Assessment and Treatment of Dynamic Obstruction in Anomalous Right Coronary Artery Using Dynamic Diastolic Pressure Gradient Change during Dobutamine Challenge with Rapid Atrial Pacing

- Operator : Jae woong Choi

Assessment and Treatment of Dynamic Obstruction in Anomalous Right Coronary Artery Using Dynamic Diastolic Pressure Gradient Change during Dobutamine Challenge with Rapid Atrial Pacing
- Operator: Jae woong Choi, MD
Clinical Information
- Relevant clinical history and physical exam:
A 54-year-old male was admitted with chest pain upon effort for two years. The pain was dull and persisted for 1-2 minutes. The location was anterior chest wall and the symptom was aggravated one month previously. He had smoked 20 cigarettes per day for the previous 40 years.

- Relevant test results prior to catheterization:
The electrocardiogram (ECG) showed normal sinus rhythm without significant ST-T abnormality and levels of CK-MB and Troponin-T were within normal range. Transthoracic echocardiogram showed normal LV ejection fraction, chamber size and wall motion. Myocardial perfusion imaging with dipyridamole was done, which showed no filling defect.

- Relevant catheterization findings:
Coronary angiography showed the abnormal origin of RCA from left coronary cusp(LCC) that ran between the aorta and pulmonary vein. (Figure 1, Figure 2) There was no significant narrowing in the left coronary artery, and intravascular ultrasound of proximal RCA revealed an intermediate stenotic lesion (reference vessel area was 15.7 mm2 and lesion lumen area was 6.0 mm2).(Figure 3) Virtual histology revealed fibrotic thickening of the endothelium. (Figure 4)

Interventional Management

- Procedural step:
To determine the severity of dynamic obstruction of RCA, we carried out the coronary pressure wire study (Figure 5). Aortic pressure was obtained by using a 6-F guiding catheter without side holes, connected to a pressure transducer (Becton, Dickinson, Singapore) and Horizon computerized polygraph (GE, USA). After calibration, a 0.014-inch micro-manometer tipped guide wire (PressureWire, Radi-Medical Systems, Uppsala, Sweden) was connected to its interface and advanced under fluoroscopy, distal to the RCA ostial lesion. Selected pressure tracings and angiographic runs were recorded during this procedure. Diastole was identified as the interval between the dichrotic notch in the aortic pressure tracing and the following R-wave peak in the ECG. Mean and diastolic components of aortic pressure (Pa), distal intracoronary pressure (Pd), and pressure gradient (P) were calculated. To obtain baseline pressure parameters, intracoronary administration of 200 µg of nitroglycerin was given for 5 minutes and an intracoronary adenosine bolus (40 µg) was given to induce hyperemia. To obtain dynamic pressure measurements, dobutamine was administered through an intravenous infusion starting at 5 µg/kg per minute; it was increased by 5 µg/kg per minute to a maximum of 30 µg/kg per minute. After dobutamine challenge, the RAP stress test was done to reach the target heart rate (as target heart rate in treadmill test). Pacing rate started at 90 bpm and increased by 20 bpm every three minutes until a final pacing rate of 140 bpm was reached. Pressure parameters were measured continuously until the patient developed symptoms. Maximal diastolic P increased from 6 mmHg at baseline to 13 mmHg, and when the pressure gradient reached to 13 mmHg, T wave inversion was observed, the chest pain was developed. (Figure 6, Figure 7) This result showed that dobutamine challenge with rapid arterial pacing may result in the dynamic obstruction in anomalous RCA, which may cause ischemia. As this result, to relieve the dynamic compression of RCA, we carried out intracoroanary stenting (Taxus 4 x16mm) of RCA ostium (Figure 8). After stenting, lesion lumen area increased from 6.0 mm2 to 12.7 mm2, and despite continuing the dobutamine challenge with rapid atrial pacing, diastolic P decreased to 2 mmHg, chest pain was relieved, and T wave inversion was disappeared. (Figure 9) He was asymptomatic at 2 months' follow-up.

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