Relationships between electrocardiographic findings, racing performance and training in Standardbred horses

SUMMARY The presence of abnormal T waves in three or more electrocardiographic leads has been used to diagnose the cause of poor race performance in horses. This study investigated the relationship between previous racing performance in Standardbred horses and T waves, and the effect of training on the T wave. Thirty-two horses were electrocardiographed in two Sydney racing stables. Sixteen horses (50%) had ECGs with three or more leads with abnormal T waves, and these horses had won more races, had a greater ratio of wins per start and a greater number of dollars earned per start than horses with less than three abnormal T waves (P < 0.05). Horses with abnormal T waves also had significantly faster racing times (P < 0.01). There were significant (P < 0.01) correlations between the number of abnormal T waves and both number of wins (R = 0.47) and dollars earned per start (R = 0.45). Fastest winning mile rate was also negatively correlated with number of leads with abnormal T waves (R =?0.52, P < 0.01). Twenty two horses were also electrocardiographed within seven days of good racing performance. The mean number of abnormal T waves was 2.7 ± 0.41, and the mean T wave amplitude in the four chest leads (CV, CR, CL, CF) was 0.9 ± 0.15 mV. Thirteen horses (59%) had abnormal T waves in three or more leads. The effect of training on the T wave was also investigated in nine previously untrained and unraced Standardbred racehorses. There were significant effects of training (P < 0.01) on the number of abnormal T waves and mean chest lead T wave amplitude. These increases occurred in the second phase of training during which faster exercise, race trials and racing were conducted. We concluded that abnormal T waves are a common finding in the race-fit Standardbred horse, and can be found in more than 50% of horses currently performing well in races. In addition, chest lead T waves become more positive after training.     

The prevalence and clinical relevance of hyperkalaemia in calves with neonatal diarrhoea

One hundred and twenty-four calves with neonatal diarrhoea were investigated in order to assess the prevalence of hyperkalaemia and the associated clinical signs. Hyperkalaemia (potassium concentration >5.8 mmol/L) was recognized in 42 (34%) calves and was more closely associated with dehydration than with decreases in base excess or venous blood pH. In 75 calves with normal blood concentrations of D-lactate (i.e. ?3.96 mmol/L), K concentrations were moderately correlated with base excess values (r = ?0.48, P < 0.001). In contrast, no significant correlation was observed in 49 calves with elevated D-lactate. Only three hyperkalaemic calves had bradycardia and a weak positive correlation was found between heart rate and K concentrations (r = 0.22, P = 0.014). Ten of the 124 calves had cardiac arrhythmia and of these seven had hyperkalaemia indicating that cardiac arrhythmia had a low sensitivity (17%) but a high specificity (96%) as a predictor of hyperkalaemia.In a subset of 34 calves with base excess values ??5 mmol/L and D-lactate concentrations <5 mmol/L (of which 22 had hyperkalaemia), changes in posture/ability to stand could be mainly explained by elevations of K concentrations (P < 0.001) and to a lesser extent by increases in L-lactate concentrations (P = 0.024). Skeletal muscle weakness due to hyperkalaemia alongside hypovolaemia may produce a clinical picture that is similar to that in calves with marked D-lactic acidosis. However, since reductions in the strength of the palpebral reflex are closely correlated with D-lactate concentrations, a prompt palpebral reflex can assist the clinical prediction of hyperkalaemia in calves presenting with a distinct impairment in their ability to stand (specificity 99%, sensitivity 29%).     

Suspected vagal reflex and hyperkalaemia inducing asystole in an anaesthetised horse

A 10-year-old 466 kg mustang gelding presented to an equine referral hospital for surgical repair of nasal, frontal and lacrimal bone fractures from an unknown trauma. Surgical repair was performed under general anaesthesia, including a right-sided maxillary regional anaesthetic block with mepivacaine hydrochloride. Progressive hyperkalaemia was documented perianaesthetically (T-3 mins; 134 mins after induction; potassium 6.4 mmol/L (ref 3.5-5.1 mmol/L). Perianaesthetic bradycardia was attributed to alpha −2 agonist infusion administration, and other characteristic ECG changes (flattened P waves, narrow T waves of increased amplitude, prolonged QRS complex) were not documented. Asystole occurred 137 min after induction of anaesthesia; however, a review of the available literature suggests the degree of hyperkalaemia documented was unlikely to be the primary cause of asystole but may have been a contributing factor. It is hypothesised that a trigeminocardiac reflex was the primary contributory factor to asystole in the described case, and may represent a maxillomandibulocardiac reflex that has not been previously described in the horse.     

