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Atrial fibrillation (AF) is common condition among the elderly, and leads to
increased risks of stroke, heart failure, dementia, and death. Diagnosing AF requires electrocardiograms (ECGs), and long recordings may be necessary since AF often occurs intermittently in its early stages.
During AF, the heart rate is irregular, and sometimes inappropriately fast. This thesis includes four papers that study long-term ECGs for AF prediction and management.

In Paper I we used the population-based Swedish CArdioPulmonary bioImage
Study to establish normal ranges for ambulatory heart rate during sinus rhythm. The normal range was wide, and largely independent of clinical correlates.

In Paper II and III we used the population-based Malmö Diet and Cancer Study to show that low heart rates at 24hECGs are associated with increased incidence of AF and that patients with short, irregular supraventricular tachycardias (SVTs) without discernible P-waves had substantially increased risk of AF (adjusted hazard ratio 4.95, 95% confidence interval (CI) 2.06-11.9).

Electrocardiograms are also used to measure resting heart rates during AF, to dose rate controlling drugs. In Paper IV we repeatedly sampled resting heart rate
measurements in patients with at least 2 days of ambulatory ECGs with AF (n=832). A single measurement differed on average by 10% compared to the average resting heart rate.

The conclusions are that low heart rates and short, irregular SVTs without P-waves are predictors of incident AF, that the resting heart rate during AF varies within the same individual, and that the range of normal ambulatory heart rate is wide.