This week I focused my research on the benefits of bilateral internal mammary artery grafts for CABG surgery. Through my past and present research, every article reaches the consensus that the left internal mammary artery to the LAD coronary artery has the greatest patency of any graft in CABG surgery. Therefore, all of the research being done since the early 1990's has been to research the best secondary conduit for CABG surgery. I focused my research on an NCBI case study performed in 2014 that compared the efficacy of RIMA grafts versus radial artery (RA) grafts in CABG surgery. A description of the study as well as the results are as follows.
Before this experiment even began the researchers stated that using a RIMA graft in CABG surgery tended to increase sternal wound infection in patients, especially in diabetic patients who are not able to heal their chest wall as well. This is the main reason why surgeons have decreased the use of bilateral IMA grafts in CABG surgery. In this case study, the surgeons used RIMA conduits in 747 patients and radial artery conduits in 779 patients (a total of 1526 patients). The results of the study found that RIMA grafts did not increase the chance of sternal wound infection in patients after completion of CABG surgery. The results also found that RA grafts increased the chance of late mortality and repeat CABG surgery in all patients, particularly obese and diabetic patients. This late mortality and repeat revascularization is a result of a lower graft patency for RA grafts than RIMA grafts. This study is salient to any prior beliefs of the harmful effects of RIMA grafts because the researchers proved that RIMA grafts do not increase any patient's (including diabetic patient's) chance of having a chest wound infection after CABG surgery. By disproving the main question mark about RIMA grafts, this case study has taken a big step in proving that RIMA grafts are one of if not the best secondary conduit in CABG surgery.
Friday, March 20, 2015
Friday, March 13, 2015
Research on cardioplegic techniques used to arrest the heart for CABG surgery
This week I researched cardioplegia and its many forms. Cardioplegia is a technique that arrests the heart for on-pump CABG surgery (on-pump refers to inserting a heart-lung machine that enhances systemic circulation in the patient's body) . Cardioplegia is essential to the success of CABG surgery because it creates a still and stable environment for the surgeon to work in. Cardioplegia has many forms, including cold crystalloid cardioplegia, normothermic blood cardioplegia, hypothermic blood cardioplegia, and warm blood reperfusion. Due to the many forms of cardioplegia I organized my research into two categories, those being cold crystalloid cardioplegia (synthetic solution) and blood cardioplegia.
Cold crystalloid cardioplegia is usually administered to patient's in slightly hypothermic room conditions (28-34 °Celsius) relative to the patient's internal body temperature (37 °Celsius). Before the physician can insert the cardioplegic solution into the patient they have to cross-clamp the ascending aorta. This clamp reduces blood flow distally to the arteries and organs (such as the renal and femoral arteries) but increases blood flow proximally to the carotid and coronary arteries (the arteries that deliver blood flow to the brain and heart respectively). This effectively reduces the systemic circulation and cardiac output (amount of blood delivered to the systemic circulation per unit time) in the patient's body. A heart-lung machine is therefore cannulated into the left ventricle of the heart as well as the upper portion of the cross-clamp in order to increase systemic blood flow and meet the minimum cardiac output the patient needs to survive. Once the heart-lung machine is established, the physician cannulates the aortic root. The physician then inserts a catheter into the aortic root with a test solution to see if the aortic valve regurgitates the solution back into the aortic root. If there is aortic valve incompetence, the physician makes an incision ~2cm above the coronary ostium (opening in the wall of the blood vessel). This incision allows the test solution to drain directly into the coronary arteries and bypass the aortic valve. Once the cardioplegic delivery route is confirmed the physician then inserts the catheter with the cold crystalloid solution (approximately 4 °Celsius) into the aortic root or coronary ostium. This cold crystalloid cardioplegic solution typically arrests the heart for the duration of the surgical procedure. However, the physician has smaller doses of the solution to insert into the patient if any electrical or mechanical activity from the heart is observed.
