The future of interventional cardiology

Aortic valve stenosis is one of the most acute and chronic cardiovascular disease conditions. Bicuspid aortic valve is the most common congenital heart abnormality and affected individuals have a 50% chance of developing severe aortic valve stenosis during their lifetime. In aortic valve disease (both aortic valve stenosis and bicuspid aortic valve), the heart valves are damaged and do not work properly. This condition can rapidly affect the pumping action of the heart and can progress to heart failure. Heart failure is a deadly disease affecting at least 26 million people worldwide and its prevalence is increasing with high mortality and morbidity.1 Most importantly, aortic valve disease commonly coexists with other cardiovascular diseases, giving rise to the most general yet fundamentally challenging scenario: complex valvular, ventricular, and vascular diseases (C3VD). In C3VD, multiple valvular, ventricular, and vascular pathologies interact with one another, while the physical phenomena associated with each pathology amplify the effects of others on the cardiovascular system.

Left ventricle (LV) pressure-volume (P-V) loop analysis is a powerful tool to assess cardiac mechanics. This analysis can reveal the pathophysiological mechanisms of heart failure, including heart failure with preserved ejection fraction and myocardial and valvular diseases. It is, therefore, instrumental in the evaluation and management of heart failure and valvular heart disease and can also help explain the short- and long-term effects of valvular and other interventions with cardiac implications. In addition, ventricular P-V loop analysis can be used to monitor the cardiac effects of related medical devices, mechanical heart support, therapeutic interventions, and medications.2-5 Indeed, ventricular P-V loop analysis has exceptional potential for integration into current clinical practice to advance the standard of care.

Aortic valvular disease increases LV pressure, LV end-diastolic pressure, LV workload, the stiffness of the systemic arterial system, and LV afterload, contributing to LV systolic and diastolic dysfunction,6 an important cause of heart failure in such patients. While transcatheter aortic valve implantation (TAVI) provides positive outcomes and has markedly reduced the mortality rate, TAVI fails in nearly 25% to 35% of patients (patients either die or do not recover a reasonable quality of life after the procedure).7 Indeed, the immediate intraprocedural as well the longitudinal hemodynamic changes affecting the aortic-left ventricular system after aortic valve replacement are poorly understood. While TAVI universally reduces the transvalvular pressure gradient, it is anticipated to improve systolic and diastolic LV function in the long-term. Despite the benefits, invasive LV P-V loop analysis revealed impaired LV systolic and diastolic function in the early phase following TAVI.6,8 LV P-V loop analysis also revealed exacerbated heart failure despite successful TAVI procedures in many patients.5,9 Indeed, LV P-V loop analysis elucidated that reductions in transvalvular pressure gradient post-TAVI were not always accompanied by improvements in LV workload. TAVI has been shown to have no effect on LV workload in many patients, while LV workload post-TAVI significantly rose in many others.2,5,10

In clinical settings, cardiac catheterization is the gold standard for evaluating pressure and flow through the heart to perform ventricular P-V loop analysis. However, due to its invasiveness, cost, and high risk, it is impractical for diagnosis in routine daily clinical applications or serial follow-up examinations. Most importantly, cardiac catheterization only provides access to the blood pressure in very limited regions rather than details of physiological flow and pressures throughout the heart and circulatory system. In addition, there is no method to invasively or non-invasively quantify the heart workload that can provide a contribution breakdown of each component of the cardiovascular diseases. This is especially crucial in the presence of TAVI and C3VD, in which quantification of left ventricular workload and its breakdown are important to guide the priority of interventions. Moreover, there is no noninvasive method for determining LV end-diastolic pressure, instantaneous LV pressure, and contractility. All these parameters provide valuable information about the patient’s cardiac deterioration and heart recovery.

Keshavarz-Motamed11,12 developed the first and the only Doppler-based noninvasive patient-specific diagnostic, monitoring, and predictive tool that can investigate and quantify the effects of interventions, medications, and C3VD constituents on the function of the heart and circulatory system at no risk to the patient (figure 1).

