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Electrical Alternans Last Updated: July 25, 2005 |
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| Synonyms and related keywords: mechanical alternans, pulsus alternans, repolarization alternans, conduction and refractoriness alternans, alternans due to cardiac motion, repolarization or conduction abnormality of the Purkinje fibers or myocardium, vasospastic angina pectoris, acute myocardial infarction, nonvasospastic angina pectoris, congenital long QT syndrome, hypocalcemia, hypokalemia, hypomagnesemia, hypertrophic cardiomyopathy, alcoholic cardiomyopathy, congestive heart failure, acute pulmonary embolism, cardiac resuscitation, myocardial ischemia, atrial fibrillation, Wolff-Parkinson-White syndrome, rheumatic heart disease, acute pulmonary embolism, myocardial contusion, left ventricular dysfunction, large pericardial effusion, hypertrophic cardiomyopathy
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AUTHOR INFORMATION
| Section 1 of 11   |
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| Author: Eric G Shaw, MD, FACEP, Staff Physician, Department of Emergency Medicine, Lewis County General Hospital Coauthor(s): Michael R Gold, MD, PhD, Director, Division of Cardiology, Professor, Medical University of South Carolina; Amal Mattu, MD, FACEP, FAAEM, Program Director, Emergency Medicine Residency, Co-Director, Emergency Medicine/Internal Medicine Combined Residency Pro, Department of Surgery, Division of Emergency Medicine, University of Maryland School of Medicine |
| Eric G Shaw, MD, FACEP, is a member of the following medical societies:
American College of Emergency Physicians |
| Editor(s): Robert E Fowles, MD, Clinical Professor of Medicine, University of Utah College of Medicine; Consulting Staff, LDS Hospital; Director and Consulting Staff, Department of Cardiology, Salt Lake Clinic; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine;
Steven J Compton, MD, FACC, FACP, Director of Cardiac Electrophysiology, Alaska Heart Institute, Providence and Alaska Regional Hospitals;
Amer Suleman, MD, Consultant in Electrophysiology and Cardiovascular Medicine, Department of Internal Medicine, Division of Cardiology, Medical City Dallas Hospital;
and Leonard Ganz, MD, Associate Professor of Medicine, Temple University School of Medicine; Cardiac Electrophysiologist, Children's Hospital of Pittsburgh, University of Pittsburgh Medical Cent, West Penn Hospital |
Disclosure
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INTRODUCTION
| Section 2 of 11   |
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Background: Electrical alternans is a broad term that describes alternate-beat variation in the direction, amplitude, and duration of any component of the ECG waveform (ie, P, PR, QRS, R-R, ST, T, U). It was first recognized by Hearing in 1909 and further characterized by Sir Thomas Lewis in 1910 as occurring "either when the heart muscle is normal but the heart rate is very fast or when there is serious heart disease and the rate is normal." Kalter and Schwartz first identified electrical alternans on surface ECG in 1948. Electrical alternans must be distinguished from mechanical alternans (eg, pulsus alternans), although both may coexist. Pathophysiology: The pathophysiologic mechanisms that cause electrical alternans can be divided into 3 categories: (1) repolarization alternans (ST, T, U alternans), (2) conduction and refractoriness alternans (P, PR, QRS alternans), and (3) alternans due to cardiac motion. True electrical alternans is a repolarization or conduction abnormality of the Purkinje fibers or myocardium. Electrical alternans due to cardiac motion is effectively artifact, as the heart swings in relation to the chest wall and electrodes, with a period twice that of the heart rate.
Repolarization alternans can be further subclassified as T-wave alternans and ST-segment alternans. T-wave alternans is associated with rapid changes in heart rate or prolongation of the QT interval. A long QT interval is associated with polymorphic ventricular tachycardia (ie, torsade de pointes); therefore, T-wave alternans is a possible precursor to torsade de pointes.
T-wave alternans has been reported with congenital long QT syndrome, electrolyte imbalances (eg, hypocalcemia, hypokalemia, hypomagnesemia), treatment with quinidine or amiodarone, hypertrophic cardiomyopathy, alcoholic cardiomyopathy, congestive heart failure, and acute pulmonary embolism. T-wave alternans has also been reported following cardiac resuscitation. Most importantly, the presence of T-wave alternans can be used as a predictor of ventricular tachyarrhythmic events, such as sudden cardiac death, sustained ventricular tachycardia, ventricular fibrillation, implantable cardioverter defibrillator (ICD) therapy for ventricular tachyarrhythmia, and cardiac arrest.
