pediagenosis: Cardiovascular
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Showing posts with label Cardiovascular. Show all posts
Showing posts with label Cardiovascular. Show all posts

Thursday, June 10, 2021

Coronary Arteries and Cardiac Veins

Coronary Arteries and Cardiac Veins

Coronary Arteries and Cardiac Veins

BLOOD SUPPLY OF THE HEART

STERNOCOSTAL AND DIAPHRAGMATIC SURFACES
STERNOCOSTAL AND DIAPHRAGMATIC SURFACES


The normal heart and the proximal portions of the great vessels receive their blood supply from two coronary arteries. The left coronary artery (LCA) originates from the left sinus of Valsalva near its upper border, at about the level of the free edge of the valve cusp. The LCA usually has a short (0.5-2 cm) common stem that bifurcates or trifurcates. One branch, the anterior inter- ventricular (descending) branch, courses downward in the anterior interventricular groove (largely embedded in fat), rounds the acute margin of the heart just to the right of the apex, and ascends a short distance up the posterior interventricular groove.

Specialized Conduction System of Heart

Specialized Conduction System of Heart

Specialized Conduction System of Heart

Specialized Conduction System of Heart


The specialized heart tissues include the sinoatrial (SA) node, atrioventricular (AV) node, common atrioventricular bundle or bundle of His, right and left bundle branches, and peripheral ramifications of these bundle branches, which make up the subendocardial and intra- myocardial Purkinje network. In addition, other fiber groups in the atria meet some of the histologic and electrophysiologic criteria for specialization. These tissues constitute Bachmann’s bundle and the inter- nodal conducting paths of the right atrium.

Valves

Valves

Valves

CARDIAC VALVES OPEN AND CLOSED
CARDIAC VALVES OPEN AND CLOSED


Each atrioventricular (AV) valve apparatus consists of a number of cusps, chordae tendineae, and papillary muscles. The cusps are thin, yellowish white, glistening trapezoid-shaped membranes with fine, irregular edges. They originate from the annulus fibrosus, a poorly defined and unimpressive fibrous ring around each AV orifice. The amount of fibrous tissue increases only at the right and left fibrous trigones.

Atria and Ventricles

Atria and Ventricles

Atria and Ventricles

RIGHT ATRIUM

Atria and Ventricles


The right atrium consists of two parts: (1) a posterior smooth-walled part derived from the embryonic sinus venosus, into which enter the superior and inferior venae cavae, and (2) a thin-walled trabeculated part that constitutes the original embryonic right atrium. The two parts of the atrium are separated by a ridge of muscle. This ridge, the crista terminalis (see Plate 1-7), is most prominent superiorly, next to the SVC orifice, then fades out to the right of the IVC ostium. Its position corresponds to that of the sulcus terminalis externally (see Plate 1-6). Often described as a remnant of the embryonic right venous valve. the crista terminalis actually lies just to the right of the valve.

Exposure of the Heart

Exposure of the Heart

Exposure of the Heart

ANTERIOR EXPOSURE
ANTERIOR EXPOSURE


STERNOCOSTAL ASPECT

Within the pericardium lies the heart, a hollow, muscular, four-chambered organ suspended at its base by the great vessels. In situ the heart occupies an asymmetric position, with its apex pointing anteriorly, inferiorly, and about 60 degrees toward the left. Its four chambers are arranged in two functionally similar pairs, separated from each other by the cardiac septum (see Plate 1-5). Each pair consists of a thin-walled atrium and a thicker- walled ventricle.

Thorax

Thorax

Thorax

LUNGS IN SITU: ANTERIOR VIEW
LUNGS IN SITU: ANTERIOR VIEW


Before describing the anatomy of the heart, it is helpful to review other anatomic features of the thoracic cavity and organs.

