THE HEART-RATE RESPONSE PATTERN TO DIALYSIS HYPOTENSION IN HEMODIALYSIS-PATIENTS

Background. Hypotension during haemodialysis may be caused by the acti vation of a cardiovascular reflex causing abrupt sympathetic withdrawa l, vasodilatation and bradycardia (bradycardic hypotension). However, the frequency of this type of hypotension is undefined and it is uncle ar whether or not it underlies a peculiar predisposition to vasodepres sor syncope. Objective. To assess the prevalence of bradycardic hypote nsion and to test the hypothesis that dialysis patients are predispose d to vasodepressor syncope. Results. Sixty hypotensive episodes were r ecorded in 20 patients (greater than or equal to 2 episodes in 15 pati ents). Heart rate increased in 35 episodes, did not change in 19 episo des and decreased in six episodes. The HR response pattern to hypotens ion was reproducible in 10 patients (always tachycardia, 6; always unc hanged heart rate 4). Patients developing bradycardic hypotension (n = 5) all had an erratic HR response to hypotension (i.e. bradycardia pr eceded or followed by tachycardia or by no HR change) and were charact erized either by the typical haemodynamic pattern of hypovolaemia (pre dialysis hypotension, tachycardia and low TBW) or by being treated wit h a very high UF rate (> 0.3 ml/kg/min). Post-dialysis echocardiograph y showed that the LVEDD was less (one-tailed P = 0.055) in patients wi th bradycardic hypotension than in those with tachycardic responses or with unchanged HR. On tilt testing (after dialysis) three of 11 (27%) dialysis hypotensive patients developed bradycardic hypotension. This proportion was identical to that expected in healthy subjects and in control patients without syncope. Conclusions. Tachycardia is the more frequent heart rate response to dialysis hypotension in uraemic patie nts. Bradycardic hypotension in dialysis patients is associated with a haemodynamic profile indicating a more severe degree of cardiovascula r underfilling. Bradycardic hypotension probably represents a physiolo gical response to hypovolaemia rather than the expression of a peculia r predisposition to vasodepressor syncope.