Left-to-Right Shunt Lesions

Medical and Nonsurgical

• 1.

  Exercise restriction is not required, unless symptomatic.

• 2.

  Nonsurgical closure of the defect using a catheter-delivered closure device has become a preferred method, provided the indications are met. Advantages of nonsurgical closure would include a less-than-24-hour hospital stay, rapid recovery, less pain, and no residual thoracotomy scar.

  • a.

    These devices are applicable only to secundum ASD. The use of the closure device may be indicated for a defect measuring ≥5 mm in diameter (but <32 mm for Amplatzer device and <17 mm for Cardioform occluder) with evidence of RA and RV volume overload. In the United States, currently the Amplatzer Septal Occluder (AGA Medical) and Gore CardioForm occluder (W. L. Gore and Associates) are approved for secundum ASD closure.

  • b.

    There must be enough rim of septal tissue around the defect for appropriate placement of the device. The size of the rim around the ASD can be estimated by two-dimensional (2D) echo study as diagrammatically shown in Fig. 7.3 . The rim size is estimated in four directions: anterosuperior, anteroinferior, posterosuperior, and posteroinferior.

    

  • c.

    The ASD devices can be implanted successfully in children younger than 2 years of age, although a weight >15 kg is preferred.

  • d.

    Following the device closure, the patients are placed on aspirin 3-5 mg/kg/day for 6 months.

  • e.

    Closure rates are excellent with small residual shunts seen in less than 5% at 1-year follow-up.

Surgical

For patients with primum ASD and sinus venosus defect, and some patients with secundum ASD for which the device closure is considered inappropriate, surgical closure is indicated when there is a significant L-R shunt with Qp/Qs of 1.5:1 or greater. Surgery is usually delayed until 2 to 4 years of age, unless CHF develops. Open repair with a midsternal incision or minimally invasive cardiac surgical technique (with a smaller skin incision) is used. The surgical mortality rate is less than 1%. High PVR (≥10 units/m ² ) is a contraindication to surgery.

Follow-Up

• 1.

  Periodic follow-up is needed after the ASD closure device implantation for arrhythmia, residual shunt, obstruction of pulmonary and systemic venous returns, interference with the AV valve function, and/or device erosion through the cardiac wall.

• 2.

  After surgery, atrial or nodal arrhythmias occur in 7% to 20% of patients. Occasional sick sinus syndrome requires pacemaker therapy.

Pathology and Pathophysiology

• 1.

  The ventricular septum consists of a small membranous septum and a larger muscular septum. The muscular septum has three components: the inlet, infundibular, and trabecular (or simply muscular) septa (see Fig. 7.4 ). A membranous VSD often involves a varying amount of muscular septum adjacent to it (i.e., perimembranous VSD).

  

• 2.

  The frequency of different isolated subtypes of VSD found may be quite different depending on the diagnostic tools used in the study.

  • a.

    By 2D echo, the incidence of muscular VSDs is much higher than perimembranous and other subtypes. Muscular VSDs accounted for 59%; perimembranous VSDs, 27%; outlet VSDs, 1%; and inlet VSDs, 1% or combination of these (12%). However, many of the muscular (trabecular) VSDs are small in size, and about 85% to 95% of them close spontaneously.

  • b.

    When studied in surgical and autopsy settings, the prevalence of subtypes of VSD is quite different from the abovementioned figures (due in part to small size and spontaneous closure of the muscular VSDs). Perimembranous VSD accounted for 80%; outlet VSD, 5%-7% (29% in the Far Easern countries); inlet VSD, 5%-8%%; and muscular VSD, 5%-20% (McDaniel, 2001).

• 3.

  The VSD seen with TOF is a large nonrestrictive perimembranous defect with extension into the subpulmonary region. The inlet VSD is typically seen with endocardial cushion defects.

• 4.

  In subarterial infundibular or supracristal VSD, the aortic valve may prolapse through the VSD, with resulting AR and reduction of the VSD shunt. The prolapse and AR may occasionally occur with the perimembranous VSD.

• 5.

  In VSDs with small to moderate L-R shunts, volume overload is placed on the LA and LV (but not on the RV). With larger defects the RV is also under volume and pressure overload, in addition to a greater volume overload on the LA and LV. PBF is increased to a varying degree depending on the size of the defect and the pulmonary vascular resistance. With a large VSD, pulmonary hypertension results. With a long-standing large VSD, pulmonary vascular obstructive disease (PVOD) develops, with severe pulmonary hypertension and cyanosis resulting from an R-L shunt. At this stage, surgical correction is nearly impossible.

Clinical Manifestations

• 1.

  Patients with small VSDs are asymptomatic, with normal growth and development. With large VSDs, delayed growth and development, repeated pulmonary infections, CHF, and decreased exercise tolerance are relatively common. With PVOD, cyanosis and a decreased level of activity may result.

• 2.

