* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Effect of experimental coronary sinus ligation on myocardial
Survey
Document related concepts
Remote ischemic conditioning wikipedia , lookup
Heart failure wikipedia , lookup
Saturated fat and cardiovascular disease wikipedia , lookup
Cardiac contractility modulation wikipedia , lookup
Cardiovascular disease wikipedia , lookup
Hypertrophic cardiomyopathy wikipedia , lookup
Quantium Medical Cardiac Output wikipedia , lookup
Echocardiography wikipedia , lookup
Cardiac surgery wikipedia , lookup
Drug-eluting stent wikipedia , lookup
History of invasive and interventional cardiology wikipedia , lookup
Arrhythmogenic right ventricular dysplasia wikipedia , lookup
Electrocardiography wikipedia , lookup
Transcript
BASIC SCIENCE Europace (2016) 18, 1897–1904 doi:10.1093/europace/euv431 Effect of experimental coronary sinus ligation on myocardial structure and function in the presence or absence of structural heart disease: an insight for the interventional electrophysiologist Osama Ali Diab 1*, Mohammed Said Amer 2, and Rania Ahmed Salah El-Din 3 1 Faculty of Medicine, Department of Cardiology, Ain Shams University, Cairo, Egypt; 2Faculty of Veterinary Medicine, Department of Surgery, Cairo University, Cairo, Egypt; and Department of Anatomy, Ain Shams University, Cairo, Egypt 3 Received 3 October 2015; accepted after revision 23 November 2015; online publish-ahead-of-print 5 February 2016 Aims To study the effect of coronary sinus (CS) occlusion on normal hearts and hearts with structural disease. ..................................................................................................................................................................................... Methods We included 32 dogs, divided into 4 groups: (1) CS ligation (CSL): subjected to CSL; (2) control group: no intervention; and results (3) MI-CSL group: subjected to myocardial infarction (MI) induction followed by CSL after 1 week; and (4) MI-control group: subjected to MI induction, then open thoracotomy after 1 week without CSL. Electrocardiography, echocardiography, histopathology, and immunohistochemistry were done before and after CSL. In CSL group, there were no significant electrocardiographic or echocardiographic changes after CSL, although there was interstitial oedema that decreased after 1 week with the appearance of Thebesian vessels and positive staining for vascular endothelial growth factor. In MI-CSL group, there was significant increase in left ventricular (LV) end-systolic diameter (P ¼ 02), decrease in LV fractional shortening (P ¼ 0.0001), and LV ejection fraction (P ¼ 0.002) in comparison with MI-control group, associated with severe myocardial degeneration. ..................................................................................................................................................................................... Conclusion Acute CS occlusion could be compensated in normal hearts, but may be detrimental in the presence of structural heart disease. ----------------------------------------------------------------------------------------------------------------------------------------------------------Keywords Coronary sinus † Coronary sinus occlusion † Thebesian vessels Introduction Coronary sinus (CS) dissection and endothelial injury, with subsequent thrombosis, may occur during procedures that use access to the right atrium, such as insertion of central venous lines,1 left ventricular (LV) lead placement during cardiac resynchronization therapy (CRT), or endocarditis affecting the LV lead.2 Radiofrequency ablation of accessory pathway using CS approach3 may result in CS occlusion. Coronary sinus can be a target for ablation in some cases of persistent atrial fibrillation (AF) and vein of Marshall tachycardia.4 The heart is drained by three separate systems: the coronary sinus, the anterior cardiac veins, and the Thebesian veins. The coronary sinus system drains 70 –80% of the total cardiac venous return.5 Since there are many anastomotic connections between the three venous systems, the Thebesian veins that drain into all four chambers can drain up to 50% of cardiac venous return in full capacity.6 Since the flow in Thebesian veins is bidirectional, they are better to refer to as ‘Thebesian vessels’. There are two distinct forms of Thebesian vessels. The first