Congenital Obstruction to Left Atrial Flow: Mitral Stenosis, Cor Triatriatum, Pulmonary Vein Stenosis

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Chapter 9 Congenital Obstruction to Left Atrial Flow

Mitral Stenosis, Cor Triatriatum, Pulmonary Vein Stenosis

Congenital obstruction to left atrial flow can originate at or near the junction of the pulmonary veins and the left atrium (pulmonary vein stenosis), within the left atrium (cor triatriatum), immediately above the mitral valve (supravalvular stenosing ring), or within the mitral apparatus (mitral stenosis; Figure 9-1; Box 9-1). Pure or relatively pure forms of each defect are emphasized in this chapter, although a variety of anomalies often coexist.¹^–³ Pulmonary veno-occlusive disease is covered in Chapter 14, total anomalous pulmonary venous connection with obstruction is covered in Chapter 15, and hypoplastic left heart with a hypoplastic mitral orifice is covered in Chapter 31.

Figure 9-1 A, Illustration of congenital obstruction to left atrial flow involving the mitral apparatus or immediately above or contiguous with the mitral annulus. B, Illustration of typical cor triatriatum. A fibrous or fibromuscular diaphragm partitions the left atrium. The proximal compartment receives the pulmonary veins and is a high-pressure zone. The distal compartment contains the fossa ovalis and the left atrial appendage (LAA) and is a low-pressure zone. C, Illustration of pulmonary vein stenosis in which one or more pulmonary veins are narrowed near their left atrial junction. (Ao = aorta; LA = left atrium; LV = left ventricle; LPV = left pulmonary veins; RPV = right pulmonary veins.)

Congenital mitral stenosis

Congenital mitral stenosis involves the annulus, the zone immediately above and contiguous with the annulus, the leaflets, the chordae tendineae, and the papillary muscles. The physiologic consequences of congenital mitral stenosis are analogous to acquired mitral stenosis.

The incidence rate has been estimated at 0.6% of necropsy cases of congenital heart disease and 0.21% to 0.42% of clinical cases.⁴ Congenital mitral stenosis with a functionally adequate left ventricle includes the following malformations in approximate order of frequency (see Box 9-1):⁵^–⁹

1. Short chordae tendineae with reduction in or obliteration of interchordal spaces and a decrease in interpapillary muscle distance (Figure 9-2A).¹

2. Parachute mitral valve, which consists of a single eccentric papillary muscle (absence of one papillary muscle or fusion of the two papillary muscles) into which all chordae tendineae from both leaflets insert (Figures 9-2B and 9-3 and video 9-1).¹^,²^,¹⁰

3. Anomalous mitral arcade characterized by a band of fibrous tissue that runs adjacent to the free margins of the mitral leaflets with short or absent chordae tendineae and multiple contiguous papillary muscles.¹¹ The arcade can permit normal function¹² or can render the valve mechanism incompetent when the chordae tendineae are well formed.¹³^,¹⁴ Rarely, an anomalous mitral arcade coexists with a tricuspid arcade and incompetence of both atrioventricular valves. A supravalvular stenosing ring consists of a circumferential diaphragm at the base of the atrial surfaces of the mitral leaflets (Figure 9-2C).⁶^,⁸^–¹⁰^,¹⁵ Rarely, a supravalvular ring occurs with an isolated obstructive lesion¹⁶ or coexists with mitral regurgitation.¹⁷

4. Accessory mitral valve tissue.¹⁸

5. Anomalous left ventricular muscle bundles or anomalous obstructing papillary muscles.¹⁸^,¹⁹

6. Double orifice mitral valve, which can be stenotic, incompetent, or functionally normal.

Figure 9-2 Illustrations of three anatomic types of congenital mitral stenosis involving the mitral apparatus. A, The typical form is characterized by decreased interpapillary muscle distance and a reduction in interchordal spaces. B, Parachute mitral valve with a single eccentric papillary muscle. C, Supravalvular stenosing mitral ring.

