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Cardiology > Arrhythmias
Multifocal Atrial Tachycardia
Article Last Updated: Jun 16, 2005
AUTHOR AND EDITOR INFORMATION
Section 1 of 11  
Author: Neeraj Tandon, MB, BS, Chief, Cardiology Section, Associate Professor of Medicine, Medical Service, Overton Brooks Veterans Affairs Medical Center
Neeraj Tandon is a member of the following medical societies: American College of Cardiology and Society of Cardiac Angiography and Interventions
Coauthor(s):
Pratap Reddy, MD, Director, Electrophysiology Service, Professor, Department of Medicine, Section of Cardiology, Louisiana State University Health Sciences Center
Editors: Alan D Forker, MD, Professor of Medicine, Program Director of Cardiovascular Fellowship, MidAmerica Heart Institute, University of Missouri at Kansas City School of Medicine; Director, Outpatient Lipid Diabetes Research Center, MidAmerica Heart Institute of Saint Luke's Hospital; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Frank M Sheridan, MD, Cardiology, Providence Everett Medical Center; Amer Suleman, MD, Consultant in Electrophysiology and Cardiovascular Medicine, Department of Internal Medicine, Division of Cardiology, Medical City Dallas Hospital; 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
Author and Editor Disclosure
Synonyms and related keywords:
MAT, chaotic atrial rhythm, chaotic atrial tachycardia, chaotic atrial mechanism, repetitive paroxysmal multifocal atrial tachycardia, intracellular calcium overload, catecholamine excess, phosphodiesterase inhibition, acidosis, hypoxemia, electrolyte imbalances associated with severe underlying illnesses, COPD, congestive heart failure, metabolic disorders, diabetes mellitus, hypokalemia, azotemia, postoperative infections, sepsis, pulmonary embolism, respiratory acidosis, coronary artery disease, valvular heart disease, hypomagnesemia, azotemia, multifocal atrial rhythm, multifocal atrial bradycardia, wandering atrial pacemaker
Background
Multifocal atrial tachycardia (MAT) is an arrhythmia with an irregular atrial rate greater than 100 beats per minute (bpm). Atrial activity is well organized, with at least 3 morphologically distinct P waves, irregular P-P intervals, and an isoelectric baseline between the P waves. Shine et al first proposed this definition in 1968. MAT has previously been described by names such as chaotic atrial rhythm or tachycardia, chaotic atrial mechanism, and repetitive paroxysmal MAT.
Pathophysiology
The mechanism of the arrhythmia has not been well defined. Delayed afterdepolarizations leading to triggered automaticity are postulated to result in the development of MAT. The evidence that links this mechanism is mainly indirect and points to intracellular calcium overload by various mechanisms (eg, catecholamine excess, phosphodiesterase inhibition, acidosis, hypoxemia). Electrolyte imbalances associated with severe underlying illnesses can further potentiate the development of this arrhythmia.
Frequency
United States
MAT is a relatively infrequent arrhythmia, with a prevalence rate of 0.05-0.32% in patients who are hospitalized. The condition is even less common in children and young adults.
Mortality/Morbidity
Patients with MAT frequently have significant comorbidities, especially chronic obstructive pulmonary disease (COPD) and respiratory failure, and are often treated in ICUs. Consequently, a high mortality rate (ie, up to 45%) is associated with this arrhythmia.
Sex
MAT is predominantly observed in males.
Age
MAT is commonly observed in older patients. The average age of patients from 9 studies was 72 years.
History
The clinical profile of patients who develop this arrhythmia includes pulmonary, cardiac, metabolic, and endocrinopathic disorders.
- COPD is the most common underlying disease process (60%). The arrhythmia is commonly precipitated by exacerbation of COPD, sometimes due to infection or cardiac decompensation. Increasing hypoxemia with respiratory acidosis and advanced disease also leads to increased bronchodilator usage, thereby increasing catecholamine levels, which may contribute to development of MAT.
- Cardiac: Patients with MAT frequently have cardiac diseases, mainly coronary artery disease and valvular heart diseases, often in conjunction with COPD. Congestive heart failure (CHF) is often present when the diagnosis of MAT is first made.
- Metabolic disorders: In various series, 24% of patients with MAT were found to have diabetes mellitus. Fourteen percent had hypokalemia, and 14% had azotemia.
- Postoperative: Twenty-eight percent of patients with MAT were recovering from major surgery, while others had postoperative infections, sepsis, pulmonary embolism, and CHF.
- Pulmonary embolism: The link between pulmonary embolism and MAT is weak (ie, 6-14% of such patients have been said to have MAT), but the methods of diagnosing pulmonary embolism have not been well documented.
- Intravenous drug abuse: Experimental evidence demonstrates that IV cocaine use may lead to the development of MAT.
Physical
Physical examination of the patient is typically related to findings associated with the underlying disease process and is not specific for MAT. The clue to the presence of an abnormal rhythm is the presence of an irregular rapid pulse and variable heart sounds.
Causes
Causes of MAT are mainly related to underlying illnesses.