Monday, April 19, 2021

Minimally Invasive Mini Thoracotomy Aortic Valve Replacement

Minimally Invasive Mini Thoracotomy Aortic Valve Replacement


Minimally Invasive, Mini-Thoracotomy Aortic Valve Replacement

Keywords: minimally invasive, minithoracotomy, aortic valve replacement, Operations for Valvular Heart Disease

Step 1. Introductory Considerations
·    Minimally invasive valve surgery has numerous benefits compared with a standard median sternotomy. These benefits include reduced surgical trauma, blood loss, transfusion require- ments, and reoperations for bleeding. Ventilation times and intensive care unit and hospital lengths of stay are also reduced. Patients undergoing minimally invasive surgery also experience a more rapid return to functional capacity and less use of rehabilitative resources, which has resulted in additional costs savings as well.1-5
·      The incisions and approaches used in minimally invasive aortic valve surgery have evolved over time. The concept was first introduced in 1996 by Cosgrove et al.,6 who described a right parasternal incision approach. This later proved to cause significant chest wall instability and has since been abandoned. Currently, minimally invasive aortic valve surgery is usually performed via an upper hemisternotomy approach, either with a T or L transection of the sternum at the level of the third or fourth intercostal space.7,8 A lower hemisternotomy and manubrial approach have also been described.9,10 The only true sternal-sparing procedures are an axillary approach or right minithoracotomy, entering the thoracic cavity via the second or third intercostal space.11 The focus of this chapter will be on the latter method.

1. Indications and Contraindications
·      The right minithoracotomy can be used in most subsets of patients requiring an aortic valve replacement (AVR). Definitive contraindications to a right anterior thoracotomy approach include patients with a severely calcified aorta (porcelain aorta), evident preoperatively by cardiac catheterization or computed tomography (CT) scan or intraoperatively by palpation, patients who cannot be safely cannulated peripherally due to peripheral vascular disease or centrally due to calcium in the aorta, and patients who require a valve-sparing operation. The aforementioned groups require greater exposure of the operative field. Patients who present with previous right thoracic surgery or dense adhesions from an inflammatory reaction may undergo a minithoracotomy approach. In this particular group, minimal dissection is performed in the pleural cavity, and the pericardial space is immediately entered and exposed.
·     The benefits of the minithoracotomy over a standard sternotomy AVR have also been seen in higher-risk patients, including older patients (> 75 years old),1 obese patients (body mass index [BMI] > 30 kg/m2),2 patients with chronic obstructive pulmonary disease (COPD),4 and patients with a low ejection fraction (< 35%). Several studies have demonstrated a lower morbidity and mortality in these higher-risk patients.12 An extended application of this procedure can be offered to patients who require replacement of the ascending aorta and hemiarch along with an AVR.13 Most of these procedures are performed under deep hypothermic circulatory arrest and retrograde cerebral perfusion. In patients requiring a full root replacement due to aneurysmal disease or a small aortic annulus, an aortic root replacement with reimplantation of the coronaries can also be performed. In addition, reoperative aortic valve surgery in patients with prior valve surgery or coronary revascularization via a right minithoracotomy approach is feasible.14,15 All these procedures are more technically challenging and require additional experience. Other applications include AVR with aortic root enlargement, AVR with a septal myectomy, and AVR with a single bypass to the proximal or distal right coronary artery (RCA). The posterior descending artery is difficult to visualize with this approach. In patients with coronary artery disease amenable to percutaneous intervention, a hybrid approach is preferable. A percutaneous intervention can be performed at any time prior to the minimally invasive valve surgery. A minithoracotomy approach can be offered to patients receiving dual antiplatelet therapy.16,17

