P-P intervals, P-R duration, and R-R intervals which vary Most episodes of MAT do not precipitate hemodynamic compromise or limiting symptoms. Thus, therapy in patients with MAT should be aimed at the inciting underlying disease. (See 'Treatment' above.) Patients with MAT and associated hypokalemia or hypomagnesemia should undergo electrolyte repletion prior to the initiation of additional medical therapy for MAT. (See 'Magnesium and potassium repletion' above.) Medical therapy for MAT is indicated only if MAT causes a sustained rapid ventricular response that causes or worsens myocardial ischemia, heart failure, peripheral perfusion, or oxygenation. Options for medical therapy for patients with symptomatic MAT requiring ventricular rate control include nondihydropyridine calcium channel blockers and beta blockers. For patients without heart failure or bronchospasm, we suggest initial therapy with a beta blocker, usually metoprolol, before calcium channel blockers (Grade 2C). Conversely, for patients with severe bronchospasm, we suggest initial therapy with a nondihydropyridine calcium channel blocker, usually verapamil, rather than a beta blocker (Grade 2C). Beta blockers may be used cautiously in some patients with heart failure. (See 'Pharmacologic therapy' above.) https://www.uptodate.com/contents/multifocal-atrial-tachycardia/print 12/20 7/5/23, 10:25 AM Multifocal atrial tachycardia - UpToDate Extensive literature has shown a lack of efficacy of numerous standard antiarrhythmic drugs (including quinidine, procainamide, lidocaine, phenytoin, and digoxin) as well as electrical cardioversion in treating MAT. (See 'Antiarrhythmic drugs' above and 'DC cardioversion' above.) Ablation of the atrioventricular (AV) node and the use of a permanent ventricular pacemaker is rarely indicated, and should be reserved for patients with ongoing symptomatic MAT who do not respond to or cannot tolerate pharmacologic therapy. (See 'Radiofrequency ablation' above.) 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Chest 2000; 117:52. Topic 901 Version 28.0 https://www.uptodate.com/contents/multifocal-atrial-tachycardia/print 16/20 7/5/23, 10:25 AM Multifocal atrial tachycardia - UpToDate GRAPHICS Relationship between fast sodium-mediated myocardial action potential and surface electrocardiogram Each phase of the myocardial action potential (numbers, upper panel) corresponds to a deflection or interval on the surface ECG (lower panel). Phase 4, the resting membrane potential, is responsible for the TQ segment; this segment has a prominent role in the ECG manifestations of ischemia during exercise testing. ECG: electrocardiogram. Graphic 64133 Version 4.0 https://www.uptodate.com/contents/multifocal-atrial-tachycardia/print 17/20 7/5/23, 10:25 AM Multifocal atrial tachycardia - UpToDate Electrocardiogram single-lead multifocal atrial tachycardia Clinical features: Elderly patients Decompensation of pulmonary disease Postoperative Arrhythmia usually does not cause severe hemodynamic compromise High mortality ECG features: P waves have 3 forms Atrial rate is usually 100 to 200 bpm Atrial rate is irregular PR interval varies Isoelectric baseline between P waves May progress to atrial fibrillation ECG: electrocardiogram; bpm: beats per minute. Courtesy of Alfred Buxton, MD. Graphic 127222 Version 1.0 https://www.uptodate.com/contents/multifocal-atrial-tachycardia/print 18/20 7/5/23, 10:25 AM Multifocal atrial tachycardia - UpToDate Pharmacologic agents for acute heart rate control in patients with multifocal atrial tachycardia and chronic obstructive pulmonary disease Initial Subsequent Maintenance Drug Onset Side effects dose doses dose Verapamil* 5 to 10 mg IV over 2 1 to 2 minutes 10 mg IV bolus over 2 120 to 480 mg daily Hypotension, heart block, heart failure minutes minutes given 15 to 30 minutes after initial dose Metoprolol 2.5 to 5 mg IV over 2 5 minutes 2.5 to 5 mg IV over 2 to 5 Long-acting: Hypotension, heart block, bradycardia, 50 mg orally to 5 minutes minutes at 10- minute intervals up to heart failure, bronchoconstriction once daily Short-acting: a maximum of 15 mg IV 25 mg orally twice daily MAT: multifocal atrial tachycardia; COPD: chronic obstructive pulmonary disease. For all patients with COPD and MAT and a rapid ventricular response, correction of hypoxemia, acidosis, and other metabolic disturbances is recommended. Theophylline can increase the ventricular response, so dosing should be regulated to keep the serum level in the range of 8 to 12 mg/mL; discontinuation of the medication should be considered. Verapamil is preferred over metoprolol for heart rate control of MAT in patients with COPD due to concerns about exacerbating bronchoconstriction. Representative of the type of selective beta-1 blockers that could be used, but similar drugs could be given in appropriate doses. Verapamil and beta blockers should not be given to patients with sinus node dysfunction or preexisting second- or third-degree block unless a temporary or permanent pacemaker has been implanted. Verapamil and beta blockers should be administered cautiously in patients with decompensated heart failure or hypotension to avoid worsening these conditions. Graphic 83358 Version 8.0 https://www.uptodate.com/contents/multifocal-atrial-tachycardia/print 19/20 7/5/23, 10:25 AM Multifocal atrial tachycardia - UpToDate Contributor Disclosures Alfred Buxton, MD No relevant financial relationship(s) with ineligible companies to disclose. Hugh Calkins, MD Grant/Research/Clinical Trial Support: Adagio Medical [Atrial fibrillation]; Boston Scientific [ARVC]; Farapulse [Atrial fibrillation]; Medtronic [Atrial fibrillation]. Consultant/Advisory Boards: Abbott [Atrial fibrillation]; Atricure [Atrial fibrillation]; Biosense Webster [Catheter ablation]; Boston Scientific [ARVC and atrial fibrillation]; Medtronic [Atrial fibrillation]; Sanofi [Atrial fibrillation]. Other Financial Interest: Atricure [Lecture honoraria]; Biosense Webster [Lecture honoraria]; Boston Scientific [Lecture honoraria]; Medtronic [Lecture honoraria]. All of the relevant financial relationships listed have been mitigated. Susan B Yeon, MD, JD, FACC No relevant financial relationship(s) with ineligible companies to disclose. Contributor disclosures are reviewed for conflicts of interest by the editorial group. When found, these are addressed by vetting through a multi-level review process, and through requirements for references to be provided to support the content. Appropriately referenced content is required of all authors and must conform to UpToDate standards of evidence. Conflict of interest policy https://www.uptodate.com/contents/multifocal-atrial-tachycardia/print 20/20