Blood cardioplegia: This is a solution that contains the patient's oxygenated blood (blood can be normothermic or hypothermic) with a crystalloid solution. The blood and crystalloid solution are mixed in a double-headed roller pump. This pump combines the patient's blood with a crystalloid solution in a ratio of 4:1. The newly formed blood cardioplegic solution is then sent through a heat exchanger system to determine if the solution will be warm, normothermic or hypothermic. The ascending aorta is then cross-clamped, and the aortic root and coronary ostia are cannulated as described earlier. The most interesting part of my research was learning about warm blood reperfusion. Data shows that warm blood reperfusion can repair ischemic (lack of blood flow to an organ or tissue) damage in patient's who had an acute myocardial infarction (heart attack). Warm blood reperfusion is able to repair ischemic damage in the heart by maximizing the efficacy of cellular respiration, which in turn decreases the demand for oxygen in the heart. It increases cellular respiration because the amino acids in its solution (glutamate and aspartate) restore the Krebs cycle intermediates. By restoring the intermediates, the Krebs cycle is able to continually produce GTP and NADH, which in turn are continually used by the electron transport chain to convert oxygen to water. By constantly converting oxygen to water, the continual turn of the Krebs cycle maximizes the amount of oxygen the body needs during cellular respiration. Typically the warm blood reperfusion solution is inserted via a catheter into the coronary sinus and grafts for one minute in order to repair any ischemic damage in the heart.
The significance of my research is that warm blood reperfusion as well as all forms of blood cardioplegia are preferred to cold crystalloid cardioplegia because they perform dual beneficial functions in the patient.Those functions being they effectively stop the heart for open-heart surgery, and they repair ischemic damage in the heart that could pose problems to the patient later in life.
Cold crystalloid cardioplegia is usually administered to patient's in slightly hypothermic room conditions (28-34 °Celsius) relative to the patient's internal body temperature (37 °Celsius). Before the physician can insert the cardioplegic solution into the patient they have to cross-clamp the ascending aorta. This clamp reduces blood flow distally to the arteries and organs (such as the renal and femoral arteries) but increases blood flow proximally to the carotid and coronary arteries (the arteries that deliver blood flow to the brain and heart respectively). This effectively reduces the systemic circulation and cardiac output (amount of blood delivered to the systemic circulation per unit time) in the patient's body. A heart-lung machine is therefore cannulated into the left ventricle of the heart as well as the upper portion of the cross-clamp in order to increase systemic blood flow and meet the minimum cardiac output the patient needs to survive. Once the heart-lung machine is established, the physician cannulates the aortic root. The physician then inserts a catheter into the aortic root with a test solution to see if the aortic valve regurgitates the solution back into the aortic root. If there is aortic valve incompetence, the physician makes an incision ~2cm above the coronary ostium (opening in the wall of the blood vessel). This incision allows the test solution to drain directly into the coronary arteries and bypass the aortic valve. Once the cardioplegic delivery route is confirmed the physician then inserts the catheter with the cold crystalloid solution (approximately 4 °Celsius) into the aortic root or coronary ostium. This cold crystalloid cardioplegic solution typically arrests the heart for the duration of the surgical procedure. However, the physician has smaller doses of the solution to insert into the patient if any electrical or mechanical activity from the heart is observed.
Blood cardioplegia: This is a solution that contains the patient's oxygenated blood (blood can be normothermic or hypothermic) with a crystalloid solution. The blood and crystalloid solution are mixed in a double-headed roller pump. This pump combines the patient's blood with a crystalloid solution in a ratio of 4:1. The newly formed blood cardioplegic solution is then sent through a heat exchanger system to determine if the solution will be warm, normothermic or hypothermic. The ascending aorta is then cross-clamped, and the aortic root and coronary ostia are cannulated as described earlier. The most interesting part of my research was learning about warm blood reperfusion. Data shows that warm blood reperfusion can repair ischemic (lack of blood flow to an organ or tissue) damage in patient's who had an acute myocardial infarction (heart attack). Warm blood reperfusion is able to repair ischemic damage in the heart by maximizing the efficacy of cellular respiration, which in turn decreases the demand for oxygen in the heart. It increases cellular respiration because the amino acids in its solution (glutamate and aspartate) restore the Krebs cycle intermediates. By restoring the intermediates, the Krebs cycle is able to continually produce GTP and NADH, which in turn are continually used by the electron transport chain to convert oxygen to water. By constantly converting oxygen to water, the continual turn of the Krebs cycle maximizes the amount of oxygen the body needs during cellular respiration. Typically the warm blood reperfusion solution is inserted via a catheter into the coronary sinus and grafts for one minute in order to repair any ischemic damage in the heart.