Figure 1. Doppler-based patient-specific diagnostic, monitoring, and predictive tool flowchart. The tool uses a few input parameters that can all be measured using Doppler echocardiography simply and reliably. This novel tool4,10–15 was validated against cardiac catheterization and 4D flow MRI in patients with C3VD (so far ~ n = 600) with substantial inter- and intra-patient variability with a wide range of (adult and congenital) cardiovascular diseases. 4D, 4-dimensional; C3VD, complex valvular, ventricular, and vascular diseases; CD, cardiovascular disease; LV, left ventricular; MRI, magnetic resonance imaging.

 

This novel method4,10-15 offers several key capabilities (figure 2, sample results): a) quantifying details of physiological pulsatile flow and pressures through the heart and circulatory system; b) tracking cardiac and vascular states based on accurate time-varying models that reproduce physiological responses; c) performing LV P-V loop analysis and quantifying heart function metrics, specifically in terms of the heart workload; d) providing a breakdown of the effects of disease constituents on global heart function (eg, heart workload) to help predict the effects of interventions and plan the sequence of interventions in C3VD; e) quantifying other heart-function metrics, including LV end-diastolic pressure, instantaneous LV pressure, and contractility. None of the above metrics can be obtained non-invasively in patients, and when invasive cardiac catheterization is undertaken, the collected metrics cannot be as complete as what the novel method can provide. While such information is vitally needed for the effective use of advanced therapies to improve clinical outcomes and to guide interventions in patients, they are not currently accessible in clinical settings.

Figure 2. Diagnosis and monitoring in sample patient 1 from baseline to 90 days: this patient did not fully benefit form transcatheter aortic valve implantation (TAVI). Instead of improving the patient’s heart condition by reducing LV workload, TAVI caused an increase in LV workload. Example of workload breakdown analysis and prediction for effects of interventions in sample patient 2: right: P-V loops of the actual disease condition and prediction of several valve interventions. Left: predicted percent decrease in LV workload following valve interventions. Both mitral valve regurgitation (38% increase) and aortic valve stenosis and regurgitation (48% increase) substantially contributed to increasing the workload. This patient only underwent TAVI. However, considering this calculation, the decision to also perform mitral intervention at the time of aortic valve intervention should have been evaluated. AS, aortic stenosis; AR, aortic regurgitation; MR, mitral regurgitation; LV, left ventricle; LA, left atrium. We retrospectively received patients’ data from multicentre in which waiver of informed consent and data transfer were approved by their Institutional Review Boards.

 

CONCLUSION

The novel method, developed and verified by Keshavarz-Motamed,11,12 purposefully uses reliable and noninvasive input parameters measured by Doppler echocardiography to continuously calculate patient-specific hemodynamics to be used for diagnosis, monitoring, and prediction of cardiac function and circulatory status. This innovative method holds potential applications: a) in clinical trials, enabling the noninvasive analysis of cardiac and circulatory function metrics; b) as a diagnostic tool to noninvasively analyze cardiac function metrics for routine care, ambulatory care, or intensive and critical care units; c) as a patient monitoring tool, potentially integrated into personal wearable devices; and d) as a module incorporated into the software of Doppler echocardiography machines for enhanced diagnosis and prediction.

FUNDING

None.

CONFLICTS OF INTEREST

None.

REFERENCES

Percutaneous coronary interventions with drug-eluting stent (DES) implantation have become a well-established treatment for obstructive coronary artery disease, improving long-term outcomes.1 However, despite recent improvements including thinner strut platforms and more biocompatible polymers, the Achilles’ heel of DES strategy remains the risk of DES-related adverse events such as in-stent restenosis or stent thrombosis in the short term,2 along with an increase in hard clinical events at a rate of 2.0 to 3.5% yearly after the first year.3,4

Drug-coated balloons (DCB) have been developed as an alternative to percutaneous coronary intervention with DES implantation in selected populations for the treatment of coronary artery disease. The main advantage of this technology is its ability to deliver an antiproliferative drug to the treated lesion without leaving any layer of metal, which might cause late adverse events. Another advantage is the potential reduction in the duration or discontinuation of dual antiplatelet therapy, especially in patients at high risk of bleeding.