- The following common underlying illnesses are associated with this arrhythmia:
- COPD
- Coronary artery disease
- CHF
- Valvular heart disease
- Diabetes mellitus
- Hypokalemia
- Hypomagnesemia
- Azotemia
- Postoperative state
- Pulmonary embolism
Atrial Fibrillation
Atrial Flutter
Other Problems to be Considered
Sinus tachycardia with frequent premature atrial contractions (PACs)
Lab Studies
- Laboratory testing mainly consists of an assessment of serum chemistry level, blood hemoglobin level, and arterial blood gas levels.
- Serum chemistry level - To exclude electrolyte disorders
- Blood hemoglobin level and RBC counts - To seek evidence of anemia
- Arterial blood gas level - To define pulmonary status
- Further testing depends on the etiology of the underlying disease process.
Imaging Studies
- Chest radiograph - To define pulmonary status
- The diagnosis of MAT is confirmed with an ECG meeting the following criteria:
- Irregular ventricular rate greater than 100 bpm
- Organized and discrete P waves with at least 3 different morphologies in the same electrocardiographic lead
- Irregular PP, PR, and RR intervals with an isoelectric baseline between the P waves
- Some authors have suggested that patients who have rhythms with a rate less than 100 bpm but who satisfy all other criteria (including the clinical profile commonly observed with MAT) be considered to have cases of multifocal atrial rhythm and multifocal atrial bradycardia, when the rate is less than 60 bpm.
- However, a controversy arises about whether this condition should be referred to as a MAT variant or a wandering atrial pacemaker. Patients with wandering atrial pacemaker usually do not have serious underlying illnesses.
- The requirement that 3 different P waves should exist has been applied since early descriptions of the arrhythmia were recorded, but whether this should be interpreted as 2 ectopic P waves and 1 sinus P wave or 3 ectopic P waves has been a matter of controversy.
- The consensus favors a minimum of 3 different waveforms in addition to sinus P waves.
Medical Care
- General: Treatment of this arrhythmia involves treatment and/or reversal of the precipitating cause. This may be all that is required; however, the arrhythmia may recur when the underlying condition worsens. Treatment of underlying diseases may sometimes have arrhythmia-promoting effects; for example, theophylline and beta-agonist drugs used in patients with COPD produce an increased catecholamine state. These therapies should be used judiciously.
- Calcium channel blockers: Diltiazem and verapamil decrease the atrial activity and slow atrioventricular (AV) nodal conduction, thereby decreasing ventricular rate, but they do not return all patients to normal sinus rhythm. Transient hypotension is the most common adverse effect, which may often be avoided by pretreating the patient with 1 g of intravenous calcium gluconate (10 mL of 10% calcium gluconate). Diltiazem may be used as a 20-45 mg IV bolus and then as a 10-25 mg/h continuous infusion. Verapamil may worsen hypoxemia by negating the hypoxic pulmonary vasoconstriction in underventilated alveoli; this is usually not clinically significant.
- Beta-blockers: Metoprolol has been used to lower the ventricular rate. More patients convert to a normal sinus rhythm when treated with beta-blockers. Both oral and intravenous dosage forms have been used. The oral dosage is 25 mg q6h until the desired effects are obtained. Intravenous bolus dosing has been administered to as much as 15 mg over 10 minutes. Although no controlled studies have evaluated the utility of short-acting beta-blockers in treatment of MAT, esmolol can also be used to control the ventricular rate as an intravenous infusion. It has a very short half-life and can be terminated quickly in the event of an adverse reaction. The use of beta-blockers is limited by transient hypotension and bronchospastic adverse effects.
- Magnesium: In a small number of patients, high-dose magnesium causes a significant decrease in the patient's heart rate and conversion to normal sinus rhythm. The dosage is 2 g intravenously over 1 minute, followed by 2 g/h infusion over 5 hours.
- Antiarrhythmics: Oral and intravenous amiodarone (300 mg PO tid or 450-1500 mg IV over 2-24 h) has been used and is effective in conversion to normal sinus rhythm. The success rate was 40% at 3 days with oral dosing and 75% on day 1 with intravenous dosing; however, this has been evaluated in a very small number of patients. Recent data support the use of amiodarone prophylactically postoperatively in COPD patients. Case reports have also supported the use of ibutilide for cardioversion.
- Digitalis and cardioversion: Despite the urge to use digoxin, it has not been found to be effective in controlling the ventricular rate or restoring normal sinus rhythm. Digoxin promotes afterdepolarizations, which may promote the arrhythmia. Ventricular arrhythmias, AV block, and death have been reported when excessive digoxin has been administered to patients who were incorrectly diagnosed to have atrial fibrillation. Direct current (DC) cardioversion is not effective in conversion to normal sinus rhythm and can precipitate worse arrhythmias.
Surgical Care
In patients who have persistent and recurrent episodes of MAT and problems with rate control, the AV node may be ablated using radiofrequency energy and a permanent pacemaker implanted.
The goals of pharmacotherapy are to reduce morbidity and to prevent complications. Calcium channel blockers are used as the first line of treatment. Antiarrhythmics are usually not indicated for treatment of MAT. Consider using antiarrhythmics when the arrhythmia is symptomatic and does not respond to correction or treatment of underlying diseases.
