Venoarterial shunting in obstructive pulmonary disease

Detection of Right to Left Shunt by Transesophageal Echocardiography in a Patient with Postoperative Hypoxemia

Intracardiac right to left shunt through a patent foramen ovale (PFO) may result in the development of hypoxemia after cardiac surgery. Cardiac tamponade and mechanical ventilation with high positive endexpiratory pressure are the most common factors responsible for enhancing intracardiac right to left shunt through a PFO. We report an 83-year-old woman with Stanford type A dissecting aneurysm who developed hypoxemia and paradoxical air embolism after reconstruction of ascending aorta and Bental's procedure. Transesophageal echocardiography (TEE) revealed right to left shunting via a PFO. Surgical closure of the PFO was done without delay. This case illustrates the role of TEE in prompt diagnosis of intracardiac right to left shunting through a PFO causing postoperative hypoxemia after cardiac surgery.

Ear oximetry: a noninvasive method for detection of patent foramen ovale: a study comparing dye dilution method and oximetry with contrast transesophageal echocardiography

BACKGROUND AND PURPOSE

Patent foramen ovale (PFO) may play an important role as a risk factor for ischemic stroke and some other neurological conditions. There is a need for low-cost and noninvasive methods for the detection of PFO. This study evaluates the accuracy of two simple bedside tests, the dye dilution method and ear oximetry, in the detection of PFO.

METHODS

Dye dilution curves and ear oximetry recordings with a noninvasive ear densitometer were obtained from consecutive cryptogenic stroke patients referred for contrast transesophageal echocardiography (TEE). All test results were blindly assessed for the presence of PFO. Sensitivity and specificity were calculated with TEE used as a reference method. kappa statistics were used to measure interrater agreement.

RESULTS

Dye dilution curves were obtained from 67 patients. Dye dilution correctly diagnosed 35 of the 46 patients who had PFO in TEE and all the 21 patients without PFO. Thus, the sensitivity (95% CI) of the dye dilution method was 76% (61% to 87%) and its specificity 100% (84% to 100%). Ear oximetry was done on 83 patients. Oximetry correctly diagnosed 45 of the 53 patients who had PFO in TEE and all of the 30 patients without PFO. Thus, the sensitivity of ear oximetry was 85% (72% to 93%) and its specificity 100% (88% to 100%). The interrater agreement was excellent (kappa value 0.94 for dye dilution and 0.90 for oximetry).

CONCLUSIONS

Dye dilution and oximetry are both sensitive and specific methods for the detection of PFO. Oximetry has the following primary advantages over the currently available diagnostic methods: it is noninvasive, safe, and inexpensive and causes no discomfort for the patient. We suggest that oximetry could be used as a first-line screening method for PFO in patients with cryptogenic stroke. Ear oximetry also has potential use in epidemiological studies.

Dye dilution and oximetry for detection of patent foramen ovale

OBJECTIVES

Patent foramen ovale (PFO) is a risk factor for stroke of undetermined (cryptogenic) origin. Low cost and non-invasive bedside tests for detection of PFO are needed as alternatives to contrast transesophageal echocardiography. We investigated whether dye dilution curves and oximeter recordings are useful for detecting PFO and what is the prevalence of PFO in patients with cryptogenic stroke determined with these bedside methods. We also studied whether stroke risk factors, number of brain lesions, and stroke recurrence rates were different in patients with an unexplained stroke with and without PFO.

MATERIAL AND METHODS

Dye dilution curves and oximeter recordings with non-invasive earpiece apparatus were obtained in 59 patients aged under 50 years who had had a cryptogenic brain infarction. The number of ischemic lesions in the brain was counted by MRI.

RESULTS

PFO was found in 24 (41%) of 59 patients. There was a 100% concordance in results obtained by dye dilution and by oximetry. Risk factors for stroke were similar in subjects with PFO and those without PFO. No significant association was found between PFO and Valsalva-like activity at stroke onset. Those with PFO did not have more ischemic lesions detected by MRI nor did they have more recurrent ischemic episodes.

CONCLUSION

Dye dilution and oximetry are cheap and useful methods for detection of PFO and could be used for screening of the risk of paradoxical embolism. Because these 2 methods were not compared with the golden standard, transesophageal echocardiography, the specificity and sensitivity of the tests remain unsettled.

Transient right-to-left shunting through a patent foramen ovale secondary to unilateral diaphragmatic paralysis

A 57 year old patient presented with unilateral diaphragmatic paralysis and severe hypoxaemia secondary to transient right-to-left interatrial shunting through a patent foramen ovale. The final diagnosis was made because of the initial detection of a shunt while the patient was breathing 100% oxygen.

