Rupert Williams

Transient limb ischemia induces remote preconditioning and remote postconditioning in humans by a K(ATP)-channel dependent mechanism.

Background— Transient limb ischemia administered before a prolonged ischemic insult has systemic protective effects against ischemia-reperfusion (IR) injury (remote ischemic preconditioning [RIPC]). It has been demonstrated that protection from IR can be achieved by brief periods of ischemia applied at a remote site during an injurious ischemic event (remote postconditioning [RPostC]). Using an in vivo model of endothelial IR injury, we sought to determine whether RPostC occurred in humans and whether it shared mechanistic similarities with RIPC. Methods and Results— Endothelial function was assessed by flow-mediated dilation before and after IR (20 minutes of arm ischemia followed by reperfusion). RIPC was induced by conditioning cycles of 5 minutes of ischemia and reperfusion on the contralateral arm or leg before IR. For RPostC induction, conditioning cycles were administered during the ischemic phase of IR. Oral glibenclamide was used to determine the dependence of RIPC and RPostC on KATP channels. IR caused a significant reduction in flow-mediated dilation in healthy volunteers (baseline, 9.3±1.2% versus post-IR, 3.3±0.7%; P<0.0001) and patients with atherosclerosis (baseline, 5.5±0.6% versus post-IR, 2.3±0.5%; P<0.01). This reduction was prevented by RIPC (post-IR+RIPC: healthy volunteers, 7.2±0.5% [P<0.0001 versus post-IR]; patients, 4.5±0.3% [P<0.01 versus post-IR]) and RPostC (post-IR+RPostC: 8.0±0.5%; P<0.0001 versus post-IR). The protective effects of RIPC and RPostC were blocked by glibenclamide. Conclusions— This study demonstrates for the first time in humans that RPostC can be induced by transient limb ischemia and is as effective as RIPC in preventing endothelial IR injury. RIPC and RPostC share mechanistic similarities, with protection being dependent on KATP channel activation. These results suggest that remote conditioning stimuli could be protective in patients with acute ischemia about to undergo therapeutic reperfusion.

Normal values for cardiovascular magnetic resonance in adults and children

Morphological and functional parameters such as chamber size and function, aortic diameters and distensibility, flow and T1 and T2* relaxation time can be assessed and quantified by cardiovascular magnetic resonance (CMR). Knowledge of normal values for quantitative CMR is crucial to interpretation of results and to distinguish normal from disease. In this review, we present normal reference values for morphological and functional CMR parameters of the cardiovascular system based on the peer-reviewed literature and current CMR techniques and sequences.

Comparison of serum procollagen III peptide concentrations and PGA index for assessment of hepatic fibrosis

In early hepatic fibrosis, increased amounts of type III collagen are deposited. Persistently high serum concentrations of aminoterminal type III procollagen propeptide (PIIIP) correlate with the activity of the fibrogenic process. Another index for the detection of fibrosis, the PGA index, combines the prothrombin time, gamma-glutamyl transpeptidase activity, and serum apolipoprotein A1 concentration (the latter falls with progressive fibrosis). We compared PIIIP measurements and PGA index in patients with various histological forms of alcoholic liver disease (104), primary biliary cirrhosis (38), and chronic B virus hepatitis (27), and in healthy age-matched controls (30). The ability of each test to identify correctly patients with fibrosis or cirrhosis was assessed with receiver operating curves. The PGA index was much higher in all groups of patients with alcoholic liver disease than in controls (p < 0.0001). PIIIP concentrations were also substantially higher than in controls (p < 0.05 for fatty liver, p < 0.0001 for all other groups), especially in the group with alcoholic hepatitis and cirrhosis. For the detection of cirrhosis the PGA was 91% sensitive and 81% specific and the PIIIP concentration was 94% sensitive and 81% specific. The two tests combined had 85% sensitivity, but 93% specificity. Among patients with primary biliary cirrhosis, both PGA index and PIIIP concentration correlated well with the severity of the disease, determined by the Mayo score (r = 0.72 and 0.66 respectively). The combined tests were 96% sensitive for the detection of fibrosis. All patients with chronic B virus hepatitis had raised PGA and PIIIP values in comparison with controls (p < 0.0001) but there were no differences between subgroups. Substantially raised PIIIP concentrations thus identify the subgroup of alcoholic patients with both hepatitis and cirrhosis. The combination of PGA index and PIIIP concentration may be useful for targeting treatment with antifibrotic drugs and to reduce the need for liver biopsy.

