The chordae tendineae and papillary muscles form the subvalvular apparatus that supports the atrioventricular valves. This complex system prevents valve prolapse during ventricular systole and contributes to ventricular function.
Overview of the Subvalvular Apparatus
The subvalvular apparatus of the atrioventricular valves consists of:
- Papillary muscles (ventricular projections)
- Chordae tendineae (fibrous cords connecting muscles to leaflets)
- Trabeculae carneae (ventricular wall irregularities that give rise to papillary muscles)
Papillary Muscles
Papillary muscles are conical projections of myocardium that arise from the ventricular walls and anchor the chordae tendineae. They contract during ventricular systole, maintaining tension on the chordae to prevent leaflet prolapse.
Right Ventricular Papillary Muscles
Anterior Papillary Muscle:
- Largest in the right ventricle
- Originates from the anterior ventricular wall (moderator band extends from its base)
- Provides chordae to the anterior and posterior tricuspid leaflets
- The moderator band connects its base to the interventricular septum, carrying the right bundle branch
Posterior Papillary Muscle:
- Originates from the inferior (diaphragmatic) wall
- May be composed of multiple smaller muscles
- Provides chordae to the posterior and septal tricuspid leaflets
Septal Papillary Muscle:
- Smallest, originates directly from the interventricular septum
- Provides chordae primarily to the septal tricuspid leaflet
- Also called the medial papillary muscle or the papillary muscle of the conus
Left Ventricular Papillary Muscles
Anterolateral Papillary Muscle:
- Location: Junction of the anterior and lateral left ventricular walls
- Structure: Typically a single large muscle with multiple heads
- Blood supply: Dual (left anterior descending artery + left circumflex artery)
- Provides chordae to the A1, P1 scallops of the mitral valve
Posteromedial Papillary Muscle:
- Location: Junction of the posterior and medial left ventricular walls
- Structure: May be single or multiple heads
- Blood supply: Single (posterior descending artery from right or circumflex depending on dominance)
- More vulnerable to ischemic dysfunction due to single blood supply
- Provides chordae to the A3, P3 scallops of the mitral valve
Chordae Tendineae
Chordae tendineae are collagenous cords that connect the papillary muscles to the valve leaflets. They are covered by endocardium and contain central cores of fibroelastic tissue.
Classification by Insertion Site
Primary (Marginal) Chordae:
- Insert at the free edge of the leaflets
- Prevent edge eversion during systole
- Thinnest chordae
- 5-10 per leaflet in the mitral valve
- Rupture causes severe mitral regurgitation (flail leaflet)
Secondary (Basal or Strut) Chordae:
- Insert on the ventricular surface of the leaflets, 5-10 mm from the free edge
- Provide structural support to the leaflet body
- Distribute tension evenly across the leaflet
- The largest strut chordae in the mitral valve connect the papillary muscles to the anterior leaflet
- Also contribute to left ventricular function by maintaining geometric relationships
Tertiary Chordae:
- Connect the ventricular wall directly to the leaflet base
- Found only on the posterior mitral leaflet and the tricuspid leaflets
- Short, thick cords
Commissural Chordae:
- Insert at the commissures (where leaflets meet)
- Fan-shaped, with multiple branches
- Stabilize the commissural junctions
Classification by Origin
True Chordae: Connect papillary muscle to leaflet Basal Chordae: Connect ventricular wall directly to leaflet (tertiary) False Chordae: Connect papillary muscle to papillary muscle or ventricular wall to ventricular wall (also called left ventricular bands)
Microscopic Structure
Each chorda has:
- Central core: Dense collagen (type I), provides tensile strength
- Middle layer: Loose connective tissue with elastic fibers
- Outer layer: Endothelial cell covering (continuation of endocardium)
- Nerve fibers: Sensory innervation (possibly mechanoreceptors)
Biomechanical Properties
- Tensile strength: Chords can withstand forces of 0.5-1.5 Newtons during systole
- Elasticity: Limited (5-10% strain before failure)
- Stiffness: Increases with age and in disease states
- Fatigue: Decades of cyclic loading can lead to chordal rupture
Functional Anatomy
Systolic Tension
During systole, the papillary muscles contract, pulling the chordae taut. This creates a parachute-like configuration that seals the valve orifice.