Figure 9-3 A, Left ventriculogram from an 8-year-old girl with a parachute mitral valve identified by the single papillary muscle (wedge of negative contrast, arrow). B, Echocardiogram (apical four-chamber) from a 10-year-old boy with Shone’s complex consisting of a supravalvular stenosing ring, seen between LA and parachute mitral valve (MV). The parachute mitral valve and single chordae are shown. C, Necropsy specimen from a 14-year-old boy with a parachute mitral valve (thick arrow), obstructing interchordal slits, and insertion into a single eccentric papillary muscle (PM). A supravalvular ring is identified by the thin arrow. Compare with the echocardiogram in part B (Video 9-1) (AO = ascending aorta; LA = left atrium; LV = left ventricle.)

Flow across a normal mitral orifice is between the leaflets (interleaflet) and the chordae tendineae (interchordal). In a parachute mitral valve, all chordae tendineae insert into a single papillary muscle and the interchordal spaces are reduced or obliterated,¹⁰ so flow cannot be interchordal (see Figures 9-2B and 9-3).

A parachute mitral valve is usually one of the components of Shone’s complex, a developmental combination of four obstructive lesions: namely, supravalvular stenosing ring, parachute mitral valve, subaortic stenosis, and coarctation of the aorta (Figures 9-3 and 9-10).¹^,²^,¹⁵^,¹⁶ All four lesions are not always present; if they are present, they may not be functionally significant.²^,¹⁰^,²⁰ The supravalvular mitral ring can be rudimentary (see Figure 9-3C), or can bridge the mitral orifice as a stenosing diaphragm (see Figure 9-3B).⁸^,⁹^,¹⁸

Figure 9-10 Echocardiograms (apical four-chamber) with Doppler scan interrogation from a 3-year-old boy with Shone’s complex. A, Unmarked paired arrowheads point to a supravalvular stenosing ring. B, Paired oblique arrows identify a parachute mitral valve with chordae tendineae that insert into a single eccentric papillary muscle (large right unmarked arrowhead). C, The Doppler sample volume within the parachute mitral valve (arrow). D, Doppler signal in diastole across the parachute mitral valve. (LA = left atrium; LV = left ventricle; RA = right atrium; RV = right ventricle.)

History

There is a male predilection in congenital mitral stenosis,¹ in contrast to rheumatic mitral stenosis, which has a female predilection. Familial recurrence has not been reported. If stenosis is severe, symptoms begin shortly after birth when pulmonary blood flow commences and suddenly enters the obstructed left atrium. Fifty percent of symptomatic infants die within 6 months, but an occasional infant is asymptomatic and a few remain relatively free of symptoms for years.²¹ With a parachute mitral valve or a supravalvular mitral ring, longevity is better (median, 10 years and 5.5 years, respectively), but short chordae tendineae and obliterated interchordal spaces result in death at a median age of 6 months.⁶^,¹⁰ Anomalous mitral arcade or double-orifice mitral valve permits adult survival when the mitral apparatus functions normally or is purely regurgitant.⁵^,¹⁴

Orthopnea, dyspnea, tachypnea, and paroxysmal cough are results of pulmonary edema that is punctuated by lower respiratory infections.¹^,²¹^–²³ Congenital mitral stenosis is occasionally associated with syncope²¹ but seldom with hemoptysis.²³ Aphonia has been attributed to compression of the recurrent laryngeal nerve by a dilated hypertensive pulmonary trunk, analogous to hoarseness in adults with pulmonary hypertension and rheumatic mitral stenosis. Infective endocarditis is rare.¹

Physical Appearance

Mild cyanosis coincides with congestive heart failure.²¹^,²² Recurrent lower respiratory infections and the catabolic effects of heart failure account for physical underdevelopment.²¹^,²³

Arterial Pulse, Jugular Venous Pulse, Precordial Movement, and Palpation

The arterial pulse is normal and confirms normal sinus rhythm, which is the rule in congenital mitral stenosis.²¹ The jugular venous pulse has an increased A wave because of pulmonary hypertension (Figure 9-4). A precordial bulge is common,²³ and a right ventricular impulse is palpable atthe lower left sternal border and subxiphoid area.²¹^,²³

Figure 9-4 Right atrial pressure pulse (RA) showing a prominent A wave in a 3-year-old girl with congenital mitral stenosis.

