Anatomical peculiarities of the cavo-tricuspid isthmus in the human heart.

The cavo-tricuspid isthmus is the term for the part of the right atrium between the ostium of the inferior vena cava and its border--the Eustachian ridge on one side and the tricuspid valve on the other side. In this area lie the coronary sinus ostium with its Thebesian valve, the fibers of Chiari (10%), and ostia of the deep cardiac veins--the Thebesian veins in close relation to the coronary sinus ostium (35%). Pacing of the coronary sinus is very often used during the treatment of cardiac arrhythmias; radiofrequency catheter ablation in cases of permanent atrial tachycardia is successfully performed through the coronary sinus; during certain cardiosurgical procedures, cardioplegia is performed by retrograde perfusion of the myocardium through the coronary sinus. Knowing and recognizing certain anatomical peculiarities of the structures in this part of the right atrium may be interesting for clinical practice.