1. 2-Dimensional Strain Studies in Open-Chest Instrumented Pigs
ABSTRACT
Background: Dobutamine and beta blockers are commonly used in clinical practice with anticipated effects on heart function. With the introduction of speckle tracking methods, it is now possible to noninvasively assess left ventricular mechanics in detail. We studied the effect of these drugs in an open chest animal model.
Methods: In 7 open-chest adult pigs, high-resolution high frame rate apical and basal short-axis images were acquired directly from the heart surface with a 10 MHz VIVID 7 Dimension ultrasound system. Left ventricular pressure and dP/dt were obtained with a solid state catheter. After acquisition of baseline data, pigs were subjected to pharmacological interventions using escalating doses of dobutamine and then doses of esmolol. Both apical and basal short-axis images for each state were obtained and exported to EchoPac PC for offline analysis of cardiac mechanics using the speckle tracking method. Hemodynamic data was analyzed in custom software.
Results: Dobutamine increased maximum dP/dt by 30-50% and shortened the time to peak contraction ([circumferential strain] 31.35% ± 2.65% to 18.90% ± 3.35%) of the RR' interval, increased the period of sustained contraction at peak (16.45% ± 1.60% to 38.90% ± 3.5%). Esmolol decreased maximum dP/dt by 30-50% and increased the time to peak strain (52.90% ± 3.5%) and decreased the time of sustained contraction (8.90% ± 4.65%).
Conclusions: Speckle tracking analysis may provide a useful tool to monitor response to cardiotonic medications.
CONCLUSIONS
Results of this study suggest that effects of these commonly used clinical drugs on imaging derived mechanical parameter s and hemodynamic indices of heart function are not dose dependant. Further studies are required to explore this relationship. Speckle tracking based analysis of high resolution echo images may provide a useful tool to evaluate and monitor response to cardiotonic medications.
DISCLOSURES
No relationships to disclose:
Muhammad Ashraf
Wei Zhou
Elizabeth Sanchez
Jennifer Corniea
Aman Mahajan
David J. Sahn
BACKGROUND
Cardiac motion has been studied by tracking surgically implanted radio opaque markers under low resolution cineradiography. Recent advances in cardiac imaging have made it possible to study dynamic cardiac function noninvasively. MRI tagging provides a noninvasive analogue to the implanted marker technique, but is limited by high cost and low temporal resolution. Although Doppler derived tissue velocities provide a high resolution motion analysis method using widely available echocardiography, extreme angle dependency and low lateral resolution make this analysis method tedious and subject to error. New developments in computer vision methods and enhanced ability to acquire high frame rate scanline data have made it possible to identify potential tissue markers (speckles) in high resolution dynamic image loops and track them in subsequent frames. Digital tracking of speckles in high resolution echo images seems to provide a robust motion analysis method. Dobutamine is a beta agonist drug that has positive ionotropic action on the heart. It is believed to increase contractility and enhance cardiac systolic performance. Similarly, beta-blockers are believed to have a negative ionotropic action on heart muscle. These drugs are commonly used in clinical practice with their anticipated effects on dynamic cardiac function. We sought to use speckle tracking based method to study the effect of these commonly used drugs on dynamic function of the heart in open chest experimental animals.
METHODS
We studied 7 adult pigs weighing between 20-25kg. All pigs were intubated, anesthetized and operated for midline sternotomy to expose the heart. Vital signs and oxygen saturation were monitored continuously throughout the procedure while keeping pigs pain free and warm. Millar conductance catheters were introduced from the right carotid artery into the left ventricle (LV) to obtain pressure-volume curves. Short axis views were acquired with a10 MHz pediatric sector probe just above and below the papillary muscle level on a Vivid 7 Dimensions ultrasound system. Frequency and frame rate were optimized before acquisition to ensure the best possible spatiotemporal resolution of 2D images. After acquisition of baseline data, pigs were subjected to pharmacological interventions using escalating doses of dobutamine and then doses of esmolol. Apical and basal short axis 2D views along with pressure-volume data were acquired at each state. Images were exported to EchoPac PC for offline analysis of strain and rotation dynamics using the speckle tracking based method. Hemodynamic data was analyzed to obtain stroke volume and cardiac output at each state.
High Resolution Echocardiography May Be Used to Monitor the Response to Cardiotonic Medication:
2-Dimensional Strain Studies in Open-Chest Instrumented Pigs
Muhammad Ashraf, MD; Wei Zhou, PhD; Elizabeth Sanchez, BS; Jennifer Corniea, MA;
Aman Mahajan, MD, PhD; David J. Sahn, MD, MACC
Oregon Health & Science University, Portland, OR; University of California, Los Angeles, CA
RESULTS
Dobutamine
Esmolol
This figure shows circumferential strain of LV after treatment with Dobutamine (left) & Esmolol (right)
Dobutamine increased heart rate and maximum dP/dt by 30-50% at moderate clinical doses. Further increase in dose just increased the heart rate with no or paradoxical effect on dP/dt.
Esmolol decreased heart rate and maximum dP/dt by 30-50% at moderate dose, as compared to baseline. Further increase in dose decreased heart rate only.
Dobutamine shortened the time to peak contraction [circumferential strain] from 31.35% ± 2.65% to 18.90% ± 3.35% of the RR' interval and increased the period of sustained contraction at peak from 16.45% ± 1.60% to 38.90% ± 3.5%.
Esmolol increased the time to peak strain to 52.90% ± 3.5% and decreased the time of sustained contraction to 8.90% ± 4.65%.
Increasing dose of Dobutamine or Esmolol had little effect on strain parameters.