type is a large diameter arterioluminal system that drains blood directly from the arteries or capillary bed into the ventricles bypassing the capillary beds, which is common in the right ventricle. The second type is a smaller-diameter thin-walled venoluminal system that shunts blood from coronary veins or capillary bed into the ventricular cavities bypassing the coronary sinus.5,6 A unique form of Thebesian vessels is ‘Thebesian sinusoids’. These are irregular spaces, channels, or lacunae, formed of a single layer of endothelium, larger than capillaries in diameter, located in the subendocardial region.7 Clinical course of CS obstruction remains unpredictable. Theoretically, no deleterious effects would be expected due to the presence of an alternative venous drainage. However, cases of CS obstruction with massive haemorrhagic necrosis, pericardial * Corresponding author. Tel: +2 0109 0555025; fax: +2 02 24820416. E-mail address: [email protected] Published on behalf of the European Society of Cardiology. All rights reserved. & The Author 2016. For permissions please email: [email protected]. 1898 O. Ali Diab et al. What’s new? 32 dogs † The current study provides an insight to the interventional electrophysiologist during techniques reported to be complicated with coronary sinus (CS) occlusion or possibly associated with this risk, the rarity of which should not hinder highlighting its consequences that are still hazy among the scientific community due to lack of follow-up studies. † We are the first to thoroughly evaluate the effect of CS occlusion by electrocardiogram, echocardiography, histopathology, and immunohistochemistry, and to add a group with structural heart disease. † We demonstrated that CS obstruction alters myocardial structure in both normal and diseased hearts, being more severe in the later. This could be compensated by normal hearts with normal physiologic reserve, but not in diseased hearts. † Based on our results, conservative treatment is recommended if CS occlusion occurred in normal hearts, while CS stenting may be considered in the case of structural heart disease. Methods Thirty-two apparently healthy mongrel dogs weighing 15 – 20 kg with the age of 2 – 5 years of both sexes were used. The animals were vaccinated and guarded from internal and external parasites. All animals were housed individually in metal cages and were fed once daily with a standard balanced diet. Control group N=4 CS ligation No intervention LAD ligation 1 week ECG Echocardiography Morphology IHC Morphology IHC CS ligation MI-CSL group N = 10 MI-control group N=8 LAD ligation 1 week Thoracotomy ECG Echocardiography Morphology IHC Figure 1 Study design. CSL, coronary sinus ligation; MI, myocardial infarction; LAD, left anterior descending coronary artery. – tamponade, LV dysfunction, and even sudden cardiac death have been reported in the literature.1,8 Currently, little is known regarding the pathologic sequences of CS occlusion in the setting of normal hearts or in the presence of structural heart disease. With the increasing use of CS access in cardiovascular interventions, it is useful to predict the consequences of incidental CS occlusion. CSL group N = 10 Myocardial infarction-control group (MI-control group): Included eight dogs subjected to LAD ligation, followed by open thoracotomy without CSL after 1 week under the same protocol of general anaesthesia used in MI-CSL group. Electrocardiogram and echocardiography were done before and after MI induction, and after open thoracotomy prior to animal sacrifice. Animals were sacrificed at 24 h (3 dogs) and 1 week (5 dogs) after open thoracotomy. Electrocardiographic assessment Twelve-lead surface ECG was done before and after experimental procedure (prior to animal sacrifice) at 10 mm/mV and 25 mm/s. RR interval, QRS complex duration, QT and QTc intervals were measured. QT interval was measured in lead II by tangent method from the average of three cardiac cycles and was corrected to RR interval according to Frip dericia’s formula (QTc ¼ QT/3 RR),9 which was preferred to Bazett’s formula in dogs.10 Apart from non-specific T wave changes and premature beats, any ST segment shift ≥1 mm was considered significant for myocardial ischaemia. Sustained or non-sustained arrhythmias, or conduction defects following CSL were assessed. Study design Animals were allocated to four groups