Sudden cardiac death: management of high-risk patients

Article Abstract:

Sudden cardiac death refers to death from cardiac causes within one hour of onset of symptoms, and causes more than 350,000 deaths each year. Sudden cardiac death generally results from degeneration of the normal rhythm of the heart into a dangerous and often fatal rhythm, such as ventricular fibrillation or ventricular tachycardia. The patients who experience this often have previously scarred heart muscle, from injuries such as heart attacks, which is vulnerable to factors that might cause abnormal rhythms. These factors include decreased oxygen supply to the heart; abnormalities in blood levels of potassium and other electrolytes; sensitivity to drugs taken by the patient; and elevations of such substances as adrenaline. Many patients with failing hearts take diuretics, drugs to reduce the body's fluid load, and these drugs often decrease potassium levels. Other patients take drugs meant to suppress abnormal rhythms, but instead these drugs promote abnormal rhythms. Patients who are resuscitated from episodes of sudden cardiac death are very prone to experiencing them again. These patients generally undergo coronary angiography, to see if there is any treatable damage to the coronary arteries. Most also undergo electrophysiologic evaluations, in which the heart is stimulated to produce abnormal rhythms, and various drugs are given to attempt to suppress them. Patients who have experienced sudden cardiac death and have survived may be treated in several ways. Some are given anti-arrhythmic drugs, others have surgery to remove the scarred heart muscle that is the presumed source of the abnormal rhythms, and others receive special devices known as implantable defibrillators. When these devices sense an abnormally fast heart rate, they deliver electric shocks to the heart to terminate the rhythms. Implantable defibrillators have been in use less than 10 years, but the preliminary data suggest that they are among the most effective means of suppressing abnormal rhythms. The technology behind these defibrillators is expanding rapidly, offering more promise to survivors of sudden cardiac death. (Consumer Summary produced by Reliance Medical Information, Inc.)

Prevention, Risk factors, Sudden death

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Unexplained syncope evaluated by electrophysiologic studies and head-up tilt testing

Article Abstract:

As many as 30 percent of adults will experience syncope, or fainting, at some time. One of the more dangerous causes of syncope is an abnormal heart rhythm, which can even in some cases be fatal. Therefore, patients with unexplained syncope are often referred for electrophysiologic testing, in which attempts are made to induce abnormal heart rhythms and then suppress them, generally with drugs. A technique known as tilt testing (in which the patient, lying on his back on a special table, is tilted to a 70-degree angle for several minutes) appears to be a new method for ascertaining the cause of syncope in some patients. A group of 86 patients with syncope underwent both electrophysiologic testing and tilt testing. Results allowed the patients to be categorized into three groups. Group 3 patients (23 people) never had the reason for their syncopal episodes identified. Group 1 patients (29) had positive electrophysiologic tests, and their syncopal episodes were attributed to abnormal heart rhythms that caused drops in blood pressure and pulse, with subsequent loss of consciousness. Group 2 patients (34) had negative electrophysiologic studies but positive tilt test results. A positive tilt test is one in which the patient develops a significant drop in pulse and blood pressure and becomes symptomatic, either by fainting or feeling faint. A discussion is presented of the physiologic mechanisms that underlie this cause of fainting (called neurocardiogenic syncope). Drugs known as beta-blockers will often suppress the decrease in pulse and blood pressure associated with neurocardiogenic syncope. In this study, the combination of electrophysiologic studies and tilt table testing was able to document the cause of syncope in 74 percent of the patients studied. (Consumer Summary produced by Reliance Medical Information, Inc.)

Diagnosis, Physiological aspects

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Comparison of cardiac pacing with drug therapy in the treatment of neurocardiogenic (vasovagal) syncope with bradycardia or asystole

Article Abstract:

Drug therapy appears to be more effective than cardiac pacing in treating neurocardiogenic syncope associated with slow or irregular heartbeat. Neurocardiogenic syncope refers to fainting or swooning due to a cardiovascular abnormality. Head-up tilt testing can be used to determine which patients with syncope are likely to develop low blood pressure and slow heartbeat. Of 22 patients with recurrent syncope, six had an irregular heartbeat and 16 had a slow heartbeat during initial head-up tilt testing. Head-up tilt testing was then performed using temporary cardiac pacing. The average blood pressure dropped significantly, 15 patients experienced presyncope and 5 experienced syncope. However, 19 patients treated only with metoprolol, theophylline or disopyramide had a negative head-up tilt test. Two patients were then treated successfully with metoprolol and a pacemaker, and the third, who had had a negative head-up tilt test during temporary cardiac pacing, received a permanent pacemaker.

Care and treatment, Evaluation, Cardiac pacing, Theophylline, Disopyramide

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