Tissue Doppler imaging and 2-dimensional speckle tracking of left ventricular function in horses exposed to lasalocid.

This research study evaluated the use of Tissue Doppler imaging (TDI) and 2-dimensional speckle tracking (2DST) techniques to quantify the left ventricular (LV) function in horses which experienced myocardial dysfunction due to accidental ingestion of lasalocid, using thorough cardiac examination and follow-up tests. The results indicated successful detection and quantification of LV dysfunction in affected horses.

Objective and Methods

• This study aimed to evaluate the left ventricular function in horses that suffered from myocardial dysfunction after accidentally ingesting lasalocid, an ionophore often used in livestock feeds which can be toxic to horses.
• For the study, 67 horses which had been exposed to diet containing lasalocid were enrolled and subjected to full cardiac examination including cardiac troponin I (cTnI) estimation, electrocardiography, and echocardiography.
• Techniques like Tissue Doppler imaging (TDI), which measured the radial systolic velocity and strain, and 2-dimensional speckle tracking (2DST), which estimated circumferential (SC) and radial (SR) strain at papillary muscle and chordal level and longitudinal (SL) strain, were utilized to measure the left ventricular function.

Results

• Among the total horses studied, 20 exhibited signs of myocardial injury and were intensively examined between day 30 and 490 after suspected exposure to lasalocid.
• Out of these 20 horses, five exhibited elevated levels of cTnI along with episodes of ventricular tachycardia, whereas 15 had increased cTnI without any ventricular tachycardia.
• Horses with mild myocardial damage did not show significant differences when compared to the control group of horses. However, those with severe myocardial injury demonstrated significant decrease in TDI, 2DST and fractional shortening measurements, indicating impaired left ventricular function.
• Long-term evaluation of two surviving horses showed full recovery in one, while the other suffered from permanent myocardial fibrosis.

Analysis and Conclusions

• The researchers found a significant correlation between the lowest TDI measurements, SL, SR at chordal level, and FS with the maximum cTnI levels among the 20 horses with signs of myocardial injury.
• Similarly, correlation between TDI, 2DST measurements and FS was noted from the 49 follow-up examinations conducted on these horses, indicating these measurements allowed precise detection and quantification of the left ventricular dysfunction in horses exposed to lasalocid.

In conclusion, the study demonstrated that TDI and 2DST measurements can enable effective detection and measurement of left ventricular dysfunction in horses exposed to harmful ionophore such as lasalocid.