Catheter Intervention of Left Ventricular Outflow Obstruction

and Coarctation of the Aorta

Sejung Sohn, MD

Department of Pediatrics, Ewha Womans University College of Medicine

Obstruction to outflow of left ventricle (LV) may occur at the valvular, subvalvular, or supravalvular level, and subvalvular outflow tract obstruction may be either fixed or dynamic. Focusing on the valvular obstruction among LV outflow obstructions, this article reviews the current status of transcatheter balloon valvuloplasty for aortic valvar stenosis and angioplasty for coarctation of the aorta.

Balloon Aortic Valvuloplasty

Aortic stenosis (AS) in infants and children has been palliated by surgical valvotomy by the mid-1980s. In 1984, Lababidi et al.1) reported the initial experience of balloon dilation to treat congenital valvar AS in 23 patients. The early results suggest that the reduction in gradient and incidence of major complications are comparable to those obtained by surgery. Balloon aortic valvuloplasty (BAV) has replaced surgical valvotomy as the initial treatment of congenital AS in many centers. A history of previous surgical valvotomy does not influence the immediate and follow-up outcome following BAV.2)

Indications

The indications include a peak systolic ejection gradient ≥50 mmHg and mild aortic regurgitation (AR). Regardless of pressure gradient, BAV should be performed in those with evidence of critical obstruction such as congestive heart failure, strain pattern on ECG, or a dilated and poorly contracting LV.

Procedure

BAV is performed through one of the several vascular accesses: transfemoral, transvenous,3) transcarotid,4) transumbilical,5) or transsubscapular.6) Complete right- and left-sided hemodynamic measurements are performed. A left ventriculogram is obtained in biplane and the aortic annulus diameter is measured at the hinge points. The balloon catheter is placed across the valve over the guidewire and inflated to 4-6 atm, or until the waist in the balloon produced by the valve disappears. The duration of inflation is 5 seconds or complete inflation-deflation cycle should be <15 seconds. The residual gradient is measured and an aortic root angiogram is performed to assess the degree of AR.

Dilation is considered successful when the percent reduction in gradient is >40-50%, residual gradient is <50 mmHg and AR remains mild. The seriously ill newborns with critical AS should be considered a medical emergency. The peak gradient in these neonates may not accurately reflect the severity of obstruction because of myocardial dysfunction and atrial/ductal shunts. In this group of patients, BAV is considered successful when left atrial or LV end-diastolic pressure is reduced, no more than mild AR results, and clinical improvement is observed.

Immediate results

In the Valvuloplasty and Angioplasty of Congenital Anomalies (VACA) Registry,7) BAV was successful in 192 of 204 patients. The peak gradient decreased from 77±28 to 30±14 mmHg. Eight of 204 (4%) required subsequent surgical valvotomy. The hemodynamic results were poorer in neonates compared with older infants. The gradient reduction did not correlate with the balloon-to-annulus ratio but with valve morphology: pliant valves had a greater gradient reduction than thick valves.8)

Technical considerations

Balloon size

Balloons 90-100% of the aortic annulus diameter are recommended.9)

Double balloon technique

Some investigators have reported a larger gradient reduction if dilations were performed using two simultaneous balloons compared with a single balloon.10) But there was no difference in outcome comparing the double- and the single-balloon techniques.8) Nevertheless, the technique is used in selected patients because it causes less acute hemodynamic compromise and should result in a low incidence of femoral arterial injury. If the valve annulus is too large to dilate with a single balloon, two balloons are also used.11) The dilation diameter for two balloons is determined as previously described by Yeager12) or calculated by a simple formula13): (D1+D2)/π +(D1+D2)/2, where D1 is the diameter of the first balloon and D2 is that of the second balloon.

Dilation approach

1. Femoral artery

2. Femoral vein3)

3. Right carotid artery4)

4. Umbilical artery5)

5. Right subscapular artery6)

Complications

Major life-threatening complications occurred in 11 of 204 (5%) subjects in VACA Registry.7) Complications were significantly related to age at BAV. Nine of 38 children <1 year of age had a major complication whereas only 2 of 166 >1 year of age had complications, yielding a relative risk of 25.5. The highest rate of complications occurred in infants <1 month of age.

Death

Aortic regurgitation

Ileofemoral arterial injury

Other complications

Follow-up results

Generally, the gradient immediately after dilation has been maintained at follow-up, but restenosis (gradient >50 mmHg) may occur. Persistent or progression of stenosis is the most common reason for reintervention. Two factors were related to a high incidence of restenosis: age ≤3 years and immediate postdilation gradient ≥30 mmHg.14)

In contrast to the reports showing no significant progression of AR, Shaddy et al.15) noted increased AR in 10 of 32 (31%) patients and aortic valve prolapse in 7 (22%) patients during follow-up for 19.2±5.6 months.

