No abstract

Background: Phthalates are employed as plasticizers in the manufacturing of flexible, plastic medical products. Patients can be subjected to high phthalate exposure through contact with plastic medical devices. We aimed to investigate the cardiac safety and biocompatibility of mono-2-ethylhexyl phthalate (MEHP), a phthalate with documented exposure in intensive care patients. Methods and Results: Optical mapping of transmembrane voltage and pacing studies were performed on isolated, Langendorff-perfused rat hearts to assess cardiac electrophysiology after MEHP exposure compared with controls. MEHP dose was chosen based on reported blood concentrations following an exchange transfusion procedure. 30-min exposure to MEHP increased the atrioventricular node (147 vs. 107msec) and ventricular (117 vs. 77.5msec) effective refractory periods, compared with controls. Optical mapping revealed prolonged action potential duration (APD) at slower pacing cycle lengths, akin to reverse use-dependence. The plateau phase of the APD restitution curve steepened and became monophasic in MEHP-exposed hearts (0.18 vs. 0.06 slope). APD lengthening occurred during late-phase repolarization resulting in triangulation (70.3 vs. 56.6 msec). MEHP-exposure also slowed epicardial conduction velocity (35 vs. 60 cm/sec), which may be partly explained by inhibition of Na v 1.5 (874 μM and 231 μM IC50, fast and late sodium current). Conclusions: This study highlights the impact of acute MEHP exposure, using a clinically-relevant dose, on cardiac electrophysiology in the intact heart. Heightened clinical exposure to plasticized medical products may have cardiac safety implications – given that action potential triangulation and electrical restitution modifications are a risk factor for early after depolarizations and cardiac arrhythmias.

Background: Optical mapping of transmembrane voltage and intracellular calcium is a powerful tool for investigating cardiac physiology and pathophysiology. However, simultaneous dual mapping of two fluorescent probes remains technically challenging. We introduce a novel, easy-to-use approach that requires a path splitter, single camera and excitation light to simultaneously acquire voltage and calcium signals from whole heart preparations, which can be applied to other physiological models - including neurons and isolated cardiomyocytes. Results: Complementary probes were selected that could be excited with a single wavelength light source. Langendorff-perfused hearts (rat, swine) were stained and imaged using a sCMOS camera outfitted with an optical path splitter to simultaneously acquire two emission fields at high spatial and temporal resolution. Voltage (RH237) and calcium (Rhod2) signals were acquired concurrently on a single sensor, resulting in two 384 × 256 images at 814 frames per second. At this frame rate, the signal-to-noise ratio was 47 (RH237) and 85 (Rhod2). Imaging experiments were performed on small rodent hearts, as well as larger pig hearts with sufficient optical signals. In separate experiments, each dye was used independently to assess crosstalk and demonstrate signal specificity. Additionally, the effect of ryanodine on myocardial calcium transients was validated - with no measurable effect on the amplitude of optical action potentials. To demonstrate spatial resolution, ventricular tachycardia was induced - resulting in the novel finding that spatially discordant calcium alternans can be present in different regions of the heart, even when electrical alternans remain concordant. The described system excels in providing a wide field of view and high spatiotemporal resolution for a variety of cardiac preparations. Conclusions: We report the first multiparametric mapping system that simultaneously acquires calcium and voltage signals from cardiac preparations, using a path splitter, single camera and excitation light. This approach eliminates the need for multiple cameras, excitation light patterning or frame interleaving. These features can aid in the adoption of dual mapping technology by the broader cardiovascular research community, and decrease the barrier of entry into panoramic heart imaging, as it reduces the number of required cameras.

Duchenne muscular dystrophy (DMD) is an inherited X-linked disorder with an incidence of 1 in 3500 male births, and cardiomyopathy is becoming the leading cause of death. While Cardiac MRI (CMR) and late gadolinium enhancement (LGE) are important tools in recognizing myocardial involvement, myocardial strain imaging may demonstrate early changes and allow patients to avoid gadolinium contrast. We performed CMR feature tracking (FT) and echo-based speckle tracking (STE) strain measures on DMD patients and age/sex matched controls who had received a CMR with contrast and transthoracic echocardiogram. Data were collected for longitudinal strain in the apical four-chamber view and circumferential strain in the mid-papillary parasternal short axis. Segmental wall analysis was performed and compared with the presence of LGE. Data were analyzed using student's t tests or one-way ANOVA adjusting for multiple comparisons. We measured 24 subjects with DMD and 8 controls. Thirteen of 24 DMD subjects were LGE positive only in the lateral segments in short-axis views. Average circumferential strain (CS) measured by FT was significantly decreased in DMD compared to controls (- 18.8 ± 6.1 vs. - 25.5 ± 3.2; p < 0.001) and showed significant differences in the anterolateral, inferolateral, and inferior segments. Average CS by STE trended towards significance (p = 0.06) but showed significance in only the inferior segment. FT showed significant differences in the inferolateral segment between LGE positive (- 15.5 ± 9.0) and LGE negative (- 18.2 ± 8.3) in DMD subjects compared to controls (- 28.6 ± 7.3; p ≤ 0.04). FT also showed significant differences between anteroseptal and inferolateral segments within LGE-positive (p < 0.003) and LGE-negative (p < 0.03) DMD subjects while STE did not. There were no significant differences in longitudinal strain measures. CMR-FT-derived myocardial strain was able to demonstrate differences between subjects with DMD and controls not detected by STE. FT was also able to demonstrate differences in LGE-positive and LGE-negative segments within patients with DMD. FT may be able to predict LGE-positive segments in DMD without the use of gadolinium contrast.

Background: Phthalates are used as plasticizers in the manufacturing of flexible, plastic medical products. Patients can be subjected to high phthalate exposure through contact with plastic medical devices. We aimed to investigate the cardiac safety and biocompatibility of mono-2-ethylhexyl phthalate (MEHP), a phthalate with documented exposure in intensive care patients. Methods: Optical mapping of transmembrane voltage and pacing studies were performed on isolated, Langendorff-perfused rat hearts to assess cardiac electrophysiology after MEHP exposure compared with controls. MEHP dose was chosen based on reported blood concentrations after an exchange transfusion procedure. Results: Thirty-minute exposure to MEHP increased the atrioventricular node (147 versus 107 ms) and ventricular (117 versus 77.5 ms) effective refractory periods, compared with controls. Optical mapping revealed prolonged action potential duration at slower pacing cycle lengths, akin to reverse use dependence. The plateau phase of the action potential duration restitution curve steepened and became monophasic in MEHP-exposed hearts (0.18 versus 0.06 slope). Action potential duration lengthening occurred during late-phase repolarization resulting in triangulation (70.3 versus 56.6 ms). MEHP exposure also slowed epicardial conduction velocity (35 versus 60 cm/s), which may be partly explained by inhibition of Na v 1.5 (874 and 231 µmol/L half-maximal inhibitory concentration, fast and late sodium current). Conclusions: This study highlights the impact of acute MEHP exposure, using a clinically relevant dose, on cardiac electrophysiology in the intact heart. Heightened clinical exposure to plasticized medical products may have cardiac safety implications—given that action potential triangulation and electrical restitution modifications are a risk factor for early after depolarizations and cardiac arrhythmias.