A high-frequency, high-resolution digital imaging platform with linear array technology and color Doppler mode for in vivo high-resolution micro-imaging was used for echocardiography (Vevo® 2100 Imaging System, FUJIFILM VisualSonics Inc., Toronto, Canada). For assessing cardiovascular function of mice a high-frequency transducer probe (VisualSonics MS400, FUJIFILM VisualSonics, Inc., Toronto, Canada with a frequency range of 18–38 MHz) was utilized as it provides appropriate resolution and depth of penetration needed. All echocardiograms were performed by one trained individual, and images were reviewed in conjunction with a clinical cardiologist and echocardiographer to ensure optimal image quality.
Both strains of mice were anesthetized with 2.5–3.0% (v/v) isoflurane mixed with room air. A second group of mice was studied in which isoflurane was mixed with 95% oxygen (v/v) to assess any effect of hypoxia on pulmonary valve hemodynamics. Mice were evaluated with a toe pinch to ensure a complete anesthesia. After achieving an adequate anesthesia, anthropomorphic measurements were taken. We measured the total body weight and nose to anus length, and secured mice on a prewarmed (37℃) imaging platform. About 2 mL of electrode gel is applied to each paw to connect them with electrocardiogram leads embedded in the imaging platform. Hairs from the ventral chest were removed by the use of commercially available hair removal cream (Nair™, Church & Dwight Co., Ewing, NJ, USA).
Mice were continuously monitored and isoflurane concentrations were titrated (1–3%) during imaging to maintain heart rate at 425 ± 50 beats per minute (bpm), compared to a basal heart rate of that is typically greater than 600 in active, conscious mice of both CD1 and C57BL/6 strains.12) (link) Isoflurane was used as this was shown to have the least effect on cardiac physiology in previous studies.12) (link) Heart rates less than 300 bpm are typically indicative of severe respiratory and cardiac depression, at which point anesthesia was stopped.7) (link) Heart rates greater than 500 bpm may indicate inadequate anesthesia. As with all anesthetics, isoflurane also decreases body temperature;13 (link)14) (link)15) (link) therefore a warming table is used to maintain core body temperature of 37℃.
The transducer probe was positioned on the mouse chest wall for imaging acquisition either by hand or by the use of a rail system. The advantages of handheld transducer probe imaging include speed and fine adjustments in changing the viewing angle (Fig. 1 ). The disadvantages of performing echocardiography holding the transducer probe are significantly longer training period to ensure reliable technique and reproducible imaging. The rail system requires less training and enhances reproducibility of imaging, therefore can be effectively utilized.
Our echocardiography protocol for assessing the right heart in mice is derived from contemporary clinical imaging guidelines written by the American Society of Echocardiography, endorsed by the European Association of Echocardiography, a registered branch of the European Society of Cardiology and the Canadian Society of Echocardiography.9) (link)
Both strains of mice were anesthetized with 2.5–3.0% (v/v) isoflurane mixed with room air. A second group of mice was studied in which isoflurane was mixed with 95% oxygen (v/v) to assess any effect of hypoxia on pulmonary valve hemodynamics. Mice were evaluated with a toe pinch to ensure a complete anesthesia. After achieving an adequate anesthesia, anthropomorphic measurements were taken. We measured the total body weight and nose to anus length, and secured mice on a prewarmed (37℃) imaging platform. About 2 mL of electrode gel is applied to each paw to connect them with electrocardiogram leads embedded in the imaging platform. Hairs from the ventral chest were removed by the use of commercially available hair removal cream (Nair™, Church & Dwight Co., Ewing, NJ, USA).
Mice were continuously monitored and isoflurane concentrations were titrated (1–3%) during imaging to maintain heart rate at 425 ± 50 beats per minute (bpm), compared to a basal heart rate of that is typically greater than 600 in active, conscious mice of both CD1 and C57BL/6 strains.12) (link) Isoflurane was used as this was shown to have the least effect on cardiac physiology in previous studies.12) (link) Heart rates less than 300 bpm are typically indicative of severe respiratory and cardiac depression, at which point anesthesia was stopped.7) (link) Heart rates greater than 500 bpm may indicate inadequate anesthesia. As with all anesthetics, isoflurane also decreases body temperature;13 (link)14) (link)15) (link) therefore a warming table is used to maintain core body temperature of 37℃.
The transducer probe was positioned on the mouse chest wall for imaging acquisition either by hand or by the use of a rail system. The advantages of handheld transducer probe imaging include speed and fine adjustments in changing the viewing angle (
Our echocardiography protocol for assessing the right heart in mice is derived from contemporary clinical imaging guidelines written by the American Society of Echocardiography, endorsed by the European Association of Echocardiography, a registered branch of the European Society of Cardiology and the Canadian Society of Echocardiography.9) (link)