Comparison with surgery

Studies comparing results of both surgery and BAV have a number of limitations, including retrospective analysis, nonradomized patients group, comparisons between different eras, different duration of follow-up, and a lack of set criteria for initial treatment and reintervention. Despite these limitations, these studies report that two modalities have equivalent outcomes16-19) and that the type of intervention is not predictive of outcomes.16)

Recently, Cowley et al.18) compared the 17-year follow-up results of BAV in 30 neonates with those of transventricular surgical dilation in 17 patients, and reported similar actuarial survival, reintervention rates (about 50% freedom from reintervention at 5 years), and freedom from aortic valve replacement (about 50% at 10 years).

A prospective, multicenter, nonrandomized study of 110 neonates with critical AS performed by Congenital Heart Surgeons Society (CHSS)19) showed similar mortality, survival rates (72% at 5 years) and reintervention rates (48% freedom from reintervention at 5 years), but a greater risk of residual obstruction with surgical valvotomy and a greater risk of significant AR with balloon valvotomy.

Balloon Angioplasty for Coarctation of the Aorta

Since transcatheter balloon dilation for coarctation of the aorta (CoA) was first described as a potential alternative to surgery in 1982,20) a number of literatures have  reported the results of balloon dilation and attempted comparisons between surgical and balloon dilation. Balloon angioplasty (BA) of recoarctation (reCoA) after surgery is now considered to be a procedure of choice, whereas controversy exists about the application of BA to native CoA. However, larger clinical studies are available with follow-up for 5-10 years after BA of native CoA.21-23)

Indications

Intervention is indicated in the setting of a discrete CoA, upper extremity hypertension, and a resting systolic pressure gradient across the CoA segment ≥20 mmHg. Excluded are patients with long-segment coarctation or severe hypoplastic isthmus.

Dilation technique

There is no consensus for the optimal balloon size. Generally, balloons 2-3 times the diameter of CoA segment, but less than the aorta at the level of the diaphragm are used.23) In addition to choosing an "optimal" balloon, manipulations of wires or catheter tips across a freshly dilated area is strictly discouraged. Rupture of the balloon should be avoided because of an explosive release of shear force. Dilation success is considered when CoA segment increases in diameter by >30% and the residual gradient is <20 mmHg.

Vascular injury

The mechanism of relief of obstruction by balloon dilation consists of intimal and medial disruptions and dissections, which often are difficult to detect by angiography. With a greater sensitivity than angiography, intravascular ultrasound (IVUS) has demonstrated intimal and medial flaps or tears, during and after the procedure. Sohn et al.24) described acute and follow-up IVUS findings after balloon dilation of CoA. They  found a high incidence of intimal flaps and dissections immediately after BA for native and recurrent CoAs, and confirmed that even significant tears can heal partly or completly during follow-up, i.e. remodeling.

Native coarctation

Immediate results

McCrindle et al.25) reported the acute results of 422 BA of native CoAs. Patients' ages ranged from 2 days to 63 years (median, 4.2 years). Procedural related mortality was 0.7% (reCoA, 0.7%; p=1.00). Suboptimal results were noted in 19% of procedures (reCoA, 25%; p=0.04). Significant independent risk factors for an early suboptimal outcome included a high predilation gradient, earlier procedure date, and older age at BA. It was concluded acute results and complications of BA of native CoA appear to be equivalent or slightly superior to those of reCoA.

Restenosis

Restenosis is defined as the reappearance of a pressure gradient >20 mmHg. Mendelsohn et al.21) reported an overall 13% incidence of restenosis, reaching 60% in infants <1 year, compared with 7.3% in the older child. Fletcher et al.22) observed an incidence of 23% restenosis, reaching 77% in neonates. Rao et al.23) described an overall 25% incidence of restenosis, reaching 83% in neonates <1 month, 39% in infants <1 year, and 8% in older children. Risk factors for restenosis include young age <1 year, isthmic hypoplasia, and a small diameter CoA segment <3.5 mm before or <6 mm after BA.

Aneurysm formation

An aneurysm is defined as a wall contour deformation, with a diameter of 1.5 times the aorta at the level of the diaphragm. An incidence, both acute and late, has been reported to be 5-6% after BA of native CoA.26) However, late aneurysm formation can occur after surgical repair regardless of the type of repair.27) Its development is related to an intrinsic abnormality of the wall that is independent of treatment modality. Preexisting cystic medial necrosis commonly noted on histologic examination of aortas with untreated native CoA may predispose to aneurysm formation.26)

Other complications

There were 24/141 (17%) complications reported with 1 death in VACA Registry.26) Other significant complications include neurologic events (stroke, transient ischemic attack), femoral artery occlusion, acute aortic dissection or rupture and rarely paradoxical hypertension.