  With a small VSD, a grade 2 to 5/6 regurgitant systolic murmur (holosystolic or less than holosystolic) maximally audible at the LLSB is characteristic ( Fig. 7.5 ). A systolic thrill may be present at the LLSB. With a large defect, an apical diastolic rumble is audible, which represents a relative stenosis of the mitral valve due to large pulmonary venous return to the LA ( Fig. 7.6 ). The S2 may split narrowly, and the intensity of the P2 increases if pulmonary hypertension is present ( Fig. 7.6 ).

  
  

• 3.

  Electrocardiographic (ECG) findings: Small VSD, normal; moderate VSD, LVH, and LAH (±); large VSD, biventricular hypertrophy (BVH) and LAH (±); PVOD, pure RVH.

• 4.

  Chest radiographs reveal cardiomegaly of varying degrees with enlargement of the LA, LV, and possibly the RV. PVMs are increased. The degree of cardiomegaly and the increase in PVMs are directly related to the magnitude of the L-R shunt. In PVOD, the heart is no longer enlarged and the MPA and the hilar pulmonary arteries are notably enlarged, but the peripheral lung fields are ischemic.

• 5.

  Two-dimensional echo studies provide accurate diagnosis of the position and size of the VSD. LA and LV dimensions provide indirect assessment of the magnitude of the shunt. Fig. 7.7 shows diagrams of 2D echo views of different parts of the ventricular septum, which helps identify different types of VSDs. The Doppler studies of the PA, TR (if present), and the VSD itself are useful in indirect assessment of RV and PA pressures.

  

• 6.

  Natural history.

  • a.

    Spontaneous closure occurs frequently, most often in small muscular VSDs, and more often in the first year of life than thereafter. Large defects tend to become smaller with age.

  • b.

    Inlet and infundibular VSDs do not become smaller or close spontaneously.

  • c.

    CHF develops in infants with a large VSD but usually not until 6 or 8 weeks of age, when the PVR drops below a critical level.

  • d.

    PVOD may begin to develop as early as 6 to 12 months of age in patients with a large VSD or earlier in a patient with trisomy.

Medical and Nonsurgical

• 1.

  Treatment of CHF with diuretics, afterload reducers, and sometimes digoxin (see Chapter 19 ).

• 2.

  No exercise restriction is required in the absence of pulmonary hypertension.

• 3.

  Nonsurgical device closure of selected muscular VSDs is possible when the defect is not too close to cardiac valves and when it is difficult to access surgically. Some centers have used so-called hybrid procedures through left thoracotomy incision and performing “perventricular” device closure without the use of cardiopulmonary bypass to close muscular VSD. Device closure is not popular for the perimembranous VSD because of the potential for postprocedure heart block or development of AR.

Surgical

• 1.

  Procedure.

  • a.

    Direct closure of the defect is performed under hypothermic cardiopulmonary bypass, preferably through an atrial approach rather than through a right ventriculotomy.

  • b.

    PA banding is rarely performed unless additional lesions make the complete repair difficult.

• 2.

  Indications and timing.

  • a.

    A significant L-R shunt with Qp/Qs of greater than 2:1 is an indication for surgical closure. Surgery is not indicated for a small VSD with Qp/Qs less than 1.5:1.

  • b.

    Timing.

  • (1)

    Infants with CHF and growth retardation unresponsive to medical therapy should be operated on at any age, including early infancy.

  • (2)

    Infants with a large VSD and evidence of increasing PVR should be operated on as soon as possible.

  • (3)

    Infants who respond to medical therapy may be operated on by the age of 12 to 18 months.

  • (4)

    Asymptomatic children may be operated on between 2 and 4 years of age.

  • c.

    Contraindications. PVR/SVR ratio of 0.5 or greater or PVOD with a predominant R-L shunt.

• 3.

  Mortality and complications.

  Surgical mortality is 0.5%. Up to 3% of patients develop complete heart block, some transient. Residual shunt occurs in less than 5%.

• 4.

  Surgical approaches for special situations.

  • a.

    VSD + large PDA. If the PDA is large, the ductus alone may be closed in the first 6 to 8 weeks, and the VSD may be closed later. If the VSD is large and nonrestrictive, the VSD should be closed early and the PDA ligated at the time of VSD repair.

  • b.

    VSD + COA. Controversies exist. One approach is the repair of COA alone initially and the closure of the VSD later if indicated. Other options include COA repair and PA banding if the VSD appears large or repair of both defects at the same time using one or two incisions.

  • c.

    VSD + AR is usually associated with subarterial infundibular (or supracristal) VSD and occasionally with perimembranous VSD. When AR is present, a prompt closure of the VSD is recommended, even if the Qp/Qs is less than 2:1, to abort progression of or to abolish AR. Some centers close the VSD if aortic prolapse is evident even in the absence of AR.

Follow-Up

Postoperatively, an office follow-up should be done every 1 to 2 years. The ECG shows RBBB in 50% to 90% of the patients who had VSD repair through right ventriculotomy and in up to 40% of the patients who had repair through the right atrial approach.