Femoral vein delivery of contrast medium enhances transthoracic echocardiographic detection of patent foramen ovale

OBJECTIVES

We postulated that femoral vein delivery of contrast medium because of streaming, might enhance precordial echocardiographic detection of patent foramen ovale.

BACKGROUND

Although precordial contrast echocardiography is widely used to diagnose patent foramen ovale, this method is limited by poor sensitivity. Previous investigators have demonstrated enhanced detection of atrial defects by the dye-dilution technique after delivery of contrast medium into the inferior rather than the superior vena cava.

METHODS

Transthoracic contrast examinations were performed in a randomly selected group of 70 patients (without previous history of cerebral or systemic embolus) undergoing cardiac catheterization. Paired contrast agent injections (10 ml dextrose in water/0.25 ml air) were administered from an upper extremity vein and femoral vein in each patient during spontaneous respiration, cough and Valsalva maneuvers. Studies were interpreted by an experienced echocardiographer unaware of the sequence and site of injections. Positive studies were semiquantitatively graded from +1 (minimal left ventricular opacification) to +4 (intense left ventricular opacification). Catheterization and echocardiographic assessment of patent foramen ovale were compared in 21 subjects.

RESULTS

Patent foramen ovale was detected significantly more often during femoral vein versus upper extremity contrast delivery (23 of 70 patients [prevalence 33%] vs. 9 of 70 patients [prevalence 13%], p < 0.001). The intensity of left ventricular opacification was also greater during femoral vein contrast injection. Precordial echocardiography combined with femoral contrast delivery was significantly more sensitive than cardiac catheterization for assessment of patent foramen ovale (8 of 21 patients vs. 2 of 21 patients, p < 0.05).

CONCLUSIONS

Femoral vein contrast delivery significantly enhances the ability of precordial contrast echocardiography to diagnose patent foramen ovale. Physiologic patency of the foramen ovale is more common (prevalence 33%) than previously documented.

The diagnostic utility of contrast echocardiography in patients with refractory hypoxemia

Three illustrative cases of refractory hypoxemia in adults are presented. In two cases contrast echocardiography was invaluable in establishing the diagnosis of a true anatomic right to left shunt, as well as in localizing the shunt to an intracardiac or extracardiac site. In the third case true anatomic right to left shunt was excluded by means of contrast echocardiography. The pathophysiology of hypoxemia is discussed with emphasis on the potential diagnostic utility of contrast echocardiology in patients with refractory hypoxemia. A diagnostic flow chart is proposed.

Right-to-left shunt across a patent foramen ovale caused by cardiac tamponade: diagnosis by transesophageal echocardiography

Cardiac tamponade can manifest as profound hypoxemia from intracardiac shunting across a patent foramen ovale. As a consequence, pulmonary embolus can be erroneously diagnosed. As demonstrated in the case described herein, transesophageal echocardiography can be useful in determining the correct diagnosis, especially if transthoracic echocardiography is technically limited. In our patient, the findings on transesophageal echocardiography also helped determine the appropriate treatment. The relative inaccessibility of the pericardial effusion to needle drainage prompted open surgical drainage.

Persistent hypoxemia due to patent foramen ovale in a patient with adult respiratory distress syndrome

This report describes a patient in the recovery phase of the adult respiratory distress syndrome in whom the persistence of severe hypoxemia was not corrected by a high fractional concentration of oxygen in the inspired gas and positive end-expiratory pressure. A right-to-left interatrial shunt was diagnosed by M-mode and cross-sectional echocardiography with saline injection, and the presence of a patent foramen ovale was confirmed at the time of cardiac surgery.

Right-to-left interatrial shunt secondary to an extensive right ventricular myocardial infarction

This case report describes a rare complication of right ventricular myocardial infarction. Hypoxemia in this setting has only been described in two previous cases with a right-to-left interatrial shunt. This is surprising, given the high incidence of probe patent foramen ovale in randomly selected necropsy cases. Two-dimensional echocardiography with contrast is the method of choice for detecting this abnormality.

Enlarged pulmonary arteriovenous vessels in COPD. Another possible mechanism of hypoxemia

Among 27 patients with moderate-to-severe chronic obstructive lung disease, 22 had anatomic intrapulmonary shunting greater than that seen in normal subjects. The shunted blood passed through enlarged pulmonary vessels, as demonstrated with particles 10-90 microns in diameter. The shunt magnitude was correlated with the decrement in lung diffusing capacity. It did not correlate well with pulmonary mechanical abnormalities such as air flows and volumes or resting blood gas data. Nevertheless, shunting through enlarged pulmonary vessels may play a role in the hypoxemia seen in COPD patients, especially at exercise.