The significance of my research is that warm blood reperfusion as well as all forms of blood cardioplegia are preferred to cold crystalloid cardioplegia because they perform dual beneficial functions in the patient.Those functions being they effectively stop the heart for open-heart surgery, and they repair ischemic damage in the heart that could pose problems to the patient later in life.
Friday, March 6, 2015
Research on endoscopic saphenous vein harvesting for CABG as well as immunosuppressant and antineoplastic qualities of verapamil.
This week I researched the technique that extracts the greater saphenous vein for CABG surgery, that technique being endoscopic saphenous vein harvesting. Endoscopy is a procedure that involves inserting a thin malleable tube with a light and camera attached onto it to observe and remove any abnormalities within the vessel wall as well as to locate and extract veins. In the past physicians used to make long open incisions down the patients leg (because the greater saphenous vein extends from the back of the venous arch in the foot to the femoral arteries near the groin) to extract the amount of the vein they needed to perform bypass surgery. This procedure was disliked by patients as well as some physicians for two reasons. The procedure increased the chance of the patient contracting an infection and it showed a long scar going down the patients leg, which the patients found aesthetically displeasing. Endoscopic saphenous vein harvesting was developed as a less invasive alternative to the open incision procedure. The endoscopic saphenous vein harvesting procedure is as follows. Physicians make a small incision in the groin (the endpoint of the greater saphenous vein) and make one-two tiny (~3cm) incisions near the medial portion of the leg (near the knee). They then insert a trocar (a sharp, pointed instrument that is used with a cannula to
puncture a portion of the body) into the incision in order to fill the tunnel created between the incisions with carbon dioxide. After the trocar is inserted a conical dissection cone is moved toward the incision in the groin because this is where the anterior surface of the greater saphenous vein is. After this circumferential blunt dissection (total circumference or perimeter of a blunt dissection,
which involves separating tissues along its natural dividing line (animal cell cleavage via mitosis) without cutting the tissue) is utilized to naturally divide the posterior and lateral sides of the vein. Before the vein can be extracted the physician wants to make sure that normal blood flow continues in the body. They ensure this normal blood flow by isolating the collateral branches in the leg through bipolar electrocautery (A small instrument that passes a high voltage
and high frequency current between its two electrodes to isolate a small portion of a vein). By isolating the collateral branches they are ensuring that blood that used to flow through the greater saphenous vein will now flow through the collateral branches. After bipolar electrocautery is performed the physician ligatures (tie up the ends of the vein) the greater saphenous vein and extracts it. Then they dilate the vein through a cannula (a tube that is inserted into the body to allow
the trocar to occupy its lumen and puncture a portion of the body) to prevent endothelial dysfunction. After this the physician double clips the ends of the vein and flushes the vein with a cleaning solution. Finally they suture up any avulsions (tears that occur by forcibly removing a structure or part of a structure) on the vein, thus making the greater saphenous vein acceptable for CABG surgery.
I also researched verapamil (a calcium++ channel blocker) and its immunosuppressant and antineoplastic (cancer cell destroying) qualities. The reason why I researched this is because paclitaxel and other chemotherapy drugs are the main drugs used in drug-coated stents. Paclitaxel has both immunosuppressant and antineoplastic qualities, and I wanted to ensure that verapamil had similar qualities in order to ensure its viability as a coated drug on an internal mammary artery graft. From researching studies from NCBI (national center for biotechnology information) I found that verapamil does exhibit immunosuppressant qualities. The study said however that most immunosuppressant drugs block adhesion molecules by blocking their secondary messengers protein kinase C (PKC)and/or calmodulin molecules in order to prevent a foreign organ or foreign object (drug-coated stent) from being rejected. The researchers did not observe verapamil blocking either PKC or calmodulin, which therefore did not inhibit adhesion molecule expression. The conclusion of the study stated that verapamil has immunosuppressive qualities, though their origins are unknown. In the second study I researched from NCBI, it stated that verapamil was able to kill multidrug resistant cells. Multidrug resistant cells typically are cancerous cells that are able to overcome the effects of certain chemotherapy drugs. The study identified that the way to destroy multidrug resistant cells is to overcome the Vinka alkaloid resistance that these cells inherently have (Vinka alkaloid's origin is from the Madagascar periwinkle plant, and they are used as chemotherapy drugs). The two Vinka alkaloid drugs the study focused on were vinblastine and vincristine. The goal of the study was to observe any similar physiological characteristics between verapamil (and other compounds) and vinblastine and vincristine. The researchers found that verapamil and vinblastine had three areas of structural homology, and by measuring the hydrophobicity and molar refractivity of verapamil they were able to determine that verapamil and a few other compounds were able to increase the antineoplastic qualities of Vinka alkaloids, thus enabling them to destroy multidrug resistant cells.
