P2272Determinants of left ventricular ATP availability measured in vivo and ex vivo in patients with severe aortic stenosis: correlation of creatine kinase activity with LVEF and ATP diffusion distance

Introduction

The transition to systolic failure in severe aortic stenosis (AS) increases mortality. There are currently no reliable markers of transition, and the guideline LVEF <50% threshold for intervention in asymptomatic severe AS does not capture all subjects at increased risk. In animal models, reduced ATP delivery capacity through creatine kinase (CK) is important, with modest increases in CK capacity conferring cardioprotection. ATP may also diffuse (independent of CK) from mitochondria to the contractile site. We have performed the first human study to test whether ATP diffusion distance relates to CK activity and whether CK activity is reduced in low LVEF severe AS.

Methods

19 patients with severe AS, LVEF ≥55% (AS-pEF, mean±SD LVEF 63±5%, mean gradient 48±14 mmHg) and 10 with severe AS, LVEF <55% (AS-rEF, LVEF 42±8%, mean gradient 32±11) underwent 31P-MRS for CK rate constant (kf) and phosphocreatine/ATP (PCr/ATP) ratio, and MRI for LV volumes. LV biopsies were taken during AVR and analysed for CK total activity, CK isoforms, total creatine, and citrate synthase (CS) activity. 9 biopsies also underwent serial block face scanning electron microscopy and mitochondria-sarcomere 3D distance distributions were plotted. Results were compared to 24 controls (LVEF 61±4%), of which 4 had LV biopsy (3 severe MS, 1 LA myxoma, MS-pEF). Surgical patients had flow-limiting atheroma excluded with invasive angiography and prior myocardial infarction excluded with late gadolinium enhancement MRI.

Results

When compared to controls, both CK total activity and CS activity were lower in AS-pEF (by 27% and 23% respectively, both p<0.05, Panels A-B). Although PCr/ATP reduced in AS-pEF (by 20%, p<0.001, panel C), kf (panel D) and CK flux estimated by kf × total creatine were not different. CK-MB expression reduced in AS-pEF (19 vs 27% of total CK, p=0.003), reflecting compensatory increases in CK-MM (p=0.26) and CK-BB (p=0.18) in the face of reduced CK activity.

AS-rEF was associated with further reduction in both CK and CS activities (by 32% and 22% respectively, both p<0.05, Panels A-B), but no differences in PCr/ATP, CK kf or relative CK isozyme expression were seen. There were no significant between-group differences in total creatine (Panel E). Overall this suggests that CK reserve and oxidative capacity potentially reduce in pressure overload, with further falls commensurate with systolic dysfunction.

When median mitochondria-sarcomere ATP diffusion distances were plotted against CK total activity a strong positive correlation was observed (r=0.86, p=0.003, Panel F). This suggests a compensatory reduction in diffusion distance develops when CK activity falls.

Conclusions

Transition to failure in severe AS is associated with lower oxidative capacity and maximal ATP delivery capacity through CK. Despite compensatory falls in ATP diffusion distance and altered CK isozyme expression, these changes may underlie susceptibility to EF decline in AS.

Acknowledgement/Funding

British Heart Foundation Clinical Research Training Fellowship (FS/15/80/31803) and Programme Grant (RG/18/12/34040).

P1611Non-invasive predictors of LV biopsy-obtained creatine kinase activity in patients with non-failing and failing myocardial hypertrophy

Introduction

Myocardial creatine kinase (CK) activity represents an important metabolic reserve: it correlates closely with contractile reserve and post-ischaemic function, keeps cytosolic [ADP] low, and optimises the free energy for ATP hydrolysis. It may also contribute to the transition to failure in the heart hypertrophied by chronic haemodynamic overload; modest up-regulation has been shown to be cardio-protective.

Total CK activity measurement requires chemical freeze-and-extract methods, which destroy tissue, precluding repeated measures. To date, non-invasive assessments of human myocardial CK flux (calculated as kf × [PCr], where kf is the pseudo-first-order forward rate constant measured by 31P-magnetic resonance spectroscopy (MRS) have not assessed creatine content or total CK activity. Thus we aimed to validate kf measurement against total CK activity and investigate predictors of CK activity.

Methods

39 subjects (median age 71, range 43–84) undergoing clinically indicated cardiac surgery had CK total activity measured from LV biopsy. 31 had severe AS (10 with impaired LVEF); 2 had severe primary MR; 5 had severe mitral stenosis (2 with impaired LVEF) and 1 had an LA mass. 35 of 39 contributed triplicate datasets: CK total activity, kf (31P-MRS TRiST sequence at 3T) and LV volumes (cine-MRI, 3T Siemens). 27 had severe AS (8 with impaired LVEF); other groups were the same. Exclusion criteria were prior myocardial infarction and flow-limiting coronary disease. Flash-frozen LV biopsies obtained within 15 min of cardiopulmonary bypass were analysed for CK total activity, total creatine, and citrate synthase (CS) activity (a marker of oxidative phosphorylation capacity).

