Electrocardiographic changes in induced hyperkalemia in ponies.

This research investigated and described the changes to the electrocardiograms (ECG) of ponies when an excess of potassium (hyperkalemia) was induced. The study found that there were distinct electrocardiographic changes that were typically classified into four stages, dependent on increasing levels of potassium present in the bloodstream.

Methodology

• The researchers induced hyperkalemia in 11 crossbred ponies. This was achieved by the acute infusion of a 0.4M solution of potassium chloride directly into the heart.
• Using electrocardiography (ECG), the scientists monitored and noted the physiological changes and irregularities within the ponies’ cardiac rhythms caused by the induced hyperkalemia.

Findings

• The ECG changes due to the hyperkalemia could be classified into four main stages.
• In the first stage, there’s a widening and lowering of the amplitude of the P wave on the ECG, eventually leading to its inversion and disappearance. P waves represent the electrical activity associated with the contraction of the atria in the heart.
• The second stage is characterized by an increase in the amplitude of the T wave, which normally represents the phase of electrical recovery or the return to the resting state of the ventricles after a heartbeat.
• In the third stage, there’s an increase in the QRS interval, which corresponds to the duration of a ventricular depolarization, or electrical activation of the heart’s ventricles. This stage also saw some irregularity in the ventricular rate.
• The final and fourth stage involves periods of cardiac arrest which either became terminal or were followed by ventricular fibrillation, a severe form of cardiac arrhythmia.
• Increases in the amplitude of the T wave and the QRS duration were usually observed at plasma potassium values greater than 7.5 mM/L.
• When the potassium values were between 9 to 10 mM/L, a 50% increase in the QRS duration was usually observed.
• P waves disappeared when plasma potassium values ranged from 9.4 to 12.6 mM/L.
• The appearance of sinusoidal-shaped QRS-T complexes and periods of cardiac arrest occurred before the development of terminal dysrhythmia (severe abnormal heart rhythm).
• At extremely high plasma potassium values of 11.3 to 17.3 mM/L, either a complete halt of cardiac activity (cardiac standstill) or ventricular fibrillation occurred.
• It was also observed that the Q-0 Tc and Q-Tc intervals, which are used to measure different aspects of heart rhythm, were not affected by hyperkalemia.