u CASE REPORTS

Refractory Hypoxemia in Right Ventricular Infarction From Right-to-Left Shunting via a Patent Foramen Ovale: Efficacy of Contrast Transesophageal Echocardiography DAVID Cox, M.D., JAMES TAYLOR, M.D., NAVIN C. NANDA, M.D., Birmingham, Alabama

We report a case in which contrast trans- esophageal echocardiography proved helpful in establishing the diagnosis of refractory hypoxe- mia from a patent foramen ovale with a right- to-left shunt due to right ventricular infarction.

From the Division of Cardiovascular Disease, University of Alabama at Birmingham. Birmingham, Alabama.

Requests for reprints should be addressed to Navin C. Nanda, M.D., University of Alabama at Birmingham, Heart Station SWB/SlOP, Birmingham, Alabama 35294.

Manuscript submitted June 15. 1990 and accepted in revised form November 19. 1990.

R ight ventricular infarction is a well-recognized complication of inferior myocardial infarction.

Increased right filling pressure during right ventric- ular infarction clinically results in an elevated jugu- lar venous pulse and a positive Kussmaul’s sign. When right atria1 pressure equals or exceeds left atrial pressure, a right-to-left shunt can occur at some point during the cardiac cycle if an interatrial channel from an atrial septal defect or a patent foramen ovale exists. Refractory hypoxemia from a patent foramen ovale with a right-to-left shunt has been reported with right ventricular infarction, but is less well recognized [l]. We report a case where contrast transesophageal echocardiography proved helpful in establishing this diagnosis.

CASE REPORT A 65year-old nurse without a prior cardiac histo-

ry presented to a local community hospital in car- diogenic shock with inferior ST-segment elevation on the electrocardiogram. Thrombolytic therapy with tissue plasminogen activator was initiated, but a traumatic intubation necessitated immediate ter- mination of this infusion. The patient was trans- ferred to University Hospital receiving dobutamine (7 pg/kg/minute) and dopamine (18 rglkglminute) .

The patient was intubated but awake and alert. Her systolic blood pressure ranged from 60 to 80 mm Hg, while her pulse rate was llO/minute. Physi- cal examination revealed mild jugular venous dis- tention, an absent Kussmaul’s sign, clear lung fields, absent Ss or Sq, no murmurs, and no periph- eral edema. The electrocardiogram revealed acute ST-segment elevation in the inferior leads. Right- sided chest leads revealed 2-mm ST-segment eleva- tion in leads Vsx through V~R. The chest radiograph showed clear lung fields without pulmonary edema. An emergency transthoracic echocardiogram re- vealed akinesis of the right ventricular diaphrag- matic wall consistent with right ventricular infarc- tion [2]. No pericardial effusion was noted. The left ventricular inferior wall was poorly visualized, but overall left ventricular function appeared normal. The study was limited by a poor acoustic window. The patient’s total creatine phosphokinase level rose to 2,306 with 15% MB fraction.

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Figure 1. Contrast transesophageal echocardiography demonstrating right-to-left shunt at the atrial level. Five-chamber view. Left, a small defect (D) is noted in the interatrial septum consistent with a patent foramen ovale. Right, after a peripheral venous bolus of normal saline, contrast echoes are noted moving from the right atrium (RA) into the left atrium (LA) through the defect whose mildly thickened edges are outlined by arrows. AV = aortic valve: LV = left ventricle; RV = right ventricle.

Hospital Course Initial Swan-Ganz catheter readings revealed a

pulmonary capillary wedge pressure (PCWP) of 15 mm Hg, right atria1 (RA) pressure of 12 mm Hg, pulmonary artery pressure of 33/19 mm Hg, and a cardiac output of 3.1 L/minute by thermodilution during dobutamine therapy. The patient was venti- lated on 100% oxygen via endotracheal intubation. Her initial arterial blood gas study showed a pH of 7.40, carbon dioxide tension (PCOz) of 30 mm Hg, and oxygen tension (POz) of 140 mm Hg with an alveolar-arterial gradient of 535. Over the next 6 to 8 hours, her POz gradually decreased to 61 mm Hg on continued 100% oxygenation. Serial Swan-Ganz readings revealed rising RA pressures to 15 to 19 mm Hg, while PCWP remained in the 15 to 19 mm Hg range. To account for the deterioration in oxy- gen exchange, a bedside perfusion scan was ob- tained and was read as low probability for pulmo- nary embolus. Serious consideration of a right-to-left shunt via a patent foramen ovale to explain refractory hypoxemia prompted another transthoracic echocardiogram with normal saline as contrast material [3]. However, a shunt could not be conclusively demonstrated. Prompt performance of contrast transesophageal echocardiography re- sulted in confirmation of right-to-left shunting. A 6.8-mm Aloka-Corometrics probe was passed into the esophagus without difficulty using standard techniques after local 20% benzocaine spray was applied to the oropharynx [4]. A mixture of normal saline was vigorously shaken at the bedside by hand and injected via the right atria1 port of the Swan- Ganz catheter. Contrast echoes were clearly seen crossing the interatrial septum and moving into the left atrium (Figure 1).

The patient was then taken to the catheterization laboratory where a shunt series verified a right-to- left shunt. During the procedure, mean RA pressure was 17 mm Hg, while mean left atrial (LA) pressure was 19 mm Hg. Left-to-right shunt ratio was calcu-

lated to equal 0.73. Coronary angiograms revealed a proximal occlusion of the right coronary artery without collateral filling. Both the circumflex and the left anterior descending arteries had a 50% ste- nosis. An 8F Goodale-Luben catheter easily crossed the patent foramen ovale. An 8F Swan-Ganz bal- loon was placed into the left atrium through the patent foramen ovale. The balloon was then filled with contrast and snugly pulled against the patent foramen ovale in an attempt to decrease shunting. The patient was returned to the coronary care unit after placement of an intra-aortic balloon pump. However, no improvement in hemodynamics or oxygenation occurred and the patient shortly died. An autopsy was refused.