2. Preoperative Preparation: Special Diagnostic or Imaging Tests
· The preoperative workup includes routine blood work, chest radiography, cardiac catheterization, and echocardiography. A routine CT angiogram is not necessary unless severe peripheral vascular disease is suspected by history or physical examination, although a CT angiogram is highly recommended when initiating a minimally invasive program. Stroke rates are low in patients undergoing femoral cannulation, despite the use of retrograde arterial perfusion,18,19 and are comparable to rates in patients undergoing a sternotomy valve procedure.
·   Routine CT scans of the chest are not necessary either, although others have defined inclusion criteria based on CT scan findings, which may be beneficial initially.5 Chest CT scans may also potentially diminish the incidence of conversions.
3. Challenging Anatomy
·  The anatomy of certain patients can pose additional challenges when performing the procedure via a right minithoracotomy approach. A chest x-ray demonstrating the right border of the heart adjacent to the right border of the vertebral column may be associated with the heart being displaced toward the left side of the chest. This is also true for patients with a pectus excavatum. If the angle of the aorta and ventricle lie at 90 degrees on the ventriculogram (cardiac catheterization), visualization of the aortic valve may be more challenging. Visualization of the aortic valve is usually more challenging in patients with a bicuspid aortic valve. Although challenging, these anatomic variants are not definitive contraindications for the surgery.
4. Ventilation
·      A single-lumen endotracheal tube is inserted, and double-lung ventilation is used throughout the operation. If visualization of the heart is impaired by the lungs, the lungs are temporarily deflated, or cardiopulmonary bypass can be initiated early in the procedure.
·   Single-lung ventilation with a double-lumen endotracheal tube or bronchial blocker is not performed unless significant pleural adhesions limit visualization and dissection. Cases of unilateral reexpansion pulmonary edema secondary to single-lung ventilation have been reported.20
Femoral arterial and venous cannulation. External landmarks for right mini thoracotomy incision.

Figure 10.1 Femoral arterial and venous cannulation.
Figure 10.2 External landmarks for right mini thoracotomy incision.


5. Monitoring Lines
·       The preoperative preparation includes insertion of a left radial arterial line and right internal jugular or left subclavian vein Swan-Ganz catheter. A left radial arterial line is always preferred in case right axillary artery cannulation is required. Patients undergoing reoperative aortic valve surgery will have a temporary transvenous pacemaker inserted after the induction of anesthesia.

Thursday, February 18, 2021

CARDIOVASCULAR EFFECTS OF AIR POLLUTANTS

CARDIOVASCULAR EFFECTS OF AIR POLLUTANTS

CARDIOVASCULAR EFFECTS OF AIR POLLUTANTS

The effects of air pollution on cardiovascular disease is a relative new area of research. Historically, air pollution has not been regarded a significant risk factor for cardiovascular disease, but the World Health Organization estimates that >7 million premature deaths each year can be attributed to urban outdoor and indoor air pollution. Short-term exposure to high levels of particulate matter (PM), especially fine particles of <2.5 µm, has been found to trigger cardiovascular mortality due to myocardial infarction and heart failure. Long-term exposure increases the risk of cardiovascular mortality and reduces life expectancy. Reductions in PM exposure are associated with decreases in mortality. A growing body of evidence has linked PM to increased systemic inflammation, oxidative stress, thrombosis, cardiac ischemia, and heart rate variability. Further investigation of PM and other air pollutants is required to better understand their effects on cardiovascular disease. This will allow development of treatment and optimized prevention strategies in the future.

