Pulmonary Artery Banding #4: Left Ventricular Training in ccTGA Before Double-Switch Repair

1. Why LV Training Is Necessary in ccTGA

Congenitally corrected transposition of the great arteries (ccTGA) is defined by atrioventricular discordance and ventriculoarterial discordance. Systemic venous blood passes through the morphologic mitral valve into the morphologic left ventricle (LV) and then to the pulmonary artery, whereas pulmonary venous blood passes through the morphologic tricuspid valve into the morphologic right ventricle (RV) and then to the aorta.

Although the circulation is physiologically “corrected,” the ventricular workload is reversed: the morphologic RV supports the systemic circulation, while the morphologic LV functions as the subpulmonary ventricle. Anatomic repair with a double-switch operation seeks to restore the morphologic LV to the systemic position and the morphologic RV to the pulmonary position.

A fundamental limitation is that a morphologic LV exposed to low pulmonary arterial afterload for a prolonged period may become insufficiently prepared to support systemic pressure. Pulmonary artery banding (PAB) is therefore used in selected patients to retrain the morphologic LV before anatomic repair by imposing a controlled pressure load. The objective is not simply to raise LV pressure, but to create a ventricle with sufficient myocardial mass, function, and pressure-generating reserve to sustain the systemic circulation after the double switch [1].

2. Progressive LV Deconditioning as PVR Falls

During fetal life and the early neonatal period, pulmonary vascular resistance (PVR) is relatively high. The morphologic LV in ccTGA therefore initially ejects against a substantial afterload and generates relatively high systolic pressure.

As PVR normally falls after birth, LV afterload decreases. This process is particularly important in patients without an unrestricted ventricular septal defect (VSD) or significant subpulmonary obstruction, because no mechanism remains to maintain systemic-range pressure in the morphologic LV. Over time, the LV becomes a low-pressure subpulmonary ventricle.

The resulting process of LV deconditioning includes:

• Reduced LV systolic pressure
• Regression of myocardial mass
• Reduction in LV wall thickness
• Alteration in ventricular geometry
• Loss of capacity to tolerate an abrupt increase in afterload

Patients entering LV-retraining programs therefore typically have a markedly sub-systemic LV pressure. In one contemporary series, the mean baseline LV/RV systolic pressure ratio was approximately 0.39, illustrating the degree of deconditioning that may be present before PAB [2].

The surgical problem becomes evident at double-switch repair. Once the arterial switch places the morphologic LV in continuity with the aorta, that ventricle must immediately transition from pulmonary to systemic workload. If it remains inadequately conditioned, postoperative low cardiac output and LV dysfunction may result.

3. Physiologic Principle of PAB for LV Retraining

PAB creates a fixed obstruction between the morphologic LV and the distal pulmonary circulation. Because the LV ejects into the pulmonary artery in ccTGA, the band increases LV afterload and systolic pressure.

The intended physiologic sequence is:

PAB → increased LV afterload → increased LV systolic pressure → myocardial hypertrophic adaptation → improved systemic-pressure reserve

This use of PAB is fundamentally different from conventional banding performed to control excessive pulmonary blood flow. In LV retraining, the principal target is myocardial conditioning, not simply reduction of pulmonary flow.

Importantly, the ventricular response is not instantaneous. LV pressure increases immediately after band placement, whereas myocardial mass develops over a longer period. Mainwaring and colleagues demonstrated this temporal and physiologic distinction in patients undergoing retraining: most patients showed a predictable relationship between increasing LV pressure and subsequent increases in LV mass, but pressure loading and structural adaptation were not synonymous [3].

Thus, achieving a high LV pressure in the operating room does not establish that the LV is ready to become the systemic ventricle.

4. Pressure Loading Versus True Ventricular Adaptation

The key endpoint of LV training is adaptive hypertrophy with preserved ventricular performance.

In a series examining the relationship between LV pressure and mass, approximately 90% of patients demonstrated a relatively proportional increase in myocardial mass as pressure increased. However, approximately 10% developed disproportionate myocardial hypertrophy relative to the achieved pressure load. Two of these three patients ultimately failed LV retraining [3].

