Infestation in the dog by the paralysis tick, Ixodes holocyclus — 4. Cardiovascular effects

Abstract

To determine the extent and significance of changes in heart rate and rhythm noticed previously in dogs paralysed with Ixodes holocyclus, two studies were undertaken. In one the electrocardiogram was recorded at stages throughout the disease and the traces analysed for changes, while in the second a detailed study of the effect of Ixodes holocyclus on the cardiovascular system was undertaken. The electrocardiographic changes were extremely variable between stages and between dogs. Generally, if a dysrhythmia occurred in stages 1, 2 or 3 it tended to be sinus tachycardia, ventricular tachycardia or sinus arrest. In stage 4 sinus arrest, sinus bradycardia, or sinus or ventricular tachycardia were the prominent dysrhythmias, whereas in stage 5 sinus bradycardia predominated. Cardiovascular measurements indicated an increase in peripheral vascular resistance leading to a significant elevation in mean arterial pressure at all stages of the disease. Cardiac output was decreased significantly only at stage 2, although it was below the control measurements at all stages. Pulmonary arterial pressure was significantly elevated at stages 2, 3 and 4 due most probably to an increase in pulmonary vascular resistance. Myocardial contractility was not significantly changed throughout the disease. The changes observed in the electrocardiogram and the cardiovascular system in stages 1, 2 and 3 are unlikely to be due to hypoxia and could represent dysfunction of the autonomic nervous system. During stages 4 and 5 oxygen levels were below normal and the bradycardia seen terminally is almost certainly due to hypoxaemia.(ABSTRACT TRUNCATED AT 250 WORDS)

NT‐proBNPand cardiac troponin I concentrations in dogs with tick paralysis caused byIxodes holocyclus

“…18 This finding, however, was not replicated in a more recent study of naturally occurring tick paralysis patients. Systemic hypertension was demonstrated in dogs experimentally infested with I. holocyclus and was attributed to central autonomic dysfunction causing excessive sympathetic stimulation.…”

“…Systemic hypertension was demonstrated in dogs experimentally infested with I. holocyclus and was attributed to central autonomic dysfunction causing excessive sympathetic stimulation. 18 This finding, however, was not replicated in a more recent study of naturally occurring tick paralysis patients. 15 Rather, the latter study demonstrated echocardiographic evidence of compromised cardiac function, primarily a reduction in the end-diastolic left ventricular dimension.…”

“…The two most useful and widely available are N-terminal pro-B-type natriuretic peptide (NT-proBNP) and cardiac troponin I (cTnI). 11,15,18,19 B-type natriuretic peptide is released primarily from ventricular myocardium in response to a variety of stimuli, including increased myocardial wall stress and hypoxia. 21,22 The clinical utility of serum biomarkers in a wide range of heart diseases is an area of current and ongoing research.…”

Management of respiratory failure from tick paralysis

“…Tick paralysis caused by the Australian paralysis tick ( Ixodes holocyclus ) is a progressive neuromuscular disease that also affects the cardiovascular, respiratory, gastrointestinal and central nervous systems . Reported fatalities approach 100% in untreated experimentally infested dogs .…”

“…T ick paralysis caused by the Australian paralysis tick (Ixodes holocyclus) is a progressive neuromuscular disease that also affects the cardiovascular, respiratory, gastrointestinal and central nervous systems. [1][2][3][4][5][6][7][8][9][10][11] Reported fatalities approach 100% in untreated experimentally infested dogs. 4,12,13 Administration of a commercially available antiserum is central to the clinical management of tick paralysis, 12,14,15 but patients continue to die despite the use of antiserum.…”