Pectinate muscles are parallel ridges of muscle found within the internal walls of the heart’s upper chambers. Their name, derived from the Latin word “pecten,” refers to their comb-like appearance. They are a normal anatomical feature of the heart.
Anatomy and Location
Pectinate muscles are muscular bands resembling a comb. These parallel ridges are primarily located on the inner surface of the heart’s atria, specifically within the right atrium and the ear-like appendages called auricles of both the right and left atria. In the right atrium, they are thicker and more numerous, extending from a vertical ridge known as the crista terminalis.
The presence of pectinate muscles gives these atrial regions a rough, trabeculated appearance. In contrast, other parts of the atrial walls, particularly in the left atrium, are notably smoother. Pectinate muscles are distinct from trabeculae carneae, which are similar muscular ridges found in the ventricles. Pectinate muscles are characteristic of the atria, helping to differentiate the chambers.
Function in the Heart
The primary role of pectinate muscles is the mechanical efficiency of the atria. Their ridged structure increases the internal surface area of the atrial walls. This increased surface area allows the atria to accommodate a greater volume of blood without experiencing increased wall stress, functioning like an accordion. This ability to stretch and expand is useful during rapid filling phases of the cardiac cycle.
The expanded surface area also contributes to effective atrial contraction. The folds of the pectinate muscles help to prevent the atrial walls from collapsing or sticking together during the heart’s pumping action. By facilitating efficient contraction and expansion, these muscles contribute to the smooth propulsion of blood into the ventricles.
Clinical Significance
Pectinate muscles are normal anatomical structures and are not a common site of disease. However, their distinct appearance can be relevant in cardiac imaging. On scans such as computed tomography (CT), prominent pectinate muscles can be mistaken for abnormal masses or blood clots (thrombi). Recognizing their parallel, comb-like pattern helps medical professionals differentiate them from actual pathology.
The complex architecture of the atria, including the pectinate muscles, can play a minor role in certain heart rhythm disorders. For example, in atrial fibrillation, the intricate network of these muscles can influence the chaotic electrical activity within the atria. While they may contribute to the substrate for such conditions, they are not the underlying cause of these arrhythmias.