The reliability of intermittent ECG sampling in arrhythmia detection.

Although intermittent ECG sampling is a commonly used method for arrhythmia detection there are no controlled studies of its efficiency. In the present study a continuous ECG was recorded for three hours in 52 patients with ventricular tachyarrhythmias. All ECGs were interpreted minute to minute to get the true arrhythmia content. Intermittent ECG samples were simulated by analyzing the first two and first five minutes of every 15 minutes in the ECG material. Two minute long ECG samples were also used every 30 minutes. The 15 and 30 minute long periods were classified as containing arrhythmias or not according to the arrhythmia content of the samples. These findings were subsequently compared with the true arrhythmia content. The arrhythmia detection rate depends on the sampling time and true arrhythmia occurrence. The distribution of arrhythmias within the periods was also of importance. With a five minute long ECG sample about 80% of the intervals containing any type of ventricular tachyarrhythmia will be detected. This is reduced to about 50% when one minute long ECG strips are used. Infrequent types of VPCs such as R on T or ventricular tachycardia are very poorly detected also when sampling as much as one-third of the total time. The study also included a comparison between the results obtained from the clinical material and the results obtained by the use of computerized arrhythmia models. It is concluded that intermittent ECG sampling besides a low detection rate for infrequent arrhythmias and short ECG samples, also brings a risk of underestimating or overemphasizing the arrhythmia occurrence depending on a periodic type of arrhythmia distribution among the patients. These factors make intermittent ECG sampling an unsuitable method for evaluating antiarrhythmic drugs.