PAROXYSMAL ATRIAL FIBRILLATION IN A RACEHORSE

A 4-year-old thoroughbred stallion with a history of loss of racing form was studied over a period of approximately 7 months. At the initial examination he showed positive T waves in 1 chest lead and wandering of the pacemaker. This was followed by an episode of paroxysmal atrial fibrillation which disappeared spontaneously and was replaced by significant T wave changes in all the chest leads. During a period when these changes persisted, there was progressive lengthening of the P wave and the P-R interval. Because the last ECG showed evidence of intra-atrial block, first degree A-V block and T wave changes, the owner was advised that a fluctuating myocarditis was affecting the horse's performance and it was retired to stud. This appears to be the first report of paroxysmal atrial fibrillation in Australia, and it demonstrates the value of regular follow-up examinations in horses with initial electrocardiographs showing only minor departures from normal. The case also suggests that when sharp reversals of racing form occur, the possibility of paroxysmal atrial fibrillation being the cause should be kept in mind.     

Experimental hyperkalaemia in rabbits: effects of salbutamol and norepinephrine treatments on blood biochemistry and electrocardiography

The effects of salbutamol and norepinephrine on the electrocardiogram (ECG), serum potassium level and enzyme activities were studied in rabbits with hyperkalaemia; norepinephrine and salbutamol may be therapeutically useful. For induction of hyperkalaemia, 300 mM KCl solution was used and then isotonic saline solution containing 6 microg salbutamol and 3.9 microg norepinephrine per ml were administered. Norepinephrine and salbutamol decreased the serum potassium from 7.36 +/- 0.26 and 7.21 +/- 0.31 mmol/L to 5.62 +/- 0.27 and 4.35 +/- 0.33 mmol/L, respectively, and caused the ECG changes (flatness of P wave, widening of QRS complex and bradycardia) to return to the control conditions (time 0). Norepinephrine, but not salbutamol, decreased the activities of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH) to the control levels. These results suggest that monitoring of the enzyme activities might be useful as it yields indexes suitable for evaluating the therapeutic approach with norepinephrine in hyperkalaemia.     

Postmortem biochemical markers of experimentally induced hypomagnesaemic tetany in sheep

Hypomagnesaemic tetany was induced in non-lactating and lactating ewes by feeding them semi-synthetic low magnesium diets containing additional potassium chloride and citric acid. Aqueous and vitreous humour were sampled from one eye at the time of death (fresh) and from the second eye after the head had been stored at ambient temperature for 24 hours (24-hour). There were significant relationships between the concentrations of magnesium in cerebrospinal fluid and plasma and its concentrations in fresh aqueous humour and fresh vitreous humour. Magnesium concentrations of < 0.33 mmol/litre in fresh aqueous humour and < 0.50 mmol/litre in 24-hour aqueous humour were associated with severe hypomagnesaemia and tetany. However, the concentration of magnesium in aqueous humour is relatively unstable and, unless the time of death was known accurately, its interpretation would be difficult. Magnesium concentrations of < 0.60 mmol/litre in fresh vitreous humour and < 0.65 mmol/litre in 24-hour vitreous humour were associated with severe hypomagnesaemia and tetany in adult sheep. The concentration of magnesium in vitreous humour was relatively stable for up to 48 hours postmortem.     