Synergistic Adaptations to Exercise in the Systemic and Coronary Circulations That Underlie the Warm-Up Angina Phenomenon

Background— The mechanisms of reduced angina on second exertion in patients with coronary arterial disease, also known as the warm-up angina phenomenon, are poorly understood. Adaptations within the coronary and systemic circulations have been suggested but never demonstrated in vivo. In this study we measured central and coronary hemodynamics during serial exercise. Methods and Results— Sixteen patients (15 male, 61±4.3 years) with a positive exercise ECG and exertional angina completed the protocol. During cardiac catheterization via radial access, they performed 2 consecutive exertions (Ex1, Ex2) using a supine cycle ergometer. Throughout exertions, distal coronary pressure and flow velocity were recorded in the culprit vessel using a dual sensor wire while central aortic pressure was recorded using a second wire. Patients achieved a similar workload in Ex2 but with less ischemia than in Ex1 (P<0.01). A 33% decline in aortic pressure augmentation in Ex2 (P<0.0001) coincided with a reduction in tension time index, a major determinant of left ventricular afterload (P<0.001). Coronary stenosis resistance was unchanged. A sustained reduction in coronary microvascular resistance resulted in augmented coronary flow velocity on second exertion (both P<0.001). These changes were accompanied by a 21% increase in the energy of the early diastolic coronary backward-traveling expansion, or suction, wave on second exercise (P<0.05), indicating improved microvascular conductance and enhanced left ventricular relaxation. Conclusions— On repeat exercise in patients with effort angina, synergistic changes in the systemic and coronary circulations combine to improve vascular–ventricular coupling and enhance myocardial perfusion, thereby potentially contributing to the warm-up angina phenomenon.

‘Warm-up Angina’: harnessing the benefits of exercise and myocardial ischaemia

The phenomenon of warm-up angina was first noted over 200 years ago. It describes the curious observation whereby exercise-induced ischaemia on second effort is significantly reduced or even abolished if separated from first effort by a brief rest period. However, the precise mechanism via which this cardio-protection occurs remains uncertain. Three possible explanations for reduced myocardial ischaemia on second effort include: first, an improvement in myocardial perfusion; second, increased myocardial resistance to ischaemia similar to ischaemic preconditioning; and third, reduced cardiac work through better ventricular–vascular coupling. Obtaining accurate coronary physiological measurements in the catheter laboratory throughout exercise demands a complex research protocol. In the 1980s, studies into warm-up angina relied on great cardiac vein thermo-dilution to estimate coronary blood flow. This technique has subsequently been shown to be inaccurate. However exercise physiology in the catheter laboratory has recently been resurrected with the advent of coronary artery wires that allow continuous measurement of distal coronary artery pressure and blood flow velocity. This review summarises the intriguing historical background to warm-up angina, and provides a concise critique of the important studies investigating mechanisms behind this captivating cardio-protective phenomenon.

Physiology of Angina and its Alleviation with Nitroglycerine- Insights from Invasive Catheter Laboratory Measurements During Exercise

Background: The mechanisms governing exercise-induced angina and its alleviation by the most commonly used antianginal drug, nitroglycerin, are incompletely understood. The purpose of this study was to develop a method by which the effects of antianginal drugs could be evaluated invasively during physiological exercise to gain further understanding of the clinical impact of angina and nitroglycerin. Methods: Forty patients (mean age, 65.2±7.6 years) with exertional angina and coronary artery disease underwent cardiac catheterization via radial access and performed incremental exercise using a supine cycle ergometer. As they developed limiting angina, sublingual nitroglycerin was administered to half the patients, and all patients continued to exercise for 2 minutes at the same workload. Throughout exercise, distal coronary pressure and flow velocity and central aortic pressure were recorded with sensor wires. Results: Patients continued to exercise after nitroglycerin administration with less ST-segment depression (P=0.003) and therefore myocardial ischemia. Significant reductions in afterload (aortic pressure, P=0.030) and myocardial oxygen demand were seen (tension-time index, P=0.024; rate-pressure product, P=0.046), as well as an increase in myocardial oxygen supply (Buckberg index, P=0.017). Exercise reduced peripheral arterial wave reflection (P<0.05), which was not further augmented by the administration of nitroglycerin (P=0.648). The observed increases in coronary pressure gradient, stenosis resistance, and flow velocity did not reach statistical significance; however, the diastolic velocity–pressure gradient relation was consistent with a significant increase in relative stenosis severity (k coefficient, P<0.0001), in keeping with exercise-induced vasoconstriction of stenosed epicardial segments and dilatation of normal segments, with trends toward reversal with nitroglycerin. Conclusions: The catheterization laboratory protocol provides a model to study myocardial ischemia and the actions of novel and established antianginal drugs. Administration of nitroglycerin causes changes in the systemic and coronary circulation that combine to reduce myocardial oxygen demand and to increase supply, thereby attenuating exercise-induced ischemia. Designing antianginal therapies that exploit these mechanisms may provide new therapeutic strategies.