as follows (Figure 1): – – – Coronary sinus ligation group (CSL group): Included 10 dogs with normal hearts subjected to CSL through open thoracotomy. Animals were sacrificed at 24 h (5 dogs) and 1 week (5 dogs) after the procedure. Electrocardiographic (ECG) and echocardiographic data before and after CSL were compared with each other. Morphologic examination and immunohistochemical (IHC) staining of this group were compared with that of the control group. Control group: Including four healthy dogs with no intervention, which were sacrificed for morphologic and IHC examination. Myocardial infarction-CS ligation group (MI-CSL group): Included 10 dogs with structural heart disease in the form of induced myocardial infarction (MI) through ligation of left anterior descending coronary artery (LAD) after the first diagonal branch. Coronary sinus ligation was done 7 days after MI induction. Surviving animals (9 dogs) were sacrificed at 24 h (4 dogs) and 1 week (5 dogs) after CSL. Due to possible remodelling with time, ECG and echocardiographic data before and after CSL were compared with that of a control-sham operated group (MI-control group). Morphologic examination and IHC were also compared with that of MI-control group. Echocardiographic assessment Echocardiographic examination was performed in lateral recumbent position through right parasternal window between 3rd and 5th intercostal spaces 1 –8 cm lateral to sternum in conscious state.11 A phased-array probe was used at a frequency of 2.5–3.5 MHz, attached to SAMSUNG MADISON-SONO ACE R3 ultrasound machine with a depth of 15 – 30 cm. Parasternal short-axis view at the mid-ventricular level was selected for two-dimensional (2-D) and M-mode images to assess the LV dimensions, diastolic wall thickness, fractional shortening (FS), and ejection fraction (EF). A simultaneous ECG was recorded for the correct timing of measurements within the cardiac cycle. At least three cardiac cycles were measured, and the mean value for each parameter was obtained. Preoperative preparation and general anaesthesia All experimental animals were examined preoperatively via routine physical examination. Animals with any chest disease or cardiac murmurs on auscultation were not enrolled in the study. Dogs were administered intravenous (IV) atropine (0.04 mg/kg SC). Anaesthesia was induced with IV ketamine (10 mg/kg) and diazepam (1 mg/kg). After 1899 Consequences of coronary sinus occlusion intubation, dogs were maintained with isoflurane 1% and fentanyl (0.25 mg/kg/min). Experimental procedure A standard left lateral thoracotomy was performed at the 5th intercostal space. Incisions for all dogs extended from 2 cm ventral to the rib head to just dorsal to the left internal thoracic artery. Finochietto retractors were used for rib retraction. The pericardium was opened followed by the proximal CS complete ligation using silk suture 3/0 near its opening into the right atrium. In MI-CSL and MI-control groups, the LAD was ligated after its first diagonal branch. Animal sacrifice Euthanasia was performed via an overdose (100 mg/kg) of IV thiopental sodium. The heart was harvested and examined grossly after removing of the pericardium. Specimens were taken from the anterior and lateral walls of the LV. In infarcted hearts, specimens were taken from the viable myocardium at least 1 cm from the infarct border. Light microscopy Specimens of the LV were fixed immediately in 10% formalin for 7 days. They were processed and embedded in paraffin blocks. Serial sections 5 mm thick were sliced and stained with haematoxylin and eosin (H&E). Immunohistochemistry Immunohistochemistry staining was performed to assess vascular endothelial growth factor (VEGF) expression in the heart after CSL, using rabbit polyclonal VEGF antibody; Cat. No. RB-9031-R7 (Thermo Fisher Scientific, Inc., Fremont, CA, USA) at a dilution of 1:200. Avidin – Biotin immunoperoxidase complex technique was used12 by applying the super sensitive detection kit (Biogenex, CA, USA). The tissue sections were fixed on poly-L-lysine-coated slides overnight at 378C. They were deparaffinized and rehydrated through graded alcohol series. The slides were placed in a target retrieval solution at a pH of 9.9, and antigen retrieval was performed overnight at 408C. After quenching in 3% hydrogen peroxide and blocking for 5 min, the sections were incubated at 48C for 