What is a pacemaker?
When the heartbeats are abnormally slow, a pacemaker might become necessary. A pacemaker is a special medical device that delivers a minimum number of electrical impulses to the heart per minute (see Figure 1). These electrical impulses stimulate the muscle of the heart to beat. A pacemaker is made of an electrical generator (that generates the electrical impulse) placed under the skin and is attached to a wire that sets in the heart and conducts the electricity from the generator to the heart muscle.
Most pacemakers work on what is called a demand mode. This means that pacemakers only "kick in" or pace the heart when the heart rate tries to slow down. Some pacemakers can only pace the bottom of the heart (the ventricles), while others can pace in both the top of the heart (the atria), as well as the ventricles. More recently, special pacemakers have been developed to make the heart beat more efficiently in certain patients who suffer from weakening of the heart muscle called congestive heart failure.
It is important to remember that in most people, the pacemaker's primary job is to prevent slow heart rhythms.
What is a defibrillator?
A defibrillator is a device that is slightly larger than a pacemaker, inserted under the skin and connected to the heart by a wire. Defibrillators can sense serious fast heart rhythms, such as ventricular fibrillation or ventricular tachycardia, and treat them by delivering an electrical shock to the heart. This electrical shock aborts abnormal heart rhythms and allows the heart to restore its normal beating.
New defibrillators are sophisticated and capable of also pacing the heart if it slows down. Current defibrillators also are pacemakers. Defibrillators are efficient and successful in treating fast as well as slow heart rhythms. The downside of defibrillator treatment is the occasional need for a shock to reset the heart to regular rhythm. These shocks, although uncomfortable, can be life-saving in patients who have these types of serious heart rhythm problems. Frequently, an anti-arrythmic medication is also prescribed for patients who have these types of serious heart rhythm problems to prevent the heart from getting out of rhythm in the first place and minimize the shocks delivered by a defibrillator.
It is important to remember that defibrillators do not prevent the heart from going into these bad rhythms; instead, they correct irregular rhythms when they occur. Often defibrillators are placed in patients who are thought by their physicians to be at high risk for having a ventricular rhythm in the future. Since these rhythms are dangerous and can lead to cardiac arrest and death, it is best to make sure that people who are at high risk have a defibrillator placed before 1 of these events can happen.
What is supraventricular tachycardia?
Supraventricular tachycardia, or SVT, is a type of fast heart rhythm that originates from the top part of the heart (atria) in some people. These episodes of heart racing can occur suddenly and last for several minutes to several hours, depending on the individual. The symptoms associated with this type of fast heart rhythm can range from mild palpitations to shortness of breath to chest pain, lightheadedness, or passing-out spells. In most patients, SVT is a benign condition.
In most cases of heart racing due to SVT, the episodes stop spontaneously after several minutes. Occasionally, these episodes can persist for longer periods of time and require a trip to the emergency room. These episodes can usually be terminated quite easily with certain types of medications that are given in the emergency room.
The long-term treatment for patients with SVT involves the use of either medications to try to suppress the fast heart rhythms or a special catheter procedure to try to get rid of the problem more definitively and permanently. Electrophysiologists are doctors who specialize in treating heart rhythm problems. Patients with frequent symptoms of SVT are often referred to electrophysiologists to be evaluated for whether they may benefit from a catheter ablation procedure. During a catheter ablation procedure, the origin of the abnormal heart rhythm is located and eliminated by an energy current called radiofrequency current delivered from the tip of a catheter placed in the heart chamber. This procedure is done under light sedation in the cardiac catheterization laboratory. If a successful catheter ablation is completed, it can eliminate the cause of SVT and can get rid of this type of heart racing altogether.
Can loss of consciousness be caused by abnormal heart rhythm?
Loss of consciousness can be caused by multiple reasons, including the heart, the brain, or the nervous system that controls the tone of the blood vessels. The heart can cause fainting spells if it beats too fast or too slowly. This can happen from any of the type of rhythm problems described in this chapter. Patients also can have severe narrowing in a heart valve, which can also cause a fainting spell, particularly with exertion. Identifying the cause of fainting or near fainting spells can be very difficult and might require multiple tests. This can include tests to the heart, such as an ultrasound (or echocardiogram), an outpatient rhythm monitoring device, a stress test, an ultrasound to the carotid arteries (arteries that supply the brain), and a CT scan of the brain. Another test that is frequently done is called a tilt table test. A patient is typically placed on a table,strapped,and tilted 80 degrees. The physician monitors the heart rhythm and blood pressure for about 20 minutes while the patient is tilted and occasionally administers medications to determine if the fainting spells recur. Usually, if this happens, the spell is probably related to an imbalance in the control of the tone of the blood vessels by the nervous system.
In about 20% of patients, the cause of the fainting spells remains unknown despite all the testing. Usually, in about 6-7% of these patients, the fainting spell can recur.
What is a Holter monitor?
A Holter monitor is a device that a patient takes home for 24-48 hours and is attached to the chest by several wires that monitor the heart rhythm. All heartbeats during these hours are recorded on a tape.If a patient experiences a symptom, he or she notes the time and type of symptom on a diary and marks the event on the monitor. The physician reviews all the recorded heart rhythm and correlates it with the recorded event and symptoms on the diary. This helps determine whether the symptom is related to a rhythm problem. This test is reserved for those patients in whom symptoms occur frequently.
What is an event care monitor?
An event care monitor is essentially the same as a Holter monitor with the exception that it records the heart rhythm on demand as requested by the patient. A patient who experiences a symptom activates the device, which records the rhythm. This is then transmitted over a phone to a central station that analyzes the rhythm and informs the doctor of the results. A patient can keep the event monitor for a month. This test is reserved for those who have infrequent symptoms.
What should patients do if they experience palpitations in the chest?
A physician should evaluate palpitations, particularly if accompanied by chest pain, shortness of breath, dizzy spells, or preceding fainting spells. Patients who experience these symptoms should not drive themselves to the emergency room but should call 9-1-1. Many palpitations are benign, but some are serious and could indicate an underlying cardiac disease, such as a heart muscle or valve problem or blockages in the coronary arteries. Palpitations, particularly those lasting for several beats, or a couple of seconds, are likely to be benign skipped beats if not accompanied by any other symptoms. Caffeinated beverages including coffee, tea, and chocolate, stress, or deconditioning can precipitate these benign skipped beats. The determination of whether skipped beats are benign or not is done after a careful and detailed evaluation by the physician. Patients should not try to self-diagnose or ignore these symptoms.
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