Lizard Spit and Reperfusion Injury

Although the incidence of ST-segment elevation myocardial infarction (STEMI) is declining in industrialized nations, there are still an estimated 500,000 events annually in the U.S. ([1][1]). Furthermore, the in-hospital mortality is 6% to 7%, and over 15% of survivors to discharge experience a

Hyperaemic microvascular resistance predicts clinical outcome and microvascular injury after myocardial infarction

Objectives Early detection of microvascular dysfunction after acute myocardial infarction (AMI) could identify patients at high risk of adverse clinical outcome, who may benefit from adjunctive treatment. Our objective was to compare invasively measured coronary flow reserve (CFR) and hyperaemic microvascular resistance (HMR) for their predictive power of long-term clinical outcome and cardiac magnetic resonance (CMR)-defined microvascular injury (MVI). Methods Simultaneous intracoronary Doppler flow velocity and pressure measurements acquired immediately after revascularisation for AMI from five centres were pooled. Clinical follow-up was completed for 176 patients (mean age 60±10 years; 140(80%) male; ST-elevation myocardial infarction (STEMI) 130(74%) and non-ST-segment elevation myocardial infarction 46(26%)) with median follow-up time of 3.2 years. In 110 patients with STEMI, additional CMR was performed. Results The composite end point of death and hospitalisation for heart failure occurred in 17 patients (10%). Optimal cut-off values to predict the composite end point were 1.5 for CFR and 3.0 mm Hg cm−1•s for HMR. CFR <1.5 was predictive for the composite end point (HR 3.5;95% CI 1.1 to 10.8), but not for its individual components. HMR ≥3.0 mm Hg cm−1 s was predictive for the composite end point (HR 7.0;95% CI 1.5 to 33.7) as well as both individual components. HMR had significantly greater area under the receiver operating characteristic curve for MVI than CFR. HMR remained an independent predictor of adverse clinical outcome and MVI, whereas CFR did not. Conclusions HMR measured immediately following percutaneous coronary intervention for AMI with a cut-off value of 3.0 mm Hg cm−1 s, identifies patients with MVI who are at high risk of adverse clinical outcome. For this purpose, HMR is superior to CFR.

Current Concepts in the Pathogenesis of Takotsubo Syndrome

Takotsubo syndrome is typically characterized by acute reversible impairment of apical and mid -left ventricular systolic function. The pathophysiology is complex and remains to be completely understood. A catecholamine surge appears to be a central feature. Patients with prior history of psychiatric disorders have a predisposition. The putative role of a switch in b-adrenoceptor signalling resulting in negative inotropy remains uncertain. Downregulation of noncritical cellular functions may offer some protection in preventing irreversible cellular necrosis. Microvascular function is a common occurrence in these patients.

Doppler Versus Thermodilution-Derived Coronary Microvascular Resistance to Predict Coronary Microvascular Dysfunction in Patients With Acute Myocardial Infarction or Stable Angina Pectoris

Coronary microvascular resistance is increasingly measured as a predictor of clinical outcomes, but there is no accepted gold-standard measurement. We compared the diagnostic accuracy of 2 invasive indices of microvascular resistance, Doppler-derived hyperemic microvascular resistance (hMR) and thermodilution-derived index of microcirculatory resistance (IMR), at predicting microvascular dysfunction. A total of 54 patients (61 ± 10 years) who underwent cardiac catheterization for stable coronary artery disease (n = 10) or acute myocardial infarction (n = 44) had simultaneous intracoronary pressure, Doppler flow velocity and thermodilution flow data acquired from 74 unobstructed vessels, at rest and during hyperemia. Three independent measurements of microvascular function were assessed, using predefined dichotomous thresholds: (1) coronary flow reserve (CFR), the average value of Doppler- and thermodilution-derived CFR; (2) cardiovascular magnetic resonance (CMR) derived myocardial perfusion reserve index; and (3) CMR-derived microvascular obstruction. hMR correlated with IMR (rho = 0.41, p <0.0001). hMR had better diagnostic accuracy than IMR to predict CFR (area under curve [AUC] 0.82 vs 0.58, p <0.001, sensitivity and specificity 77% and 77% vs 51% and 71%) and myocardial perfusion reserve index (AUC 0.85 vs 0.72, p = 0.19, sensitivity and specificity 82% and 80% vs 64% and 75%). In patients with acute myocardial infarction, the AUCs of hMR and IMR at predicting extensive microvascular obstruction were 0.83 and 0.72, respectively (p = 0.22, sensitivity and specificity 78% and 74% vs 44% and 91%). We conclude that these 2 invasive indices of coronary microvascular resistance only correlate modestly and so cannot be considered equivalent. In our study, the correlation between independent invasive and noninvasive measurements of microvascular function was better with hMR than with IMR.