1 h. Biotinylated anti-mouse immunoglobulin and streptavidin conjugated to horseradish peroxidase were added. Then, 3,3′ -diaminobenzidine as the substrate or chromogen was used to form an insoluble brown product. Haematoxylin was used as counterstain. Statistical analysis Statistical Package for Social Sciences (SPSS, Inc., version 21, Chicago, IL, USA) was used. Continuous data were expressed as mean + standard deviation. The D’Agostino– Pearson test was used to ascertain normality of data, then paired t-test was used to compare ECG and echocardiographic data before and after CSL in CSL group, and unpaired t-test was used to compare data of MI-CSL with that of MI-control group. P-value was considered significant if ,0.05. Table 1 Electrocardiographic and echocardiographic measures before and after coronary sinus ligation in animals with normal hearts (CSL group) Before CSL After CSL P-value ................................................................................ RR interval (ms) 459 + 51.73 QRS duration (ms) 55.5 + 8.95 QT interval (ms) QTc (ms) 451 + 92.18 0.77 57 + 11.59 0.19 203 + 15.67 204 + 22.21 0.87 262.84 + 14.94 267.28 + 32.73 0.62 6.95 + 0.68 7.4 + 1.07 6.71 + 0.69 23.46 + 2.22 7.2 + 0.91 23.97 + 2.54 0.1 0.7 LVESD (mm) 13.96 + 1.85 14.78 + 1.77 0.26 FS (%) EF (%) 39.88 + 5.24 72.6 + 6.76 37.83 + 5.58 69.98 + 7.16 0.29 0.28 IVSd thickness (mm) LVFWd thickness (mm) LVEDD (mm) 0.068 CSL, coronary sinus ligation; IVSd, interventricular septum in end diastole; LVFWd, left ventricular free wall in end diastole; LVEDD, left ventricular end diastolic diameter; LVESD, left ventricular end-systolic diameter; FS, fractional shortening; EF, ejection fraction. Histopathology at 24 h after CSL revealed congested epicardial coronary vessels with interstitial and subendocardial oedema denoted by widened interstitial and subendocardial spaces, with intact cardiomyocytes, nuclei, and intercalated discs. No abnormalities were found in the control group (Figure 2). Histopathology at 1 week after CSL showed Thebesian vessels and sinusoids (Figure 3), with less interstitial oedema and intact myocardial tissue apart from vacuolar degeneration seen in two animals (Figure 3C). No Thebesian vessels were noted in the control group. Thebesian vessels were lined with a single layer of endothelial cells with no media or adventitia. Luminal vessels opened directly into the ventricular cavity; since they are lacking medial layer, they were considered as venoluminal vessels; some were guarded by a sphincteric opening (Figure 3B), or a tiny valve formed of a thin endothelial layer (Figure 3C). From the ventricular cavity to the Thebesian vessels, the endocardium continued as an endothelial lining, while the subendocardial space that contains the Purkinje fibres disappeared at the venoluminal junction (Figure 3B). Thebesian sinusoids were seen in the subendocardial region (Figure 3D), with irregular shapes, larger than capillaries (the latter accommodate a single red blood cell), formed of a single layer of endothelium with no media or adventitia. Immunohistochemistry for VEGF in the myocardium showed negative staining in the control group (Figure 3E) and positive staining in the CSL group at 1 week after CSL (Figure 3F). Results Myocardial infarction-coronary sinus ligation group Coronary sinus ligation group There were no abnormalities in baseline ECG and echocardiography prior to MI induction. One out of the 10 dogs with induced MI died intraoperatively during CSL due to bradycardia that progressed to asystole. There were no differences between MI-CSL group and MI-control group regarding ECG and echocardiographic measures before and after MI induction (Table 2). After CSL in MI-CSL group or open thoracotomy in MI-control group, there There were no abnormalities in baseline ECG and echocardiography. Following CSL, there were no deaths among this group until animals were sacrificed. Electrocardiographic and echocardiographic measures after CSL did not significantly differ from that before CSL (Table 1). There was no ST segment shift, sustained arrhythmia or conduction defects following CSL prior to animal sacrifice. 