Force balance:
- Ventricular pressure pushes leaflets toward the atrium
- Chordal tension resists this force
- Papillary muscle contraction shortens the chordae to maintain optimal tension
The papillary muscles contract approximately 10-20 ms before the ventricular free wall, providing pre-tension to the chordae before peak systolic pressure.
Geometric Relationships
The valvular apparatus maintains precise spatial relationships:
- Annulus-to-papillary distance: Determines chordal length requirements
- Coaptation zone: The area of leaflet overlap during systole (5-7 mm for mitral valve)
- Tenting height: The distance between the annular plane and the coaptation point (normally < 5 mm in mitral valve)
- Tenting area: The area between the leaflets and the annular plane during systole
Age-Related Changes
- Neonatal period: Chordae are relatively thick and gelatinous
- Childhood: Progressive collagen deposition and thinning
- Adult: Stable collagen structure with age-related cross-linking
- Elderly: Increased stiffness, reduced elasticity, possible chordal elongation
- Myxomatous degeneration: Thickening, elongation, and redundancy of chordae (associated with mitral valve prolapse)
Clinical Significance
Chordal Rupture
Sudden disruption of chordae tendineae, causing acute valvular regurgitation.
Mitral chordal rupture:
- Spontaneous: Idiopathic or myxomatous degeneration
- Ischemic: Papillary muscle dysfunction extending to chordal apparatus
- Infectious: Endocarditis causing chordal erosion
- Traumatic: Blunt chest trauma
Presents as acute severe mitral regurgitation with pulmonary edema. The flail leaflet segment loses support and prolapses into the atrium.
Tricuspid chordal rupture:
- Less common than mitral
- Causes acute right heart volume overload
- Usually traumatic or iatrogenic (pacemaker lead)
Papillary Muscle Dysfunction
Ischemic Papillary Muscle Dysfunction:
- The posteromedial papillary muscle is more vulnerable (single blood supply)
- Presents as mitral regurgitation during angina episodes
- Can be transient (ischemia) or permanent (infarction)
Papillary Muscle Rupture:
- Catastrophic complication of acute myocardial infarction
- Typically occurs 2-7 days post-infarction
- Posteromedial papillary muscle affected more frequently (3:1)
- Presents with acute pulmonary edema and cardiogenic shock
- Emergency surgical intervention required
Papillary Muscle Calcification
- Associated with chronic kidney disease, diabetes, hypertension
- Can cause restriction of papillary muscle motion
- Leads to mitral regurgitation
- Identified on echocardiography or CT
Left Ventricular False Tendons (LV Bands)
- Present in 40-60% of normal hearts
- Connect papillary muscle to papillary muscle or septum to free wall
- Usually incidental findings
- May be associated with benign ventricular arrhythmias or precordial murmurs
- Can be mistaken for pathology on echocardiography
Surgical and Interventional Considerations
Valve Repair:
- Chordal transfer (moving healthy chordae to unsupported segments)
- Chordal shortening (folding elongated chordae)
- Artificial chordae (Gore-Tex neochordae)
- Papillary muscle repositioning
Valve Replacement:
- Subvalvular apparatus preservation (important for post-operative LV function)
- Severing the apparatus reduces LV ejection fraction by 15-20%
- Posterior leaflet preservation is critical for mitral valve replacement
Transcatheter Approaches:
- MitraClip: Edge-to-edge repair, grasping leaflets
- Chordal repair devices: Transapical neochordal implantation
- Understanding chordal anatomy is essential for these procedures