COMMENTS Interatrial shunting through a patent foramen

ovale is becoming more recognized as a complication of right ventricular infarction. A patent foramen ovale may occur in up to 27% of normal adults. Me- chanical ventilation by itself can produce refractory hypoxemia via this mechanism by increasing right- sided filling pressures [5]. When mechanical ventila- tion is coupled with right ventricular infarction, re- fractory hypoxemia can be a difficult management problem. Attempts to use low tidal volumes and to decrease forced inspiratory oxygen (FIOz) were met only with further decreases in PO2 in this patient.

Although recent reports suggest balloon catheter closure of a patent foramen ovale may result in im- provement of hypoxemia and decreased shunting, others suggest surgical closure can be lifesaving [6-81. Early and prompt recognition of this clinical problem may allow correction before irreversible hemodynamic compromise occurs, as was the case with our patient. To this end, transesophageal echocardiography utilizing a contrast agent may be a useful and simple bedside diagnostic tool in those patients so critically ill that a transthoracic ap- proach proves to be a limited study [Q]. In our pa-

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tient, transesophageal echocardiography was easily and quickly performed without sedation and with a small probe. Contrast echocardiography may reveal a patent foramen ovale with a significant shunt that even a careful color Doppler examination could miss.

Shunting via an interatrial defect can occur whenever RA pressure exceeds LA pressure (a con- tinual RA-LA gradient) or can occur intermittently during the cardiac cycle when mean atrial pressures are equal. RA pressure, along with LA pressure, usually decreases slightly with inspiration. How- ever, during right ventricular infarction, RA pres- sure may not decrease with inspiration and, if the right ventricular wall is quite noncompliant, may actually increase with inspiration (Kussmaul’s sign). Therefore, in right ventricular infarction, in- spiration may produce an intermittent atrial gradi- ent during which right-to-left shunting may occur. Mean LA and RA pressures may be equal, but a gradient occurs when LA pressure decreases with inspiration.

Optimal management of patients with right ven- tricular infarction and a significant right-to-left shunt involves the avoidance of positive end-expir- atory pressure and high FIOz concentrations [5]. Furthermore, maximizing spontaneous ventilation by using intermittent mandatory ventilation modes with low respiratory rates rather than assist control modes of ventilatory support is beneficial. Avoid- ance of afterload reduction is essential, since de- creased afterload resulting in decreased LA pres- sures will increase the pressure gradient across the interatrial septum and will potentially worsen shunting [lo]. Recent reports suggest a trial of short-acting B-blocker infusion may prove benefi- cial in improving oxygenation [S]. Finally, transtho- racic or transesophageal echocardiography can help

in ensuring continued proper balloon placement, as the migration of contrast-filled balloon catheters will result in recurrent hypoxemia.

Optimal management cannot occur without a timely diagnosis. Refractory hypoxemia in the set- ting of inferior infarction should lead to a prompt search for a right-to-left shunt via a patent foramen ovale or unrecognized atrial septal defect. Contrast transesophageal echocardiography is a valuable tool in confirming this diagnosis should transtho- racic echocardiography prove unhelpful.

REFERENCES 1. Rietveld AP, Merrman L. Essed CE, Trimbos JB. Hagemeijer F. Right-to-left shunt, with severe hypoxemia, at the atrial level in a patient with hemodynami- caky important right ventricular infarction. J Am Coil Cardiol 1983; 2: 776-9. 2. D’Arcy B. Nanda NC. Two-dimensional echocardiographic features of right ventricular infarction. Circulation 1982; 65: 167-73. 3. Rothbard RL, Nanda NC. Contrast echocardiography. Seminars in Ultra- sound 1981; 2: 113&5. 4. Seward JB. Khandheria BK. Oh JK, et al. Transesophageal echo: technique, anatomic correlations, implementation, and clinical applications. Mayo Clin Proc 1988; 63: 649-80. 5. Lemaire F. Richalet JB. Carlet J, Brun-Buisson C. MacLean C. Postoperative hypoxemia due to opening of patent foramen ovale confirmed by a right atrium- left atrium pressure gradient during mechanical ventilation. Anesthesiology 1982; 57: 233-6. 6. Bansal RC, Marsa RJ. Holland D, Beehler C, Gold PM. Severe hypoxemia due to shunting through a patent foramen ovale: a correctable complication of right ventricular infarction. J Am Coil Cardiol 1985; 5: 188-92. 7. Uppstrom EL, Kern MJ, Mezei L. Mrosek C, Labovitz A. Balloon catheter closure of patent foramen ovale complicating right ventricular infarction: im- provement of hypoxia and intracardiac venous shuntg. Am Heart J 1988; 116: 1092-7. 8. Broderick TM, Dilon JC. Therapeutic balloon occlusion and pharmacological therapy of a right to left atrial shunt produced by right ventricular infarction. Am Heart J 1989; 118: 1044-7. 9. Pearson AP, Castello R. Labovitz AJ. Safety and utility of transesophageal echocardiography in the critically il l patient. Am Heart J 1990; 119: 1083-9. 10. Lain JF. Slama M, Petitpretz P, Girard P, Motte G. Danger of vasodilator therapy for pulmonary hypertension in patent foramen ovale. Chest 1986; 89: 894-5.

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