The clinical setting has as great a significance as the arrhythmia on choice of work-up and possible risk to the patient. Some arrhythmias are potentially fatal regardless of the clinical setting, whereas others are potentially dangerous because of the clinical setting. The usual progression is from the less expensive, simpler noninvasive test to tests that are more complex and invasive. Certain clinical circumstances, however, necessitate a more complex initial study (e.g., electrophysiology study) before a Holter monitor or signal-averaged electrocardiogram (SAECG). The Holter monitor and SAECG are usually the initial tests. SAECG is especially appropriate if ventricular arrhythmias are expected. The type of Holter monitor should be individualized to the patient, depending on associated symptoms as well as frequency and awareness of arrhythmia. An important consideration in the work-up of rhythm disturbance is underlying heart disease (e.g., valve disease, cardiomyopathy, myocardial infarction). A resting ECG and echocardiogram may answer several of these questions and help to categorize the patient as high risk (e.g., low ejection fraction) or low risk (a normal ejection fraction and normal ECG). If the rhythm disturbance is associated with ischemia, an exercise stress test may be appropriate. If the data are positive or if a diagnosis is not established but symptoms or potentially fatal arrhythmias recur, an electrophysiology test should be performed.
Is there a particular subset of patients post myocardial infarction (MI) who should have a Holter monitor evaluation before discharge?
The whole patient needs to be considered for risk stratification, but certain patients are likely candidates for Holter monitoring after MI. Patients with an anterior infarction and bundle-branch block are at high risk for arrhythmia. Up to 35% have late ventricular fibrillation (VF) in the hospital, and the risk persists for 6 weeks after infarction. In addition, atrioventricular (AV) block and intraventricular conduction abnormalities were found in 90% of patients who had recurrent VF during hospitalization and prehospital resuscitation for cardiac arrest. Patients with frequent ventricular ectopy after approximately 48 hours post MI or high-grade heart block after 48-72 hours following an acute MI should be evaluated with Holter monitoring before discharge, 24 along with patients in whom marked bradycardia persists for 48-72 hours after MI. Finally, patients at risk for sudden death (e.g., low ejection fraction) may be considered for predischarge Holter monitoring.
Should patients with suspected arrhythmias have a Holter monitor and an exercise tolerance test (ETT)?
During ETT about one-third of patients with normal hearts may develop ventricular ectopy, usually occasional monomorphic pairs or even 3-6-beat nonsustained runs. Ectopy may occur in older patients with no coronary artery or other heart disease and is not a predictor of increased mortality or morbidity. Although ETT is more sensitive than a resting, standard 12-lead ECG in detecting ventricular arrhythmias, a Holter monitor is more sensitive than ETT. However, because each may uncover serious arrhythmias that the other does not detect, both tests may be indicated in selected patients, such as those with known or suspected coronary artery disease.