Iron Deposition following Chronic Myocardial Infarction as a Substrate for Cardiac Electrical Anomalies: Initial Findings in a Canine Model

Purpose: Iron deposition has been shown to occur following myocardial infarction (MI). We investigated whether such focal iron deposition within chronic MI lead to electrical anomalies. Methods: Two groups of dogs (ex-vivo (n = 12) and in-vivo (n = 10)) were studied at 16 weeks post MI. Hearts of animals from ex-vivo group were explanted and sectioned into infarcted and non-infarcted segments. Impedance spectroscopy was used to derive electrical permittivity () and conductivity (). Mass spectrometry was used to classify and characterize tissue sections with (IRON+) and without (IRON-) iron. Animals from in-vivo group underwent cardiac magnetic resonance imaging (CMR) for estimation of scar volume (late-gadolinium enhancement, LGE) and iron deposition (T2*) relative to left-ventricular volume. 24-hour electrocardiogram recordings were obtained and used to examine Heart Rate (HR), QT interval (QT), QT corrected for HR (QTc) and QTc dispersion (QTcd). In a fraction of these animals (n = 5), ultra-high resolution electroanatomical mapping (EAM) was performed, co-registered with LGE and T2* CMR and were used to characterize the spatial locations of isolated late potentials (ILPs). Results: Compared to IRON- sections, IRON+ sections had higher, but no difference in. A linear relationship was found between iron content and (p1.5%)) with similar scar volumes (7.28%±1.02% (Iron (1.5%)), p = 0.51) but markedly different iron volumes (1.12%±0.64% (Iron (1.5%)), p = 0.02), QT and QTc were elevated and QTcd was decreased in the group with the higher iron volume during the day, night and 24-hour period (p<0.05). EAMs co-registered with CMR images showed a greater tendency for ILPs to emerge from scar regions with iron versus without iron. Conclusion: The electrical behavior of infarcted hearts with iron appears to be different from those without iron. Iron within infarcted zones may evolve as an arrhythmogenic substrate in the post MI period

Overdrive pacing of early ischemic ventricular tachycardia: evidence for both reentry and triggered activity

To access publisher full text version of this article. Please click on the hyperlink in Additional Links fieldEntrainment can be a useful method to identify reentry as a mechanism of ventricular tachycardia (VT). In this study, we evaluated the effect of gradually decreasing cycle lengths of overdrive pacing for stable VT induced in a canine model 1-3 h after coronary occlusion. Intact dogs underwent anterior descending coronary artery occlusion after instrumentation of the risk zone with 21 multipolar plunge needles, each recording 6 bipolar electrograms. Overdrive pacing was attempted if the animals had sustained hemodynamically stable VT, looking for evidence of entrainment. Subsequent three-dimensional mapping determined the mechanism of VT. Fifteen of the 21 dogs studied demonstrated entrainment with overdrive pacing by progressive QRS fusion alone (1), the first nonpaced QRS entrained to the paced cycle length only (7), or both (7). Five of these 15 dogs also had postpacing acceleration of the VT at a subsequent faster pacing cycle length. The mechanism of acceleration in four was a change to a VT with a focal origin. The prepacing mechanism in all 15 dogs was subsequently mapped to reentry. Regarding the six VTs, which demonstrated no evidence for entrainment, the site of earliest activity was mapped to a focal origin in all. These data showing entrainment of inducible reentrant VTs and lack of such for focal VTs support that the focal VTs seen in this study are unlikely the result of microreentry but possibly a mechanism as triggered activity

Confocal laser scanning microscope, raman microscopy and western blotting to evaluate inflammatory response after myocardial infarction

