The compression of the left main coronay artery (LMCA) secondary to pulmonary artery trunk dilatation is a relatively new entity that has been associated with severe pulmonary hypertension. It is associated with acyanogen congenital cardiopathies or idiopathic pulmonary arterial hypertension. The natural history is unknown and its treatment has been based more on the severity of the angiographic compression than on the objective demonstration of myocardial ischemia. We report a case of a woman with severe pulmonary arterial hypertension due to an atrial septal defect with extrinsic compression of the LMCA and a physiopathologic approach to guide its treatment.

       The extrinsic compression of the left main coronary artery (LMCA) secondary to pulmonary artery trunk (PA) dilatation is a relatively new syndrome that has been associated with severe pulmonary hypertension.^1–5 It is mostly associated with acyanogen congenital cardiopathies or to idiopathic pulmonary arterial hypertension.^1–4,6–9 Its natural history is unknown and its treatment has been based more on the severity of the angiographic compression than on the objective demonstration of myocardial ischemia.^1,10,11 To our knowledge, there are 45 reported cases. These patients have different degrees of pulmonary arterial hypertension, but the determining factor for the compression of the LMCA is the PA dilatation.¹² This condition may have a potential role in the genesis of angina, left ventricular dysfunction, arrhythmias and/or sudden death¹³ in patients with pulmonary arterial hypertension. The natural history of this disease and its proper treatment, however, remain unclear. We report a case of a woman with severe pulmonary arterial hypertension due to an atrial septal defect with extrinsic compression of the LMCA secondary to PA dilatation and the physiopathologic evaluation undertaken to guide its treatment.

       Case Report. A 55-year-old Hispanic woman with a history of systemic arterial hypertension, diabetes mellitus and dyslipidemia, was referred for right and left cardiac catheterization due to the presence of an atrial septal defect with severe pulmonary hypertension. Her complaints included dyspnea,

Figure 1

(A) Coronary angiography in 45º left anterior oblique projection (LAO) showing the left main coronary artery stenosis (arrow); (B) LAO caudal view that does not show the irregularity.

palpitations and an episode of amaurosis fugax. She denied experiencing angina. The physical exam revealed an intense second heart sound and a left paraesternal 3/6 systolic murmur. The electrocardiogram showed right ventricle hypertrophy, and the 2-dimensional echocardiogram demonstrated an ASD with bidirectional shunt and severe pulmonary hypertension; the right side chambers were dilated and the ventricle showed hypertrophy with normal left ventricular wall motion and function. A ventilation-perfusion scan ruled out pulmonary embolism. Right heart catheterization revealed PA pressure of 132/40 mmHg (mean 74 mmHg), with a wedge pressure of 8 mmHg, pulmonary vascular resistance of 1,278 dynes-seg/cm-5, cardiac output of 4.13 L/minute, and a Qp/Qs of 0.93. Coronary angiography revealed a proximal 70% LMCA stenosis, best visualized on the left oblique projections (Figure 1); the rest of the coronary arteries did not show any angiographic abnormalities. An intravascular ultrasound demonstrated a dynamic systolic compression of the LMCA, without atherosclerotic disease (Figure 2). The minimal luminal area was 12.4 mm². A pressure wire was then used to evaluate the fractional flow reserve, demonstrating a 0.98 ratio. An MRI demonstrated pulmonary artery enlargement with LMCA compression. A myocardial

Figure 2

Cross sectional intravascular ultrasound views demonstrating an absence of atherosclerotic plaque and the dynamic nature of the compression. (A) Systole. (B) Diastole.

perfusion scan did not demonstrate ischemia. After 6 months, the patient still denies feeling angina and remains under close medical surveillance.

       Discussion. This case report is the first to combine IVUS and guidewire pressure to guide the treatment for extrinsic compression of the LMCA secondary to dilatation of the pulmonary artery. To date, 12 reports and 3 series of cases have been reported (Table 1). Treatment options have included correction of the culprit defect (e.g., ASD closure), coronary artery bypass graft surgery (CABG), pulmonary artery angioplasty, percutaneous intervention, or medical treatment. Roughly 16% of these cases were treated either with CABG or combined CABG and ASD closure.¹⁴ Three patients underwent percutaneous intervention with either bare metal stents or drug-eluting stents, with good clinical and angiographic results at 6-month follow up.^10,11 Pulmonary artery angioplasty has been performed successfully in 3 patients, decreasing the LMCA compression at the 3- to 6-month follow up point.^7,12,15 In 1 patient, improvement of LMCA compression after surgical thromboendarterectomy was reported.¹⁶ When pulmonary hypertension was found to be irreversible, heart-lung transplantation has been performed in 2 cases.^2,9 Medical treatment using drugs such as bosentan has not been reported in patients with extrinsic LMCA compression and pulmonary hypertension; however, intravenous prostacyclin has been used as a bridge to LMCA percutaneous intervention.¹¹
       Pulmonary hypertension has been regarded as a predictor of mortality in patients undergoing CABG surgery,¹⁷ therefore, patients with this condition may benefit from a physiologically guided treatment. Both intravascular ultrasound and fractional flow reserve have been validated to guide the treatment of left main coronary artery disease.^18–20 We consider that the indication for percutaneous or surgical treatment should be based on objective evidence of myocardial ischemia by abnormal fractional flow reserve (< 0.80 ratio)²⁰ or an intravascular ultrasound cross sectional area ? 0.75 mm².^18,19

       Conclusion. Given the increased operative risk for patients with pulmonary hypertension, patients with LMCA compression due to dilatation of the PA should be extensively examined by intravascular ultrasound and/or fractional flow reserve to demonstrate myocardial ischemia before revascularization. We believe that percutaneous or surgical revascularization should be performed if the intravascular ultrasound minimum lumen area is < 5.9 mm²,^18,19 and/or abnormal fractional flow reserve is < 0.80.

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