Johannes A. Moolman

Ischemic preconditioning: infarct size is a more reliable endpoint than functional recovery.

Abstract.The search for the mechanism of preconditioning-induced cardioprotection has been hampered by controversial results obtained by workers using different animal species, experimental models, protocols and endpoints. The aim of this study was to evaluate the role of the perfusion model (retrograde vs working), the infarct size and severity of ischaemia (regional vs global) as well as the endpoint (functional recovery vs infarct size) in preconditioning. The isolated perfused rat heart was preconditioned by 3 × 5 min global ischaemia, followed by different periods of regional or global ischaemia and reperfusion. Ischaemic preconditioning of working hearts resulted in increased functional recovery after 25–35 min global ischaemia, while retrogradely perfused hearts showed no significant improvement (except after 30 min global ischaemia). In addition, the percentage reduction in functional performance during reperfusion observed in the latter group was significantly less than in working hearts. Hearts were also subjected to regional ischaemia, perfused in either retrograde or working mode and infarct size determined. Regionally ischaemic working as well as retrogradely perfused hearts when preconditioned showed a significant increase in functional recovery after 35 min ischaemia only. In contrast to global ischaemia, the percentage recovery in mechanical performance of regionally ischaemic hearts was not affected by the mode of perfusion. Preconditioning of working hearts caused a significant reduction in infarct size after both 30 and 35 min ischaemia. However, preconditioned retrogradely perfused hearts showed a significant decline in infarct size after 35 min regional ischaemia only. In conclusion, the effect of the perfusion mode on functional recovery is dependent on the size and severity of ischaemia. It also affects the ischaemic time at which infarct size reduction by prior preconditioning occurs in the retrogradely perfused heart.

Comparison Between Ischaemic and Anisomycin-Induced Preconditioning: Role of p38 MAPK

To further evaluate the significance of p38 MAPK as trigger or mediator in ischaemic preconditioning, anisomycin and SB 203580 were used to manipulate its activation status. Special attention was given to the concentration of the drugs and protocols used.The isolated perfused rat heart, subjected to either 25 min global ischaemia or 35 min regional ischaemia, was used as experimental model. This was preceded by anisomycin (2 or 5 μM: 3 × 5 min; 5 μM: 5 min or 10 min; 5 μM: 10 min + 10 min washout or 20 μM: 20 min) or SB 203580 (2 μM: 3 × 5 min; before and during 3 × 5 min or 1 × 5 min ischaemic preconditioning; 10 min). Endpoints were functional recovery during reperfusion and infarct size.Anisomycin, regardless of the protocol, reduced infarct size, but did not improve functional recovery. In a number of experiments activation of JNK by anisomycin was blocked by SP 600125 (10 μM). SP 600125 had no effect on the anisomycin-induced reduction in infarct size. SB 203580 when administered for 10 min before sustained ischaemia, improved functional recovery and reduced infarct size. SB 203580 could not abolish the beneficial effects of a multi-cycle preconditioning protocol, but it significantly reduced the outcome of 1 × 5 min preconditioning. In all hearts improved functional recovery and reduction in infarct size were associated with attenuation of p38 MAPK activation during sustained ischaemia-reperfusion.The results indicate that activation of p38 MAPK acts as a trigger of preconditioning, while attenuation of its activation is a prerequisite for improved recovery and a reduction in infarct size.

No evidence for mediation of ischemic preconditioning by alpha1-adrenergic signal transduction pathway or protein kinase C in the isolated rat heart

SummaryThe purpose of this study was to elucidate the role of activation of the alpha1-adrenergic signal transduction pathway and of protein kinase C (PKC) in the mechanism of protection of functional recovery by ischemic preconditioning in the isolated perfused rat heart. After a stabilization period, nonpreconditioned and preconditioned isolated perfused rat hearts were subjected to sustained ischemia for 25 and 30 minutes of reperfusion. Preconditioning consisted of three episodes of 5 minutes of ischemia, interspersed with 5 minutes of reperfusion. The endpoint was postischemic functional recovery. The effectiveness of preconditioning in the presence of the alpha1-adrenergic blocker prazosin, the selective PKC blockers chelerythrine and bisindolylmaleimide (BIM), and the ability of repetitive alpha1-adrenergic activation to mimic preconditioning were compared with the appropriate nonpreconditioned and preconditioned control groups. Alpha1-adrenergic blockade with prazosin (3×10-7 M) during the preconditioning phase did not abolish the protective effect of preconditioning on functional recovery, and repeated intermittent alpha1-adrenergic activation with phenylephrine in different concentrations (1×10-8 to 3× 10-5 M) did not mimic the protective effect of preconditioning. PKC blockade with the selective PKC inhibitors, chelerythrine (10 μM) and BIM (4 μM), did not abolish the protective effect of preconditioning on functional recovery is isolated perfused rat hearts when given either during the preconditioning phase or shortly before the onset of sustained ischemia. The characteristic metabolic changes of preconditioning during sustained ischemia, namely, energy sparing as manifested in reduced accumulation of lactate, were also not abolished by preconditioning in the presence of selective PKC blockers. We conclude that no evidence could be found for alpha1-adrenergic or PKC activation in the mechanism of ischemic preconditioning in the isolated rat heart.

