Action potential duration and contractility are reduced following premature excitations, and gradually increase as the stimulus interval is lengthened. To examine these phenomena of electrical and mechanical restitution in the human heart, we simultaneously measured action potential duration and the maximum rate of left ventricular pressure in five patients undergoing electrophysiological study. Test beats were introduced at varying intervals after the last of a series of steady state intervals. By plotting action potential duration and maximum rate of left ventricular pressure as a function of the test interval, we formed electrical and mechanical restitution curves. When the rate of steady state pacing was increased, there was a decrease in action potential duration and an increase in the maximum rate of left ventricular pressure for all test intervals; i.e., a change in pacing rate affected action potential duration and maximum rate of left ventricular pressure of test responses in a reciprocal fashion. In addition, a higher steady state pacing rate allowed action potentials and contractile responses to be elicited at shorter test intervals, thereby displacing the electrical and mechanical restitution curves to the left. The magnitude of the leftward shift of both curves corresponded closely to the shortening of the steady state action potential duration induced by the increase in pacing rate. These findings confirm for the human heart that both electrical and mechanical restitution occur after membrane repolarization, i.e., as a function of the electrical diastolic interval preceding a beat, and not the stimulus interval.
Cardiac monophasic action potentials (MAPs) and contractility have been simultaneously measured in man while the heart rate was being changed by right atrial pacing. A new non-suction electrode was used for safe and long-term recording of MAPs from the endomyocardium. Abrupt changes in cycle-length were followed first by a fast, then a slow response in the adaptation of MAP-duration and of contractility (LV dp/dt max) to the new steady state. After increasing the heart rate then slow phase of MAP shortening appears to be related to the slow staircase of contractility, whereas after the step decrease of frequency no such a relation could be observed. The consistency of these results with those obtained in corresponding in-vitro experiments indicates that this methodical approach may be suitable for assessing the process of E-C coupling in the human heart.
National strategies for preparedness for future outbreaks of COVID-19 often include timely preparedness with vaccines. Fiscal health modelling (FHM) has recently been brought forward as an additional analysis by defining the public economic impact from a governmental perspective. As governments are the main decision-makers concerning pandemic preparedness, this study aimed to develop an FHM framework for infectious diseases in the Netherlands. Based on the Dutch COVID-19 outbreak of 2020 and 2021 and publicly available data on tax income and gross domestic product (GDP), the fiscal impact of COVID-19 was assessed using two approaches. Approach I: Prospective modelling of future fiscal impact based on publicly available laboratory-confirmed COVID-19 cases; and Approach II: Retrospective assessment of the extrapolated tax and benefit income and GDP. Approach I estimated the consequences that can be causally linked to the population counts reducing income taxes by EUR 266 million. The total fiscal loss amounted to EUR 164 million over 2 years (excluding pension payments averted). The total losses in terms of tax income (2020 and 2021) and GDP (2020) (Approach II), were estimated at, respectively, EUR 13.58 billion and EUR 96.3 billion. This study analysed different aspects of a communicable disease outbreak and its influence on government public accounts. The choice of the two presented approaches depends on the perspective of the analysis, the time horizon of the analysis and the availability of data.
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