Needle phobia: a neglected diagnosis

Journal of Family Practice, August, 1995 by James G. Hamilton

Although most victims of needle phobia who faint are unconscious for only a few seconds, a survey of 298 vasovagal fainters found that several had a loss of consciousness for 10 to 30 minutes, and a few lost consciousness for 1 to 2 hours.(40) Although blood pressure usually returns to normal within 2 hours, and most vasovagal victims feel well enough to resume normal activity within several hours, others have anxiety, malaise, and weakness for 1 to 2 days after a vasovagal attack.(38)(40)

Convulsions during vasovagal fainting, which are much more frequent than commonly realized, are a general response of the central nervous system (CNS) to the cerebral hypoxia of vasovagal shock. Of 84 blood donors who fainted, 14.3% had prominent tonic--clonic episodes, and another 27% had tonic muscular rigidity.(38) Furthermore, even having a finger pricked for blood typing can cause syncope with convulsive seizures.(38)

Electrocardiogram Changes

In several case reports, ECG changes during the vasovagal reflex among patients with needle phobia have included sinus arrhythmia, premature atrial contractions, premature junctional contractions, unifocal and multifocal premature ventricular contractions, bigeminy, first- and second-degree block, changes in P waves, ST waves, and T waves, sinus bradycardia, sinus tachycardia, ventricular tachycardia, ventricular fibrillation, and asystole.(1)(2)(5)(26)(27)(28)(37) Presumably, these ECG changes are secondary to vagal influence on the sinoatrial and atrioventricular nodes, and perhaps also to the antagonism between the activated sympathetic and parasympathetic systems on the heart.(27)

Stress Hormone Changes

At least 11 stress hormones have been reported to elevate during needle stimulation. Increased cortisol and corticotropin (ACTH) levels secondary to venipuncture and needle phobia have been documented.(1)(2)(41)(42) In one study, cortisol levels rose above average in 7 of 15 subjects, with a positive correlation between cortisol level and the number of vasovagal symptoms.(42) In my experience, corticotropin-releasing factor also can elevate during needle procedures, as can dopamine. In 25% of 28 subjects in 112 trials, human growth hormone levels rose in response to venous catheterization.(42) In three needle-induced vasovagal subjects, [beta]-endorphin levels were observed to rise,(42) but sometimes they do not rise.(1)

Similarly, epinephrine and norepinephrine levels do not always become elevated during episodes of needle phobia.(1) They have been observed to decrease in eight subjects who fainted after venipuncture, presumably related to the withdrawal of sympathetic vascular tone.(43) In another study, however, 21 young women dental patients had increased levels of epinephrine, but not norepinephrine, with a decrease in epinephrine after the procedure.(44) The findings of both of these studies are compatible with a biphasic cardiovascular response.

Probably because the pituitary perceives a reduced intravascular volume during vasovagal shock, vasopressin or antidiuretic hormone (ADH) rises in the vasovagal reflex with venipuncture,(1)(2)(45) as does endothelin.(45) Renin also increased by 200% in one patient with needle phobia,(46) but aldosterone and angiotensin levels have not yet been tested in needle phobic patients. The ADH rise causes pallor during the vasovagal reflext by sharply decreasing cutaneous blood flow, and may also contribute to nausea.(1) This ADH rise is often dramatic, reaching as high as 46 times normal values,(45) and may be responsible, along with the catecholamine elevation, for the intense fear that victims of needle phobia learn in response to their vasovagal reflexes.(1)