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Impulses can travel retrograde (3 to 2) but not orthograde.
An AP will travel down the branch 1, into the common distal path (br 3), then travel retrograde through the unidirectional block in branch 2.
When the AP exits the block, if it finds the tissue excitable, it will continue by traveling down (reenter) the branch 1.
If it finds the tissue unexcitable (ERP) the AP will die.
Tming is critical –AP exiting the block must find excitable tissue to propagate.
If it can re-excite the tissue, a circular pathway of high frequency impulses (tachyarrhythmia) will become the source of APs that spread throughout a region of the heart (ventricle) or the entire heart.
“ The ideal antiarrhythmic agent does not yet exist, and it is unlikely that it will in the foreseeable future. All the available agents have side effects, and therapy should be regarded as each patient’s dysrhythmia remain an individuals pharmacologic experiment, determined empirically by clinical judgment. Although in some patients one drug may suppress a ventricular tachycardia that is refractory to all other agents, other patients require several combination of drugs. (D.P. Zipes, new eng. J. Med. 304:475, 1981)”
Implantable cardioverter defibrillator (ICD) reduces the chances of dying from a second SCA. An ICD is surgically placed under the skin in the chest or abdomen. The device has wires with electrodes on the ends that connect to the heart's chambers. The ICD monitors the heartbeat. If the ICD detects a dangerous heart rhythm, it gives an electric shock to restore the heart's normal rhythm. The electrodes are inserted into the heart through a vein.