Hammocking of Mitral Valve Leaflet: Definition
Hammocking (or "hammock mitral valve") is a rare congenital mitral valve anomaly where the mitral leaflets attach directly to hypertrophied, fused papillary muscles with absent or severely shortened chordae tendineae, creating a hammock-like appearance that restricts leaflet motion and causes mitral stenosis and/or regurgitation. 1
Anatomical Characteristics
The hammock mitral valve represents a specific subtype of congenital mitral stenosis characterized by:
- Direct attachment of one or both mitral leaflets to abnormally developed papillary muscles
- Absent or markedly shortened chordae tendineae - the normal fibrous chordal structures are missing 2, 3
- Hypertrophied and fused papillary muscles that form a muscular band or palisade directly beneath the leaflets 4
- Restricted leaflet motion throughout the cardiac cycle, particularly affecting diastolic opening
Clinical Presentation Spectrum
Complete Hammock Valve
In the classic form, both anterior and posterior leaflets arise directly from abnormal papillary muscles, creating severe obstruction. This typically presents in neonates and infants with:
- Acute heart failure within days to weeks of birth 2
- Severe mitral stenosis or regurgitation
- Pulmonary congestion and respiratory distress 2
Partial Hammock Valve
A "forme fruste" variant involves primarily the posterior leaflet 4:
- Three to four papillary muscles implanted high on the posterior wall forming a palisade under P2 and P3 segments
- May present later in childhood or even adulthood 5, 4, 6
- Causes mitral regurgitation more commonly than stenosis in adults
Distinction from Other Mitral Abnormalities
Critical differentiation: Hammocking should not be confused with:
- Billowing/prolapse: Where leaflet tissue protrudes above the annular plane into the left atrium 7
- Systolic anterior motion (SAM): Abnormal anterior motion of the leaflet toward the septum during systolic contraction 1
- Leaflet tethering: Displacement due to LV dilation and abnormal chordal tension in functional MR 1
- Doming: Outward rounding/outpouching that causes incomplete opening 1
The hammock valve has a fixed structural abnormality with direct muscular attachment, whereas these other conditions involve abnormal motion of otherwise structurally intact leaflets with normal chordal anatomy.
Diagnostic Recognition
On echocardiography, look for:
- Absence of normal chordal structures
- Direct continuity between leaflet tissue and papillary muscles
- Restricted motion in both systole and diastole (Carpentier Type IIIa) 8
- Abnormal muscular band beneath the mitral leaflets 6
- Associated mitral stenosis (mean gradient) and/or regurgitation
Clinical Significance
Prognosis depends on timing of diagnosis:
- Undiagnosed neonatal cases can be fatal within days due to acute heart failure 2
- Early recognition and referral to specialized cardiac centers is life-saving
- Surgical repair is possible with leaflet augmentation techniques and papillary muscle division 5, 4
- Adult presentations may be misdiagnosed as acquired valve disease 6
The term "hammock" derives from the visual appearance of the leaflets suspended between abnormal papillary muscles like fabric in a hammock, rather than hanging freely from normal chordae.