomy and future extraction needs should be considered before implantation.
Ageing, pregnancy, previous device surgery and limited local access can alter the balance between ablation, medication and palliative rhythm management. The wider journal platform also contains nonclinical consumer material, such as an Ethereum gambling resource, which has no role in clinical education. Decisions should instead rely on peer-reviewed articles, guidelines and specialist assessment. Patients with complex anatomy benefit from joint review by adult congenital cardiology, electrophysiology, imaging, pharmacy and device teams.
Clinicians should establish a clear pathway for adults with Mustard or Senning repairs who develop recurrent atrial tachycardia. Referral should include a rhythm tracing, device report, echocardiographic findings, medication list, anticoagulation history and records of syncope or heart failure. Early involvement of an adult congenital electrophysiologist allows the team to define the mechanism, protect systemic ventricular function and prevent recurrent admissions.
Patients should receive written instructions about medication adherence, anticoagulation, device follow-up and warning symptoms. Sustained palpitations with breathlessness, chest pain, faintness or marked light-headedness require urgent assessment, while collapse or severe breathlessness should prompt an ambulance through 000. The immediate priority is to refer recurrent or poorly tolerated episodes for combined congenital and electrophysiology review and to ensure that every patient has a coordinated plan for rhythm control, stroke prevention and device care.