A pacemaker is needed when the function of the sinus node becomes too slow from age, heart disease, or heart medications. Another leading cause for pacemaker implantation is heart block-the failure of the electrical signal to reach the main pumping chambers of the heart, which in turn causes a slow heart rate.
When the heart beats too slowly, the brain and body may not get enough blood flow, leading to fainting, dizziness, easy fatigability, shortness of breath, and low tolerance for exercise and physical activity. Extreme slowing or complete stopping of the heartbeat can be fatal.
Who needs an ICD?
ICDs have been proven to prolong survival in some patients with dangerous heart rhythms, usually those who have damaged hearts. Patients may be survivors of cardiac arrest caused by ventricular tachycardia or fibrillation (VT or VF), heart rhythm disorders that originate in the ventricles . VT or VF patients may feel faint or dizzy, or even pass out. During VT or VF, the heart does not pump blood adequately because rapid contractions prevent it from filling adequately with blood between beats. VT or VF can be fatal, if not properly treated.
In some cases, depending upon the underlying cardiac status atrial fibrillation (AF) can be cause significant patient instability. During atrial fibrillation, electrical signals move chaotically through the atria, and if the rapid stimuli pass to the ventricles and result in loss of consciousness. If left untreated, it may result in sudden cardiac death.
An ICD can deliver several types of therapies. These therapies include defibrillation, which delivers a brief, high-energy electric shock, and cardioversion, which consists of synchronized shock impulses that may progress from low-energy to high-energy levels, depending on what is needed to stop the rapid rhythm.
An ICD can act like a pacemaker by stimulating the heart if the rate is too slow. This requires little energy, so it is not felt. If an ICD detects a rapid beat, it can emit a series of pulses, which will be perceived as a fluttering in the chest. If this fails, the ICD can deliver one or more mild shocks, which may be felt as thumps to restore normal rhythm.