Several studies have investigated the role of DCB in real-world patients, who are those mainly affected by in-stent restenosis or de novo small vessel disease.5-9 The only randomized study of DCB in de novo small vessels with a clinical primary endpoint was BASKET-SMALL-2. This study demonstrated the noninferiority of DCB vs DES (vessel size 2-3 mm), which was maintained up to 3 years follow-up in terms of all clinical endpoints.5

The initial fear of leaving behind a residual coronary dissection, especially in de novo lesions, could limit the widespread use of DCB. However, it has been shown that a nonflow-limiting dissection after DCB treatment tends to heal during the first few months, with both the paclitaxel and sirolimus technologies, without leading to acute or subacute vessel closure.10,11

The main message regarding DCB is that they should be used as the final step of percutaneous coronary intervention and only when a proper lesion preparation has been performed with a fully expanded balloon of the correct size for the vessel, with accurate management of calcifications and no residual stenosis greater than 30% that could impair drug delivery to the vessel and limit the potential of this technology.

Recently, a new generation of DCB eluting sirolimus (SCB, Magic Touch, Concept Medical, United States) has been introduced that uses nanoparticles composed of a dual layer of phospholipids encapsulating the antiproliferative agent. Histopathologic studies have demonstrated therapeutic concentrations of the drug within the vessel wall for up to 60 days after percutaneous coronary intervention.12

Notably, the angiographic performance of this class of drug seems to be inferior to that provided by paclitaxel. The recently published TRANSFORM I trial showed that SeQuent Please DCB (B. Braun, Germany) outperformed SCB in terms of angiographic parameters at 6 months of follow-up, but without showing any difference in clinical endpoints. This lower performance of SCB seems to occur particularly in cases of complex lesions, emphasizing the importance of adequate lesion preparation, especially with the less lipophilic drug sirolimus (figure 1).13 Somewhat reassuringly, the performance of SCB in terms of clinical endpoints has been demonstrated in all-comer populations, especially in the prospective EASTBOURNE study, which showed a good safety and efficacy profile up to 2 years of follow-up in 2123 patients/2440 lesions.14

Figure 1. Differences in terms of types of lesion and outcomes among 2 top enroller centers for the TRANSFORM II trial. PCB, paclitaxel-coated balloon; SCB, sirolimus-coated balloon.

 

The next step to ensure wider use of this new generation DCB will be direct comparison with DES, as in the TRANSFORM II (NCT04893291) trial. This is an international, multicenter, prospective, investigator-driven, open-label, randomized (1:1) clinical trial designed to test the efficacy of SCB vs DES in native coronary artery vessels with diameters between 2.0 and 3.5 mm. Inclusion and randomization are being performed after adequate lesion preparation in the absence of flow-limiting dissection and acute vessel recoil. The study population has been calculated expecting the noninferiority of SCB in terms of target lesion failure at 12 months, and its sequential superiority in terms of net-adverse clinical events, including BARC 3-5 bleeding events. Interestingly, patients will be followed up clinically for 5 years to observe the potential superiority of DCB in the long-term. This trial, which includes 7 Spanish centers, is including patients at 40 centers allocated in 11 countries in Europe, Asia, and South America.15 By November 20^th, 2023, 600 patients out of the planned 1820 had been enrolled.

The TRANSFORM II trial will be an essential test of the maturity of DCB in such an established, prognostically significant arena, challenging DES as the gold standard for the treatment of patients with native coronary artery disease.

FUNDING

None.

CONFLICTS OF INTEREST

B. Cortese serves on the advisory board or as a consultant for several companies producing or marketing DCB: Cordis, Medalliance, BBraun, Concept Medical, Medtronic, Innova HTS, and ANT.

