Electrolyte and Electrocardiogram Changes in Dehydrated Male Bovine Calves

Experimental animal
 
Study was conducted with twelve male bovine calves suffering from acute dehydration due to prolonged diarrhoea at an organized Military Farm in Satwari, Jammu in 2018. The ages of calves were between 2-5 months. Dehydration in the animals was assessed by clinical examination of the animal with sunken eyes, dry mouth and nose, weight loss, fast or very slow pulse, cold ears and legs. The experiment was approved by the Institutional Animal Ethics Committee. All animals were immediately treated after the observations and the hydration status restored. Analysis of data was carried out in the Division of Veterinary Physiology and Biochemistry, SKUAST-Jammu, RS Pura.
 
Procedure of recording ECG
 
Electrocardiographic recording of the calves were taken, by single channel electrocardiograph as described by Schultz and Pretorius (1973). Care was taken to keep the animal as still as possible with manual restraint for least electrical interference. The single channel electrocardiograph was used for tracing the ECG. The site for attachment of electrodes was trimmed and cardia gel (lubricating gel) was applied to increase conductivity. Electrodes were attached with small crocodile clips with flattened teeth as previously described by Ahmed (2002). Three bipolar standard leads (Lead I, II and III) were taken with crocodile clips in suitable position on the antero-lateral aspect just below the elbow and stifle joint. Positioning was consistent to avoid QRS axis change. Animals were allowed to acclimatize for 10 to 15 minutes before each recording. ECG machine was calibrated to give 10 mm deflection per mV of input and recordings were traced with a paper speed of 25 mm/second. The machine was charged thoroughly each day before recording.
 
After recording of ECG heart rate, amplitude of waves (P, QRS and T waves), duration of waves (P, P-R, QRS, Q-T, S-T and T) and cardiac axis were evaluated.
 
Haematology and serum biochemical parameters
 
PCV (Packed Cell Volume), TEC (Total Erythrocytic Count), DLC (Differential Leucocytic Count) and osmotic fragility were calculated. Serum calcium, magnesium, potassium and sodium were also evaluated by standard commercially available kits.
 
Rehydration therapy
 
After recording of ECG and collection of blood for haemato-biochemical studies, the following rehydration therapy was immediately given- calves with rapidly progressing dehydration and consistent profuse watery diarrhoea were treated intravenously with Normal saline (NaCl) @ 90 mMol/L, Lactated Ringer´s (RL) solution @ 80 mMol/L or dextrose solutions @ 7 L/day and maintaining fluid @ 80-100 ml/kg to maintain their hydration status. Different parameters were again recorded one month after treatment.
 
Statistical analysis
 
Data obtained in the present experiment were analyzed statistically by standard procedure of Snedecor and Cochran (1994).

Electrocardiographic parameters
 
The amplitude and duration of the various waveforms, and cardiac axis recorded in dehydrated and normal animals are depicted in Table 1.
 

 
Heart rate
 
During dehydration, the heart rate was elevated (104.33 ± 9.03 bpm) when compared to normal recordings (90.33 ± 9.71 bpm) and cardiac arrhythmia was commonly observed (Fig 1A).
 

 
Amplitude of waves
 
In the dehydrated animals, a flat P wave was very commonly observed (Fig 1B-i). In certain cases the P wave could not be discerned on the electrocardiograph. QRS amplitudes were significantly (P<0.05) decreased in dehydrated calves. T waves were non-significantly decreased in dehydrated animals. In some cases tall and peaked T waves were noticed (Fig 1B-ii).
 
Duration of waves
 
The QRS duration significantly (P<0.05) increased (Fig 1C) in dehydrated calves, while the ST segment was significantly decreased and elevated (Fig 1D). No significant changes were recorded in the duration of P wave, T wave, PR, QT interval and cardiac axis.
 
Haematological parameters
 
The haematological parameters recorded for dehydrated and rehydrated calves are represented in Table 2.
 

       
Non-significant increase in TEC and PCV was seen in dehydrated calves. Significant (P<0.05) decrease in lymphocytes and eosinophil count were observed in dehydrated calves. A significant (P<0.05) increase in osmotic fragility was also observed in dehydrated calves.
 
Serum biochemical parameters
 
The serum biochemical parameters recorded for dehydrated and rehydrated calves are represented in Table 3.
 

       
A significant decrease (P<0.05) of sodium and magnesium serum levels was seen in dehydrated calves; whereas a significant increase (P<0.05) of potassium levels was seen.
       
During dehydration excessive loss of body water and electrolyte imbalance alters cardiac current kinetics, promoting proarrhythmic or antiarrhythmic effects (El-Sherif and Turitto, 2011).

