The posterior descending artery (PDA), also known as the posterior interventricular artery, descends in the posterior interventricular groove and supplies the inferior wall of the left ventricle and the posterior one-third of the interventricular septum.
Origin and Course
The PDA originates at the crux of the heart (the junction of the atrioventricular and interventricular grooves on the posterior surface). Its origin defines coronary dominance.
The PDA descends in the posterior interventricular groove toward the cardiac apex. It typically ends before reaching the apex but may anastomose with the LAD in some individuals.
Coronary Dominance
Coronary dominance is defined by which artery gives rise to the PDA:
| Dominance | PDA Origin | Frequency |
|---|---|---|
| Right-dominant | RCA | 70-80% |
| Left-dominant | LCx | 10-15% |
| Co-dominant | Both RCA and LCx | 10-15% |
Right-Dominant Circulation
The RCA reaches the crux and gives off the PDA as its terminal branch. The RCA then continues as posterolateral branches to supply the posterior left ventricle.
Left-Dominant Circulation
The LCx courses through the left atrioventricular groove to the crux, where it gives off the PDA. In these individuals, the RCA is small and supplies only the right atrium and right ventricle.
Co-Dominant Circulation
Both the RCA and LCx reach the crux and contribute to the PDA. The PDA may be double (one from each artery) or there may be a dual supply to the posterior septum.
Branches
Septal Perforators
- 3-7 small branches that penetrate the interventricular septum
- Supply the posterior one-third of the septum
- Shorter than LAD septal perforators
- Anastomose with LAD septal perforators
Inferior Ventricular Branches
- Small branches to the adjacent ventricular walls
- Supply the inferior left ventricle and (less commonly) the inferior right ventricle
Dimensions
| Parameter | Typical Value |
|---|---|
| Diameter | 2.0-3.0 mm |
| Length | 3-8 cm |
| Number of septal perforators | 3-7 |
| Wall thickness | 0.3-0.5 mm |
Anatomic Variants
Dual PDA
Two PDAs arise from separate origins, one from the RCA and one from the LCx.
Wrap-Around LAD Supplying the PDA Territory
In some hearts, the LAD wraps extensively around the apex and supplies a significant portion of the posterior interventricular groove.
Hypoplastic PDA
The PDA is small and supplies only a limited portion of the posterior septum.
Clinical Significance
PDA Infarction
PDA occlusion typically causes an inferior myocardial infarction.
ECG findings:
- ST elevation in II, III, aVF
- Often associated with posterior involvement (ST depression in V1-V3)
- Q waves in inferior leads
PDA in Interventional Cardiology
Challenges:
- The PDA is often small and tortuous
- Ostial lesions can be difficult to access
- The acute angle from the RCA may require specialized catheters
- Stent sizing is critical (vessel tapers rapidly)
PDA Collateral Circulation
The PDA forms important collateral connections with:
- LAD septal perforators (deep septal collaterals)
- Distal LAD (apical collaterals)
These collaterals can protect the inferior wall and septum in the setting of chronic LAD occlusion and vice versa.