REFERENCES

Simply stated, the goal of diagnostic coronary angiography is to distinguish the cause of a patient’s chest pain from 1 of 4 endotypes: a) epicardial stenosis; b) coronary spasm; c) coronary microvascular disease (CMD); and d) —equally important—noncoronary chest pain. Crucially, the latter is a diagnosis of exclusion and consequently cannot be confirmed without formal assessment of the other mechanisms (figure 1). Despite this truism, the interpretation of most coronary angiograms is limited to simple “eyeballing” of an epicardial “shadowgram”. This approach has a low diagnostic yield with 40% of patients found to have no significant epicardial stenoses—an entity known as angina with no obstructive coronary arteries (ANOCA).1 Despite the presence of typical angina or evidence of ischemia during noninvasive testing, these patients, are frequently nonchalantly dismissed without a formal diagnosis.

Figure 1. Patients with compelling, recurring, and debilitating chest pain should undergo catheterization with coronary angiography and—when needed—coronary function testing to unravel the mechanism of their pain. Noncoronary chest pain is a diagnosis of exclusion and consequently can only be confirmed if the 3 other mechanisms have been assessed. FFR, fractional flow reserve; PPG, pullback pressure gradient.

 

This very large group of patients is heterogeneous, and establishing the underlying cause of ANOCA requires a thorough coronary function testing (CFT) protocol that includes diagnostic angiography, provocation testing for microvascular or epicardial vasospasm, and assessment of CMD.2 In many centers, however, diagnostic angiography is rarely complemented with CFT. Among those that do, testing is often incomplete, with the result that patients often do not receive a diagnosis of the underlying cause of their ANOCA or benefit from potential endotype-specific treatments. Possible explanations for this behavior include a lack of familiarity with the causes of ANOCA, a lack of knowledge of available testing modalities, concerns about the accuracy of tests, and a belief that the underlying diseases are untreatable.

In a recent article published in REC: Interventional Cardiology, Rinaldi et al.3 describe their single-center experience of the implementation of a specific ANOCA diagnostic and therapeutic protocol at Hospital Clínic in Barcelona, Spain. In this program, all patients with ANOCA underwent systematic CFT including bolus thermodilution for the calculation of coronary flow reserve and the index of microvascular resistance, as well as intracoronary provocation testing to assess epicardial or microvascular spasm. Based on the results of these tests, patients were classified into 4 endotypes: a) microvascular angina (MVA) (CMD or microvascular spasm); b) vasospastic angina (epicardial spasm); c) both MVA and vasospastic angina; and d) noncoronary chest pain.

The authors demonstrated that, as a result of the identification of specific ANOCA endotypes, there were significant increases in targeted medical prescriptions such as beta-blockers, nondihydropyridine calcium channel blockers, and long-acting nitrates. While this did not translate into a statistically significant improvement in quality of life between baseline and 3 months, angina significantly improved in terms of physical limitation, angina stability, and disease perception. Importantly, the protocol was shown to be safe, with only 3 minor adverse events being reported, all occurring during acetylcholine administration (transient bradycardia, paroxysmal atrial fibrillation with spontaneous cardioversion).

This work has significant strengths that should be highlighted. The CorMicA trial provided the first evidence from a randomized controlled trial of the benefits of systematic CFT with targeted medical therapy.4 However, to date, scarce real-world data have been available on the implementation of such protocols in routine clinical practice. As such, this small, real-world, observational study is strongly welcomed. More than the clinical results obtained in a relatively small number of patients, the work by Rinaldi et al.3 is particularly worthwhile for several methodological aspects, 3 of which are discussed below.

(i) Which patients should enter such a program and how? Patients were screened at a specific outpatient clinic and their inclusion was based on well-standardized criteria. Ideally, only patients with compelling, recurrent and invalidating symptoms should undergo CFT. The usefulness of such a program is significantly reduced by the referral of patients with unconvincing symptoms, or those with a high pretest probability of epicardial disease. Notably, the increasing role of coronary computed tomography angiography for the screening of epicardial disease in patients with angina currently allows diagnosis of ANOCA without the use of invasive diagnostic angiography and patients can thus be referred directly for CFT.