Auscultation

Neither a loud first heart sound nor an opening snap are heard; the necessary preconditions of these two auscultatory signs—abrupt opening and closing movements of the belly of a mobile anterior mitral leaflet—are not features of congenital mitral stenosis (Figures 9-5 and 9-6).¹^,¹⁰^,¹¹^,²³

Figure 9-5 Phonocardiogram from a 2-year-old girl with Shone’s complex (supravalvular stenosing ring, parachute mitral valve, coarctation of the aorta) and a patent ductus arteriosus with pulmonary vascular disease and reversed shunt. The first heart sound (S₁) is soft, and there is no opening snap. There is a soft mid-diastolic murmur (DM). (S₂ = second heart sound.)

Figure 9-6 Phonocardiogram from the 3-year-old girl with congenital mitral stenosis referred to in Figure 9-4. The first heart sound (S₁) is loud, but there is no opening snap. A soft mid-diastolic murmur (DM) is followed by presystolic accentuation.

In the presence of a parachute mitral valve or a supravalvular ring,¹⁷ a holosystolic murmur at the apex or lower left sternal edge is the result of mitral regurgitation or pulmonary hypertensive tricuspid regurgitation.²² An apical mid-diastolic murmur with presystolic accentuation (see Figures 9-5 and 9-6) is exceptional because the rapid heart rate in infants shortens diastole¹^,²³ and because a dilated hypertensive right ventricle displaces the left ventricle from the apex.^24,²⁵ The pulmonary component of the second heart sound is loud because of pulmonary hypertension that sets the stage for the Graham Steell murmur of high-pressure pulmonary regurgitation.¹^,¹⁸

Electrocardiogram

Atrial fibrillation is exceptional in contrast to rheumatic mitral regurgitation.¹ Pulmonary hypertension results in right atrial P wave abnormalities,¹ right axis deviation,¹ and right ventricular hypertrophy (Figure 9-7).¹

Figure 9-7 Electrocardiogram from the 2-year-old girl with Shone’s complex and pulmonary vascular disease referred to in Figure 9-5. Tall peaked right atrial P waves are present in leads 1, 2, and V₂. There is marked right axis deviation. Right ventricular hypertrophy is manifested by the tall monophasic R wave in lead V₁ and the deep S wave in lead V₆. Large RS complexes in lead V₂ and V₃ suggest biventricular hypertrophy because of coarctation of the aorta.

X-Ray

Pulmonary venous congestion includes Kerley’s lines (Figure 9-8).¹^,²³ Mild to moderate left atrial enlargement is recognized in the lateral projection (see Figure 9-8B). Straightening of the left cardiac border (Figure 9-9) by an enlarged left atrial appendage is much less common than in rheumatic mitral stenosis.¹ Calcification of the mitral valve is absent in the x-ray and absent histologically.²⁶ The pulmonary trunk, right ventricle, and right atrium are enlarged because of pulmonary hypertension (see Figures 9-8 and 9-9).

Figure 9-8 X-rays from the 2-year-old girl with Shone’s complex whose phonocardiogram is shown in Figure 9-5. A, Pulmonary venous congestion is striking. The pulmonary trunk (PT) and right atrium (RA) are dilated. B, The lateral film shows displacement of the barium esophagram by an enlarged left atrium (LA).

Figure 9-9 X-ray from the 3-year-old girl with congenital mitral stenosis referred to in Figures 9-4 and 9-6. There is bilateral hilar pulmonary venous congestion. The right atrium (RA) and pulmonary trunk (PT) are dilated, and the left cardiac border is straightened by an enlarged left atrial appendage (arrow).

Echocardiogram

Congenital mitral stenosis is characterized by two well-formed papillary muscles with a reduced interpapillary distance.¹⁰ A parachute mitral valve is characterized by a single papillary muscle into which all chordae tendineae converge (Figures 9-3B,C and 9-10).¹⁶^,²⁷^–²⁹ The effective orifice size cannot be determined with two-dimensional echocardiography because flow is interchordal and the valve is eccentric (see Figure 9-10B), but Doppler scan interrogation can determine the gradient and the functional orifice size (see Figure 9-10C,D). A supravalvular ring is more readily identified when it is not attached to the mitral leaflets (see Figures 9-3B and 9-10A).⁶ Otherwise, the ring is imaged only in diastole.⁶