Ventricular septal defect

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Definition

Ventricular septal defect (VSD) is defined as a lack of continuity in the interventricular septum which allows the direct circulation of blood between the two ventricles. The lesion can be congenital – isolated or in association with other congenital heart defects – or acquired, usually as a complication of a myocardial infarction or chest trauma.

Incidence

A recent meta-analysis (incorporating 24.091.867 live births) evaluating the frequency of congenital heart defects in the new born population yielded VSD to have the highest worldwide prevalence of around 2.62 for every 1000 live births, atrial septum defects coming in second with 1.64 for every 1000 live births[1]. As some of the defects will spontaneously close and a significant part ot the reminder are treated (surgically or percutaneous), the prevalence of VSD in the adult population decreases to around 0.3% per 1000[2]. Around 2% of patients presenting with ST elevation myocardial infarction develop an interventricular septal rupture, although the incidence appears to have steadily declined in the last decade in the context or reperfusion therapy (lyses or primary percutaneous intervention)[3]

Classification

Based on their localization, VSD can be classified in [4]

  • membranous
  • muscular

Membraneous VSD

The membranous septum is delineated by the aortic valve and the inlet and outlet portions of the interventricular septum with the septal leaflet of the tricuspid valve separating the membraneous septum into two components: atrioventricularis and interventricularis. Membraneous VSD that extend in the muscular part of the interventricular septum are called perimembranous VSD

Muscular VSD

The muscular septum can be divided in three parts: inlet, trabecular and outlet component. A defect can be present at any of these levels taking the name of the anatomical part of the interventricular septum. Defects at the level of the infundibular Septum are named: conal, outlet, supracristal, conoventricular, subpulmonary or double commited subarterial defects [5].

Echocardiography

Echocardiography plays an important role in the diagnosis of the defect, planning for the optimal therapeutic approach and guiding the percutaneous closure of the defect when appropriate [6]. Echocardiography (transthoracic, transesophageal and/or three dimensional) allows the:

  • Diagnosis of the defect
  • Localization of the defect
  • Assessment the hemodynamic relevance of the defect
  • Assessment of the impact of the defect on the morphology and function of the cardiac chambers
  • Diagnosis of possible associated cardiac anomalies
  • Guidance of the interventional closure
  • Evaluation of the outcomes of therapy

Using the standard transthoracic echocardiographic views a complete morphological and functional description of a VSD can be obtained in most of the patients

Echocardiographic techniques

  • 2D greyscale Echocardiography allows the visualisation of the continuity defect at the level of the interventricular septum. Furthermore, morphological and functional information related to the heart chambers can be acquired (i.e. right ventricular dimensions and function, left ventricular ejection fraction, etc.).
  • Colour Doppler echocardiography is essential in the diagnosis of VSD as it confirms the presence of a flow between the two ventricles and identifies the direction of the shunt. In cases when grey scale echocardiography cannot demonstrate a VSD, colour Doppler imaging can show the presence of flow turbulence at the level of the interventricular septum, therefore establishing the diagnosis of VSD. Additional shunts (i.e. atrial septum defect) can be visualised using colour Doppler imaging.
  • Continuous wave Doppler interrogation confirms the direction of the shunt and allows the measurement of the pressure gradient between the two ventricles. The typical continuous wave Doppler envelope in the presence of a left-right VSD displays a high velocity left to right signal in both systole and diastole. During the isovolumic periods a reversal of flow (right to left shunt) can be seen [7].
  • Pulsed wave Doppler can be employed in evaluating the hemodynamic relevance of the shunt by measuring the ratio between pulmonary flow and systemic flow.

Echocardiographic views used to evaluate a VSD [8]

  • In a parasternal long axis view a muscular septal defect, either trabecular or outlet or a membranous/perimembranous septal defect can be visualized.
  • The parasternal short axis view at the base of the great vessels is an important view in which a membranous/perimembrenous or a muscular – outlet type – defect could be visualised just above the right coronary cusp
  • Further short axis views of the left ventricle demonstrate muscular – trabecular type – septal defects
  • An apical four chamber view can further confirm the presence of a muscular VSD
  • Further rotating the transducer and displaying a so called an apical five chamber view that contains the aortic valve can help in visualising a sinus type (inlet) VSD.
  • The subcostal view displaying the four cardiac chambers can further demonstrate the presence of a muscular septal defect

Morphological and functional assessment of the cardiac chambers

Echocardiographic assessment of patients with VSD presenting with left to right shunt shows usually a normally dimensioned right ventricle and a dilatated left ventricle and atrium. These morphological changes are related to the volume overload of the left heart as a result of the direct flow of the shunt volume in the pulmonary artery [7]. The presence of left ventricular volume overload on echocardiography is a finding that indicates VSD closure [9]. A hemodynamically significant shunt left untreated can progress to Eisenmenger Syndrom (equalization of the pressures between the two ventricles or suprasystemic pulmonary pressure). The picture in this case is characteristic for the pressure overloaded right heart with a right ventricle that is dilated and displays a reduced performance and a dilated right atrium [10].