Cardiac muscle necrosis is associated with inflammatory cascade that clears the infarct from dead cells and matrix debris, and then replaces the damaged tissue with scar, through three overlapping phases: the inflammatory phase, the proliferative phase and the maturation phase. Western blotting, laser confocal microscopy, Raman microscopy are valuable tools for studying the inflammatory response following myocardial infarction both humoral and cellular phase, allowing the identification and semiquantitative analysis of proteins produced during the inflammatory cascade activation and the topographical distribution and expression of proteins and cells involved in myocardial inflammation. Confocal laser scanning microscopy (CLSM) is a relatively new technique for microscopic imaging, that allows greater resolution, optical sectioning of the sample and three-dimensional reconstruction of the same sample. Western blotting used to detect the presence of a specific protein with antibody-antigen interaction in the midst of a complex protein mixture extracted from cells, produced semi-quantitative data quite easy to interpret. Confocal Raman microscopy combines the three-dimensional optical resolution of confocal microscopy and the sensitivity to molecular vibrations, which characterizes Raman spectroscopy. The combined use of western blotting and confocal microscope allows detecting the presence of proteins in the sample and trying to observe the exact location within the tissue, or the topographical distribution of the same. Once demonstrated the presence of proteins (cytokines, chemokines, etc.) is important to know the topographical distribution, obtaining in this way additional information regarding the extension of the inflammatory process in function of the time stayed from the time of myocardial infarction. These methods may be useful to study and define the expression of a wide range of inflammatory mediators at several different timepoints providing a more detailed analysis of the time course of the infarct

147. Carbon monoxide

Carbon monoxide (CO) is an odourless and colourless gas produced by incomplete burning of carbon-based fuels. CO is also a constituent of tobacco smoke. Exposure to CO is common in many occupational areas, including those associated with vehicle exhaust. CO is an important industrial gas used in the production of chemical intermediates. CO is formed endogenously and acts as a signalling substance in the neuronal system. The main mechanism behind CO-induced toxicity is the binding of CO to haemoglobin in the blood, resulting in carboxyhaemoglobin (COHb) formation, reduced oxygen transport capacity of the blood and hypoxia. The relation between CO in air and COHb is well known and can be calculated using the Coburn-Forster-Kane (CFK) equation. Endogenous CO formation leads to a background COHb of 0.4– 0.7%. Non-smokers typically have COHb levels up to 2% whereas smokers may have COHb levels up to 10% immediately after smoking. The effects seen in acute CO poisoning cover a wide range, from mild symptoms, like shortness of breath during exercise or occasional headache at COHb 20%, to more severe ones like headache, dizziness, disturbed judgement, dimness of vision, confusion, unconsciousness, intermittent convulsion and respiratory failure at COHb above 30%. COHb levels of 50–60% are often lethal. Even COHb levels of 20% may be lethal for patients with coronary artery disease. The foetus is at higher risk than the healthy adult because of higher CO haemoglobin affinity. From controlled human and animal exposure studies the adverse effects of concern are impaired exercise performance, i.e. decreased maximal aerobic capacity in healthy volunteers (lowest observed adverse effect level (LOAEL) COHb 4.3%), increased myocardial ischaemia in patients with coronary artery disease (LOAEL COHb 2.4%), and persistent changes in the developing auditory system of the rat (LOAEL 12 ppm, corresponding to COHb 1.8% and 2.0% assuming 8 hours constant exposure at rest and heavy work, respectively). It was not possible to identify any no observed adverse effect levels (NOAELs) in these studies. No or limited data were found regarding genotoxicity, carcinogenicity, irritation and sensitisation. Combined exposure to CO and dihalomethanes causes increased formation of COHb. Combined exposure to CO and noise may potentiate noise-induced hearing loss

Myoblast transplantation and adenoviral VEGF-C transfer in porcine model of coronary artery disease