Results

Multiple, novel correlations were observed between CK total activity (IU/mg protein) and CS activity (r=0.87, p=9e-13), total creatine (r=0.59, p=8e-5), kf (r=0.42, p=0.013), total creatine × kf (r=0.64, p=4e-5), LVESVi (r=−0.52, p=8e-4), LVEF (r=0.48, p=0.002) and LVMi (r=−0.42, p=0.009) (Panels A-E) (LVEDVi and non-indexed counterparts were also significant correlates.) The most predictive linear regression model incorporating elements of the CK rate equation included total creatine (nmol/mg protein), kf (/s), and kf × LVESVi (ml/m2) (adjusted R2=0.56, beta=0.426, 0.618, −1.968 and p=0.001, 5e-5, 0.003 respectively, Panel F).

Figure 1

Conclusions

These results are the first evidence of agreement between non-invasive estimates of human cardiac CK activity (kf) and freeze-extracted chemical methods. The key original finding is that it is feasible to attempt to predict CK capacity in vivo by using a combination of techniques (creatine by 1H MRS, CK kf by 31P-MRS and LVESVi by cine imaging). The key insight is that CK capacity is best estimated not simply from what the rate equation would predict (creatine and kf), but that other factors relating to failing contractility reduce CK activity independently from creatine content and enzyme kf.

Acknowledgement/Funding

British Heart Foundation Clinical Research Training Fellowship (FS/15/80/31803) and Programme Grant (RG/18/12/34040).

The effect of heptanol on the electrical and contractile function of the isolated, perfused rabbit heart

Changes in cardiac gap junction expression, such as those following myocardial infarction and produced in connexin knockout mice, are associated with a predisposition to arrhythmias. The present experiments investigated the effects of heptanol, a reversible gap junction inhibitor, on isolated Langendorff-perfused rabbit hearts. The introduction and withdrawal of heptanol inhibited both pressure generation and electrical conduction. These effects were completely reversible. Possible mechanisms for these findings were investigated through measurement of the concentration dependence of heptanol's effects upon conduction velocity and repolarization duration. Low concentrations of heptanol (less than 0.3 mM) caused small but significant increases in the delay between the stimulus (delivered to the basal septum) artefact and local activation of the left ventricle, as measured from bipolar electrogram (BEG) recordings. There was a steep increase in the latency between stimulus and left-ventricular activation at concentrations of heptanol above 0.3 mM. These findings are explicable by earlier reports of heptanol actions on gap junctions in vitro and modelling studies of the effects of reduced gap junction conductance on conduction velocity. Heptanol decreased repolarization duration, measured from the activation recovery interval (ARI) of BEGs, and monophasic action potential duration at 70% repolarization (MAPD70). Heptanol also reduced left-ventricular developed pressure (LVDP), and the maximum rates of contraction and relaxation of the left ventricle; these effects were concentration dependent and reversible. However, changes in ARIs, LVDP and the maximum rates of change of pressure lacked the steep response to 0.3-1.0 mM heptanol shown by the latency. These other effects are therefore likely to be mediated by cellular targets other than gap junctions. Perfusion of hearts with heptanol was also associated with a high incidence of arrhythmias. During premature stimulation protocols arrhythmias could be induced in hearts perfused with 0.1-0.3 mM heptanol but not at higher concentrations. This suggests that there is a critical range of slowed conduction that permits the development of re-entrant arrhythmias in the normal heart, although the effects of heptanol on repolarization duration may also contribute to its pro-arrhythmic activity.

Successful thrombolysis for massive pulmonary embolism after pulmonary resection

We report the successful use of thrombolysis for acute massive pulmonary embolism 2 days after right lower lobectomy for bronchial adenocarcinoma. Pulmonary angiography revealed extensive clot unsuitable for surgical embolectomy. A bolus infusion of recombinant tissue plasminogen activator produced an immediate improvement in the patient's hemodynamic state. There was substantial blood loss requiring the transfusion of 21 units of blood over the postoperative period. The patient made a successful recovery and remained well at 1 year.

Quality of life after transthoracic endoscopic sympathectomy for upper limb hyperhidrosis

OBJECTIVE

To assess the outcome after transthoracic endoscopic sympathectomy (TES) for upper limb hyperhidrosis.

DESIGN

Prospective cohort study.

SETTING

District general hospital.

SUBJECTS

Consecutive patients undergoing TES for upper limb hyperhidrosis over a fifteen month period.

INTERVENTIONS

One-stage bilateral TES.

MAIN OUTCOME MEASURES

Change in quality of life as shown by the Short Form-36 health assessment questionnaire.

RESULTS

Sixteen patients (11 women and 5 men, median age 26 years) underwent operation without complications. At median follow-up of 6.2 months, symptomatic improvement was found in 26 of 32 limbs treated (82%). Truncal compensatory hyperhidrosis was reported by 13 patients but was severe in only three. There were significant improvements in social function (p = 0.01) and mental health (p = 0.025) as assessed by the SF-36.

CONCLUSION

Despite a high incidence of compensatory hyperhidrosis, TES improved both the symptoms and overall quality of life in patients with upper limb hyperhidrosis.

Modification to dissecting/ligature forceps

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