Comparison of the measurement of total carbon dioxide and strong ion difference for the evaluation of metabolic acidosis in diarrhoeic calves

Eighty-four calves with diarrhoea were treated with fluids and 13 apparently healthy calves of similar ages were sampled as controls. Their total blood carbon dioxide (TCO2) was measured with a Harleco apparatus and 31 of the calves were treated with oral fluids and 53 with parenteral fluids. The oral fluid contained 118 mmol/litre Na+, 25 mmol/litre K+, 110 mmol/litre glucose, 108 mmol/litre bicarbonate (HCO3- as citrate), 43 mmol/litre Cl-, 4 mmol/litre Ca++, 4 mmol/litre Mg++ and 20 mmol/litre glycine, and the parenteral fluid contained 144 mmol/litre Na+, 4 mmol/litre K+, 35 mmol/litre HCO3- and 113 mmol/litre Cl-. Both treatments resulted in significant improvements in acid-base status as demonstrated by an increase in TCO2, and the treatment was successful in 27 of the 31 calves receiving oral fluids and in 45 of the 53 calves receiving parenteral fluids. Thirty-seven of the calves treated parenterally were very severely acidotic (TCO2 <8 mmol/litre) initially and they received an additional 400 mmol HCO3- added to the first 5 litres of infusion. Treatment was successful in 33 of these calves. The decision to administer additional bicarbonate was made on the basis of their acid-base status as measured with a Harleco apparatus. The strong ion difference (Na++K+-Cl-) (SID) of the calves was calculated retrospectively. There was a significant correlation between the SID and TCO2 of the calves treated with oral fluids but not among the control calves or the calves treated parenterally. Furthermore, measurements of the change in SID during therapy gave little indication of the change in acid-base status as measured by the Harleco apparatus, with the SID decreasing (suggesting a worsening of acid-base status) in 16 calves in which the TCO2 increased (suggesting an improvement in acid-base status). There was a significant correlation between the change in SID and the change in TCO2 during treatment in the calves receiving oral fluids but not in the calves treated parenterally.     

Changes in haematology and plasma biochemistry during maximal exercise in greyhounds

The haematological and biochemical changes associated with racing over 235 and 420 metres were studied in 23 greyhounds. Blood samples were collected while the dogs were resting and immediately after and 30 minutes after racing. Significant increases in red blood cell count, haemoglobin concentration and haematocrit occurred. The increase in haematocrit was accompanied by increases in total plasma protein and creatinine concentrations. Blood lactate increased to 11.4 and 13.2 mmol/litre over 235 and 420 metres, respectively, and plasma glucose increased to 7.9 and 8.2 mmol/litre. After the 420 metres, the mean plasma ammonia concentration was 256 mumol/litre. Plasma free fatty acid concentrations also increased after dogs had run both distances. The highest concentrations of glycerol and uric acid were found 30 minutes after exercise.     

Production of volatile fatty acids in the rumen of calves during dietary-microbial stimulation and early weaning

The contents of volatile fatty acids in the rumen fluid were studied in calves at an early (seven weeks of age) and traditional weaning term (nine weeks of age). Weaning at the age of seven weeks enabled to save 16.2 kg of milk replacer per calf; there was also a lower content of concentrates in the starter feed with a supplement of Amylastim. The health condition of the calves was good in both groups. The average daily weight gains for the period from the second to the ninth week of age were 0.550 kg in the early weaned calves and 0.690 kg in the calves weaned at a normal time. Early weaning had a positive influence on the development of rumen metabolism. Calves weaned at the age of seven weeks, compared with those weaned at the age of nine weeks, had much higher concentrations of VFA (p less than 0.05) in rumen fluid (at the age of seven weeks: 130.49 mmol per litre vs. 111.53 mmol per litre; at the age of eight weeks: 119.74 mmol per litre vs. 96.98 mmol per litre). Early weaned calves had the statistically significantly (p less than 0.05) higher proportions of propionic acid, butyric acid, i-butyric acid, and valeric acid. Later-weaned calves had the significantly higher (p less than 0.05) contents of acetic acid and i-valeric acid.     

