Why do I feel dizzy?
There are many medical causes of dizziness, and determining the cause in any individual case requires a review of symptom history, physical exam, and, in some cases, diagnostic tests. Anyone concerned about dizziness should consult a doctor promptly to determine the cause.
Speaking in general, doctors try first to distinguish between neurologic (brain and nerves) and cardiovascular (heart and blood vessel) causes. Dizziness caused by neurologic illness is often associated with a sensation known as vertigo, which is a feeling of motion or spinning often accompanied by nausea. Vertigo itself has many causes, including benign problems of the inner ear and more serious conditions that affect the nerve that connects the ear to the brain and the brain itself. Vertigo is often reproduced by certain positions and may be associated with difficulty with balance, coordination, and posture.
Dizziness due to cardiovascular causes is often associated with lightheadedness, a sense of graying of the vision, and a feeling that you might pass out. Loss of consciousness in this setting is known as syncope. Dizziness from cardiovascular causes results from temporarily impaired blood flow to the brain, which may result either from low blood volume, impaired blood output from the heart, or an abnormal nerve reflex.
Low blood volume may be caused by either loss of blood cells (from bleeding, iron or vitamin deficiency, or impaired cell production), or by dehydration (from sweating, inadequate fluid intake, or excessive urination from uncontrolled diabetes). Dizziness due to these causes is often worsened by standing up quickly or standing for prolonged periods of time. Doctors can test for these conditions by measuring blood pressure in different positions, and checking the blood for red cell count, glucose, and electrolytes.
Many people with dizziness are concerned that something is wrong with their heart. Abnormal heart rhythms, known as arrhythmias, come in two varieties: slow and fast. A slow heart rhythm (bradycardia) may be caused by disease of the heart's natural pacemaker (known as sick sinus syndrome) or by a block of impulses from the top part of the heart (the atria) to the pumping part of the heart (the ventricles). A fast heart rhythm (tachycardia) may be caused by numerous conditions originating in either the atria or the ventricles. Tachycardias are often accompanied by palpitations, a sense of strong or fast contraction of the heart within the chest. To diagnose an arrhythmia, a doctor will usually start with an electrocardiogram (an electrical recording of the heart that gives information on the heart's rhythm) and may also suggest wearing a cardiac monitor, or, in certain cases, to undergo an invasive electrophysiologic test. This procedure involves placing several catheters in the heart from a large vein in the leg (the femoral vein), then assessing how electrical impulses are conducted from one chamber to another and stimulating the heart with pacing to induce abnormal fast or slow heart rhythms.
Other heart conditions may cause dizziness even when the heart is in normal rhythm. These include problems with the heart valves (narrowing or leaking) and problems with the pumping function of the heart. Such conditions can usually be discovered with physical examination, an electrocardiogram, and an ultrasound examination of the heart (an echocardiogram). In some cases, more invasive testing is required.
A nervous reflex involving the heart is a common cause of dizziness and syncope. These neurocardiogenic reflexes have many causes, but all result in some combination of relaxation of the blood vessels and slowing of the heart rate, which in turn causes low blood pressure and dizziness or fainting. The reflexes are usually transient and the chief concern lies in the potential for physical injury caused by loss of consciousness. These spells may be triggered by certain stimuli, such as coughing, swallowing, straining, pain, or fright, or they may occur for no apparent reason. When the symptoms are very typical, no further testing is needed; in less certain cases, a doctor may recommend tilt table testing, in which a patient is tilted upright on a table for 30 to 40 minutes while the heart rate and blood pressure is monitored.
This is a long answer to a simple question, but it illustrates why it is often difficult to find a definite cause of dizziness in a given patient. You can help your doctor by making note of any associated feelings you have when you become dizzy, the circumstances during which dizzy spells occur, and also by measuring your pulse rate during an episode.
What is an irregular heart beat?
An irregular heart beat can have many causes. Sinus arrhythmia is a normal finding in younger people and in athletes, and consists of a gradual slowing and acceleration of the heart rate (by 10 to 20 beats per minute) over a five to ten second period.
Some people feel skipped beats as an irregularity in the heart rate. This sensation is usually caused by extra beats (known as extrasystoles) coming from the atria or ventricles. Occasional extra beats are seen in many normal people and generally do not indicate disease. More frequent extra beats may indicate intrinsic heart disease, which can result in more serious arrhythmias.
Intermittent tachycardia (fast heart rate) may also cause an irregular heart beat. Doctors divide tachycardias into supraventricular (originating in the top part of the heart) and ventricular (originating in the bottom part of the heart) causes. One common supraventricular cause is atrial fibrillation, which occurs when the atria (top part of the heart) beat rapidly and chaotically and the ventricles follow suit. Atrial fibrillation may be paroxysmal (comes and goes) or chronic. Other supraventricular tachycardias tend to be paroxysmal and may cause feelings of chest or neck pressure, dizziness, or breathlessness in addition to an irregular heart beat. The ventricular tachycardias may cause similar symptoms. Their seriousness depends on whether underlying heart disease, such as prior heart attack or weakness of the heart muscle is present.