Contrast echocardiographic visualization of cough-induced right to left shunt through a patent foramen ovale

In a series of 24 consecutive patients referred to the echocardiography laboratory because of suspected patent foramen ovale, contrast two-dimensional and M-mode echocardiographic studies were performed during normal breathing and during two provocative tests: the Valsalva maneuver and cough. A right to left shunt was visualized in 8 patients during normal breathing, in 11 patients during the Valsalva maneuver and in 17 patients during the cough test. Cardiac catheterization performed in all 24 patients and postmortem examination available in 3 patients confirmed the patency of the foramen ovale in only 15 patients. In these 15 patients, echo contrast appeared in the left heart cavities in early systole and almost simultaneously with complete right heart opacification. In contrast, for the two false positive results during the cough test, ultrasound contrast appeared at any time of the cardiac cycle when the right heart cavities had been partially cleared of contrast material. Right and left atrial pressures were simultaneously measured in four patients, and the normal interatrial pressure gradient was reversed during the Valsalva maneuver and the cough test. Echocardiography during both provocative tests showed that the interatrial septum flattened or became convex toward the left atrium. The cough test appears to be more reliable and easier to perform in critically ill patients than the Valsalva maneuver for the detection of right to left shunting through a patent foramen ovale.

Platypnea-orthodeoxia: clinical profile, diagnostic workup, management, and report of seven cases

Platypnea-orthodeoxia is a rare and poorly understood syndrome of orthostatic accentuation of a right-to-left shunt, usually across a patent foramen ovale. The syndrome is most commonly recognized in patients with a history of a major pulmonary disorder such as pneumonectomy, recurrent pulmonary emboli, or chronic lung disease. Pulmonary artery pressures are typically normal. The physiologic mechanism is unknown. We recommend that initial assessment consist of measurement of blood gases with the patient in the supine and upright positions. Orthostatic desaturation should prompt further investigation. A definitive diagnosis can most easily be obtained by tilt-table two-dimensional echocardiography with peripheral venous contrast medium. The shunt can be localized at the atrial level and directly visualized and semiquantitated. The decision about surgical closure of the patent foramen ovale is based on the degree of clinical disability. Because a significant shunt is manifest only in the upright position, astute clinical suspicion is of paramount importance for proper diagnosis. Increased awareness of this syndrome and ease of echocardiographic diagnosis will facilitate recognition of this potentially treatable cause of orthostatic hypoxia.

Incidence and size of patent foramen ovale during the first 10 decades of life: an autopsy study of 965 normal hearts

The incidence and size of the patent foramen ovale were studied in 965 autopsy specimens of human hearts, which were from subjects who were evenly distributed by sex and age. Neither incidence nor size of the defect was significantly different between male and female subjects. The overall incidence was 27.3%, but it progressively declined with increasing age from 34.3% during the first three decades of life to 25.4% during the 4th through 8th decades and to 20.2% during the 9th and 10th decades. Among the 263 specimens that exhibited patency in our study, the foramen ovale ranged from 1 to 19 mm in maximal potential diameter (mean, 4.9 mm). In 98% of these cases, the foramen ovale was 1 to 10 mm in diameter. The size tended to increase with increasing age, from a mean of 3.4 mm in the first decade to 5.8 mm in the 10th decade of life.

Pulmonary embolism and intracardiac shunt: a unique indication for operation

Pulmonary embolism with right-to-left intracardiac shunt presents a special problem for the clinician. A review of the literature and 4 personal cases, all diagnosed antemortem, are presented. On the basis of this information certain conclusions are drawn, and we suggest the problem to be a unique indication for the consideration of surgical intervention.

Venous air embolism during neurosurgery. A comparison of various methods of detection in man

A comparison of the various methods available for the detection of air embolus has been carried out in patients undergoing posterior fossa exploration in the sitting position. A group of 17 patients (Group A) was comprehensively monitored by a central venous catheter, an infra-red carbon dioxide analyser and a Doppler ultrasonic flow transducer in addition to more traditional clinical methods. Group B (19 patients) was monitored by commonly used clinical methods consisting of continuous palpation of the radial pulse, intermittent blood pressure measurement, the use of an oesophageal stethoscope and the electrocardiograph. In Group A the detection of air embolus varied from 6% using an oesophageal stethoscope to 58% by the Doppler method. In Group B air embolus was diagnosed in 10% of patients. One patient in each group died from air embolus; one patient had a paradoxical embolus to the coronary arteries. It is concluded that comprehensive monitoring for air embolus, including the use of Doppler ultrasound, is an essential part of the management of these patients, for both diagnosis and treatment.

Paradoxical embolism: its pathophysiology and clinical recognition

Images