HEART-RATE RESPONSE PROFILES DURING HEAD-UPRIGHT TILT TEST IN INFANTSWITH APPARENT LIFE-THREATENING EVENTS

Sympatheticovagal imbalance causing episodes of severe bradycardia has been suggested as a cause of apparent life threatening events (ALTEs) . The autonomic control of the heart rate in 18 infants with ALTEs and 12 controls was evaluated by the head upright tilt test. Five differe nt heart rate response profiles (compared with the baseline) were obse rved during the tilt: (1) increase followed by a decrease and return t o baseline; (2) sustained increase; (3) decrease followed by an increa se and return to baseline; (4) sustained decrease; (5) no change. Eigh ty eight per cent of controls responded with heart rate increase follo wed by decrease or sustained increase compared with 55% of infants wit h an ALTE; a significantly greater proportion of infants with ALTEs th an controls responded with heart rate decrease or no change in rate (4 5% v 8%). This altered reaction during a head upright tilt test may be an expression of an underlying autonomic dysfunction in infants who h ave experienced an ALTE.