This observation is clinically important because hypertrophy itself is not necessarily evidence of successful preparation. Excessive wall thickening without appropriate improvement in pressure-generating capacity may represent maladaptive remodeling rather than effective training.

Therefore, successful retraining requires integration of:

• LV systolic pressure
• LV myocardial mass and wall thickness
• LV dimensions
• LV systolic function
• LV diastolic tolerance
• Interventricular septal configuration
• Mitral valve function
• Systemic RV and tricuspid valve function
• Clinical tolerance of the imposed pressure load

The central principle is:

LV pressure is the training stimulus; durable myocardial adaptation is the therapeutic endpoint.

5. Who Requires LV Retraining?

Not every patient with ccTGA requires PAB before double-switch repair.

Patients with an unrestricted VSD or significant subpulmonary stenosis may maintain a relatively pressure-loaded morphologic LV and therefore may already have sufficient myocardial preparation for anatomic repair. In contrast, patients with an intact ventricular septum, no VSD, or a restrictive VSD and no effective pulmonary outflow obstruction are at greatest risk for progressive LV involution [2].

Typical features prompting consideration of retraining include:

• ccTGA without an unrestricted VSD
• Absence of significant subpulmonary obstruction
• Low LV/RV systolic pressure ratio
• Reduced LV wall thickness or myocardial mass
• Septal configuration reflecting a low-pressure LV
• A planned double-switch repair in a patient whose LV is considered insufficiently prepared for systemic work

The severity of deconditioning varies. In an older patient reported by Honjo and colleagues, the LV/RV pressure ratio was only 0.32 before retraining [4]. Such markedly low-pressure ventricles require careful staged preparation rather than abrupt conversion to systemic loading.

6. How the LV Is Assessed During Retraining

Evaluation of LV preparedness is multimodal.

Hemodynamic assessment

Cardiac catheterization can directly define:

• LV systolic pressure
• RV/systemic ventricular systolic pressure
• LV/RV pressure ratio
• Distal pulmonary artery pressure
• Filling pressures
• Hemodynamic response to the band

The LV/RV systolic pressure ratio is a useful marker of the degree of pressure preparation. During successful retraining, this ratio generally progresses from markedly sub-systemic values toward systemic levels.

For example, in the teenage patient described by Honjo and colleagues, the LV/RV pressure ratio increased from 0.32 before training to 0.93 after staged PAB, together with a substantial increase in LV wall thickness and mass [4]. Other staged-repair series have similarly achieved LV pressure approaching systemic pressure before proceeding to double-switch repair [5].

Imaging assessment

Serial echocardiography evaluates:

• LV posterior wall thickness
• LV dimensions
• Global systolic function
• Septal position
• Mitral regurgitation
• Systemic RV function
• Tricuspid regurgitation

Cardiac magnetic resonance imaging may provide more detailed assessment of ventricular volumes and myocardial mass when needed.

No single measurement independently establishes readiness. A systemic-range LV pressure without adequate mass or with deteriorating ventricular function should not be interpreted as successful retraining.

7. Technical Balance During Pulmonary Artery Banding

The band must provide sufficient afterload to stimulate adaptation while avoiding acute LV injury.

If the PAB is too loose, LV pressure may remain insufficient and retraining may be ineffective. If it is excessively tight, acute consequences can include:

• LV systolic dysfunction
• Elevated LV filling pressure
• Pulmonary venous hypertension
• Reduced cardiac output
• Mitral regurgitation
• Myocardial ischemia
• Hemodynamic instability

The degree of banding is therefore individualized according to ventricular response rather than determined solely by an anatomical band circumference or a universal Doppler gradient.

Furthermore, the effective obstruction changes as the child grows and as the ventricle adapts. A band that initially provides appropriate training may later become insufficient or excessively restrictive. Consequently, rebanding is common. In one 24-patient retraining series, 9 of the 18 patients who eventually underwent double-switch repair required a second PAB [2].

This emphasizes that LV retraining is a longitudinal program rather than a single operation.

8. Age Is a Major Determinant of Retraining Success

The ability of the LV to adapt to renewed pressure loading is strongly age-dependent.

Infancy appears to provide the most favorable substrate for adaptive ventricular hypertrophy. Barron and Mahendran emphasized that the best results of LV retraining are generally achieved when banding is initiated early, with increasing concern when attempting retraining beyond approximately 2 years of age [1].

