Cardiac electrophysiology (EP) is the study of the electrical system of the heart. Our heart is an organ charged with moving 4,300 gallons of blood each day through the intricate vascular network of our body. Although displacement of blood is its primary function, each and every of the 100,000 beats generated daily is initiated and finely regulated by electrical impulses that originate in the heart itself.


Electrical currents, not in the form of electrons like those that course through the wires of our house, but in the form of chemical ions, flow across the membrane of each cell causing voltage surges that set the heart in motion. Sodium ions rush into the cells, to be followed by potassium and chloride ions leaving. The resulting voltage spike or action potential regulates the influx of calcium ions that mediate the sliding motion of filaments within each cell causing their shortening or contraction.

This process, repeated in each adjoining cell of the heart, causes the orderly spread of electrical activity and the synchronous contraction of the myocardium (heart muscle). Like other “excitable” tissues, the cells of the heart are electrically connected through low resistance pathways. These pathways facilitate the spread of the electrical impulse, ensuring efficient activation and pumping motion. Without electrical activity, the heart lies motionless and serves no useful purpose.

When these electric signals are disrupted, and the heart contraction is not uniform, we have an abnormal heartbeat or arrhythmia. When the heart beats abnormally, its efficiency decreases and its capacity to pump blood is reduced. Extreme arrhythmia within the heart can lead to sudden death, the single most prevalent mechanism of death in the United States, taking the lives of over 350,000 Americans each year. Nearly every minute of every day someone in this country dies of sudden cardiac death, very often the result of an arrhythmia known as ventricular fibrillation.


Other forms of Arrhythmias


  • Atrial fibrillation: an irregular, fast heart rhythm in the upper chambers of the heart.
  • Bradycardia: a heartbeat that is too slow.
  • Tachycardia: a heartbeat that is too fast.
  • Ventricular tachycardia: a dangerous type of very fast heartbeat.
  • Supraventricular tachycardia. This is a sudden, very fast heartbeat.
  • Ventricular fibrillation: a dangerous fluttering of the heart muscle that doesn’t let it pump blood and can be fatal.
  • Sudden cardiac arrest: when the heart suddenly stops beating.
  • Long QT syndrome: a disorder of the heart that can cause sudden arrhythmias.
  • Brugada syndrome. an increased risk of abnormal heart rhythms from the lower chambers of the heart.
  • Other arrhythmias. Arrhythmias can be caused by pregnancy, medicine interactions, or metabolic problems.

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MMRL experimental cardiologists have also gained notoriety for developing experimental models of arrhythmias in which the proarrhythmic effect of a wide variety of drugs used in medicine can be evaluated and in which the actions of antiarrhythmic drugs can be evaluated.

MMRL has long been a major player in the development of a number of heart medications that work together with devices such as the pacemaker, implantable cardioverter defibrillator (ICD) and automatic external defibrillator (AED) to prevent sudden death during a heart attack.

MMRL has recently discovered a new class of drugs that are atrial-selective and provide for safe and effective management of atrial fibrillation, the most prevalent arrhythmia seen by clinicians.