ST-segment alternans describes alternating levels of ST elevation, usually in the presence of myocardial ischemia. It has been reported with vasospastic angina pectoris, acute myocardial infarction, nonvasospastic angina pectoris, during exercise tests, during percutaneous transluminal coronary angioplasty (PTCA), and after subarachnoid hemorrhage. ST alternans during acute ischemia has been associated with appearance of ventricular arrhythmia, including ventricular tachycardia and ventricular fibrillation.
Conduction alternans is an alternation of impulse propagation along any of the anatomic structures involved in conveyance of electrical impulse and is usually precipitated by changes in heart rate or input from nervous, humoral, or pharmacologic components. Conduction alternans may be seen in the setting of myocardial ischemia, atrial fibrillation, Wolff-Parkinson-White syndrome, rheumatic heart disease, acute pulmonary embolism, myocardial contusion, and left ventricular dysfunction. It may manifest on the surface ECG as alternation of the P wave, QRS complex, PR interval, R-R interval, or any combination of these. QRS alternans during narrow complex tachycardia has been suggested as a marker for orthodromic atrioventricular (AV) reentrant tachycardia using an accessory pathway as a retrograde limb.
Electrical alternans associated with cardiac motion is due to alternation in the position of the heart with relation to recording electrodes. The most common underlying disorder is an enlarged pericardial sac; however, not all pericardial effusions cause electrical alternans. The presence of pericardial disease and total electrical alternans (P, QRS, and T wave) frequently suggests cardiac tamponade, but total electrical alternans is seen in only 5-10% of patients with cardiac tamponade. Heart movement in patients with hypertrophic cardiomyopathy also may result in electrical alternans of this type. Frequency:
- In the US: Incidence is estimated to be about 1-6 of 10,000 ECGs. Overall, QRS alternans is the most common type. ST alternans incidence has been reported as 5–7.7% of patients during PTCA using intracoronary ECG recordings. T-wave alternans was observed in 45% of patients with congenital long QT syndrome after examining 24-hour Holter monitors.
Mortality/Morbidity: The finding of electrical alternans does not alter the morbidity and mortality rates of the underlying cause or association.
History: The presence of electrical alternans has no clinical manifestations outside those present from the underlying cause or association. A search for the underlying cause of electrical alternans is warranted. For example, the patient with ST-T alternans may complain of chest pain, shortness of breath, or profuse sweating caused by myocardial ischemia. The patient with QRS alternans may complain of syncope resulting from underlying hypertrophic cardiomyopathy. Physical: Electrical alternans does not result in physical findings separate from the underlying cause of the alternans. A physical examination, searching for the underlying cause, is necessary. This may reveal, for example, jugular venous distention and hypotension from cardiac tamponade. Making the distinction between electrical alternans and mechanical alternans is important. Mechanical alternans may have physical findings (eg, pulsus alternans). Causes: - The reported causes or associations of electrical alternans have been mentioned already and are relisted here for convenience.
- Repolarization (ST–T alternans)
- Vasospastic angina pectoris
- Acute myocardial infarction
- Nonvasospastic angina pectoris
- Congenital long QT syndrome
- Electrolyte imbalances, such as hypocalcemia, hypokalemia, and hypomagnesemia
- Treatment with amiodarone
- Hypertrophic cardiomyopathy
- Following cardiac resuscitation
- During exercise tests
- Acute mental stress
- During PTCA
- After subarachnoid hemorrhage
- Conduction (QRS alternans)
- Myocardial ischemia
- Atrial fibrillation
- Wolff-Parkinson-White syndrome
- Rheumatic heart disease
- Acute pulmonary embolism
- Myocardial contusion
- Left ventricular dysfunction
- Large pericardial effusion
- Hypertrophic cardiomyopathy
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DIFFERENTIALS
| Section 4 of 11 |
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Atrial Fibrillation
Atrial Flutter
Atrial Tachycardia
Atrioventricular Block
Atrioventricular Dissociation
Atrioventricular Nodal Reentry Tachycardia (AVNRT)
First-Degree Atrioventricular Block
Long QT Syndrome
Second-Degree Atrioventricular Block
Sinus Node Dysfunction
Torsade de Pointes
Ventricular Fibrillation
Ventricular Tachycardia
Wolff-Parkinson-White Syndrome
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Patient Education
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Lab Studies:
- Direct laboratory investigations toward discovery of the primary underlying etiology. Based on other clinical information, appropriate lab studies include cardiac enzymes for myocardial ischemia and infarction as well as serum calcium, potassium, and magnesium if electrolyte abnormalities are suspected. In the setting of a large pericardial effusion, laboratory studies searching for a malignancy may be warranted.
