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| EDITORIAL |
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| Year : 2017 | Volume
: 2
| Issue : 2 | Page : 58-61 |
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Multifocal atrial tachycardia: Looking for new solutions to an old problem
Elpidio Santillo
Department of Geriatric Rehabilitation, Rehabilitative Cardiology Unit, Italian National Research Center on Aging, 63900 Fermo, Italy
| Date of Web Publication | 31-Jan-2018 |
Correspondence Address:
Elpidio Santillo
Department of Geriatric Rehabilitation, Rehabilitative Cardiology Unit, Italian National Research Center on Aging, Contrada Mossa 2, Fermo 63900
Italy
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/IJHR.IJHR_2_17
Multifocal atrial tachycardia (MAT) is a cardiac rhythm disorder frequently diagnosed in elderly patients affected by several comorbidities. However, MAT can be observed also in younger ages as an incidental finding or in association with heart and lung diseases. MAT is characterized by heart rate >100 beats/min and at least three different P waves when compared to sinus P wave. Recent guidelines recommend the use of beta-blockers and verapamil for rate control and ongoing management of MAT. Unfortunately, electrical cardioversion and antiarrhythmic drugs have been demonstrated not always effective in MAT treatment. Intravenous magnesium seems a promising therapy in restoring sinus rhythm in patients who developed MAT. Moreover, in the last years, innovative strategies such as atrioventricular junction modification, ablate and pace approach, and electrophysiological isolation of firing sites have been successfully tested as curative treatment in selected cases of MAT resistant to drug therapy.
Keywords: Atrial arrhythmias, multifocal atrial tachycardia, radiofrequency catheter ablation
How to cite this article:
Santillo E. Multifocal atrial tachycardia: Looking for new solutions to an old problem. Int J Heart Rhythm 2017;2:58-61 |
| Introduction | |  |
Multifocal atrial tachycardia (MAT), also known as chaotic atrial tachycardia or multifocal atrial rhythm, is a heart arrhythmia primarily observed in old and diseased patients.[1],[2] In hospital setting, the prevalence of MAT has been estimated to be from 0.05% to 0.40%.[1],[3],[4]
In most participants, especially outpatients, MAT frequently occurs as a harmless condition, which does not impact on mortality and requires no specific treatment.[5] On the other hand, it is well known that elderly patients with MAT are commonly affected by acute illness and several associated chronic diseases such as atherosclerotic heart disease, valvular heart diseases, and chronic obstructive pulmonary disease (COPD) which may heavily impact on their prognosis.[1],[4] In particular, in patients with severe COPD needing mechanical ventilation, MAT presence has proved to be associated with a worse survival.[6]
MAT development has been reported also as a consequence of electrolyte imbalance and drugs' toxicity, especially from digitalis and sympathomimetic amines such as theophylline and aminophylline.[7],[8],[9],[10],[11]
Although it is more frequently diagnosed during senescence, MAT can be detected even in subjects of younger ages, including infants and children, sometimes as an incidental finding in otherwise healthy individuals, while, in a minority of cases, concomitant diseases of heart and lung can be present.[12] The occurrence of sudden cardiac death in infants with chaotic atrial rhythm has been also described.[13]
Hence, finding of MAT represents often a clinical diagnostic challenge for clinicians and imposes to search and treat eventual underlying pathological conditions beyond the arrhythmia itself.[3],[4]
The objectives of the present article are to summarize the available evidences on MAT treatment, including invasive approaches, after briefly reviewing diagnosis criteria and pathophysiological mechanisms of MAT.
| Diagnosis of Multifocal Atrial Tachycardia | | |
Electrocardiographic diagnosis of MAT requires a heart atrial rate >100 beats/min and the identification of at least three different P waves with distinct morphology when compared to the sinus one.[14] Moreover, in the course of MAT, P-P and R-R wave intervals exhibit a marked variability as well as PR tract.
Reduction of diagnostic threshold rate to 90 beats/min for definition of MAT has been proposed due to its better association with exacerbations of COPD.[15] Differential diagnosis between MAT and atrial fibrillation (AF) through surface ECG may be challenging. However, in MAT, well-defined isoelectric periods are usually detectable betweenPand R waves. Oppositely, in AF, beyond the evidence of an irregular rhythm, P waves are absent, and “f” waves can be recognized between R waves instead of isoelectric line. Computerized electrocardiography has been suggested as a useful technological tool for the detection of MAT since the arrhythmia is frequently misdiagnosed as AF.[16]
| Pathophysiological Mechanisms of Multifocal Atrial Tachycardia | | |
Pathophysiological mechanisms of MAT have not been fully elucidated yet. However, in the genesis of MAT, anatomic factors seem not as important as in AF. Indeed, an echocardiographic study on hospitalized patients showed significantly less structural abnormalities in MAT cases compared to ones with AF.[17] On the other hand, it has been argued that right atrial hypertension and distension could facilitate MAT development.[18]
On the electrophysiological point of view, MAT could originate from triggered activity, ectopic foci, and abnormal automaticity or result from an accelerated wandering pacemaker.[3],[19] Conversely, reentry phenomena appear not a probable mechanism of the arrhythmia for the typical irregularity of cycle length observed in MAT and for its poor response to electrical cardioversion.