This relationship was demonstrated clinically by Myers and colleagues. Among patients undergoing PAB for LV preparation, moderate or greater LV dysfunction after subsequent anatomic repair developed in 4 of 6 patients banded after 2 years of age, compared with 0 of 12 patients banded before 2 years [6]. Similarly, postoperative LV dysfunction was more frequent when definitive anatomic repair occurred at an older age.

Age should not be treated as an absolute contraindication. Successful retraining has been reported in older children and even adolescents [4]. However, these cases may require prolonged or repeated banding and should not be assumed to have the same myocardial adaptive potential as infants.

Therefore:

If anatomic repair is the intended long-term strategy and LV retraining will be required, early recognition and early initiation of training are preferable.

9. Duration of LV Training

There is no universally appropriate training interval.

Reported retraining periods range from weeks to several years, reflecting substantial heterogeneity in age, baseline LV pressure, ventricular mass, anatomy, and response to PAB [2,4,6].

The decision to proceed to double-switch repair should therefore be based on physiologic readiness rather than elapsed time.

Features supporting readiness include:

• LV pressure approaching systemic range
• Appropriate increase in LV wall thickness and myocardial mass
• Preserved LV systolic function
• Acceptable filling pressures
• Favorable septal configuration
• Absence of important mitral regurgitation
• Stable clinical tolerance of the band
• Overall anatomical suitability for the planned double switch

Conversely, pressure elevation accompanied by progressive dysfunction, excessive hypertrophy, elevated filling pressure, or inadequate increase in functional reserve should raise concern for unsuccessful or maladaptive training.

10. Pressure Plus Volume Loading: An Alternative Retraining Strategy

Conventional PAB predominantly produces pressure loading. An alternative approach has been developed to combine pressure loading with increased LV preload.

Zartner and colleagues described enhanced LV training using a relatively loose PAB together with creation of an atrial communication, thereby increasing both LV afterload and volume load. Six patients underwent this strategy; systemic LV pressure was achieved without the repeated sequential band tightening typically required in conventional retraining, and the patients proceeding to double switch had favorable outcomes [7].

The conceptual advantages of combined loading include:

• More physiologic ventricular conditioning
• Increased LV volume as well as myocardial mass
• Dynamic modulation of loading conditions
• Potential reduction in excessive fixed pressure stress
• Reduced need for repeated PAB adjustment

The experience remains limited, and conventional PAB remains the better-established strategy. Nevertheless, these observations reinforce an important concept: preparing the LV for systemic work involves more than simply maximizing pressure.

11. Transition to the Double-Switch Operation

Once the LV is considered adequately prepared, definitive anatomic repair can be performed.

For ccTGA without major LV outflow obstruction, this commonly consists of:

1. Atrial switch to redirect systemic and pulmonary venous return
2. Arterial switch to restore the morphologic LV to the aorta and morphologic RV to the pulmonary artery

Depending on anatomy and institutional strategy, the atrial-level component may involve a Senning procedure or a hemi-Mustard/bidirectional Glenn configuration.

After repair:

Morphologic LV → systemic circulation

Morphologic RV → pulmonary circulation

PAB therefore serves as the physiologic bridge between a deconditioned subpulmonary LV and a durable systemic LV.

12. Outcomes After LV Retraining and Double Switch

Clinical results demonstrate that appropriately selected patients can achieve excellent early and mid-term outcomes.

In the 24-patient Stanford retraining series, 18 patients (75%) ultimately underwent double-switch repair, with no operative mortality. There was no late mortality among those undergoing double switch during a mean follow-up of approximately 5 years [2].

More recent experience has reinforced these findings. In a contemporary series of 45 patients undergoing double switch after LV retraining, there were no in-hospital deaths. At follow-up, 41 of 44 survivors (93%) had normal or low-normal LV function, and 91% had no or trace mitral regurgitation. Early and mid-term survival were 100% and 97%, respectively [8].

These results support PAB-based retraining as a viable pathway to anatomic repair in carefully selected patients with a regressed morphologic LV.

13. The Important Limitation: Late LV Dysfunction

Successful completion of retraining and double switch does not guarantee permanent normal LV function.