1900 O. Ali Diab et al. A B C D e Figure 2 Light microscopic images (H&E) of a control dog (A) and CSL group (B – D) 24 h after CSL. (A) Normal appearance of the epicardial coronary vessels with underlying compact myocardium. (B) Engorged epicardial coronary vein (right thick arrow) and artery (left thick arrow) with widened interstitial spaces (thin arrows) denoting interstitial oedema. (C) Endocardium (e), Purkinje fibre cells (thin arrow), and widened subendocardial space (thick arrows). (D) High-power image showing intact cardiomyocytes with normal branching appearance, normal nuclei (thick arrow), and intercalated discs (thin arrows). were significant differences in left ventricular end-systolic diameter (LVESD), FS, and EF (P ¼ 0.02, 0.0001, and 0.002, respectively). Histopathologic examination of the non-infarcted myocardium of the MI-control group was unremarkable (Figure 4A). Non-infarcted myocardium of CSL-MI group at 24 h following CSL showed interstitial oedema with focal areas of hypereosinophilic necrosis (Figure 4B). At 1 week, there was myocardial degeneration with loss of contractile apparatus and loss of normal myocardial architecture (Figure 4C) and dilated congested Thebesian sinusoids (Figure 4D). Immunohistochemistry for VEGF in the myocardium showed negative staining of the viable myocardium in the MI-control group 1 week after MI induction (Figure 4E) and positive staining in the MI-CSL group 1 week after CSL (Figure 4F). Discussion Recent developments in cardiac device and ablation therapy required not only an orientation with CS anatomy, but also a thorough knowledge of the consequences of possible CS occlusion in either normal or diseased hearts. Main findings In the present study, acute CS occlusion did not significantly affect normal hearts regarding ECG and echocardiographic parameters. However, at the microscopic level, there was remarkable interstitial oedema that decreased by the 7th day post-CSL. This was concomitant with the appearance of Thebesian vessels and sinusoids, and expression of VEGF. Echocardiographically, there was an increase in LV septal and free wall thickness, likely due to myocardial oedema, which did not reach statistical significance. We studied the left ventricle as the right side is normally rich in Thebesian vessels. The development of observable Thebesian vessels in the LV after CSL suggests either dilatation of pre-existing vessels or neovascularization. It has been demonstrated that the Thebesian vessels are able to carry out the majority of venous return in situations where the epicardial coronary veins are compromised.13 In the case of normal CS pressure, the CS drains the majority of blood, but in the case of high CS pressure, the blood is drained through the Thebesian system. The small resistance Thebesian vessels can explain some reports that retrograde delivery of cardioplegic solutions via the coronary sinus at a pressure of 30 – 40 mmHg resulted in large draining of solution into the ventricles without traversing capillary beds.14 In the present study, we thoroughly combined electrocardiography, echocardiography, histopathology, and immunohistochemistry; and we added a group with structural heart disease, with timed follow-up design. This may serve the field of 1901 Consequences of coronary sinus occlusion A cav PM B cav C D cav E F Figure 3 Light microscopic images (H&E) of the LV myocardium of CSL group at 1 week after CSL. (A) Papillary muscle (PM) showing Thebesian vessel at its base (rectangle). (B) Magnification of the rectangle in A, showing venoluminal vessel opening into the ventricular cavity (cav) through a sphincter-like neck (large arrow), with some red blood cells inside. The junction between the endocardium and the vessel lining is marked with disappearance of the subendocardial space (small arrow). (C) Thebesian vessel opening into the ventricular cavity (cav), guarded by a valve formed of a thin endothelial layer (arrow). The surrounding myocardium shows vacuolar degeneration. (D) Thebesian sinusoids (arrows) seen in the subendocardial region, of irregular shapes, larger than capillaries in diameter, formed of a single layer of endothelium with no media or adventitia. (E) Immunohistochemistry of the control group showing negative staining for VEGF. (F) Immunohistochemistry of CSL group 1 week after CSL showing positive staining for VEGF. electrophysiology and device therapy in which the effect of CS injury is still questioned. In one study, Miyahara et al. 15 induced CS thrombosis in dogs with normal hearts through injection of thrombin in a balloon-occluded CS. They