In Vivo Recording of the Adult Zebrafish Electrocardiogram - Zebrafish: Methods for Assessing Drug Safety and Toxicity - page 64

0.1 V

( a )

100 ms

Figure 6.2 (a) Initial attempts at
electrocardiographic zebrafish
recordings were contaminated by
skeletal muscle artifacts, especially gill
motion that can be seen as a sinusoidal
baseline signal. (b) Signal averaging
allowed some reduction of this artifact
as seen in this 50-beat average. (c)
Further reduction in
electrocardiographic artifacts was
achieved with the combination of signal
averaging and paralysis with
m-conotoxin GIIIB (10-beat average).
(Figure adapted from Milan et al.,
2006.)

( b )

Signal averaged ECG

( c )

Signal averaged ECG + CTX

prevent this, we had to construct a perfusion system compatible with electrocar-
diographic recording outside of the normal aqueous environment for several
hours. Recordings from fish whose gills were superfused with oxygenated and
buffered medium did not exhibit significant RR or QT interval variation (Fig. 6.1,
circles).
This system allowed recordings for several hours, but did not eliminate electro-
myographic noise, primarily from gill motion (Fig. 6.2a). Signal averaged electro-
cardiograms were still inadequate for the reproducible measurement of cardiac
repolarization parameters (Fig. 6.2b). However, we were able to reduce noise
sufficiently for high fidelity recording with the intraperitoneal injection of conotoxin,
and consequent skeletal muscle paralysis (Fig. 6.2c).
Optimal signal filtering used a high-pass cutoff value of 0.5 Hz in order to
eliminate excessive baselinewander, but such filtering would be predicted to blunt the
terminal T wave. To assess this, we performed duplicate measurements in five fish,
varying the high-pass cutoff value. Reducing the cutoff frequency from 0.5 to 0.1 Hz
resulted in a 1.5% increase in the measured QT interval (p 0.2). Based on this

minimal effect, and the improved recordings with the higher value, we chose a cutoff
of 0.5 Hz for the remainder of our work. T-wave morphologies vary between
individual fish presumably as a result of subtle changes in the electrode placement
or the orientation of the heart.

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