Loss of Consciousness

Acute loss of consciousness is often caused by simple problems with volume status and hydration. When a patient is dehydrated or ill from diarrhea or dehydration, loss of consciousness or blackouts can happen simply because the water content in the body is not sufficient to maintain adequate blood pressure. The central nervous system and cardiovascular system respond by working in concert to improve blood flow to the brain by whatever means are necessary (which is usually by making you fall to the ground). This is a relatively harmless cause of blackouts that is easily correctable. Serious cardiovascular causes of blackouts include rapid heartbeats, slow heartbeats, heart attack and problems with the heart's pump action.

Syncope or blacking out from rapid heartbeats can be the result of an arrhythmia. Most arrhythmias are harmless and can be treated easily with medications. The types of arrhythmias that cause syncope are more serious and can be life threatening. If an arrhythmia results in documented loss of consciousness it is considered pathologic. The most serious arrhythmias are caused by scared or damaged heart muscle, and by congenital problems with the electrical system that allow rapid heartbeats to overdrive the heart's inherent control system. These disorders are often identified in the hospital after a blackout or by prolonged ambulatory monitoring by a cardiologist. Treatment depends on the underlying cause and may be a catheter ablation or insertion of a defibrillator.

Slow heart rhythms are often seen in older patients. As we age, the heart's wiring system can become faulty. In elderly patients many factors can exacerbate this problem such as medications and other medical conditions (both acute and chronic). It is not uncommon to require a pacemaker to assist the heart in maintaining adequate electrical function in the elderly. In fact, sometimes a pacemaker is inserted so patients can take certain heart medications to prevent rapid heartbeats.

The classic symptom of a heart attack is crushing chest pain. In a small percentage of patients, this pain can be so intense that it causes a blackout. It is more common that a heart attack patient loses consciousness due to one of the rhythm disturbances mentions above. Slow rhythms are the result of injury to the heart's conduction system. Patients usually are experiencing a clot in the right coronary artery which supplies this electrical center. Restoration of blood flow usually returns the heart rate back to normal, but a temporary pacemaker may be inserted to help. Fast heartbeats develop when the injured muscle conducts poorly and irregularly in small circuit around the injured area. This is Ventricular Tachycardia, which can degenerate into Ventricular Fibrillation which is usually fatal if the patient is not shocked or defibrillated out of it. These fast rhythm changes with a heart attack account for at least 10 percent of patients that die suddenly of a heart attack. It is paramount to call 911 at the start of symptoms of a heart attack as approximately 1/3 of patients will die in the first 24 hours from rhythm disturbances like these.

When heart valves are affected, a blackout can occur because the heart can't pump the blood out effectively. Narrowing of the valve leading out of the heart is a very common cause of blackouts in the elderly. This condition, Aortic Stenosis, is very common in patients over 75 years of age. A physical examination can often detect the murmur. If the arotic stenosis is present and the patient has syncope, chest pain or heart failure, surgery is needed.

After a large heart attack, muscle injury can damage the heart's pump function. The medications used to improve heart function often cause dizziness or lightheadedness. It is rare to blackout because of the medications. Patients with low heart function after a heart attack should be considered for an implanted defibrillator if the function is less than 35 percent. A simple cardiac ultrasound after heart attack can determine the ejection fraction (estimate of pump efficiency). The lower the number the worse the prognosis and higher the risk for ventricular arrhythmias that can be life threatening.