There are many causes of an irregular heart beat, ranging from the trivial to the very serious. After a history and physical exam, a doctor evaluating someone with an irregular heart beat will usually obtain an electrocardiogram. Further testing might include a Holter monitor (a heart monitor worn for 24 hours) or an ultrasound of the heart. Sometimes an exercise test can bring out the irregularity in the heart rate. The choice of tests would depend on your particular medical situation.
When I feel my heart racing or pounding, am I having a heart attack?
Anyone concerned that they are having a heart attack should seek immediate emergency medical attention. Symptoms of a heart attack are highly variable, and no one symptom can rule in or rule out a heart attack. In general, a heart attack is accompanied by feelings of pain or discomfort in the chest, upper abdomen, neck, shoulders, or arms. Other common symptoms include sweating, nausea, and shortness of breath. In some people, the symptoms of a heart attack can be very subtle; some people have no symptoms at all. For more information on the warning signs of a heart attack, visit the American Heart Association Web site at www.americanheart.org.
The medical term for a feeling of one's heart racing or pounding is palpitations. Many people have this sensation after vigorous exercise or during emotional stress. In this circumstance, the heart rhythm is usually normal and is simply accelerated due to nervous input to the heart and increased adrenaline circulating in the blood. This is known as sinus tachycardia. In this situation, the heart is often contracting more forcefully than usual, which contributes to the sensation.
In some people, palpitations may be due to an abnormal tachycardia (fast heart rate). Doctors classify tachycardias into two types, depending on the site of origin. Ventricular tachycardia (or VT) is a fast heart rate originating from the right or left ventricle (bottom part of the heart). Most people with ventricular tachycardia have some kind of heart disease (prior heart attack or disease of the heart muscle), but there are VTs that occur in people with normal hearts. In addition, there are causes of VT such as the long QT syndrome and Brugada syndrome, which are rare cardiac arrhythmia syndromes caused by genetic defects, occurring in people with mutations in genes that regulate the flow of chemical ions in and out of the heart.
A fast heart rate originating in the top part of the heart (atria) is known as supraventricular tachycardia (or SVT). There are many types of SVT, including atrial fibrillation, atrial flutter, and AV nodal reentry. These arrhythmias are generally not as dangerous as the ventricular tachycardias, but may cause significant symptoms such as dizziness, fainting, chest pressure, or stroke.
Getting back to the original question, some of the above listed causes of palpitations also occur in the setting of a heart attack, although palpitations as the sole symptom of a heart attack is uncommon. Sinus tachycardia, atrial fibrillation, and ventricular tachycardia are all well-established causes of fast heart rates during heart attacks and carry a higher risk for complications. In general, however, most people with palpitations are not having a heart attack.
What is a pacemaker and how do I know if I need one?
A pacemaker is an electronic device that monitors the heart rate and paces the heart at a programmed rate if the rate gets too low. First developed in the 1950s, a modern pacemaker system consists of two coated wires (known as leads), each two to three millimeters in thickness, which are implanted in the right atrium (top part of the heart) and right ventricle (bottom part of the heart) through the large vein that runs under the collarbone. In some situations, only one lead is needed, and in some special heart conditions, a third lead may be useful. The opposite ends of the wires are attached to a pulse generator, which contains a battery (which usually lasts five to ten years) and sophisticated electronics which measure the heart rate and compute the appropriate pacing response to every situation. Modern pulse generators are about two inches in width and length and less than half an inch in thickness. They are usually implanted under the skin of the chest.
A special kind of device related to the pacemaker, which also has the ability to electrically defibrillate (shock) the heart out of fast heart rhythms, is called an implantable cardioverter-defibrillator (or ICD). These devices are used in people with life-threatening fast heart rhythms such as ventricular tachycardia or ventricular fibrillation.
A decision to implant a pacemaker should be made together with a doctor who is skilled in the assessment of patients with heart rhythm disturbances after one has been informed of all the important risks, benefits, and alternatives to having a pacemaker. The most common reasons for needing a pacemaker are a slow native heart beat (known as sick sinus syndrome) and heart block, which is caused by an abnormal block of communication between the top part (atria) and bottom part (ventricles) of the heart, usually resulting in a slow heart rate. Most people who need a pacemaker have had symptoms such as dizziness, weakness, or syncope (fainting), although pacemakers are sometimes needed in people who have had very slow heart rates without these symptoms.
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