Heart failure is a common and highly challenging medical disorder. The progressive increase of elderly population is expected to further reflect in heart failure incidence. Recent progress in cell transplantation therapy has provided a conceptual alternative for treatment of heart failure. Despite improved medical treatment and operative possibilities, end-stage coronary artery disease present a great medical challenge. It has been estimated that therapeutic angiogenesis would be the next major advance in the treatment of ischaemic heart disease. Gene transfer to augment neovascularization could be beneficial for such patients. We employed a porcine model to evaluate the angiogenic effect of vascular endothelial growth factor (VEGF)-C gene transfer. Ameroid-generated myocardial ischemia was produced and adenovirus encoding (ad)VEGF-C or β-galactosidase (LacZ) gene therapy was given intramyocardially during progressive coronary stenosis. Angiography, positron emission tomography (PET), single photon emission computed tomography (SPECT) and histology evidenced beneficial affects of the adVEGF-C gene transfer compared to adLacZ. The myocardial deterioration during progressive coronary stenosis seen in the control group was restrained in the treatment group. We observed an uneven occlusion rate of the coronary vessels with Ameroid constrictor. We developed a simple methodological improvement of Ameroid model by ligating of the Ameroid–stenosed coronary vessel. Improvement of the model was seen by a more reliable occlusion rate of the vessel concerned and a formation of a rather constant myocardial infarction. We assessed the spontaneous healing of the left ventricle (LV) in this new model by SPECT, PET, MRI, and angiography. Significant spontaneous improvement of myocardial perfusion and function was seen as well as diminishment of scar volume. Histologically more microvessels were seen in the border area of the lesion. Double staining of the myocytes in mitosis indicated more cardiomyocyte regeneration at the remote area of the lesion. The potential of autologous myoblast transplantation after ischaemia and infarction of porcine heart was evaluated. After ligation of stenosed coronary artery, autologous myoblast transplantation or control medium was directly injected into the myocardium at the lesion area. Assessed by MRI, improvement of diastolic function was seen in the myoblast-transplanted animals, but not in the control animals. Systolic function remained unchanged in both groups.Pitkälle edennyt sydämen vajaatoiminta on hyvin vaikeahoitoinen tauti. Vanhuusväestön suhteellinen lisääntyminen lisää taudin merkittävyyttä ja sydänlihaksen solusiirtoja on ehdotettu uudeksi vaihtoehtoiseksi hoitomuodoksi. Huolimatta parantuneesta lääkehoidosta ja kehittyneistä pallolaajennus- ja leikkausmenetelmistä, loppuvaiheen sepelvaltimotauti on lääketieteellinen haaste. On arvioitu, että geenihoito olisi seuraava merkittävä hoitomenetelmä vaikeassa sepelvaltimotaudissa. Kokeilimme koe-eläimellä adenoviruksella siirretyn VEGF-C-kasvutekijän vaikutusta uudissuonten kehittymiseen. Sialle asetettiin hitaasti elimistössä turpoava rengastin sepelvaltimon tyveen. Kolme viikkoa rengastimen asettamisesta sioille siirrettiin VEGF-C-hoitogeeni tai kontrolligeeni hapenpuutetta kärsivälle sydänlihaksen alueelle. Sydänlihaksen verenkierto tutkittiin verisuonten varjoainekuvauksilla, sekä PET- ja SPECT kuvauksin. Lopuksi tutkittiin kudosnäytteet. Hoitoryhmällä havaittiin merkittävästi enemmän uudissuonia ja rengastimen aiheuttama sydänlihaksen toiminnanvajaus ei edennyt, toisin kuin kontrolligeeniä saaneilla eläimillä. Kyseinen rengastin on käytetyin laite sepelvaltimotaudin mallintamisessa isoeläimellä. Havaitsimme kuitenkin ahtautuma-asteen vaihtelevan yksilöiden välillä. Kehitimme yksinkertaisen menetelmän, jossa kiristimen asetuksen yhteydessä jätettiin suonen ympärille sulkulanka. Langalla varmistetaan suonen tukkeutuminen kolmen viikon kohdalla, kun luontainen uudissuonimuodostus on kehittynyt sydämen suojaksi. Menetelmä osoittautui toimivaksi ja kuvasimme uuden mallin luontaisen paranemistaipumuksen magneetti- SPECT ja PET- kuvauksin sekä verisuonten varjoainekuvauksilla. Kudostutkimuksissa havaitsimme immunohistokemiallisin kaksoisvärjäyksin sydänlihassolujen tumien jakautumista luontaisen paranemisen merkkinä. Aiemmin on uskottu, että sydänlihassolujen jakaantumista ei tapahdu enää hyvin varhaisen lapsuuden jälkeen. Myoblastit ovat luurankolihassolujen esiasteita, joista voi kehittyä uusia lihassoluja. Kokeilimme eläimestä itsestään kerättyjen myoblastien vaikutusta sydänlihaskuolion ja -hapenpuutteen hoidossa. Sioille luotiin pienet sydäninfarktit ja hapenpuutteesta kärsivä alue. Jokaisesta eläimestä kerättiin lihasnäytteet, joista myoblastit eristettiin ja solujen lukumäärää lisättiin miljooniin laboratoriossa kasvattamalla. Siat saivat sokkoutetusti joko myoblasti-solusiirron tai kontrolliliuosta sydämen vaurioalueelle. Sydänlihaksen toiminta ja -hapensaanti arvioitiin magneetti- ja sepelvaltimoiden varjoainekuvauksin. Myoblasteja saaneilla eläimillä sydämen diastolinen toiminta oli parempi kuin kontrolliryhmällä. Tämä tutkimussarja tukee sydämen solu- ja geenihoitojen vaikuttavuutta sydäntautien hoidossa