(ii) How should CFT be performed? As described by the authors, both microvascular function and coronary vasomotion should be investigated in a strictly standardized manner, preferably in the left anterior descending artery. However, the order of these tests is debatable. In our opinion, it does not make sense to investigate endothelial function and coronary vasomotion with a guidewire in the coronary artery or when the patient has already received vasoactive medications such as nitrates and calcium channel blockers. Consequently, we believe that acetylcholine testing should come first, with epicardial vasodilation being induced with nitrates at the end of acetylcholine testing. The latter also represents an important step (and good clinical practice) before commencing wire-based measurements of microcirculatory function. As for the choice of testing modality, bolus thermodilution should be replaced by continuous thermodilution as it enables the calculation of coronary flow reserve, absolute microvascular resistance (R_µ) and microvascular resistance reserve from absolute volumetric flow rather than from surrogates of flow.5 Future studies are expected to clarify the clinically relevant cutoff values for the indices derived from continuous thermodilution. These values should allow a more robust definition of CMD, which is currently an unmet need.

(iii) How should these patients be followed up? Patients should be followed up by the same physicians in a dedicated outpatient clinic, and be asked about their symptoms in a structured and systematic way. In this regard, the authors should be commended for the use of structured questionnaires to assess angina and quality of life. The classic Canadian Cardiovascular Society grading system for angina is not appropriate for ANOCA patients as their symptoms often differ from those reported by patients with epicardial disease. Moreover, objective signs of ischemia are often lacking. In the future, it is likely that patients will be given an app on their smartphone to closely monitor their symptoms.6

Overall, as with any new program, it is important to recognise that there is a learning phase. However, with a well-structured and standardized program, such as that proposed by Rinaldi et al.,3 this learning phase is likely to be short. There is now a need for future work addressing the implications of such a protocol on both time and cost in routine clinical practice. For example, in the setting of a busy, real-world catheterization laboratory, how much time, on average, does such a protocol add to the length of the procedure? Furthermore, what are the cost implications, and are they sufficiently counterbalanced by an increase in quality of life and/or symptom control?

To conclude, there are now strong clinical grounds for the systematic implementation of CFT in ANOCA patients. Furthermore, as demonstrated by Rinaldi et al., a standardized and robust testing program can be effectively implemented in real-world practice.3 Validation of clear diagnostic criteria for CMD is now needed for the results of CFT to be easily interpreted and acted upon. Patients and their referring clinicians deserve nothing less.

FUNDING

No funding was received to assist with the preparation of this editorial.

CONFLICTS OF INTEREST

T. Mahendiran is supported by a grant from the Swiss National Science Foundation (SNSF). B. De Bruyne has a consulting relationship with Boston Scientific, Abbott Vascular, CathWorks, Siemens, and Coroventis Research; receives research grants from Abbott Vascular, Coroventis Research, Cathworks, Boston Scientific; and holds minor equities in Philips-Volcano, Siemens, GE Healthcare, Edwards Life Sciences, HeartFlow, Opsens, Sanofi, and Celyad.

REFERENCES

INTRODUCTION

Right ventricular outflow tract (RVOT) disease is a common finding in children and adults with congenital heart disease and often occurs as a sequel of previous surgery. Over the past 2 decades, percutaneous pulmonary valve implantation has become more widely used and is recommended by current clinical practice guidelines1 as the preferred option for patients with previous conduits or bioprostheses.

However, many patients have native or patched tracts (hereafter referred to as native RVOTs) with pulmonary regurgitation as the predominant lesion. In these patients, percutaneous valve placement is more complex due to the RVOT anatomy, its dynamic behavior, larger pulmonary annulus size, and lack of a proper landing zone for the valve. Because of the differences in underlying heart diseases, previous surgical repairs, and various pulmonary artery configurations, RVOT morphology varies widely but can be categorized into 5 subtypes2 (figure 1).