Hemodynamic assessment

The presence of a shunt between the ventricles and the significant pressure difference that exists between the left ventricle and the right ventricle translates into a bigger volume of blood passing through the pulmonary valve as compared to the aortic valve. The ratio between pulmonary flow and systemic flow (Qp/Qs) can be calculated echocardiographically using the time velocity integral (TVI) at the level of each valve and the diameter of the pulmonary ring and left ventricular outflow tract respectively [11]. Another important hemodynamic assessment refers to the evaluation of the level of systolic pulmonary pressure. This can be achieved in two ways in patients with VSD. The conventional method refers to estimating the right ventricular right atrial pressure gradient by the modified Bernoulli equation from the tricuspid regurgitant jet and adding the estimation of the right atrial pressure from the diameter of the inferior cava [12]. In patients with VSD a second method can be employed which consists of subtracting the maximum gradient through the shunt as measured using continuous wave Doppler from the maximum systolic pressure measured with a sphygmomanometer at the arm. The estimation of the systolic pulmonary pressure carries important value in patients with VSD as it can indicate a progression of the hemodynamic status of the patient towards an equalisation of pressures between the two ventiricles

Transesophageal echocardiography [8]

  • can help in detecting small defects that were missed during the transthoracic examination
  • can guide the percutaneous closure of defect and confirm the complete closure of the shunt.


Reference List

  1. van der Linde D, Konings EE, Slager MA, Witsenburg M, Helbing WA, Takkenberg JJ, et al. Birth prevalence of congenital heart disease worldwide: a systematic review and meta-analysis. J Am Coll Cardiol 2011 Nov 15;58(21):2241-7.
  2. Warnes CA, Liberthson R, Danielson GK, Dore A, Harris L, Hoffman JI, et al. Task force 1: the changing profile of congenital heart disease in adult life. J Am Coll Cardiol 2001 Apr;37(5):1170-5.
  3. Figueras J, Alcalde O, Barrabes JA, Serra V, Alguersuari J, Cortadellas J, et al. Changes in hospital mortality rates in 425 patients with acute ST-elevation myocardial infarction and cardiac rupture over a 30-year period. Circulation 2008 Dec 16;118(25):2783-9.
  4. Soto B, Becker AE, Moulaert AJ, Lie JT, Anderson RH. Classification of ventricular septal defects. Br Heart J 1980 Mar;43(3):332-43.
  5. Minette MS, Sahn DJ. Ventricular septal defects. Circulation 2006 Nov 14;114(20):2190-7.
  6. Badano L, Fox K, Sicari R, Zamorano J. Adult congenital heart diseae. The EAE Textbook of Echocardiography. 1st ed. Oxford University Press; 2011. p. 389-92.
  7. 7.0 7.1 Otto C. The adult with congenital heart disease. Textbook of clinical echocardiography. third ed. Philadelphia: Elsevier Saunders; 2004. p. 455-93.
  8. 8.0 8.1 Ginghina C, Popescu B, Jurcut R. Boli cardiace congenitale. Esentialul in ecocardiografie. 1st ed. Editura Medicala Antaeus; 2005. p. 211-36.
  9. Baumgartner H, Bonhoeffer P, De Groot NM, de HF, Deanfield JE, Galie N, et al. ESC Guidelines for the management of grown-up congenital heart disease (new version 2010). Eur Heart J 2010 Dec;31(23):2915-57.
  10. Diller GP, Dimopoulos K, Kafka H, Ho SY, Gatzoulis MA. Model of chronic adaptation: right ventricular function in Eisenmenger syndrome. Eur Heart J Suppl 2007 Dec;9(suppl H):H54-H60.
  11. Vargas BJ, Sahn DJ, Valdes-Cruz LM, Lima CO, Goldberg SJ, Grenadier E, et al. Clinical utility of two-dimensional doppler echocardiographic techniques for estimating pulmonary to systemic blood flow ratios in children with left to right shunting atrial septal defect, ventricular septal defect or patent ductus arteriosus. J Am Coll Cardiol 1984 Jan;3(1):169-78.
  12. Yock PG, Popp RL. Noninvasive estimation of right ventricular systolic pressure by Doppler ultrasound in patients with tricuspid regurgitation. Circulation 1984 Oct;70(4):657-62.
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