Effects of hypoxia on endocrine and metabolic responses to anaesthesia in ponies

Some metabolic and endocrine effects of hypoxaemia were studied during halothane anaesthesia in six ponies. Each was anaesthetised twice; on one occasion a 20-minute period of hypoxaemia (arterial oxygen tension between 4.4 and 5.8 [mean 5.3] kPa) was imposed during 120 minutes of anaesthesia. On the second occasion arterial oxygen tension was maintained above 17 kPa throughout. Routine cardiovascular monitoring was performed and blood samples were taken to measure haematocrit, cortisol, insulin, glucose and lactate. Anaesthesia was associated with hypotension in both groups (mean ABP < 70 mmHg) but pulse rate changed little from control. Hypercapnia (PaCO2 > 7.0 kPa) developed in the normoxic group and acidosis was more severe than in the hypoxic group. Haematocrit changed little but was higher in the hypoxic group after the hypoxic period (0.39[0.06] vs 0.32[0.06] litre litre(-1)). Plasma cortisol increased significantly during anaesthesia in both groups (maximum values: hypoxic group 418[96], normoxic group 492[102] nmol litre(-1)) and there was no significant difference between them. Glucose concentration increased in the hypoxic group and was significantly higher than in the normoxic group during the hypoxic period (8.8[1.5] vs 6.4[1.5] mmol litre(-1)). Insulin decreased in both groups but this was significant only in the normoxic group (from 34[19] to a nadir of 12[9] iu ml(-1)) and the groups were not significantly different. Lacticacidaemia developed in both groups but was more severe in the hypoxic group (maximum values 2.3[0.6] and 1.3[0.5] mmol litre(-1)). It was concluded that 20 minutes of hypoxia during halothane anaesthesia in ponies did not markedly alter the stress response already induced by anaesthesia.     

Abdominal distension in collapsed diarrhoeic calves: biochemical findings and treatment.

Thirty-seven of 53 diarrhoeic calves hospitalised for intravenous fluid therapy were classified as very severely acidotic (total carbon dioxide less than 8 mmol/litre) by using a Harleco apparatus. All the calves were given intravenously 10 to 20 litres of electrolyte solution which contained 144 mmol/litre sodium, 4 mmol/litre potassium, 113 mmol/litre chloride and 35 mmol/litre bicarbonate, and in addition the 37 very severely acidotic calves received 400 ml of 1M sodium bicarbonate in the first 5 litres of fluid administered. Sixteen of the 37 very severely acidotic calves had a distended right flank, suggesting the presence of a dilated fluid-filled viscus. Neither their history nor other clinical signs were useful predictors of the distension. The distended calves had significantly higher plasma concentrations of sodium and chloride, and significantly lower plasma creatinine concentrations than the calves which were not distended. Treatment was successful in all the 21 non-distended calves but four of the distended calves died despite treatment. The resolution of the distension in the successfully treated calves, coincided with a significant increase in plasma bicarbonate concentration and the passage of large amounts of malodorous mucoid faeces.     

Iatrogenic hypocalcaemia during parenteral fluid therapy of diarrhoeic calves

Acid-base balance and electrolyte concentrations, including ionised calcium, were monitored during intravenous fluid therapy of 11 collapsed diarrhoeic suckler calves aged five to 10 days. Six healthy calves of similar age and type were used to provide control data. All the diarrhoeic calves were severely acidotic (TCO2<12 mmol/litre). Isotonic sodium bicarbonate (1-3 per cent) was administered until the metabolic acidosis was half corrected, as indicated by the TCO2 increasing to 17 to 24 mmol/litre when the infusion was changed to an extracellular volume replacement fluid containing 144 mmol/litre Na+, 35 mmol/litre HCO3-, 4 mmol/litre K+ and 113 mmol/litre Cl- which was administered until the calf was discharged. Milk feeding was started as soon as the calf had a suck reflex. The treatment was successful in 10 calves. At admission the diarrhoeic calves were hypocalcaemic compared with the control calves, but their ionised calcium was significantly higher, with significantly less calcium being protein bound. Treatment with isotonic sodium bicarbonate resulted in a significant improvement in acid-base balance, but both total and ionised calcium decreased significantly, the decrease in ionised calcium being proportionately greater owing partly to a significant increase in the protein binding of calcium. The mean total, bound and ionised calcium concentrations were all significantly lower in the treated calves after they had received isotonic sodium bicarbonate than in the control calves. Further treatment with replacement fluid had no significant effect on any of the parameters apart from pCO2 which increased significantly. Milk feeding had no significant effect on plasma calcium concentrations. The calves' mean ionised calcium concentration was significantly lower at the end of the treatment than before it, but there was no difference in the mean total and bound calcium concentrations. The calves' mean plasma potassium and magnesium concentrations decreased significantly during the course of the treatment.     

