The study evaluated patients with an implantable cardioverter-defibrillator (ICD). An ICD is an electrical generator the size of a pocket watch that is inserted into the heart to monitor heart rhythm. It detects life-threatening abnormal rhythms, called arrhythmias, and delivers an electrical shock to restore normal rhythm.

Beginning a few days after the terrorist attack on the World Trade Center, the rate of ICD discharges increased and remained elevated throughout the next month.

Researchers evaluated 200 patients (average age 69) with ICDs at six clinics within 100 miles of the World Trade Center. The devices had been implanted an average of 2.5 years before the terrorist attack.

ICDs can store monitoring data, allowing comparison of rhythm patterns and shock rates from different times. The researchers compared ICD discharge rates for the 30 days before and after the terrorist attack. In the month before the attack, 3.5 percent (seven patients) had heart rhythm disturbances that required electrical shocks from their ICDs. In the 30 days after the attack, 8 percent (16 patients) did – a 2.3-fold increase.

The results provide compelling evidence of the impact of stress on the heart, says Marcin Kowalski, M.D., a resident at St. Luke's-Roosevelt Hospital Center in New York. Even more important, the findings demonstrate the life-saving value of ICDs, he says.

"These patients all had potentially lethal arrhythmias in the 30 days after the attack, and they were all successfully treated by ICDs," Kowalski says. "This is just another example showing that patients really benefit from ICDs and that ICDs can help save lives."

Previous studies have evaluated how stressful events such as earthquakes and missile attacks have affected the heart in terms of heart attack and sudden death.

"These previous studies showed a spike in the occurrence of heart attack or sudden death for a short period after the incidents," says Jonathan S. Steinberg, M.D., chief of cardiology at St. Luke's-Roosevelt. "The increase in cardiac events tends to be short-lived and very closely coupled to the inciting event, such as an earthquake."

However, the New York spike in ICD activity was not short-lived, perhaps documenting the persistence of increased psychological stress after the World Trade Center disaster.

The increases in ICD discharge did not occur until three days after the terrorist attack and continued to occur at a cumulative rate throughout the remainder of the 30-day study period. The discharge rate returned to pre-attack levels and remained at 2 percent to 3 percent per month during several months of monitoring.

Why the pattern of cardiac events in the arrhythmia study differed from the patterns seen in other studies is unclear.

"We don't know why arrhythmias occur at a particular time or have a full understanding of why stress causes arrhythmias," Steinberg says.

Stress induces several physiologic changes that could predispose a person to a heart attack, heart rhythm disturbance, or other cardiac events, he says. Chief among the changes are increased clot formation and nervous-system stimulation.

"If these changes occur on a regular basis or if they are persistently present, they could promote arrhythmias or heart attacks; and heart attacks can cause arrhythmias,” Steinberg says.

The researchers looked at various medical and demographic factors that might have contributed to the increase in arrhythmias. The only predictor of an arrhythmia after the terrorist attack was the patients' history of life-threatening heart rhythm disturbances.

"It's not surprising to find that people who have had arrhythmias are more likely to have arrhythmias again," Steinberg says.

A future study will evaluate whether proximity to the attack site – specifically, living closer to Ground Zero – influenced a patient’s likelihood of having an arrhythmia after the terrorist attack. Several medical centers around the country will participate.

"Physicians and patients need to be aware that real-life, stressful events can trigger arrhythmias," Steinberg says. "Physicians should encourage patients with ICDs to practice stress-reduction and stress-avoidance techniques. It's also important to protect patients against the effects of increased nervous-system stimulation by giving them beta-blockers."

Co-authors are Aysha Arshad, M.B.B.S.; Atul Kukar, D.O.; Valentin Suma, M.D.; Margot E. Vloka, M.D.; Frederick A. Ehlert, M.D.; Bengt Herweg, M.D.; Jacqueline E. Donnelly; Julie Philip; George Reed, Ph.D.; and Alan Rozanski, M.D.