Figure 1. Five types of native RVOT anatomy: I - pyramidal; II - cylindrical or tubular; III - inverted pyramidal; IV - central enlargement; V - central narrowing. (Reproduced from Schievano et al.2 with permission from the author.)

 

Repaired tetralogy of Fallot serves as the paradigm, and in these cases, surgery remains the standard of care. However, the development of percutaneous procedures has enabled a larger number of patients with these substrates to be eligible for percutaneous treatment (figure 2).

Figure 2. Self-expanding pulmonary valve implantation in an aneurysmal right ventricular outflow tract (RVOT). A: severely dilated RVOT on magnetic resonance imaging, with interventricular septal flattening. B: balloon sizing test in the RVOT with simultaneous injection into the left main coronary artery. C: successful venus-P valve (MedTech, China) implantation in the RVOT.

 

Two different models of balloon-expandable valves have been authorized to treat dysfunctional bioprostheses and conduits: the Melody (Medtronic, United States) and the SAPIEN valves (XT model, Edwards Lifesciences, United States). Although they have not yet been authorized for implantation in native RVOTs, both (along with the SAPIEN S3) have been used off-label in this setting.

To address the specific characteristics of native RVOTs, several models of self-expanding valves have been developed, such as the Venus-P (Venus MedTech, China, with CE marking for use in Europe since 2022), PULSTA (TaeWoong Medical, South Korea), and Harmony valves (Medtronic, United States, with prior FDA approval). The Alterra valve (Edwards Lifesciences) has also been used. This valve serves as a self-expanding prestent onto which a SAPIEN valve is later implanted.

The characteristics of each of these devices have already been described in detail in a previous issue of REC: Interventional Cardiology.3

RESULTS OF PERCUTANEOUS VALVES IN THE NATIVE RIGHT VENTRICULAR OUTFLOW TRACT

More information has gradually become available on the favorable results and durability of percutaneous valves. The largest multicenter registry to date,4 with 2476 patients (82% implanted with the Melody valve and 18% with the SAPIEN device, including 16% with native RVOTs), reported an 8-year survival rate of 91.1% after implantation, and a reintervention rate of 25.1%, which is similar to the rates reported in some surgical series.5 Nonrandomized comparative studies6 and a recent meta-analysis7 also found similar reintervention rates. Some series report higher rates in patients implanted with the Melody compared with the SAPIEN valve,8,9 although the 2 groups were not directly comparable, with reintervention-free survival rates in patients with SAPIEN being similar to those reported in patients with surgical valves.8

The SAPIEN device can be implanted with or without prestenting, depending on the patient’s characteristics, with good outcomes. The largest trial published to date included 774 patients implanted with the XT and S3 models10, 51% of whom had native RVOTs (table 1).

 

Table 1. Summary of some of the main trials of patients with native right ventricular outflow tract