The canine T wave: a retrospective analysis on qualitative and quantitative T wave variables obtained in 129 healthy dogs and proposed reference intervals

Introduction/objectiveThe T wave is a poorly characterized electrocardiographic variable in small animals. Therefore, this study aimed to describe T wave features in a large population of healthy dogs.Animals, materials, and methodsMedical records were reviewed to identify healthy dogs ≥one-year-olds that underwent an electrocardiogram. T wave qualitative (morphology, polarity, and concordance between R and T waves) and quantitative (duration, amplitude, mean electrical axis, ratio between T and R waves amplitudes, interval from the peak to the end of the T wave, and ratio between the duration of the latter interval and that of the QT) variables were evaluated. Continuous and categorical variables were compared between dogs of distinct sex, body weight (BW), age and somatotype using the Mann–Whitney U test and χ² test, respectively. Spearman's correlation coefficients between quantitative variables and age and BW were calculated. Reference intervals of quantitative variables were determined in the overall population.ResultsOne hundred and twenty-nine dogs were enrolled. Concerning morphology, the asymmetrical (slow/fast) pattern occurred more frequently than the symmetrical and biphasic ones. Concerning polarity, positive T waves occurred more frequently than negative and neutral ones. T and R waves were predominantly concordant. No meaningful differences were found when comparing qualitative and quantitative variables between dogs of distinct sex, BW, age and somatotype. No significant correlations were found between quantitative variables and age and BW. Reference intervals of quantitative variables are provided.ConclusionsCanine T wave features were addressed and statistically reliable reference intervals made available for clinical use.     

Concentrations of ketones in milk in early lactation, and reproductive performance of dairy cows

Samples of blood and milk were taken from clinically ketotic cows at 12-hour intervals before and after treatment The concentration of beta-hydroxybutyrate was determined in plasma and milk, and the concentration of acetone was determined in milk. Measurement of milk acetone had the optimal combination of sensitivity, specificity and positive predictive value to identify ketotic cows and was subsequently used in a comparison of the fertility of ketotic and normal cows. Two samples of milk were taken approximately two weeks apart, between 12 and 60 days after calving, from 410 cows on three farms and the concentration of acetone in the milk was measured. Thirty cows with milk acetone concentrations of at least 0.4 mmol/litre were compared with paired control cows with milk acetone concentrations less than 0.3 mmol/litre. The ketotic cows had a significantly longer calving-to-conception interval and a significantly higher culling rate due to a failure to conceive (P<0.05).     

Wide-complex tachycardia associated with severe hyperkalemia in three cats

The well recognized cardiac effects of severe hyperkalemia include progressive rhythm and conduction disturbances such as bradycardia, spiked and narrow T waves, widening QRS complex, widening and flattening P wave, disappearance of the P wave, and cardiac arrest. Paradoxically, a heart rate greater than 200 beats/min may coexist with hyperkalemia in some cats. This report describes three cats with moderate to severe hyperkalemia and concurrent rapid heart rate. In each cat, the serum potassium (K(+)) concentration was > or =7.5 mEq/dl with a concurrent heart rate > 200 beats/min. In each cat, nine-lead electrocardiograms demonstrate an absence of P waves and a wide-complex tachycardia. Hyperkalemia should be considered in the differential diagnosis when a feline electrocardiogram demonstrates a wide-complex tachycardia without identifiable P waves.     

Effects of feeding ewe colostrum, cow colostrum or ewe milk replacer on plasma glucose in newborn lambs

The plasma concentration of glucose was monitored for six hours in lambs fed either ewe colostrum, cow colostrum or milk replacer by stomach tube at one hour of age. The feeding of ewe colostrum resulted in an elevation of the mean (+/- se) plasma glucose concentration from 2 . 6 +/- 0 . 3 mmol/litre before feeding to 7 . 3 +/- 0 . 92 mmol/litre three hours after feeding and this elevation was maintained. A similar rise was observed in the lambs fed cow colostrum but this was of shorter duration. A marked hyperglycaemia was observed after the feeding of milk replacer with a maximum value of 23 . 4 +/- 1 . 33 mmol/litre three hours after feeding. The practical implications of these results are discussed.     

