NORMAL CORONARY SINUS

1. The coronary sinus drains the majority of myocardial venous return.
2. It runs in the atrioventricular groove and enters the right atrium just below the level of the foramen ovale and just above the valve of the IVC.
3. It lies adjacent to and slightly posterior to the mitral valve annulus within the atrio-ventricular groove.
4. The entire length of the coronary sinus can be demonstrated from the lateral free wall of the left ventricle to the ostium. The ostium of the coronary sinus is found in the same plane as the inter-atrial septum, just posterior to the crux.
5. During diastole blood flows:
1. From the coronary sinus to the right atrium.
2. Across the foramen ovale towards the left atrium.

ULTRASOUND

• Examine the heart in the lateral 4-chamber view (most favorable insonation angle to study blood flow across the coronary sinus).
• By tilting the transducer caudally from the level of the foramen ovale, flow along the axis of the atrioventricular sulcus is representative of coronary sinus flow.
• The coronary sinus blood flow can be seen entering the right atrium at the inferior edge of the foramen ovale just above the tricuspid valve. Blood flow is directed towards the right atrium.
• Diameter at its midportion = 1mm at 16 weeks to 3.2 mm at 40 weeks.
• Length is measured from the inner aspect of the left wall of the heart to the sinus ostium. Length increases from about 5mm at 16 weeks to 12 mm at 40 weeks. The length is four times larger than the diameter.
• Shape is constant throughout gestation.

FLOW VELOCITY WAVEFORM IN THE CORONARY SINUS (1)

• Sample the jet of blood entering the right atrium.
• Sample gate must cover the entire coronary sinus but must not be too large as this increases the likelihood of contamination from intracardiac flows, or interference from either the interatrial septum of atrioventricular valves.
• Keep angle of insonation below 15 degrees.
• Measure in the absence of fetal breathing.
• Waveform is similar to the adult waveform and has triphasic appearance with a predominant diastolic component.
• S wave = Peak velocity during ventricular systole.
• D wave = Peak velocity during ventricular diastole.
• A wave = Peak velocity during atrial contraction (retrograde flow).
• Quantification of flow cannot be accurately determined due to the large variability in the size of the vessel.

REFERENCES

1. Baschat AA, Gembruch U. Examination of fetal coronary sinus blood flow by doppler. Ultrasound Obstet Gynecol 1998;11:410-414.
2. Kronzon I, Tunick PA, Jortner R et.al. Echocardiographic evaluation of the coronary sinus. J Am Soc Echocardiogr 1995;8:518-526
3. Rein AJJT, Nir A, Nadjari M. The coronary sinus in the fetus. Ultrasound Obstet Gynecol 2000;15:468-472