According to triggered activity hypothesis, MAT could originate from delayed atrial afterdepolarizations due to intracellular calcium overload, which is a sort of “common ground” of various associated pathological conditions (i.e., catecholamine excess, hypoxemia, acidosis, and hypokalemia).[1] Ectopic foci or a single focus with variable impulse propagation in the atrium are further plausible electrophysiological mechanisms of MAT.[19]
| Therapeutic Recommendations from Guidelines | | |
Recent guidelines for the management of patients with supraventricular tachycardias include a specific section on MAT.[20]
According to guidelines, during MAT, heart rate control should be properly obtained using drugs that slow the conduction at atrioventricular node. Intravenous verapamil or metoprolol is recommended for acute treatment of MAT (Class of recommendation: IIa; Level of Evidence: C for limited data). In particular, guidelines underline that verapamil has been shown to facilitate the conversion of the arrhythmia to sinus rhythm. However, the use of intravenous verapamil requires caution for possible hypotension occurring as an adverse effect. On the other hand, the beta-blocker should not be administered in patients with decompensated heart failure for risk of worsening the hemodynamic status as well as in subjects with severe bronchopulmonary disease for the possibility of inducing bronchospasm.
Oral verapamil and diltiazem are recommended for ongoing management of MAT (Class of recommendation IIa). The level of evidence favors verapamil (Level of Evidence B: Data from nonrandomized studies) since data existing on the use of diltiazem are limited (level of evidence C). However, before employing such drugs, relevant sinus dysfunction and conduction anomalies should be excluded.
Electrical cardioversion has proved not useful for MAT while efficacy of antiarrhythmic drugs is still debated.[20] Indeed, in a study of 41 patients with MAT, quinidine, procainamide, lidocaine, and phenytoin did not affect the rhythm.[21] However, more recent evidence suggests that treatment with amiodarone, flecainide, and ibutilide can be effective in suppression of MAT.[10],[22],[23]
| Therapeutic Prospects | | |
In few studies, parenteral magnesium has proved to reduce the ventricular rate of MAT and to facilitate reversion to normal sinus rhythm [Table 1].[24],[25],[26] Magnesium's mechanism of action comprises the restoration of ionic equilibrium in atrial cardiomyocytes, so preventing supraventricular ectopic activities. In fact, magnesium is able to antagonize L- and T-type calcium channels antagonism.[27] Moreover, when magnesium is administered in supraphysiological doses, it favors cellular membrane's stabilization through reduction of potassium outward current density.[27]
Interestingly, in the last years, various electrophysiological invasive approaches have been tested for treatment of MAT cases refractory to medical therapy [Table 2].[28],[29],[30],[31],[32],[33] | Table 2: Published papers on invasive electrophysiological approaches for MAT treatment
Click here to view |
Tucker et al.[28] observed in three patients with drug-resistant MAT that ablation of atrioventricular junction followed by implantation of permanent transvenous pacemaker resulted safe and effective. More recently, Ueng et al. described the better quality of life and function of left ventriculum in 13 patients with COPD and MAT not responsive to medical therapy after they underwent atrioventricular junction modification.[29] Patients' improvement after AV modification could be explained by the reduction of ventricular response and less need of drugs which impair ventricular function. However, interpretation of such results remains problematic since the study did not provide a control group.[18]
Electrophysiological evidence of atrial multifocality has been considered as criteria that render radiofrequency catheter ablation more difficult or unsuccessful, so ablative option is often excluded for patients with MAT.[34] In fact, in a study of 105 patients with atrial tachycardias, success rate of radiofrequency catheter ablation resulted lower when there was a multifocal origin of the arrhythmia.[30]
However, radiofrequency ablation of MAT has been demonstrated feasible in selected cases in which catheter mapping found easily treatable sites of firing.[31],[32] Of note, it has been observed that such aggressive management can favor the regression of associated tachycardia induced cardiomyopathy.[32] It could be expected that recent three-dimensional mapping systems will confer a great advantage in detection of MAT, in efficacy of ablative procedures, and in limitation of time of exposure to radiations.[33],[35]
| Conclusions | | |
Due to the aging of populations worldwide, physicians will face more frequently MAT in their clinical practice. Recent guidelines and evidences from small studies indicate few drugs for management of MAT as effective choices for rate control. Invasive approaches such as “ablate and pace” and atrioventricular junction modification should be reserved to drug-resistant cases. However, further studies should investigate in various age groups which are the optimal medical strategy to adopt, also considering the eventual hemodynamic burden derived from the arrhythmia. Finally, in the near future, technical advancements in radiofrequency catheter ablation procedures of MAT could provide a more effective and safe option for cases of MAT not responsive to medical therapy, but an accurate selection of eligible patients will be always indispensable.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2]
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