Instantaneous heart rate patterns in newborn infants

The instantaneous heart rate, i.e., the reciprocal of the time interval between successive heart beats was measured and recorded over long periods in newborn, fullterm, and premature children. The following patterns predominated in normal children: 1.1. Phasic variation. A slightly irregular sinoatrial node (normal sinus) rhythm.2.2. Cry pattern. A smooth parabolic rise in pulse rate interrupting phasic variation, associated with crying and the Valsalva maneuver in general.3.3. Respiratory pulse rate variation. A slight rise in the pulse rate line with inspiration and slight fall with expiration.4.4. V shape falls. Sharp, steep, short rate falls, most frequently seen in the first 3 hours, infrequently after the twelfth hour of life. The following patterns were associated predominately with illness, at times leading to death: 1.1. Flat rate line. Thirteen of the 21 subjects demonstrating this pattern died; survivors were ill or exposed to maternal noxious factors. A “smooth mound” shaped rate line pattern was seen in patients with a flat rate line when artificial or assisted respiration was administered.2.2. Bradycardia. Periods of marked (60 to 80 beats per minute) sinoatrial (normal sinus) bradycardia lasting 30 seconds or longer. Ten of the 18 subjects demonstrating this pattern died; survivors were ill.3.3. Moderate and marked respiratory rate variation. Marked rise in pulse rate with inspiration and fall with expiration, most frequently associated with respiratory distress. Only minor changes in the instantaneous heart rate pattern appeared during the exchange transfusions monitored in this series. Alterations in the rate patterns were reversed by calcium administration. All children who died (Table II) had flat line and/or bradycardia patterns for hours or days before death, and frequently when clinical examination gave no indication of impending tragedy. Instantaneous heart rate monitoring is a valuable adjunct in the care of newborn infants.