Long-term observations of retrained ventricles have raised concern that some patients develop late LV dysfunction after apparently successful anatomic repair [9]. This finding is particularly relevant when the LV underwent prolonged deconditioning before retraining or when banding was initiated at an older age [6].

A pressure-trained LV may therefore not be biologically identical to a ventricle that has supported the systemic circulation from birth. Adaptive hypertrophy, myocardial architecture, coronary reserve, fibrosis, and diastolic function may all influence long-term performance.

For this reason, lifelong surveillance after double switch should include assessment of:

• Systemic LV systolic function
• LV dimensions and remodeling
• Mitral valve function
• Neo-aortic valve function
• Outflow tract obstruction
• Atrial-switch pathway obstruction
• Arrhythmias and conduction disease
• Exercise capacity and clinical heart failure

The success of LV training should ultimately be judged not only by the ability to reach the double-switch operation, but by the durability of the morphologic LV as the systemic ventricle.

14. Key Surgical Principle

In ccTGA without an unrestricted VSD or significant pulmonary stenosis, the morphologic LV may progressively decondition as PVR falls. When anatomic repair is planned, a severely regressed LV cannot simply be transferred from the pulmonary to the systemic circulation.

PAB provides controlled pressure loading that can restore LV systolic pressure and stimulate myocardial hypertrophy. The response is most predictable when retraining begins in infancy, while older age is associated with a greater risk of incomplete retraining and late LV dysfunction [1,6].

The objective should therefore not be expressed simply as “achieving systemic LV pressure.” The real endpoint is:

a systemic-pressure LV with appropriate myocardial mass, preserved function, acceptable filling characteristics, and sufficient durable reserve to support the systemic circulation after double-switch repair.

References

[1] Barron DJ, Mahendran K. Left ventricular re-training: feasibility and effectiveness—what are the limits? Semin Thorac Cardiovasc Surg Pediatr Card Surg Annu. 2019;22:43-50.

[2] Ibrahimiye AN, Mainwaring RD, Patrick WL, Downey L, Yarlagadda V, Hanley FL. Left ventricular retraining and double switch in patients with congenitally corrected transposition of the great arteries. World J Pediatr Congenit Heart Surg. 2017;8(2):203-209.

[3] Mainwaring RD, Patrick WL, Arunamata A, Chan F, Newman B, Rosenblatt TR, Kamra K, Hanley FL. Left ventricular retraining in corrected transposition: relationship between pressure and mass. J Thorac Cardiovasc Surg. 2020;159(6):2356-2366.

[4] Honjo O, Kawada M, Akagi T, Kotani Y, Ishino K, Sano S. Left ventricular retraining and anatomic correction in teenage patient with congenitally corrected transposition of the great arteries. Circ J. 2007;71(4):613-616.

[5] Cui B, Li S, Yan J, Shen X, Wang X, Yang K, Hua Z, Wang Q, Tian M. The results of a two-stage double switch operation for congenital corrected transposition of the great arteries with a deconditioned morphologically left ventricle. Interact Cardiovasc Thorac Surg. 2014;19(6):921-925.

[6] Myers PO, del Nido PJ, Geva T, Bautista-Hernandez V, Chen P, Mayer JE Jr, Emani SM. Impact of age and duration of banding on left ventricular preparation before anatomic repair for congenitally corrected transposition of the great arteries. Ann Thorac Surg. 2013;96(2):603-610.

[7] Zartner PA, Schneider MB, Asfour B, Hraška V. Enhanced left ventricular training in corrected transposition of the great arteries by increasing the preload. Eur J Cardiothorac Surg. 2016;49(6):1571-1576.

[8] Mac Felmly L, Mainwaring RD, Ho DY, Arunamata A, Algaze C, Hanley FL. Results of the double switch operation in patients who previously underwent left ventricular retraining. World J Pediatr Congenit Heart Surg. 2024;15(3):279-286.

[9] Brawn WJ, Barron DJ, Jones TJJ, Quinn DW. The fate of the retrained left ventricle after double switch procedure for congenitally corrected transposition of the great arteries. Semin Thorac Cardiovasc Surg Pediatr Card Surg Annu. 2008;11:69-73.