reported histologic changes similar to that of haemorrhagic MI associated with cardiac enzyme elevation and ischaemic ECG changes. The difference between their results and ours may be explained by the following: (1) They induced CS thrombosis by thrombin injection, which might leak into the capillary bed or into the arterioles through Thebesian vessels. (2) They noticed the presence of fresh thrombi in the CS, great cardiac vein, and small vessels. Thrombus could also be propagated back to the arterioles. (3) Thrombus might embolize to the arterial side. In agreement with our findings, no MI or haemorrhage were found on postmortem microscopic examination in a patient with CS thrombosis due to injury by central venous catheter.8 As reported by the authors, the cause of death in this case might be pulmonary embolism as evidenced by the presence of microemboli in both lungs. However, we found two cases with myocardial vacuolar degeneration at 1 week after CSL in CSL group. This abnormality was reported to occur in myocardial ischaemia.16 It has been demonstrated that CS occlusion may result in decrease in coronary arterial 1902 O. Ali Diab et al. Table 2 Electrocardiographic and echocardiographic measures before and after MI induction and CS ligation in MI-CSL compared with MI-control groups Baseline After MI induction After CSL/open thoracotomy .................................................. .................................................. .................................................. MI-control (n 5 8) MI-CSL (n 5 10) P-value MI-control (n 5 8) MI-CSL (n 5 10) P-value MI-control (n 5 8) MI-CSL (n 5 9)a P-value ............................................................................................................................................................................... RR (ms) QRS (ms) QT (ms) QTc (ms) IVSd (mm) 477.5 + 34.5 52.5 + 8.8 480 + 74.8 54 + 9.6 0.93 0.73 422.5 + 54.9 58.7 + 11.2 200 + 15.1 204 + 11.7 0.53 230 + 32 256.6 + 21.2 6.5 + 0.8 261.3 + 20.7 6.6 + 0.73 0.64 0.92 307 + 45.1 7.1 + 1.3 6.6 + 0.93 0.79 0.88 406.6 + 22.3 60 + 5.5 395.3 + 39.6 60 + 7.5 0.45 1.00 230 + 28.6 1.00 217.5 + 22.5 224.4 + 27.8 0.58 308.4 + 39.9 6.8 + 1.4 0.94 0.63 296.5 + 31.1 6.3 + 0.7 302.5 + 37.5 6.6 + 0.5 0.72 0.35 0.95 7 + 1.3 6.9 + 1.4 0.88 7 + 0.7 7.2 + 0.8 0.57 LVEDD (mm) LVESD (mm) 23.5 + 1.8 13.8 + 1.9 23.1 + 2.2 14 + 1.7 0.69 0.88 27.3 + 3.7 21.3 + 4.1 26.3 + 4.5 20.1 + 4.6 0.59 0.55 26.7 + 3.2 20.1 + 1.7 27 + 2.8 23.1 + 3.1 0.86 0.02 FS (%) 37.1 + 4.9 36.5 + 4.5 0.78 21.1 + 9.1 24.4 + 9.9 0.48 19.6 + 2.8 13.8 + 1 0.0001 EF (%) 69.7 + 6.9 68.9 + 6.9 0.8 39.1 + 16.6 0.31 38.5 + 5.1 30.8 + 3.2 0.002 LVFWd (mm) 6.6 + 0.91 416 + 49.7 58 + 10.3 47 + 15.5 MI, myocardial infarction; CSL, coronary sinus ligation; IVSd, interventricular septum in end diastole; LVFWd, left ventricular free wall in end diastole; LVEDD, left ventricular end diastolic diameter; LVESD, left ventricular end-systolic diameter; FS, fractional shortening; EF, ejection fraction. a One animal died intraoperatively. blood flow. Nevertheless, it is unknown if this finding was due to CS occlusion or pre-existing atherosclerosis. Owing to the relatively few Thebesian vessels in canine LV, if any decrease in coronary blood flow following CS pressure elevation occurred, it would be compensated by an increase in oxygen extraction to maintain oxygen supply within normal range. Therefore, our findings should not be interpreted as completely ‘harmless’ CS occlusion, but rather a ‘compensated harm’ in hearts with normal physiologic reserve. On the other side, in the presence of structural heart disease, MI-CSL group in the present study showed significant increase in LVESD and deterioration of LV systolic function after CS occlusion, in addition to a case with intraoperative death. At the microscopic level, non-infarcted myocardium showed focal necrosis and marked degenerative changes. This indicates that acute CS occlusion cannot be tolerated by compromised hearts. In a similar context, Hazan et al. reported a case with poor LV systolic function, post-mitral valve replacement, who developed CS thrombosis that resulted in acute clinical decompensation.17 Another case was reported to develop CS thrombosis with underlying chronic heart failure and EF of 10%, who was admitted with acute decompensation.18 Few cases with normal hearts, in whom CS thrombosis