Author and year	Patients with native RVOT/Total patients	Valve type	Follow-up	Implant success	Other results	Complications
Malekzadeh-Milani et al.23, 2014	34/34	Melody	2.6 years	100%	Paravalvular leak in 2 patients during follow-up	3 acute complications (9%): 1 hemoptysis, 1 RVOT obstruction, 1 stent embolization
Meadows et al.18, 2014	31/31	Melody	15 months (1 month- 3.8 years)	100%	No mortality or valve regurgitation	Stent fractures (32%) associated with a higher rate of stenosis. 3 cases of endocarditis. Reintervention in 3 patients
Garay et al.13, 2017	10/10	Venus P	12 months (4 to 21)	100%	Normally functioning valve, no stent fractures, right ventricular remodeling, and NYHA functional class improvement	None
Martin et al.11, 2018	132/132	Melody	No follow-up		Complete cohort of 229 patients, but only 58% implanted. Good immediate hemodynamic outcomes	Complication rate of 4% (mostly due to stent migration)
Morgan et al.24, 2019	41/57	SAPIEN (S3, XT)	5.3 months (1 to 26)	100%	No prestenting. Normally functioning valve at follow-up. No mortality	1 aortic compression, 2 tricuspid valve injury, 1 valve regurgitation
Shahanavaz et al.10, 2020	397/774	SAPIEN S3 (78%) XT (22%)	12 months (n = 349)	97.4%	Normally functioning valve: 91.5%	Adverse events: 10%. Emergency surgery: 14 patients (1.8%). Tricuspid injury: 3%
Goldstein et al.19, 2020	143/530	Melody (88%) SAPIEN (22%)	1 year	98%	Normally functioning valve: 98%	1 death. Reintervention rate of 13.3% (mostly unrelated to the valve)
Lee et al.12, 2021	25/25	PULSTA	33 (± 14) months	100%	Zero cases of valve dysfunction	No significant adverse events
Gillespie et al.16, 2021	21/21	Harmony	5 years	100%	Implantation in all but 1 patient due to pulmonary hypertension. Normally functioning valve in nonreoperated patients	Valve explantation in 2 patients, 1 death 3 years after implantation, 2 reinterventions (valve-in-valve)
Morgan et al.25, 2021	38/38	Venus	27 months	97.4%	Normally functioning valve at follow-up	Migration: 2 cases (surgery in 1)
Houeijeh et al.9, 2023	99/214	SAPIEN XT/S3 (85%) Melody (15%)	2.8 years (3 months-11.4 years)	Only cases with successful implantation included	Reintervention-free survival at 5 to 10 years: 78.1% to 50.4% (Melody) and 94.3% to 82.2% (SAPIEN)	Severe complications: 2.3%, 1 valve-related death. Endocarditis 5.5/100 patient-years (Melody) and 0.2/100 patient-years (SAPIEN)
Álvarez et al.14, 2023	8/8	Venus	No follow-up	100%	Normally functioning valve in all	No significant adverse events
Lin et al.15, 2023	53/53	Venus (28%), PULSTA (72%)	27.5 months	98.1%	No valve regurgitation at 12 months	1 embolization, 1 endocarditis
NYHA, New York Heart Association; RVOT, right ventricular outflow tract. In studies that are not specific to native RVOT, the results and complications refer to the overall cohort, as the results of native, or non-native RVOTs are often not detailed independently. Some centers participated in > 1 study, which allowed the same patient to be included in multiple publications. The most recent series with larger numbers of patients have been prioritized.

 

In a study of patients with native RVOTs that included 229 candidates for the Melody valve, the device was finally implanted in 132 patients (58%).11 The most common reason for avoiding implantation was a prohibitively large RVOT, followed by coronary or aortic root compression. The immediate outcomes of patients with successful implantation were good. However, the low implantation rate demonstrates the limitation of treating native RVOTs with these valves.

Self-expanding valves fill this gap by allowing treatment of larger RVOTs, as they adapt to the anatomy of the RVOT and provide more stable attachment. The series published to date indicate a very high implantation success rate—close to 100%—with good short- and mid-term outcomes and few complications.12-16 (table 1 illustrates a selection of series representative of patients with native RVOTs).

Drawing comparisons between the results of surgical and percutaneous pulmonary valves is challenging because the types of patients and the anatomies treated are very different. Overall, patients undergoing percutaneous valve implantation are at higher risk and often have bioprostheses or small conduits that require smaller percutaneous valves, which is associated with a higher residual gradient, leading to a greater need for reintervention,4,8,9 and a higher rate of endocarditis. This aspect has traditionally led to less favorable results with the Melody series (with a maximum diameter of 22 mm), with durability being one of the issues initially identified, although more recent series have shown positive results. Only indirect comparisons can be drawn with valve procedures in the native RVOT.