Drug Category: Calcium channel blockers
Diltiazem and verapamil have been used to control the ventricular rate.
| Drug Name | Diltiazem (Cardizem, Dilacor, Tiazac) |
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| Description | During depolarization, inhibits calcium ions from entering the slow channels and voltage-sensitive areas of vascular smooth muscle and myocardium. |
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| Adult Dose | 10-20 mg IV bolus, followed by 5-15 mg/h continuous infusion; alternatively, 120-360 mg PO divided tid/qid or qd in long-acting preparations |
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| Pediatric Dose | Not established |
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| Contraindications | Documented hypersensitivity; severe CHF, sick sinus syndrome, second- or third-degree AV block, hypotension (<90 mm Hg systolic) |
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| Interactions | May increase carbamazepine, digoxin, cyclosporine, and theophylline levels; when administered with amiodarone, may cause bradycardia and a decrease in cardiac output; when administered with beta-blockers, may increase cardiac depression; cimetidine may increase diltiazem levels |
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| Pregnancy | C - Safety for use during pregnancy has not been established.
|
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| Precautions | Caution in impaired renal or hepatic function; may increase LFT levels, and hepatic injury may occur |
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| Drug Name | Verapamil (Calan, Covera, Verelan) |
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| Description | During depolarization, it inhibits the calcium ion from entering slow channels or voltage-sensitive areas of the vascular smooth muscle and myocardium. By interrupting reentry at AV node, verapamil can occasionally restore normal sinus rhythm. |
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| Adult Dose | 0.075-0.15 mg/kg IV bolus over 5-10 min, followed by 0.005 mg/kg/min continuous infusion for 1 h; alternatively, 240-480 mg PO divided tid/qid |
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| Pediatric Dose | <2 years: Not established
>2 years: 0.075-0.15 mg/kg IV bolus over 2 min, followed by 0.005 mg/kg/min infusion |
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| Contraindications | Documented hypersensitivity; severe CHF, sick sinus syndrome, second- or third-degree AV block, hypotension (<90 mm Hg systolic) |
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| Interactions | May increase carbamazepine, digoxin, and cyclosporine levels; coadministration with amiodarone can cause bradycardia and a decrease in cardiac output; when administered concurrently with beta-blockers, may increase cardiac depression; cimetidine may increase verapamil levels; may increase theophylline levels |
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| Pregnancy | C - Safety for use during pregnancy has not been established.
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| Precautions | Hepatocellular injury may occur; transient elevations of transaminases with and without concomitant elevations in alkaline phosphatase and bilirubin have occurred (elevations have been transient and may disappear with continued verapamil treatment); monitor liver function periodically |
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Drug Category: Antiarrhythmic agent
| Drug Name | Magnesium sulfate |
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| Description | Used IV or IM, found to significantly slow the ventricular rate and to convert patients to normal sinus rhythm. |
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| Adult Dose | 2 g IV over 1 min followed by 2 g/h over 5 h continuous infusion; 1g IM q6h |
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| Pediatric Dose | 25-50 mg/kg IV |
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| Contraindications | Documented hypersensitivity; heart block; Addison disease; myocardial damage; severe hepatitis |
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| Interactions | Concurrent use with nifedipine may cause hypotension and neuromuscular blockade; may increase neuromuscular blockade seen with aminoglycosides and potentiate neuromuscular blockade produced by tubocurarine, vecuronium, and succinylcholine; may increase CNS effects and toxicity of CNS depressants, betamethasone, and cardiotoxicity of ritodrine |
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| Pregnancy | A - Safe in pregnancy
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| Precautions | Magnesium may alter cardiac conduction, leading to heart block in patients who are digitalized; monitor respiratory rate, deep tendon reflex, and renal function when electrolytes are administered parenterally; caution when administering magnesium dose because it may produce significant hypertension or asystole; in overdose, a 10-20 mL IV of 10% calcium gluconate solution can be administered as an antidote for clinically significant hypermagnesemia |
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Further Inpatient Care
- Further inpatient care is dictated by the underlying illness and treatment of this illness.
- In patients with persistent and refractory MAT, AV junctional ablation and permanent pacemaker implantation should be considered, both for symptomatic and hemodynamic improvement, and to prevent the development of tachycardia mediated cardiomyopathy.
Deterrence/Prevention
- The best means of prevention of MAT is prevention of respiratory failure plus careful monitoring of all electrolyte disorders, namely, hypokalemia, hypomagnesemia, and drug therapy (mainly digoxin toxicity).
Complications
- Potential complications include development of tachycardia-induced cardiomyopathy if the arrhythmia is persistent. Other complications include those due to drug therapy used to treat the arrhythmia.
Medical/Legal Pitfalls
- Clear differentiation of MAT from atrial fibrillation is very important because the treatment of atrial fibrillation differs from that of MAT.
- MAT with aberration or preexisting bundle branch block may be misinterpreted as ventricular tachycardia.
- Address underlying medical and metabolic issues.
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Multifocal Atrial Tachycardia excerpt Article Last Updated: Jun 16, 2005
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