Olga Shindler MD, Masoud Bamdad MD, Daniel Shindler MD
Reprinted by permission from Primary Cardiology October 1994.
A 70 year old patient underwent transesophageal echocardiography to rule out aortic dissection. During the study, the interatrial septum was noted to bulge toward the left atrium. Routine injection of saline contrast into the venous chambers revealed prominent contrast transit from the right atrium to the left atrium. There was a fainter, more transient contrast effect in the ascending aorta. The intermittent atypical chest pain that prompted the initial suspicion of aortic dissection became more severe the next day. At that time, twelve lead electrocardiogram showed new ST segment elevation in inferior leads indicating acute myocardial infarction which retrospectively had a "stuttering" onset, herein the initial mistaken suspicion of aortic dissection. The myocardial infarction was complicated by progressive hypotension and intractable arrhythmias leading to the patient's demise.
On autopsy the patient was found to have a patent foramen ovale with easy introduction of a probe across the atrial septum. There was evidence of inferior myocardial infarction with right ventricular involvement. There was also diffuse, patchy myocardial fibrosis. The appearance of the foramen ovale was markedly different when viewed from the left atrial surface compared to the right atrial surface. On the left atrial surface the foramen ovale resembled a flap. On the right atrial surface there was a crater like indentation into the atrial septal wall surrounded by a rim of tissue, the limbus of the fossa ovalis. This anatomical arrangement promotes the passage of contrast from right to left only if the right atrial pressure exceeds the left atrial pressure. Normally the left atrial pressures exceed the right atrial pressures and the flap-like foramen ovale remains closed. This has been borne out in many transesophageal studies where contrast does not pass from right to left until the patient is asked to cough or to perform a Valsalva maneuver (thereby increasing the right atrial pressure relative to the left atrial pressure). The availability of transesophageal echocardiography makes the diagnosis of patent foramen ovale fairly easy. Once the diagnosis is made, however, many questions remain about its significance and about the course of therapy. Although this remains clinically unproved, it is possible to qualitatively estimate the degree of shunting by viewing the contrast appearance in the left side chambers. It is unlikely that a small amount of contrast will actually opacify the lumen of the ascending aorta. The ascending aorta is in plain view in most transesophageal studies next to the right atrium and to the left atrium. Therefore, visual (qualitative) densitometry can be easily performed with contrast injections to subjectively assess the degree of shunting from the right atrium to the left atrium. The upcoming availability of densitometry on ultrasound equipment promises to convert this to a quantitative assessment by measuring the pixel luminance of the contrast and comparing the right atrium, left atrium, and ascending aorta in the same image frame during the transesophageal study.(1)
This patient illustrates the fact that a foramen ovale can be found in all age groups.(2) Often, as in this case, it is unsuspected and found incidentally during a transesophageal study. In contrast, young people with unexplained stroke may actually be referred for transesophageal echocardiography to look for a patent foramen ovale.(3) Certain conditions may predispose the flap like foramen ovale to open; namely, the many causes of increased right atrial pressure (be it permanent or temporary). The causes can be esoteric or mundane. A rare condition known as platypnea orthodeoxia results in shunting right to left through a foramen ovale when a patient sits up (platypnea is dyspnea in the upright position) with resultant arterial blood desaturation (deoxia).(4) Another, perhaps more recognizable, condition that can increase right atrial pressures, is pulmonary hypertension (diagnosable using Doppler echocardiography). In this particular patient, a combination of unexplained myocardial fibrosis with an all too common myocardial infarction involving the right ventricle caused the shunting from right to left. Her initial presentation was atypical chest symptoms followed by acute inferior myocardial infarction. Autopsy showed that the infarction involved the right ventricular wall and was superimposed on myocardium that already showed fibrosis. This combination presumably created a rise in right atrial pressure relative to the left, thereby causing the right to left interatrial shunt through the patent foramen ovale.(5)
REFERENCES
1. Hagler DJ, Tajik AJ, Seward JB, Ritman EL. Videodensitometric quantitation of left-to-right (sic) shunts with contrast echocardiography. in Meltzer RS, Roelandt J (eds.). Contrast Echocardiography. The Hague. Martinus Nijhoff, p. 298, 1982.
2. Hagen PT, Scholz DG, Edwards WD. Incidence and size of patent foramen ovale during the first ten decades of life: an autopsy study of 965 normal hearts. Mayo Clin Proc 1984;59:17-20.
3. Webster AWI, Smith HJ, Sharpe DN. Patent foramen ovale in young stroke patients. Lancet 1988;2:11-12.
4. Herregods MC, Timmermans C, Frans E, Decramer M, Daenen W, De Geest H. Diagnostic value of transesophageal echocardiography in platypnea. J Am Soc Echocardiogr 1993;6:624-7.
5. Lopez-Sendon J, Lopez de Sa E, Roldan I, Fernandez de Soria R, Ramos F, Martin Jadraque L. Inversion of the normal interatrial septum convexity in acute myocardial infarction: incidence, clinical relevance, and prognostic significance. J Am Coll Cardiol 1990;15:801-5.
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