Native CoA in neonates and infants

In this age group of patients, BA should be considered as palliation rather than definitive therapy because of a high rate of restenosis.22)28) Femoral artery injury and occlusion remain an additional concern in this age group. Therefore, these concerns have directed many authors to be reluctant to adopt BA for native CoA in neonates and infants, except for the severely ill patients who are at high surgical risks.29) Other authors continue to advocate BA as the treatment of choice in these patients, arguing that it reduces symptoms of heart failure and hypertension, and helps to avoid immediate operation. If restenosis occurs, repeat BA or surgery can be performed when the patient is stable and less acutely ill.23)30)

Recoarctation

Surgical repair for reCoA after attempted primary surgical repair is associated with a high recurrence rate, significant mortality and morbidity. BA offers a satisfactory alternative to surgery for reCoA.

In VACA Registry,31) success rate was 78.4%. Hemodynamic results were similar regardless of the previous surgical techniques. Better results seemed to occur when BA was performed at an earlier rather than a later age after reCoA was found. In one series, the optimal results were obtained in 87%, and 72% of freedom from reintervention at follow-up up to 12 years.28) There were 5/200 deaths (2.5%) in VACA Registry.31) Other complications included femoral artery injury, postcoarctectomy syndrome, neurologic events but not neurologic complications involving the spinal cord.

Although the periadventitial surgical scar was thought to be protective against aortic rupture and make aneurysm formation unlikely, large dissections and fatal aortic rupture have been reported.31)

Comparison with surgery

The inconsistences of available data make objective comparisons impossible. Johnson et al.32) compared their surgical results and data available in the surgical literatures with those of BA in the same age group, and noted similar low mortality rates between the two procedures but significant higher restenosis rates after BA. Shaddy et al.33) compared the results of surgery and BA in patients aged 3-10 years. Immediate hemodynamic results were similar in both groups. Aneurysm formation was 20% in the BA group vs none after surgery. Restenosis was also higher in the BA group (25% vs 6%), although not statistically significant. There were neurologic complications after surgery although the incidence of complications was similar in both groups. Rao et al.30) analyzed data from 29 infants <3 months of age (14 surgery vs 15 BA). Early and late mortality, restenosis rate (46% vs 50%) were not significantly different between the groups. Morbidity and complication rates were lower with BA than with surgery. It is of note, however, that in most recent surgical studies, restenosis rates are reported to be 4-5%, much lower than those reported by Rao et al.34)

It is clear that no single or ideal treatment algorithm exists for CoA in the neonates and infants. The arch morphology, condition of the patients, and local institutional results for both procedures in reference to mortality and restenosis should be taken into account in the decision process.

Endovascular stenting and CoA

Balloon-expandable stents have been used in the vascular system since the mid-1980s. These devices were designed to oppose the recoil of elastic vascular stenoses after failed primary BA, providing vessel wall support. Additionally, stents provide a framework of endothelial growth, reducing thrombosis risk. Several experimental studies and the early clinical reports demonstrated the feasibility and immediate effectiveness of the balloon-expandable stents placement in patients with CoA or reCoA, and recently, a few relatively larger clinical series have been reported with follow-up.35-37)

Indications

The indications are postoperative reCoA and native CoA. Hypoplasia of the isthmus or transverse aortic arch and tortuous CoA are another indications for stent implantation.

Age at implantation

From the several studies reported, the ages at implantation were variable from infants and younger children to older children and adults. However, limiting the use to older subjects is justified.

Results

Marshall et al.36) reported the Boston Children's Hospital experience in 33 patients with CoA. Median age and weight were 14 years and 53 kg respectively. Twenty-seven (82%) had postoperative reCoA and 6 (18%) native CoA. Palmaz stents were used in all patients. Thirty-two (97%) patients had successful stent implantation. Median systolic gradient decreased from 25 to 5 mmHg. Median CoA diameter increased from 8 to 13 mm. Complications occurred in 3/33 (1%). At follow-up, there was no evidence of aortic rupture, dissection, stent fracture, or new pseudoaneurysm formation. Redilation of stents was successfully performed in 8 patients up to 16 months postimplant. Hamdan et al.37) also reported the results comparable to those from Boston group.

Anticoagulation

Heparinization is given during the procedure. Patients are maintained on aspirin for 3-6 months to 1 year. To use warfarin is not necessary because of a high pressure, high flow in this area.

Complications

Major complications in the setting of CoA stenting have been rare. No deaths have been reported. The most common procedural related complication is stent migration. Other complications include balloon entrapment within the stent, myocardial infarction by migration of the guidewire into a coronary ostium, femoral arterial disruption, arterial bleeding and aortic perforation.

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