Imaging Studies:
- Chest radiograph may reveal an enlarged cardiac silhouette, possibly indicating cardiomyopathy or large pericardial effusion.
- Evidence of the Westermark sign or Hampton hump may suggest pulmonary embolism as the cause of electrical alternans.
- Echocardiography should be performed on those patients with total electrical alternans (P, QRS, and T wave) to evaluate for pericardial effusion.
- Echocardiography is also necessary for evaluation of patients with hypertrophic cardiomyopathy, alcoholic cardiomyopathy, or congestive heart failure.
Other Tests:
- ECG is the main study through which electrical alternans is discovered. Any or all components of the electrical waveforms may exhibit alternans (see Images 1-2).
- High-resolution ECG with spectral analysis can detect alternans in the microvolt range of amplitude. This detailed study is appropriate when searching for T-wave alternans as a predictor of ventricular tachyarrhythmia events.
- Routine ambulatory ECG monitoring of T-wave alternans, using dynamic, nonspectral, modified moving average analysis, may be helpful for risk stratification for arrhythmias.
- T-wave alternans may be seen best in lead V2.
Procedures:
- Electrical alternans due to a large pericardial effusion should resolve completely after the effusion is drained. Pericardiocentesis must be performed emergently in the setting of cardiac tamponade.
- In selected cases, cardiac catheterization may be indicated to further evaluate those patients with suspected vasospastic or nonvasospastic angina pectoris.
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TREATMENT
| Section 6 of 11 |
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Medical Care: Direct treatment toward correction of the underlying cause of electrical alternans. For example, myocardial infarction should be treated using standard measures (eg, consider thrombolytic administration or PTCA). Long QT syndrome may be treated with removal of offending drugs or correction of metabolic abnormalities. Surgical Care: Most diseases that cause true electrical alternans do not require surgical treatment. Pulmonary embolectomy may be required for unresolved large pulmonary emboli. Left-sided cervicothoracic sympathetic ganglionectomy may be required for patients with congenital long QT syndrome who continue to have episodes of syncope despite drug therapy. Recurrent pericardial effusions may benefit from pericardiectomy. Consultations: Cardiology consultation is usually indicated. Diet: No specific dietary restrictions are required aside from those required for the underlying cause (eg, salt restriction for congestive heart failure). Activity: No specific activity restrictions are required aside from those required for the underlying cause (eg, avoidance of stress and strenuous exercise for patients with congenital long QT syndrome in order to prevent an arrhythmia in susceptible patients).
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MEDICATION
| Section 7 of 11 |
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No medications are specifically indicated for correction of electrical alternans. Biomedical research on canines may result in future pharmacotherapy for T-wave alternans. Please refer to the corresponding articles on underlying diseases for specific medications.
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FOLLOW-UP
| Section 8 of 11 |
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Complications:
- No known complications exist. All complications are due to the underlying disease process.
Prognosis:
- The finding of electrical alternans does not change the prognosis of the underlying disease process.
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MISCELLANEOUS
| Section 9 of 11 |
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Medical/Legal Pitfalls:
- Failure to recognize electrical alternans on ECG, resulting in detrimental progression of the underlying disease process
- Delay of emergent pericardiocentesis for correction of cardiac tamponade due to failure of recognition of electrical alternans
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PICTURES
| Section 10 of 11 |
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| Caption: Picture 2. Supraventricular tachycardia with alternans. Note the phasic nature to the QRS morphology, particularly in the rhythm strip in V1.
|  |  View Full Size Image |
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Picture Type: ECG |
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BIBLIOGRAPHY
| Section 11 of 11 |
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