Cardiac Testing During Pregnancy

Cardiac Magnetic Resonance Imaging Scan

Cardiac MRI scans can be invaluable in diagnosing complex cardiac lesions and have the advantage that there is no radiation exposure. The use of MRI in evaluating patients with many different cardiac conditions is rapidly expanding. It is the method of choice for evaluating right ventricular (RV) function. Experience in pregnancy is relatively limited, but adverse effects on fetuses have not been demonstrated. Most indications for cardiac MRI can be fulfilled without the need for intravenous contrast agents such as gadolinium. Per the recent updated guidelines of the American College of Obstetricians and Gynecologists, the use of gadolinium contrast with MRI should be limited; it may be used as a contrast agent in pregnant women only if it significantly improves diagnostic performance and is expected to improve fetal or maternal outcome.

Chest Radiography

As with most radiologic studies, chest radiography is not contraindicated during pregnancy, but one must be even more careful in judging whether the potential benefits justify the radiation exposure to the mother and the fetus. Appropriate lead shielding over the abdomen should always be used. It is estimated that a chest x-ray exposes the fetus to less than 10 uGray. An estimated exposure of more than 50,000 uGray (5 rad) is necessary to harm a fetus.

Changes on the chest radiography caused by normal pregnancy include prominent vascular markings, a horizontal position of the heart, a flattened heart border, and an elevated diaphragm. Small pleural effusions are common postpartum.

Chest radiography is most useful in evaluating patients for pulmonary congestion related to left ventricular (LV) dysfunction.

Computed Tomography Scan

As with other studies involving radiation, CT scans are not contraindicated in pregnancy, but of course, they should be ordered only after careful consideration that the diagnostic benefit outweighs the risk of radiation exposure to the mother and the fetus. The estimated radiation exposure to the fetus for a CT pulmonary angiogram is less than 500 uGray; as noted earlier, an estimated exposure of 50,000 uGray is needed to harm a fetus.

The most common reason to consider a CT scan in pregnancy is to diagnose a pulmonary embolus (by means of a pulmonary CT angiogram).

In addition to the radiation exposure, the mother will be exposed to 50 to 150 cc of iodinated radiocontrast. Iodinated radiocontrast can worsen renal function in patients with renal impairment, particularly in the setting of diabetes or dehydration.

Electrocardiogram

A number of changes to the electrocardiogram (ECG) occur during pregnancy. Sinus tachycardia (ST) is common, as are sinus rates of 90. The axis shifts leftward about 15 degrees because of elevation of the diaphragm. Nonspecific ST-segment changes and T-wave inversion also are common. Typically, T-wave inversion occurs in the inferior leads. Small q waves may develop. Premature atrial contractions (PACs) and premature ventricular contractions (PVCs) occur frequently.

The ECG is, of course, the immediate test of choice to evaluate suspected cardiac chest pain or acute myocardial infarction. It may be useful in diagnosing the cause of palpitations or arrhythmias if they are occurring at the time the ECG is performed. The ECG also is useful in diagnosing channelopathies, such as Brugada syndrome and the long QT syndromes. A 12-lead ECG should be performed in cases of syncope.

Graded Exercise Testing

Graded exercise testing can be performed safely in pregnancy. It may be ordered to investigate possible ischemic disease, assess functional capacity, or evaluate exercise-induced arrhythmias. A baseline ECG should be obtained before a graded exercise test is ordered. If the resting ST segments are depressed, the test is of little value in detecting ischemia. If safe, beta blockers should be held for 48 hours before the test to allow an adequate heart rate response. False-positive results may occur, so an abnormal ST-segment response to exercise should not be considered definitive evidence of coronary artery disease.

Contraindications to exercise testing during pregnancy include vaginal bleeding, preeclampsia, and placenta previa.

Holter Monitor and Other Wearable Event Recorders

Holter monitoring and other wearable event recorders can be used to document arrhythmias in the same manner as in nonpregnant patients. The expected findings in pregnancy are a relative sinus tachycardia and PACs and PVCs. Because of the short duration of monitoring, Holter monitors are of less value in patients with syncope; longer monitoring with an event recorder should be considered.

Implantable Loop Recorders

Implantable loop recorders are tiny monitoring devices that can be implanted subcutaneously under local anesthesia. They can be programmed to automatically detect arrhythmias and, through the use of remote telemetry, alert the patient’s cardiologist. Implantable loop recorders have become invaluable in monitoring nonpregnant patients with infrequent or undiagnosed arrhythmias or syncope, and for monitoring arrhythmia burden and response to therapy. Their use in pregnant patients is limited, but they can be very helpful. We have used an implantable loop recorder to monitor a patient with idiopathic ventricular tachycardia of pregnancy. By carefully monitoring the number and duration of episodes and using alerts, we were able to avoid antiarrhythmic therapy. We also have found loop recorders valuable in monitoring patients with a prior history of atrial fibrillation who may need to receive anticoagulation during pregnancy if atrial fibrillation recurs.

Stress Echocardiography

Preexercise and immediate postexercise echocardiography may be performed in combination with a graded exercise test, providing an additional method to detect ischemia by identifying exercise-induced wall motion abnormalities. When the resting ECG results are abnormal, stress echocardiography may be useful, but data about its use in pregnancy are limited. Contraindications during pregnancy include vaginal bleeding, placenta previa, and preeclampsia.