Most reflections in the amplitude changes can be attributed to hyperkalemia. Elevated potassium levels mediate via specific voltage-gated potassium channels that causes increased membrane repolarization of the cardiac action potential, resulting in peaked T waves (Kour et al., 2016). As hyperkalemia worsens, no more synchronous repolarization across the ventricular wall occurs. Classical tall, peaked T waves were also reported by Slovis and Jenkins (2002) under similar conditions. Subsequently, the P wave broadens and decrease in amplitude or eventually disappear. Flat ‘P’ waves or their absence could be due to lack of coordinated atrial activity. In the electrocardiograph, even if the P waves are formed or present, they remain very less obvious (Nelson and Waggner, 1964). The QRS complex also widens due to cardio-vascular slowing. Dehydration leads to hypovolemia and ultimately decreased QRS voltage. This has also been corroborated by Saltykova (2007) and Ozkan et al., (2011).
 
In electrolyte disorders associated with hyperkalemic, potassium accelerates the repolarisation and shortens the duration of the P-R interval (El-Sherif and Turitto, 2011). This has also been observed in dehydrated animals when compared to treated healthy animals (Ozkan et al., 2011). Increase in QRS duration may be due to both hyperkalemia and hypomagnesemia. Hyperkalemia may inactivate many sodium channels and ultimately, a sluggish conduction of the electrical wave around the heart results in widening of QRS complex (Saltykova, 2007). This has also been observed by Ozkan et al., (2011) in diarrhoeic and hyperkalemic calves and Kour et al., (2016) in Lead II recordings of dehydrated rabbits. Marked widening of QRS complex was recorded in one of five hypokaelemic human patients with serum potassium level usually above 5.56 to 6.5 mMol/Litre, including increase in the duration of all the waves (Slovis and Jenkins 2002). The cardiac axis remains unchanged as suggested by various earlier observations (Ozkan et al., 2011; Kour et al., 2016). 

Increased PCV is due to decrease in the amount of water in the vascular compartment relative to the number of circulating red cells (relative polycythaemia). The changes in the differential leucocyte count are speculative. There have been many reports of decreased count of leucocytes without any clinical corroboration. Decreasing lymphocytes were recorded in albino rats (Owoyele et al., 2011); goats during transportation (Kannan et al., 2007) and in Yankasa sheep (Igbokwe and Ajuzieogu, 1997) with progressive water deprivation. A significant decrease in lymphocytes in local Iraqi calves infected with bovine viral diarrhoea was recorded (Hassan et al., (2013). In the latter case, a decrease in lymphocyte count is justified due to the immunosuppressive nature of similar pathogens.
       
Dehydration also imbalances salt and water content leading to extracellular and intracellular osmotic disturbances and ultimately perturbed volume homeostasis that jeopardize the erythrocyte leading to its fragile disposition and premature destruction (Gallagher, 2017).
       
Sodium ions may be lost at the expense of the extracellular fluid in calves with diarrhoea. Resulting hyponatremia only aggravates the existing dehydration status, with increase in the renal water excretion to maintain the normal osmotic pressure. This could result in a decrease in the extracellular fluid space leading to further dehydration. Increased renal excretion of sodium and chloride may also inhibit aldosterone activity, resulting in decreased plasma volume in calves with dehydration (Skrzypczak et al., 1993). On the other hand, increase in serum potassium level may be due to metabolic acidosis. During severe diarrhoea there may be loss of much sodium bicarbonate from the body. The redistribution of potassium from the intracellular space to the extracellular space is buffered intracellularly, because of large proportion of the excess hydrogen ions. Potassium also has a significant correlation with Mg levels (coefficient of 0.466). It is recommended that serum magnesium level be measured in all cases of acute diarrhoea with moderate to severe dehydration (Niharpatel et al., 2017). Hypomagnesaemia often could cause sinus tachycardia as well as cardiac arrhythmias, including other ECG abnormalities like prolonged PR or QT interval, T wave flattening or inversion and ST straightening (Niharpatel et al., 2017).
               
All electrolytes are invariably lost in the diarrheal fluid, mainly Na⁺, K⁺, Cl^-, HCO^-3 and their serum alterations have a profound bearing on the ECG. The systemic effects are likely to increase with progressive and continued losses of the important electrolytes, unless they are adequately and immediately compensated. It would be interesting to observe continued electrical conductive disturbances with constant monitoring (halter ECG monitors) under very controlled conditions. However, subtle changes associated with mild alterations may not be readily discernible in the electrocardiograph and for the most part may remain undiagnosed. Besides, the changes that are visible on the ECG need a trained understanding for its correct interpretations. It is assumed that the present communication would be a helpful guide for the clinical veterinarian or those monitoring supportive therapy to dehydrated animals.