Figure 1.
Detection of electrocardiographic signal.
A) Depiction of an electrocardiogram and associated components, created using Adobe Photoshop CS6, B) 2 second section of a raw ECG recording from a larval zebrafish (3 dpf) without digital filtering, C) digitally filtered version of the ECG recording using low pass filtering to reduce background noise and produce a waveform suitable for analysis, D) analysed trace showing waveform reproducibility and stability during the recording period, with each line representing one cardiac cycle. The dark line in the middle represents the mean of all cycles from a 1 minute record.
Figure 2.
Exclusion of motion artefact and signal contamination.
A) Mean ECG interval measurements obtained from 3 dpf larvae following motion artefact exclusion using cromakalim drug treatment (n = 5 per concentration), B) parallel invasive and non-invasive recordings (n = 4), C) prior MESAB anaesthesia for 5–10 minutes (n = 10 per concentration), and D) continuous tubocurarine exposure (n = 10 per concentration). Abbreviations: RR = time between the peak of one QRS complex to the next, QT = time of ventricular depolarisation and repolarisation, QTc = QT corrected for heart rate.
Figure 3.
Optimisation of ECG recording system.
A) Mean ECG interval measurements obtained from 3 dpf larvae following exposure to different ambient temperatures (n = 10), and B) over different developmental periods (2, 3, 4 and 5 days; n = 8).
Figure 4.
Investigation of effect of electrode position on ECG waveform.
A) Mean ECG interval measurements obtained from 3 dpf larvae at different electrode positions over the heart (n = 10 per position), B) diagram of a 3 dpf larva with numbers identifying the different measurement positions; image created using Adobe Photoshop CS6, C) 1) 2 second raw ECG recording and 2) 2 second raw ECG recording from a 5 dpf larva after moving positive electrode 10 µm forward longitudinally, D) comparison of QTc intervals measured from 5 dpf larvae (n = 3) at starting position (atrium/ventricle boundary) and after movement of electrode longitudinally by 5 µm and 10 µm. Key: 1 = sinus venosus, 2 = between atrium and sinus venosus, 3 = base of atrium, 4 = apex of atrium, 5 = between atrium and ventricle, 6 = base of ventricle, 7 = apex of ventricle and 8 = bulbus arteriosus.
Figure 5.
Effect of QT prolonging drugs on ECG measurements.
A) Mean percentage change in QTc interval durations in 3 dpf larvae following treatment with terfenadine (n = 10 per concentration), B) verapamil (n = 10 per concentration), C) haloperidol (n = 10 per concentration) and D) penicillin (n = 10 per concentration). E) A raw ECG recording of a 3 dpf zebrafish before and 1 hour after treatment with 1 mM verapamil.
Table 1.
Z-factor scores for different treatment regimes.