Postmortem biochemical markers of experimentally induced hypomagnesaemic tetany in cattle

Severe hypomagnesaemia and tetany were induced in 10 lactating cows by feeding them semi-synthetic low magnesium diets and the animals were used to study the stability of postmortem markers of hypomagnesaemic tetany. There were significant relationships between the concentrations of magnesium in either cerebrospinal fluid (CSF) or plasma and either aqueous or vitreous humour. The onset of hypomagnesamic tetany was also associated with low magnesium concentrations in plasma, CSF and aqueous and vitreous humour. Magnesium concentrations less than 0.25 mmol/litre in fresh aqueous humour may be indicative of severe hypomagnesaemia and possible tetany in lactating cows, but the concentration of magnesium in aqueous humour was unstable postmortem. The concentration of magnesium in vitreous humour was relatively stable and a concentration of less than 0.55 mmol/litre could be used as a diagnostic marker of tetany in cattle for up to at least 48 hours postmortem, at ambient temperatures typical of Northern Ireland.     

Physiological stimuli of thirst and drinking patterns in ponies

The stimuli that elicit thirst were studied in four ponies. Nineteen hours of water deprivation produced an increase in plasma protein from 67 +/- 0.1 g/litre to 72 +/- 2 g/litre, a mean (+/- se) increase in plasma sodium from 139 +/- 3 to 145 +/- 2 mmol/litre and an increase in plasma osmolality from 297 +/- 1 to 306 +/- 2 mosmol/litre. Undeprived ponies drank 1.5 +/- 0.9 kg/30 mins; 19 h deprived ponies drank 10.2 +/- 2.5 kg/30 mins and corrected the deficits in plasma protein, plasma sodium and plasma osmolality as well as compensating for the water they would have drunk during the deprivation period. In order to determine if an increase in plasma osmolality would stimulate thirst, 250 ml of 15 per cent sodium chloride was infused intravenously. The ponies drank when osmolality increased 3 per cent and when plasma sodium rose from 136 +/- 3 mmol/litre to 143 +/- 3 mmol/litre. Ponies infused with 15 per cent sodium chloride drank 2.9 +/- 0.7 kg; those infused with 0.9 per cent sodium chloride drank 0.7 +/- 0.5 kg. In order to determine if a decrease in plasma volume would stimulate thirst, ponies were injected with 1 or 2 mg/kg bodyweight (bwt) frusemide. Plasma protein rose from 68 +/- 2 g/litre pre-injection to 75 +/- 2 g/litre 1 h after 1 mg/kg bwt frusemide and to 81 +/- 1 g/litre 1 h after 2 mg/kg bwt frusemide.(ABSTRACT TRUNCATED AT 250 WORDS)     

Observations on the T wave of the equine electrocardiogram.

The paper describes changes observed in the T wave and T vectorcardiogram in horse after various periods of exercise. Using radiotelemetry and a bipole lead all horses showed negative T waves immediately after exercise. In some of them this was followed by a markedly positive T deflection. Possible reasons for these changes are briefly discussed.     

Electrocardiography of rock partridges (Alectoris graeca) and chukar partridges (Alectoris chukar).

Standard limb, six lead (I, II, III, aVR, aVL, and aVF) electrocardiograms (ECGs) were recorded in 10 awake mature rock partridges (Alectoris graeca) and 10 chukar partridges (Alectoris chukar). Durations and amplitudes of P and T waves and QRS complexes, durations of P-Q and Q-T intervals, and mean heart rates were calculated from the lead II ECGs. All observable P and T waves were negative in aVR and aVL, whereas they were positive in all remaining leads. The most frequent forms of QRS complex were r-s (r-S) and q-r (q-R). A Q wave was observed in all aVR and aVL leads in both species. Chukar partridges had significantly higher amplitudes of P and T waves and QRS complexes than rock partridges. Mean heart rates were 310+/-15 beats/min and 317+/-19 beats/min for chukar partridges and rock partridges, respectively. Mean electrical axes, calculated from leads II and III, were -99+/-6.3 degrees and -95+/-1.7 degrees for chukar partridges and rock partridges, respectively. Clear ECGs were easily obtainable without anesthesia or sedation.