Time and left ventricular function: the forgotten dynamic factor

This article refers to ‘The significance of left ventricular ejection time in heart failure with reduced fraction’ by A.S. Alhakak et al., published this issue on pages 541–551. ‘Time present and past are both perhaps future contained past’—Thomas S. Eliot Cardiac function is continuous without a beginning or end, thus one phase the cardiac cycle, certain degree, dependent from previous phase. Systolic intervals (STIs), which offer temporal description sequential phases nicely illustrate continuation.1 The evaluation (LV) performance has been subject research for more than century. For several years, studies were performed mostly laboratory where factors that influence LV could be individually controlled.2, 3 Clinician scientists, however, limited as they cannot completely control multiple complex interactions can affect performance. Consequently, clinicians forced rely indices not pure measurement performance, since these usually affected many other such preload, afterload, intrinsic extrinsic inotropic effects, geometry, just mention few. In diseases disorders (e.g. failure), all (preload, other) simultaneously reason need taken into consideration when assessing Left contraction results generation force, shortening myocardial walls blood systemic circulation precisely defined periods time. Indices therefore, should based ability ventricle generate force (pressure, dP/dt, other), capacity pump (stroke volume, output), shorten each (ejection fraction, global longitudinal strain, relationship (STI), combination above.1, 2, 4, 6 Most methods used today evaluate deal stroke volume/cardiac output, distance (i.e. systole); STI only test utilizing assess performance.1, 6-9 To determine STI, three primary systole measured (Figure 1). Electromechanical systole, QS2 (total duration systole), spans period onset QRS electrocardiogram closure aortic valve, second sound, echocardiogram Doppler1, 7-10; (LVET) during ejects aorta; pre-ejection (PEP) interval ejection, obtained subtracting LVET QS2. All components vary inversely rate, corrected rate obtain their respective (QSI, LVETI, PEPI).1, 7, 8 STIs cycle physiologically influenced same variables measurements inotropy, other). Multiple have shown interventions alter produce similar directional changes also seen (invasive non-invasive).1-3, 8, 10 When dysfunction occurs, regardless aetiology, PEP lengthens, generally shortens ratio PEP/LVET increases. prolongation attributed diminished increase pressure isovolumic (dP/dt) resulting complex. During velocity fibre theoretically prolong LVET; extent fraction) tends LVET. Further, related volume decrease its well. Since lengthens shortens, provides sensitive index Although manifested directionally opposite (prolongation) (shortening), remains unchanged, unless catecholamine effects present. agents shortened LVET, most judging presence positive effect. addition, short absence pharmacologic effect suggests high adrenergic tone.1, Thus, give information systolic but tone drugs.1, 11 activity patients acute infarction (AMI), chronic coronary artery disease, arterial hypertension, cardiomyopathy failure, haemodialysis, among others.1, post-AMI patients, assessed stratify various risk groups degree accuracy. first demonstrate survival benefit β-blocker therapy bypass graft (CABG) surgery STI.1 define AMI perioperative undergoing CABG, mitral valve prolapse, diseases.1, instances, abbreviation (QS2I) correlated 24 h excretion.11 extensively studied heart. onset, magnitude, dose response established. Positive drugs PEP, while negative PEP.1, contrast, general rule, both. follows PEP. Lengthening occur cases increases substantially.12 greatly enhanced our understanding receptor modulation showing rebound hypersensitivity after β-blockade withdrawal.13 cardiotoxic antineoplastic agent adriamycin studied.8 It electrical (QT) normal subjects consistently shorter Studies demonstrated AMI, QT > sudden death. case, correcting was found superior prognostic indicator compared correction rate.14 diastolic perfusion filling time) (QS2) entire (RR interval). RR × 100, percent diastole, varies non-linearly it rapidly decreasing rate. Diastolic important clinical implications (especially subendocardial perfusion), particularly disease hypertrophy, flow distal significant stenosis occurs diastole.15 Journal, al.12 provide an extensive excellent review fraction (HFrEF). However, discussed authors focus hope al. will stimulate further almost forgotten topic. ‘Biology study complicated things. …The objects phenomena physics book describes simpler single cell body author’—Richard Dawkins. Though techniques practice become increasingly refined, method purpose limitations advantages. practice, we aware shortcomings select better suited particular setting. multidimensional and, thus, requires approach. One parameter accurately function. use (STI) another dimension assist understand underlying pathophysiologic mechanisms addition assessment (QS2 shortening). calculate (myocardial time, (QT). Finally, due extreme sensitivity, remarkable reproducibility, accuracy, easy ideally Conflict interest: none declared.