The most exciting event that happened this week was Tuesday in the afternoon. I witnessed a patient have tachycardia and go into cardiac arrest after finishing his stress echo test. Allan the Echo tech rushed to get the crash cart and Dr. Goldberg immediately performed chest compressions and a precordial thump (this generates 10 joules of electricity in the patient's chest) to the patient's chest to get a stable heart rate. When the crash cart arrived the patient got their heart rate down to 200 bpm and were slowly stabilizing their heart rate. The patient was given beta-blocker medicines to lower their heart rate and the paramedics arrived within 15 minutes and took the patient to TMC. The patient is undergoing CABG surgery today at TMC. This experience opened my eyes in my outlook on medicine because it showed me that there has to be a constant alertness by the physician and medical staff to react instantly to any medical emergency.
I also researched verapamil (a calcium++ channel blocker) and its immunosuppressant and antineoplastic (cancer cell destroying) qualities. The reason why I researched this is because paclitaxel and other chemotherapy drugs are the main drugs used in drug-coated stents. Paclitaxel has both immunosuppressant and antineoplastic qualities, and I wanted to ensure that verapamil had similar qualities in order to ensure its viability as a coated drug on an internal mammary artery graft. From researching studies from NCBI (national center for biotechnology information) I found that verapamil does exhibit immunosuppressant qualities. The study said however that most immunosuppressant drugs block adhesion molecules by blocking their secondary messengers protein kinase C (PKC)and/or calmodulin molecules in order to prevent a foreign organ or foreign object (drug-coated stent) from being rejected. The researchers did not observe verapamil blocking either PKC or calmodulin, which therefore did not inhibit adhesion molecule expression. The conclusion of the study stated that verapamil has immunosuppressive qualities, though their origins are unknown. In the second study I researched from NCBI, it stated that verapamil was able to kill multidrug resistant cells. Multidrug resistant cells typically are cancerous cells that are able to overcome the effects of certain chemotherapy drugs. The study identified that the way to destroy multidrug resistant cells is to overcome the Vinka alkaloid resistance that these cells inherently have (Vinka alkaloid's origin is from the Madagascar periwinkle plant, and they are used as chemotherapy drugs). The two Vinka alkaloid drugs the study focused on were vinblastine and vincristine. The goal of the study was to observe any similar physiological characteristics between verapamil (and other compounds) and vinblastine and vincristine. The researchers found that verapamil and vinblastine had three areas of structural homology, and by measuring the hydrophobicity and molar refractivity of verapamil they were able to determine that verapamil and a few other compounds were able to increase the antineoplastic qualities of Vinka alkaloids, thus enabling them to destroy multidrug resistant cells.
The most exciting event that happened this week was Tuesday in the afternoon. I witnessed a patient have tachycardia and go into cardiac arrest after finishing his stress echo test. Allan the Echo tech rushed to get the crash cart and Dr. Goldberg immediately performed chest compressions and a precordial thump (this generates 10 joules of electricity in the patient's chest) to the patient's chest to get a stable heart rate. When the crash cart arrived the patient got their heart rate down to 200 bpm and were slowly stabilizing their heart rate. The patient was given beta-blocker medicines to lower their heart rate and the paramedics arrived within 15 minutes and took the patient to TMC. The patient is undergoing CABG surgery today at TMC. This experience opened my eyes in my outlook on medicine because it showed me that there has to be a constant alertness by the physician and medical staff to react instantly to any medical emergency.
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