Why the study?
The role of isovolumic intervals during the cardiac cycle and their impact on left ventricular intracavitary flow dynamics were unclear.
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“Blood flow dynamics are extremely intriguing, particularly the symmetric flow across the cardiovascular system. The asymmetry of the blood flow is extremely intriguing and important for a better understanding of cardiac form and function.”
Isovolumic intervals are dynamic phases of intracavitary flow redirection that are disrupted by aberrant epicardial electrical activation.
OBJECTIVES We sought to clarify the role of isovolumic intervals during a cardiac cycle by in vivo visualization of left ventricular (LV) intracavitary flow dynamics. BACKGROUND Asynchronous LV deformation during isovolumic contraction (IVC) and isovolumic relaxation (IVR) might represent a transient feature of myocardial wall mechanics that reverses the direction of blood flow. METHODS In 10 beating porcine hearts, the changes in LV intracavitary flow were recorded at baseline and after LV epicardial and right atrial pacing with high-resolution Doppler and contrast echocardiography. Two-dimensional vector flow fields were generated offline from B-mode contrast images with particle imaging velocimetry. RESULTS During IVC, flow from the LV apex accelerated toward the base, whereas blood from the base was redirected toward the outflow through formation of an anterior vortex. Conversely, during IVR, flow was initially directed toward the apex and then briefly reversed toward the base. Epicardial pacing from the LV base altered the stages of flow redirection during the pre-ejection period and delayed mitral valve closure (28 +/- 14 ms vs. 61 +/- 13 ms, p < 0.001) and aortic valve opening (77 +/- 18 ms vs. 111 +/- 18 ms, p = 0.004). CONCLUSIONS Isovolumic intervals are not periods of hemodynamic stasis but, rather, phases with dynamic changes in intracavitary flow. Experimentally induced aberrant epicardial electrical activation alters stages of flow redirection and prolongs the pre-ejection period. Normal electromechanical activation through the His-Purkinje system in mammalian hearts maintains an inherent synchrony with the sequence of intracavitary flow redirection.
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Sengupta et al. (2007) studied this question. Left ventricular epicardial pacing vs. Baseline normal electromechanical activation was evaluated on Mitral valve closure time (ms) (p=<0.001).
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