Doctors said yesterday that President Bush suffered common irregularity of the heart that, given his history of vigor and good health, probably does not signal a life-threatening illness or a condition that will force him to slow his pace.
Experts in heart disease cautioned that the condition, known as atrial fibrillation, is common in people with a serious underlying heart disorder such as a leaky heart valve.
But they said that when it strikes people like the president, who keep an active pace and have never reported chest pains or other symptoms of a serious abnormality, it usually is a relatively harmless condition that can be managed effectively with drugs.
"People don't keel over dead from atrial fibrillation except in the rarest of circumstances when their hearts are in very bad shape to begin with, which we know he wasn't because he was out jogging," said Dr. Alan Guerci, director of the coronary care unit at Johns Hopkins Hospital.
Atrial fibrillation is a condition in which the atria, or the upper chambers of the heart, suddenly pump very rapidly and in an uncoordinated fashion. "As a consequence of this, the heart doesn't work efficiently, they have some shortness of breath and they feel palpitations, meaning they are aware of their heart beating," Dr. Guerci said.
A person can simulate a normally beating heart by closing his hand into a tight fist, opening it all the way, and then closing it tightly again. In atrial fibrillation, it is as if the hand is half-open and the fingers are fluttering out of control.
"It's a rapid and discoordinated activity," Dr. Guerci said. "Typically, when healthy people get atrial fibrillation, they get it in the kind of setting President Bush reported. They're jogging on a hot day, or it's after strenuous exercise on a hot day, or they're rapidly drinking large volumes of very cold fluids."
The early reports of President Bush's symptoms were hopeful, he said. Chest pains would have been a likely indication of a heart attack, an interruption of blood flow in the arteries leading to the heart that leaves the heart muscle damaged and unable to beat as efficiently as before.
"If he just had atrial fibrillation with shortness of breath, the odds are that he didn't have a heart attack," Dr. Guerci said.
Tests at Bethesda Naval Hospital did not indicate any evidence of a heart attack or of a serious abnormality of the heart's structure, White House press secretary Marlin Fitzwater said. The tests included an electrocardiogram, which measures the heart's electrical activity, and ultrasound, which gives a picture of the heart.
The president was placed on digoxin, a drug that increases the force of the heart muscle's contractions and slows the abnormally rapid nerve impulses passing between the
upper and lower chambers of the heart.
"I think there's probably an 80 percent chance that there's going to be no explanation of why this occurred," said Dr. Myron Weisfeldt,chairman of cardiology at Johns Hopkins and a former president of the American Heart Association.
"Even in the unlikely case that [there's a serious underlying problem], the chances are extremely likely that it's treatable and curable," he said.
Dr. Weisfeldt said shortness of breath is very rarely a first sign of a heart attack -- the early symptoms of which are usually chest pain, nausea, a cold clammy feeling and "a feeling of impending difficulties."
The likelihood that a person who experienced shortness of breath but no chest pains suffered a heart attack is "2 percent to 3 percent," he said.
Approximately 5 percent of the U.S. population will have atrial fibrillation sometime during their lives, Dr. Weisfeldt said.
Dr. Stephen Gottlieb, a cardiologist at the University of Maryland Hospital, said treatment with digoxin or other heart-regulating drugs is common.
If drugs don't work, doctors will often restore the heart's normal rhythm by administering an electric shock to the chest.
In rare instances, patients with atrial fibrillation will develop blood clots in the upper heart chambers -- clots that could enter the bloodstream and cause a stroke. To prevent this, doctors will often give patients blood-thinning drugs such as aspirin. But less than 1 percent of the patients actually develop clots.
Atrial fibrillation is far less serious than ventricular fibrillation -- the rapid and out-of-control beating of the heart's lower chambers.