Multifocal Atrial Tachycardia (MAT) | drbeen

About This Video

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Dr. Mobeen discusses following topics in the context of multifocal atrial tachycardia.

  • Terms and definition of abnormal rate
  • Definition of MAT
  • Causes of MAT
  • EKG representation
  • Diagnostic criteria
  • Pathological mechanisms behind the causative factors
  • Treatment

Abnormal Impulse Terms

  • Automaticity

    • Change in the heart rate driven by the pacemaker cells.

    • Sinus Tachycardia
    • Sinus Bradycardia
    • Sick sinus syndrome (alternating sinus tachycardia and sinus bradycardia.)
  • Drivers

    • Non-nodal cardiac tissue that incorrectly starts to generate new impulses without the need to be triggered by another impulse. These ectopic foci are called drivers instead of pacemakers.
  • Reentry

    • Entrapment of an impulse originated somewhere else in a reentrant circuit.
    • As the impulse cycles in this reentrant circuit, it sends new impulses to the neighboring cells.
  • Triggered activity

    • An impulse giving rise to further impulses due to the abnormal state of myocardial cells.
    • Note: these cells in the abnormal state cannot produce a new impulse on their own, they need an impulse acting as a trigger.
    • Drugs that prolong action potential duration (APD), e.g. class III antiarrhythmic, can cause triggered activity.
    • This triggered activity is called afterdepolarization (AD). It is of two types.
      • Early Atrial Depolarization (AED). Caused by slow activation and prolonged action potential.
      • Delayed afterdepolarization (DAD). Caused by the Ca++ overload.

 

MAT

(A type of Supraventricular Tachycardia)

  • Irregular rhythm occurring at the rate of 100 to 200 bpm.
    • The rate can be less than 100 bpm somtimes. In such cases, the arrhythmia is called wandering atrial pacemaker (WAP) or multifocal atrial rhythm.
    • Wandering atrial pacemaker can be detected in healthy individuals too.
    • If the rate is lesser than or equal to 60 then the term is multifocal atrial bradycardia.
  • MAT occurrs due to the random firing of several different atrial foci.
  • Common in patients with severe lung disease.
    • Older people with the chronic obstructive pulmonary disease (COPD,) and hypoxia.
    • Theophylline toxicity can also cause MAT. (Given in COPD.)
  • MAT can occur with myocardial infarction.
  • Low blood magnesium levels1 (<1.5 mg/dl) can lead to MAT.
    • Diuretics can cause hypomagnesemia.
    • Mg acts similar to Ca++ channel blockers.
    • Mg depletion reduces Na+/K+ pump action, leading to intracellular K+ depletion.
  • Hypokalemia can lead to MAT. (<3.5 mg/dl or severe hypokalemia <2.5 mg/dl.)
  • Rarely, digitalis toxicity in patients with heart disease can cause MAT.
  • Treatment is usually not needed other than fixing the underlying disease.
    • Carotid massage has no effect as the rate is not originating from a pacemaker.

 

Clinical Presentation

  • Patients are often asymptomatic.
  • Exacerbated underlying disease symptoms may be present.
    • Shortness of breath, wheezing, productive cough, or the symptoms of acute metabolic derangement.
  • Irregular heart rate/pulse.
  • Heart rate > 100 bpm.
  • Can worsen the systemic oxygenation in patients with advanced COPD.
  • Can worsen the cardiovascular dynamics in patients with coronary artery disease or heart failure.
    • Signs and symptoms of exacerbated heart disease may be observed e.g. angina, dyspnea, and orthopnea.

MAT’s Diagnostic Criteria

  • As the P waves appear from many different sites in the atria. The shapes of the P waves vary.
  • For diagnosing MAT:
    • One must find three morphologies (shapes) of the P waves.
    • Note: one shape of a P wave can appear for a few beats before another shape of the P wave appears.
    • P waves must be separated by isoelectric lines.
    • Varying PR intervals, R-R intervals duration, and R-R intervals are observed.
  • QRS complexes are of narrow type (no problem in the ventricle.)
    • Unless there are ventricular conduction pathologies present too.
  • MAT is observed in about 3 patients out of every 1000 hospitalized adults.

 

EKG Presentation

(Credit: By Jer5150 - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=20243829)

Note the varying shapes of the p waves in the v6 rhythm lead at the bottom of this EKG image. You have to find at least three different shapes of p waves.

Multifocal Atrial Tachycardia (EKG representation.)

 

Difference of MAT and Atrial Fibrillation

  • MAT usually has easily identifiable P waves before the QRS complex.
  • There are clear isoelectric intervals between the P waves. Atrial fibrillation either does not have easily discernable P waves, or the P waves appear on the EKG with a higher frequency than the QRS complexes without isoelectric intervals between them.
  • In atrial fibrillation, there is no discernible association between the P waves and the QRS complexes.
  • In MAT PR intervals vary in size. Depends on the distance of the impulse origin from the AV node.

 

Chronic obstructive pulmonary disease (COPD) and MAT

  • Hypoxia causes cell depolarization.
    • Na+/K+ pump function decreases due to the lack of ATP.
      • Reduced levels of hyperpolarizing currents.
      • Reduced pump activity leads to increased extracellular K+ levels. Which initially cause hyperpolarization but then cause depolarization because of increase extracellular K+ concentration.
    • Reduced ATP also slows down Na+ channels which causes action potential duration (APD) to become variable.
  • Hypoxia affects the L-type Ca++ channel’s function.
    • These channels are important for the plateau phase of the cardiac action potential.
    • Disturbance in these L-type Ca++ channel function can result in life threatening arrhythmia. This happens as some cells end up with longer action potential duration and some with shorter durations. (An abnormal function of the L-type Ca++ channels.)
  • In patients of severe COPD hypercapnia causes vasodilatation.

 

Treatment of the multifocal atrial tachycardia (MAT)

  • Treat the underlying cause.
  • Electrical cardioversion has no effect.
  • Carotid massage has no effect.
  • The following therapy can be applied (if the tachycardia due to MAT is causing hemodynamic issues.)
    • Ca++ channel blockers (verapamil.)
      • Verapamil is negatively inotropic and a vasodilator. It can cause severe hypotension in patients with heart failure. Use with caution.
    • Beta blockers (metoprolol.)
      • Patients with severe lung disease often cannot tolerate beta blockers.
    • Verapamil and beta blockers should not be given to patients with sinus node dysfunction or existing second or third-degree block without a pacemaker.
    • In patients with pulmonary disease start with calcium channel blockers. Use beta blockers with lots of care.
    • In patients who do not have pulmonary disease, you can start with beta blockers.
    • Amiodarone is effective but dangerous.
      • Long-term therapy with amiodarone is avoided due to its toxicity, especially pulmonary fibrosis.
    • Oxygen
    • Simultaneously correct magnesium and potassium levels.
    • Radiofrequency ablation of the AV node with a pacemaker installation is indicated in patients who are not responding to the drug therapy or who cannot tolerate drug therapy.

Disclaimer

  • All information contained in and produced by the drbeen corp., is provided for educational purposes only. This information should not be used for the diagnosis or treatment of any health problem or disease.
  • THIS INFORMATION IS NOT INTENDED TO REPLACE CLINICAL JUDGMENT OR GUIDE INDIVIDUAL PATIENT CARE IN ANY MANNER.

Instructor

Dr. Mobeen Syed

Dr. Mobeen Syed

Mobeen Syed M.D, MS Graduated from King Edward Medical University. Entrepreneur, Medical Educator, CEO and founder of Drbeen corp.