Aerobic interval training partly reverse contractile dysfunction and impaired Ca2+ handling in atrial myocytes from rats with post infarction heart failure

Background: There is limited knowledge about atrial myocyte Ca2+ handling in the failing hearts. The aim of this study was to examine atrial myocyte contractile function and Ca2+ handling in rats with post-infarction heart failure (HF) and to examine whether aerobic interval training could reverse a potential dysfunction. Methods and results: Post-infarction HF was induced in Sprague Dawley rats by ligation of the left descending coronary artery. Atrial myocyte shortening was depressed (p<0.01) and time to relaxation was prolonged (p<0.01) in sedentary HF-rats compared to healthy controls. This was associated with decreased Ca2+ amplitude, decreased SR Ca2+ content, and slower Ca2+ transient decay. Atrial myocytes from HF-rats had reduced sarcoplasmic reticulum Ca2+ ATPase activity, increased Na+/Ca2+-exchanger activity and increased diastolic Ca2+ leak through ryanodine receptors. High intensity aerobic interval training in HF-rats restored atrial myocyte contractile function and reversed changes in atrial Ca2+ handling in HF. Conclusion: Post infarction HF in rats causes profound impairment in atrial myocyte contractile function and Ca2+ handling. The observed dysfunction in atrial myocytes was partly reversed after aerobic interval training.© 2013 Johnsen et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

Small Conductance Calcium-Activated Potassium Current is Activated During Hypokalemia and Masks Short Term Cardiac Memory Induced by Ventricular Pacing.

Background: Hypokalemia increases the vulnerability to ventricular fibrillation (VF). We hypothesize that the apamin-sensitive small conductance calcium-activated potassium current (IKAS) is activated during hypokalemia and that IKAS blockade is proarrhythmic. Methods and Results: Optical mapping was performed in 23 Langendorff perfused rabbit ventricles with atrioventricular block and either right ventricular (RV) or left ventricular (LV) pacing during normokalemia or hypokalemia. Apamin prolonged the action potential duration (APD) measured to 80% repolarization (APD80) by 26 ms [95% confidence interval, CI, 14–37] during normokalemia and by 54 ms [CI, 40 to 68] during hypokalemia (P=0.01) at 1000 ms pacing cycle length (PCL). In hypokalemic ventricles, apamin increased the maximal slope of APD restitution, the PCL threshold of APD alternans, the PCL for wavebreak induction and the area of spatially discordant APD alternans. Apamin significantly facilitated the induction of sustained VF (from 3/9 hearts to 9/9 hearts, P=0.009). Short term cardiac memory was assessed by the slope of APD80 versus activation time. The slope increased from 0.01 [CI, −0.09 to 0.12] at baseline to 0.34 [CI, 0.23 to 0.44] after apamin (P<0.001) during RV pacing, and from 0.07 [CI, −0.05 to 0.20] to 0.54 [CI, 0.06 to 1.03] after apamin infusion (P=0.045) during LV pacing. Patch-clamp studies confirmed increased IKASin isolated rabbit ventricular myocytes during hypokalemia (P=0.038). Conclusions: Hypokalemia activates IKAS to shorten APD and maintain repolarization reserve at late activation sites during ventricular pacing. IKAS blockade prominently lengthens the APD at late activation sites and facilitates VF induction