PROCEDURAL PLANNING

Multimodal imaging modalities, especially magnetic resonance imaging and computed tomography, are crucial for patient selection and procedural planning. Key aspects include measurement of the RVOT and the pulmonary annulus, and assessment of both the RVOT and the coronary anatomy. Recently, computed tomography guidelines for RVOT assessment17 have been published with detailed information on the measurements that should be taken, and the cardiac cycle phase.

POTENTIAL PROBLEMS

Valve or stent migration or embolization is a potential complication in patients with large RVOTs due to the lack of an adequate landing zone, with incidence rates between 0% and 4.5%,11,10,18 and consequently proper valve sizing is of paramount importance.

Stent fractures can lead to loss of integrity and contribute to prosthetic valve dysfunction. Nonetheless, the implications of the occasional finding of an isolated strut fracture remain unclear.

Tricuspid valve injury has been reported in 3% to 6% of patients.10 However, this rate has dropped significantly with the use of DrySeal introducer sheaths (W.L. Gore & Associates, United States).10

Coronary compression is a rare complication nowadays, because coronary angiography is simultaneous and systematically performed during RVOT balloon inflation testing. However, it can be a reason for not performing percutaneous implantation in nearly 3% of patients.11

A higher incidence of infective endocarditis has been reported, especially after Melody valve implantation,6,8,9 with a higher risk when smaller valves are implanted and there is a greater residual gradient. The risk involved with other types of device such as the SAPIEN—whether because of its different composition (bovine jugular vein graft in the Melody compared with bovine pericardium in the SAPIEN) or because of its larger size—is much lower9 and seems comparable to that of surgical series.

Self-expanding valves are larger, and the proximal end often remains inside the RVOT, which could increase the risk of ventricular arrhythmias. The incidence of nonsustained ventricular tachycardia varies widely (between 0.6% and 40%11,19,20), although it is usually a transient phenomenon during the early postimplantation phase, and its long-term implications remain unclear. Of note, when comparing surgical with percutaneous pulmonary valve replacement, the early incidence of arrhythmias was lower in the latter.21 A potential caveat is that catheter access to the arrhythmic substrate can be limited after valve implantation.

The presence of the valve metal mesh with or without previous stents inside the RVOT can pose additional challenges for the surgeon if surgical valve replacement is subsequently required. This is a relative problem, because surgical pulmonary valve replacement also increases the risk of future reinterventions related to resternotomy.

BENEFITS OF PERCUTANEOUS VALVE IMPLANTATION

The possibility of performing percutaneous pulmonary valve implantation offers clear advantages: the procedure is much less invasive, length of stay is shorter,8 recovery is faster, the mortality rate is very low (from 0.2% to 0.8%),19 and the cost-effectiveness ratio is more favorable.22 In patients at high surgical risk, it might be the only available treatment option. The path followed by its “left-sided relatives”—transcatheter heart valves in the aortic position—illustrates that the threshold for the use of percutaneous techniques is decreasing as more experience is gained and technology becomes further refined. In cases of intermediate or low risk, percutaneous valve implantation may delay or avoid the need for surgery in patients who often require multiple interventions during their lifetime. This concept of avoiding sternotomies is relevant due to the added risk of further surgeries and for patients who are candidates for heart transplants. The decision on the best approach to valve implantation in each patient should be made by a multidisciplinary heart team, including health professionals experienced in these types of heart disease.

CONCLUSIONS

Percutaneous pulmonary valve implantation is particularly challenging in patients with native RVOTs. Nonetheless, it is a feasible option that is being used with a high success rate and few complications. However, appropriate candidate selection is essential. Several models of self-expanding valves have been specifically developed for this purpose, with good short- and mid-term results, allowing the treatment of patients with large RVOTs that were previously not amenable to balloon-expandable devices. The latest information suggests that the durability of percutaneous valves may be comparable to that of surgical bioprostheses, although long-term data are lacking, especially with the latest models. Although more studies and follow-up are necessary, percutaneous techniques are already an option for many patients and will likely become an alternative to surgical treatment in the near future.

FUNDING

None declared.

CONFLICTS OF INTEREST

None declared.

REFERENCES