was life threatening, were reported. Coronary sinus thrombosis in such cases has resulted in cardiac tamponade or pulmonary embolism.1,8 If these conditions were properly managed, CS obstruction alone would not likely to be fatal. Onset of CS occlusion may influence the clinical outcome. Despite the presence of chronic heart failure, CS obstruction was tolerated in a patient with CRT, probably due to the gradual onset of obstruction as evidenced by the gradual increase in LV lead threshold, likely due to fibrosis at the lead tip.2 Gradual CS obstruction might give chance to collaterals to develop between CS, anterior cardiac veins, and Thebesian vessels. From the available data and our findings, we suggest that the clinical outcome of CS obstruction is determined by the presence or absence of underlying heart disease, and the onset of obstruction whether acute or gradual. The worst-case scenario is an acute CS occlusion in a diseased heart. Thebesian vessels The coronary venous system has received little attention over many decades; hence, little is known regarding the consequences of CS obstruction. Thebesian system is made up of canals that open into the cavity, or sinusoids that are located in the subendocardial layers which lack the middle muscular layer in their walls.5 – 7 This was far similar to our description of Thebesian system. We demonstrated that the Thebesian vessels at their openings into the LV cavity showed a valve or a sphincter-like outlet. Similarly, Ratajczyk-Pakalska et al. 19 have observed the presence of a monocuspid valve, or sphincter, at the outlet of the Thebesian vessels. We also demonstrate that Thebesian vessels that drained into the LV cavity did not have medial layers. This is in agreement with what previously reported that the LV is lacking arterioluminal vessels that are present only in the right chambers.5,6,13 We observed that the subendocardial space that contains the Purkinje fibres is lost at the junction between the endocardium and the endothelium of Thebesian vessel. This may help to differentiate between Thebesian vessels and normal endocardial recesses associated with ventricular trabeculations. In the present study, no Thebesian vessels were observed in any of the control animals. Those vessels might be absent or collapsed and open only when CS pressure increases. Thebesian system is known to be poorly developed or absent in the left heart chambers.5,6,13 Although we observed Thebesian sinusoids in the subendocardial region, we did not observe the so-called ‘sponge-like’ appearance, which described large networks of Thebesian sinusoids surrounding myocardial tissue islands; an assumption that was the rationale behind transmyocardial laser revascularization (TMR) which was abandoned.7 1903 Consequences of coronary sinus occlusion A B C D S E F Figure 4 Light microscopic images (H&E) of the non-infarcted LV myocardium of MI-control group (A) and the CSL-MI group (B – D). (A) Normal myocardial tissue appearance. (B) Specimen taken at 24 h after CSL showing widened interstitial spaces with focal areas of hypereosinophilic necosios (arrows). (C) Specimen taken at 1 week after CSL showing myocardial degeneration with partial (small arrow) and complete (large arrow) loss of the contractile apparatus and loss of normal myocardial architecture. (D) Specimen taken after 1 week of CSL showing a large Thebesian sinusoid (S) filled with red blood cells (arrow) surrounded with degenerated hypereosinophilic myocardium. (E) Immunohistochemistry of the non-infarcted myocardium of MI-control group at 1 week after MI induction showing negative staining for VEGF. (F) Immunohistochemistry of the MI-CSL group at 1 week after CSL showing positive staining for VEGF. Vascular endothelial growth factor Vascular endothelial growth factor is the key cytokine in angiogenesis in myocardial ischaemia. In infarcted hearts, angiogenesis started in the border zone and peaked at 7th day post-MI in the infarcted zone.20 In CSL group in our study, VEGF was expressed in the myocardium after CSL by the 7th day, denoting certain degree of ischaemia, likely due to some decrease in coronary arterial flow being compensated by angiogenesis. Hence, no significant ECG or echocardiographic changes occurred. In MI-CSL group in our study, VEGF was expressed in the non-infarcted myocardium 1 cm from the border zone, indicating that