I read with interest the recent letter from Drs. Srivastava and Undesser [1] discussing the occurrence of two transient ischemic attacks from among 46 patients having contrast studies with echocardiography using 10 mL of agitated air and normal saline.

We see many patients with severe chronic pulmonary artery hypertension who are referred for pulmonary thromboendarterectomy. Many of these patients have pulmonary artery pressures near systemic levels, substantial tricuspid regurgitation, and elevated right atrial pressures. These patients have routine contrast echocardiography as part of their preoperative evaluation to determine the presence of patent foramen ovale. If detected, the patent foramen is closed at the time of thromboendarterectomy so that the risk for paradoxical emboli and early postoperative right-to-left shunting is diminished.

We previously described 50 consecutive patients who were evaluated for pulmonary thromboendarterectomy and found two transient ischemic events after injection of agitated air and saline [2]. In both cases, a large volume of microbubbles passed through the patent foramen from the right atrium into the left atrium and was easily seen on transthoracic echocardiography.

We agree with Drs. Srivastava and Undesser that transient ischemic attacks may occur when an interatrial communication exists and when agitated air and saline are used as the contrast agent. No manual agitation technique can prevent microbubbles large enough to temporarily obstruct the microvasculature.

A newly approved ultrasound contrast agent, Albunex (Molecular Biosystems, Inc., San Diego, California) can be used to detect right-to-left shunting. Although Albunex crosses the lungs and has been shown to be useful for enhancing left ventricular endocardial definition [3], it also can be used to detect right-to-left shunts before they appear on the left side of the heart. The agent has an excellent safety profile when given either intravenously or through intra-aortic or intracoronary injections [4]. No neurologic abnormalities have been identified with direct aortic injections.

Although commonly used, agitated air and saline pose a potential risk that can be avoided by the use of an approved ultrasound contrast agent.