Electrical Alternans Workup

Updated: Sep 12, 2019
  • Author: Bharat K Kantharia, MD, FRCP, FAHA, FACC, FESC, FHRS; Chief Editor: Mikhael F El-Chami, MD  more...
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Workup

Laboratory Studies

Laboratory investigations in patients with electrical alternans are directed toward the underlying etiology as suggested by the patient's electrocardiogram and clinical presentation. Although elevated levels of cardiac enzymes such as the troponins, and biomarkers such as B-type natriuretic peptide (BNP) and N-terminal-pro-BNP (NT-pro-BNP), suggest myocardial ischemia and heart failure from cardiomyopathy, clinicians should evaluate the appropriate laboratory markers for malignancy, autoimmune disease, or renal failure in patients with large pericardial effusions, with or without tamponade physiology. [4]

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Imaging Studies

Echocardiography

Transthoracic echocardiography (TTE) is usually the first line of investigation in patients with electrical alternans, especially in the setting of hemodynamic instability in which a life-threatening pathology is suspected. [4]

The presence of a large pericardial effusion or features of tamponade-like diastolic collapse of the right-sided cardiac chambers can be identified.

Evidence of pulmonary embolism may be found, as indicated by right ventricular (RV) dysfunction or a relative hyperkinesis of the RV apex relative to the RV free wall (McConnells sign).

Echocardiography is also necessary for the evaluation of patients with hypertrophic cardiomyopathy, dilated cardiomyopathy, or congestive heart failure.

Chest radiography

A chest radiograph may reveal an enlarged cardiac silhouette, possibly indicating cardiomyopathy or a large pericardial effusion.

Evidence of the Westermark sign or Hampton hump may suggest pulmonary embolism as the cause of electrical alternans.

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Other Tests

Electrocardiography

Electrocardiography (ECG) is the primary modality used for identification of electrical alternans. Any or all components of the electrical waveforms may exhibit alternans (see the following images).

Electrical alternans. This electrocardiogram shows Electrical alternans. This electrocardiogram shows a typical alternate-beat QRS electrical alternans. Note that the QRS voltage is low.
Electrical alternans. This electrocardiogram revea Electrical alternans. This electrocardiogram reveals supraventricular tachycardia with alternans. Note the phasic nature to the QRS morphology, particularly in the rhythm strip in V1.
Electrical alternans. This electrocardiogram shows Electrical alternans. This electrocardiogram shows ventricular tachycardia from the right ventricular outflow tract (RVOT) region. Note the R wave alternans seen in the wide QRS complexes.
Electrical alternans. This electrocardiogram revea Electrical alternans. This electrocardiogram reveals macro-T wave alternans with switched polarity seen in all leads.

T-wave alternans (TWA) can be detected based on stored ECGs of implantable cardioverter-defibrillators (ICDs). [26]  This entity often precedes the onset of torsades de pointes in congenital long QT syndrome (LQTS). Additionally, T-wave alternans often indicates a higher risk of progression to ventricular dysrhythmias in patients with any form of long QT syndrome or cardiomyopathy. [27, 28]

The presence of ST-T alternans is highly suggestive of ischemia in a large area of myocardium or the development of severe spasm of a proximal vessel. [29, 30]

Microvolt T-Wave alternans testing

Advances in ECG analysis software have led to the detection and analysis of T-wave alternans at a microvolt level (MTWA), which have significantly improved the sensitivity of testing, as visually evident T-wave alternans is quite uncommon. (For example, LQTS-MTWA [1.2%] vs MTWA [44%]).

Beta blockers are generally held for 24-48 hours prior to testing. However, this is often problematic, considering the population under study—those with cardiomyopathy/high arrhythmia burden.

T-wave alternans analysis tools (eg, spectral decomposition analysis, modified-moving average method) are used to quantify the extent of MTWA, which allows the categorization of patients into high, low, and indeterminate risk groups. [31, 32, 33, 34]

The main utility of MTWA testing is in its high negative predictive value (97%) for arrhythmias in the following year. It has been shown to be equivalent to invasive electrophysiologic testing in risk stratifying patients for placement of an implantable cardioverter-defibrillator (ICD). [25, 35, 36, 37]  Clinically, MTWA testing is used for risk stratification in two main populations, those with LQTS and patients undergoing evaluation for placement of ICDs for primary prevention. [27, 38, 39, 40, 41, 42, 43]

It remains unclear whether the disappearance of MTWA indicates an adequate degree of medical management of these patients.

Implantable loop recorder

Placement of a loop recorder may be of benefit in patients with T-wave alternans in whom there is a high suspicion of underlying dysrhythmias.

Cardiac magnetic resonance imaging

Advanced cardiac imaging could be of benefit for further evaluation of cardiomyopathies and heart failure of uncertain etiology.

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Procedures

Pericardiocentesis

Emergent pericardiocentesis must be performed in the setting of a large pericardial effusion or cardiac tamponade.

Cardiac catherization

Cardiac catheterization may be indicated to further evaluate or treat patients with myocardial ischemia or ischemic cardiomyopathy.

Electrophysiologic studies/ablative procedures

Electrophysiologic studies and possible ablative procedures may be required in the setting of atrioventricular reentrant arrhythmias/accessory pathways, etc.

ICD implantation

Patients with advanced heart failure or cardiomyopathies may require placement of an implantable cardioverter-defibrilator (ICD). This would benefit select patients with long QT syndrome, and it may be considered in those found to be at high risk by T-wave alternans testing.

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