Preconditioning with a single short episode of global ischemia in the isolated working rat heart: Effect on structure, mechanical function, and energy metabolism for various durations of sustained global ischemia

SummaryPurpose Preconditioning in the setting of global ischemia, using functional recovery during reperfusion as the endpoint, has recently been demonstrated in the isolated perfused rat heart. It has been suggested that its beneficial actions have a metabolic basis. The isolated rat heart has not been fully characterized with respect to the metabolic, functional, and structural changes associated with this phenomenon in the setting of global ischemia. The purpose of this study was to determine (1) the time course of protection conferred by a single episode (5 minutes) of preconditioning; (2) changes in tissue high energy phosphates, lactate, and glycogen levels at different time intervals; and (3) morphological appearance of the heart at the end of ischemia as well as after reperfusion.Methods Isolated perfused working rat hearts were used. Preconditioning consisted of a single episode of 5 minutes of global ischemia and 15 minutes of reperfusion. Preconditioned and non-preconditioned hearts were subjected to global ischemia of 20–35 minutes duration. Functional recovery, energy metabolism (high energy phosphates, lactate, and glycogen), and structural appearance were studied at different stages.Results The functional recovery of the preconditioned hearts was significantly higher than in the corresponding nonpreconditioned group during reperfusion for all durations of ischemia longer than 25 minutes. The degree of protection observed was less than reported previously. A minor degree of energy sparing was reflected by differences in the rate of depletion of glycogen and accumulation of tissue lactate during the sustained episode of ischemia. Semiquantitative light microscopy evaluation revealed that ischemia-induced structural damage was less in the preconditioned hearts, both at the end of the sustained ischemic episode as well as after reperfusion.Conclusions A single episode of global ischemia successfully preconditions the isolated working rat heart. The protection elicited was demonstrated on a functional and structural level, and was accompanied by a small energy-sparing effect.

A comparison between ischemic preconditioning and anti-adrenergic interventions: cAMP, energy metabolism and functional recovery

ObjectivesThe postulate that ischemic preconditioning caused an attenuation in ischemia induced increases in tissue cAMP, and that this may pertain to the mechanism of ischemic preconditioning, was investigated in the isolated rat heart. A significant reduction in tissue cAMP in preconditioned hearts was observed for all time periods of global ischemia studied. The significance of this observation was evaluated by comparing the effect of antiadrenergic interventions on energy metabolism and post-ischemic functional recovery of both non-preconditioned and preconditioned hearts.MethodsThe isolated perfused rat heart was used as experimental model. Six groups were studied: Non-preconditioned rat hearts: i) untreated controls (Non-PC), ii) reserpinised (Non-PC Res), iii) propranolol treated (10−7M) (Non-PC Prop); Preconditioned rat hearts: iv) preconditioned controls (PC), v) reserpinised (PC Res) and vi) propranolol (10−7M) treated (PC Prop).ResultsAfter 25 min global ischemia the concentration of cAMP was increased by 79.6% in the Non-PC group. This increase was attenuated in all of the treated groups, although in varying degrees. Energy utilization in these hearts also differed markedly between the groups. Functional recovery was however similar in all Non-PC and PC treated groups and significantly superior to that of Non-PC control hearts. Prior reserpinisation mimicked the protective effect of preconditioning on energy metabolism and functional recovery. To determine the significance of attenuation of the increase in cAMP in the protection conferred by preconditioning, hearts were pretreated with forskolin (10−6M). This caused an accumulation of tissue cAMP in preconditioned hearts to similar absolute values as seen in untreated non-preconditioned hearts during 25 min global ischemia. However, the percentage increase in forskolin-pretreated preconditioned hearts during sustained, ischemia was only 50% vs. 71% in non-preconditioned hearts treated with forskolin, confirming an attenuated β-response induced by preconditioning. Forskolin treatment of preconditioned hearts did not abolish the protective effect.ConclusionsThe findings suggest that the protection against ischemic damage conferred by preconditioning is associated with an attenuated β-adrenergic response. However, whether the changes in cAMP occurring during sustained global ischemia is the cause or consequence of the elicited protection, remains to be established.

An unusual presentation of an anomalous left coronary artery arising from the pulmonary artery (ALCAPA) in an adult: anterior papillary muscle rupture causing severe mitral regurgitation.

We describe a 29‐year‐old male, previously in good health, with no history of angina pectoris and no risk factors for ischemic heart disease presenting with biventricular failure and severe mitral valve regurgitation. There were no signs or serological test results to suggest infective endocarditis. Transthoracic echocardiography (TTE) revealed severe anterior mitral valve prolapse secondary to papillary muscle rupture, severe mitral valve regurgitation, as well as an anterior myocardial wall hypokinesis. Parasternal short‐axis view showed an anomalous left coronary artery arising from the pulmonary artery (ALCAPA), which was confirmed on coronary angiography. This is an unusual presentation of ALCAPA in an adult.

Continuing Medical Education Program in Echocardiography

Article Title: An Unusual Presentation of an Anomalous Left Coronary Artery Arising from the Pulmonary Artery (ALCAPA) in an Adult: Anterior Papillary Muscle Rupture Causing Severe Mitral Regurgitation

Bilateral ostial coronary stenosis and rheumatic aortic valve stenosis.

A 49‐year‐old patient presented with angina pectoris and clinical findings of aortic valve stenosis and regurgitation. Rheumatic aortic valve stenosis and regurgitation was diagnosed on echocardiography. Coronary angiography findings showed severe calcification in the aorta root with right coronary ostial occlusion, and were suggestive of left main ostial stenosis and proximal main stem stenosis, which was confirmed on CT angiography. Curvilinear calcification of the aorta was present on CT angiography. The findings suggested syphilitic aortitis. Syphilis serology was positive (RPR titre 1/16). The angina was caused by severe coronary ostial disease likely due to syphilitic aortitis and exacerbated by the rheumatic aortic valve stenosis and regurgitation.