Takeshi Imaoka

Total Ca handling in canine mild Ca overload failing heart

SummaryWe analyzed total Ca handling of the left ventricle (LV) in the mildly failing heart preparation induced by a temporary intracoronary Ca overloading intervention in eight excised and cross-circulated canine hearts. This Ca intervention consisted of interruption of coronary blood perfusion by Ca-free oxygenated Tyrode perfusion for 10min followed by high-Ca (16 mmol/l) oxygenated Tyrode perfusion for 5 min. This intervention decreased the LV contractility index,Emax (end-systolic maximum elastance), by 40% after restoration of the blood cross-circulation. We expected a Ca overload or paradox failing heart resembling the postischemic stunned heart and being characterized by an increased O2 cost ofEmax. However, LV O2 consumption under mechanically unloading conditions decreased by 30% from control without increasing the O2 cost ofEmax. To obtain a mechanistic view of this failing heart, we investigated cardiac total Ca handling by our integrative analysis method. In this method, we obtained the internal Ca recirculation fraction (RF) from the decay beat constant of the postextrasystolic potentiation following each sporadic spontaneous extrasystole in these failing LVs. We combined the RF with the decreasedEmax and the unchanged O2 cost ofEmax in our recently developed formula of total Ca handling. We found that these failing LVs had a slightly but significantly increased RF accompanied by either a slightly increased futile Ca cycling or a slightly decreased Ca reactivity ofEmax, or both. Any of these three possible changes can account for the unchanged O2 cost ofEmax. This result indicates that the present mildly failing heart has not yet fallen into a typical Ca overload or paradox by the temporary Ca overloading intervention.

Myocardial mechanical restitution and potentiation partly underlie alternans decay of postextrasystolic potentiation : simulation

SummaryWe have reported that the postextrasystolic potentiation (PESP) decays in alternans or monotonically, respectively, depending on whether the first postextrasystolic beat interval has a compensatory pause or not, in the canine left ventricle. To get better mechanistic insight into the alternans PESP decay, we hypothesized that the myocardial mechanical restitution and potentiation could partly account for both types of PESP decay. To test this hypothesis, we simulated PESP decay on a computer using a documented equation combining myocardial mechanical restitution and potentiation. We changed the first postextrasystolic beat interval after a fixed extrasystolic beat interval without changing regular and other postextrasystolic beat intervals. The simulated PESP decayed in alternans or monotonically as a function only of the first postextrasystolic beat interval. Thus, the myocardial mechanical restitution and potentiation could partly account for both alternans and monotonic decay of PESP. We conclude that myocardial mechanical restitution and potentiation may partly underlie the initial two alternating beats, the first beat being the most potentiated and the second beat being the most depressed, of alternans PESP decay in the canine heart.

Evaluation of Cross-Sectional Area of Small Vessels by a Miniature Conductance Catheter: Toward Its Application to Coronary Arteries

The purpose of this study was to evaluate the feasibility of the conductance catheter (CC) method in measuring cross-sectional area (CSA) of small vessels like human coronary arteries. Lumen CSA (A) of phantom tubes (2–10 mm in diameter) and excised canine arteries (n = 10, 2.3–4.5 mm in diameter) were measured with 3-F CC (Acc) and intravascular ultrasound (Aus). To investigate the influence of parallel conductance in accuracy of Acc, solution with various resistivities was applied to the surrounding of the arteries (n = 4). Acc showed an excellent agreement with phantom model CSA. In the excised arteries, Acc and Aus highly correlated (R2 = 0.906) with each other. When the resistivities of the solution surrounding the vessels was changed, Acc–Aus regression lines were similar regardless of different resistivities. The conductance method is feasible to measure CSA of small vessels like human coronary arteries.