the stimulus of angiogenesis was the same as in CSL group rather than MI itself, in which VEGF is almost restricted to the infarcted and border zones.20 Conclusions In normal hearts, CS occlusion did not result in significant ECG or echocardiographic changes, although there were microscopic 1904 abnormalities that were compensated by Thebesian system, and likely aided by VEGF expression. In the presence of structural heart disease, an abrupt CS occlusion might have deleterious effects on the myocardial structure and function. All institutional and national guidelines for the care and use of laboratory animals were followed and approved by the ethical committee of Faculty of Veterinary Medicine, Cairo University, Egypt. No human studies were carried out by the authors for this article. Conflict of interest: None declared. Funding The study was funded by our institute and we received no grants or contracts from elsewhere. References 1. Figuerola M, Tomas MT, Armengol J, Bejar A, Adrados M, Bonet A. Pericardial tamponade and coronary sinus thrombosis associated with central venous catheterization. Chest 1992;101:1154 –5. 2. De Voogt WG, Ruiter JH. Occlusion of the coronary sinus: a complication of resynchronisation therapy for severe heart failure. Europace 2006;8:456 –8. 3. Haissaguerre M, Gaita F, Fischer B, Egloff P, Lemetayer P, Warin JF. Radiofrequency catheter ablation of left lateral accessory pathways via the coronary sinus. Circulation 1992;86:1464 –8. 4. Polymeropoulos KP, Rodriguez LM, Timmermans C, Wellens HJJ. Radiofrequency ablation of a focal atrial tachycardia originating from the Marshall ligament as a trigger for atrial fibrillation. Circulation 2002;105:2112 –3. 5. Saremi F, Muresian H, Sánchez-Quintana D. Coronary veins: comprehensive CT-anatomic classification and review of variants and clinical implications. RadioGraphics 2012;32:E1– 32. 6. Ansari A. Anatomy and clinical significance of ventricular Thebesian veins. Clin Anat 2001;14:102 –10. O. Ali Diab et al. 7. Tsang JCC, Chiu RCJ. The phantom of ‘myocardial sinusoids’: a historical reappraisal. Ann Thorac Surg 1995;60:1831 –5. 8. Suarez-Penaranda JM, Rico-Boquete R, Munoz JI, Rodriguez-Nunez A, Soto MIM, Rodrı́guez-Calvo M. Unexpected sudden death from coronary sinus thrombosis. An unusual complication of central venous catheterization. J Forensic Sci 2001;45: 920 –2. 9. Fridericia LS. The duration of systole in the electrocardiogram of normal subjects and of patients with heart disease. Acta Med Scand 1920;53:469–86. 10. Agudelo CF, Scheer P, Tomenendalova J. How to approach the QT interval in dogs – state of the heart: a review. Vet Med 2011;56:14–21. 11. Gugjoo MB, Saxena AC, Hoque M, Zama MMS. M-mode echocardiographic study in dogs. Afr J Agric Res 2014;9:387 – 96. 12. Hsu SM, Raine L, Fanger H. Use of avidin-biotin-peroxidase complex (ABC) in immunoperoxidase techniques: a comparison between ABC and unlabelled antibody (PAP) procedures. J Histochem Cytochem 1981;29:577 –80. 13. Echeverri D, Cabrales J, Jimenez A. Myocardial venous drainage: from anatomy to clinical use. J Invasive Cardiol 2013;25:98– 105. 14. Ardehali A, Laks H, Drinkwater DC, Gates RN, Kaczer E. Ventricular effluent of retrograde cardioplegia in human hearts has traversed capillary beds. Ann Thorac Surg 1995;60:78–83. 15. Miyahara K, Satoh F, Sakamoto H. Experimental study of acute coronary sinus thrombosis: clinical references to coronary sinus thrombosis and coronary venography. Jpn Circ 1988;52:44 –52. 16. Geer JC, Crago CA, Little WC, Gardner LL, Bishop SP. Subendocardial ischemic myocardial lesions associated with severe coronary atherosclerosis. Am J Pathol 1980;98:663 –80. 17. Hazan MB, Byrnes DA, Elmquist TH, Mazzara JT. Angiographic demonstration of coronary sinus thrombosis: a potential consequence of trauma to the coronary sinus. Cath Cardiovasc Diagn 1982;8:405–8. 18. Kachalia A, Sideras P, Javaid M, Muralidharan S, Stevens-Cohen P. Extreme clinical presentations of venous stasis: coronary sinus thrombosis. J Assoc Physicians India 2013;61:841 –3. 19. Ratajczyk-Pakalska E, Fortak W, Gołab B. Sphincters and valves in the walls of the smallest cardiac veins. Folia Morphol (Warsz) 1984;43:121 – 7. 20. Zhao T, Zhao W, Chen Y, Ahokas RA, Sun Y. Vascular endothelial growth factor (VEGF)-A: role on cardiac angiogenesis following myocardial infarction. Microvasc Res 2010;80:188 –94.