CARDIAC ARRHYTHMIAS
The normal heartbeat results from an orderly sequence of electrical stimulation passing from the upper to the lower chambers through a well defined circuit. It begins in the sinus node (the natural 'pacemaker') and spreads from there. Under influence from the nervous system, the rate varies with stress, exertion, and many other factors. A slow leakage of chemicals through the cell membrane sets up the next beat at the correct moment.
Normally, the resting heart beat is between 60 and 100 per minute, though frequently these limits are briefly exceeded in normal people. Under exertion or stress, maximum rates of 140 to 200 depending on age and conditioning are seen, and rates as low as 40 at rest may occur in athletes. Minor fluctuations normally occur with the breathing cycle.
When the normal rhythm is no longer functional, the term arrhythmia is used. The common arrhythmia’s are discussed below; first it is important to understand the possible symptoms which they cause.
Palpitations--skipped, pounding, or otherwise noticeable heart beats of brief duration. Often of no significance, and brought on by fright, caffeine, nicotine, etc., they can also signal serious arrhythmia’s.
Blood Pressure Drop (hypotension)--when the normal rhythm is lost, the heart sometimes has insufficient time to fill with blood between beats, at least when rates are very rapid. This results in low heart output and low blood pressure.
Cardiac Arrest--when the rhythm is so chaotic that no effective contractions occur, or when there is no electrical activity at all, cardiac arrest occurs. Within seconds to minutes, the brain, lungs, and the heart itself lose their blood supply and death occurs unless cardiac resuscitation are carried out. If very brief, fainting or transient lightheadedness may be the only symptom.
The common arrhythmia’s are discussed below. The usual causes are idiopathic (unknown), ischemic (poor circulation to the electrically important cells due to clogged arteries), and drug-induced or related to other chemical imbalances in the blood.
Atrial Fibrillation and Atrial Flutter--these arrhythmia’s result from very rapid stimulation of the upper chambers, too fast for the important lower chambers or ventricles to keep up with. Thus only random or occasional beats get through in a random and irregular pattern. The pulse is irregular, with some weak and some strong beats. Untreated, the rate can be rapid--up to 200 or more per minute. Symptoms depend on the rate (see above). Treatment is either mild electric shocks to restore normal rhythm, or medications such as digitalis, verapamil, quinidine and others to slow the rate down to safe levels.
Ventricular Tachycardia-- beats originating in the lower chambers, often but not always very rapid. When the rate is slow, symptoms may be mild; when rapid the severe symptoms and death may occur. Especially worrisome is that this may lead to ventricular fibrillation. Treatment is with electric shock and intravenous lidocaine or procainamide. Procainamide, propranolol, quinidine, and phenytoin are sometimes used preventatively long-term
Ventricular Fibrillation-- this is the classic cause of cardiac arrest and is fatal unless treated within seconds to minutes with electric shocks, intravenous drugs and resuscitation. It is commonest shortly after heart attacks. No effective heart contractions can occur when this occurs.
Premature Atrial Beats-- occasional extra beats of the upper chambers, often quite benign and requiring no treatment, other than avoidance of caffeine and other stimulants.
Premature Ventricular Contractions-- arising in the lower chambers, these may be benign and of no significance, especially if no other heart problems are present. On the other hand, in the presence of coronary disease or other heart disorders, these may sometimes be a warning of the more serious arrhythmia’s noted above.
Paroxysmal Supraventricular Tachycardia (PSVT, or PAT)--some otherwise normal young and occasionally older patients experience "runaway" rapid heart beats similar to the normal rhythm electrically, but very rapid, often to 180 to 200 beats per minute. In a healthy heart this is usually well-tolerated, if frightening. A variety of maneuvers, each of which elicits a primitive "diving" reflex, may terminate the spell, via stimulation of nerve impulses which slow the heart. These include bearing down while holding the breath for several seconds, immersing the face in ice water and applying pressure to certain areas of the neck. These are advisable only after the diagnosis has been confirmed by a doctor, and found safe to do. They can sometimes be quite effective. When necessary, and this is often not the case, drugs such as digoxin, verapamil, and propranolol can prevent or reduce recurrences.
All arrhythmia’s must be evaluated by a physician, and treatment based on careful EKG, exam, and lab evaluation. The area is complex, and changing rapidly. Not a disease for self-care or diagnosis, cardiac arrhythmia’s should be thoroughly assessed by an internist, cardiologist or other qualified physician.
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