DIABETES AND CARDIOVASCULAR EVENTS

DIABETES AND CARDIOVASCULAR EVENTS

DIABETES AND CARDIOVASCULAR EVENTS

Type 2 diabetes (T2DM) is common in adults and is characterized by insulin resistance that results in hyperglycemia. Diabetes increases the risk of microvascular and macrovascular events. As a result, patients with diabetes have a higher risk of dying from cardiovascular disease and are at a higher risk for developing heart failure. The duration of diabetes and degree of glycemic control with diabetes is a significant predictor of future events. Thus, identification of patients at risk for diabetes, prediabetes, and new-onset diabetes allows for intensified therapy that may reduce the chances of developing diabetes and mitigate the risk of complications from diabetes. Patients are considered to have diabetes if they have a fasting plasma glucose of ≥126 mg/dL, oral glucose tolerance test with a 2-hour postprandial glucose ≥200 mg/dL, glycosylated hemoglobin of ≥6.5%, or random plasma glucose ≥200 mg/dL. Exercise, weight loss, and metformin improve insulin sensitivity and are effective strategies to reduce the risk of developing diabetes in patients with prediabetes. Drugs from two different classes have been shown to be effective in reducing cardiovascular events specifically in patients with diabetes. The sodium/glucose cotransport-2 inhibitors, liraglutide, and semaglutide have been shown to reduce cardiovascular events in patients with diabetes. Because of the high degree of cardiovascular disease in patients with diabetes, efforts to use drugs with proven cardiovascular benefit, together with intensive cardiovascular risk factor modification, offer the ability to reduce the incidence of cardiovascular events in this high-risk population of patients.

MANAGEMENT OF LIPID ABNORMALITIES

MANAGEMENT OF LIPID ABNORMALITIES

MANAGEMENT OF LIPID ABNORMALITIES

The management of lipid disorders in reducing the risk of coronary heart disease (CHD) has evolved in the past few years. There are a number of factors that account for these changes the introduction of the 2013 American Heart Association/American College of Cardiology (AHA/ACC) guideline report on cholesterol management and a series of clinical trials on nonstatin therapies (notably, several trials involved the cholesteryl ester transfer protein inhibitors [CETPis] for high density lipoprotein [HDL] elevation), as well as the introduction of proprotein convertase subtilisin/kexin type 9 (PCSK-9) therapies. The aforementioned 2013 recommendations are a key resource because of their evidence-based approach to patient care. They have simplified both the treatment approach to lipids and challenging issues such as dose titration, as well as achieving a specific and perhaps unreachable “target” lipid value. Of great importance, they allow for discretion on the part of the provider to engage with the patient in shared decision making and as stated, “Guidelines attempt to define practices that meet the needs of patients in most circumstances and are not a replacement for clinical judgment.”

Saturday, October 31, 2020

HYPERTENSION

HYPERTENSION

HYPERTENSION

ETIOLOGY AND PATHOGENESIS

Hypertension is a disorder of BP regulation that results from an increase in cardiac output, or most often, an increase in total peripheral vascular resistance. Cardiac output is usually normal in established essential hypertension, although increased cardiac output plays an etiologic role. The phenomenon of autoregulation explains that an increase in cardiac output causes persistently elevated peripheral vascular resistance, with a resulting return of cardiac output to normal. Fig. 15.1 shows mechanisms that can cause hypertension. Inappropriate activation of the renin-angiotensin system, decreased renal sodium excretion, and increased sympathetic nervous system activity, individually or in combination, are probably involved in the pathogenesis of all types of hypertension. Hypertension also has genetic and environmental causes; the latter includes excess sodium intake, obesity, and stress. The inability of the kidney to optimally excrete sodium, and thus regulate plasma volume, leads to a persistent increase in BP whatever the etiology.

VASCULOGENESIS AND ARTERIOGENESIS: ALTERNATIVES TO ANGIOGENESIS

VASCULOGENESIS AND ARTERIOGENESIS: ALTERNATIVES TO ANGIOGENESIS

VASCULOGENESIS AND ARTERIOGENESIS: ALTERNATIVES TO ANGIOGENESIS

New vessel growth in chronic ischemic syndromes is an attractive idea. Fortunately, more than one mechanism exists to create new blood vessels. Angiogenesis is the creation of blood vessels from sprouts off the existing vessels. In contrast, vasculogenesis is the creation of de novo blood vessels by differentiation of new blood cells. Endothelial cell precursors in the bone marrow and circulating in the bloodstream can integrate into developing vessels and contribute to vessel growth in a manner similar to the vasculogenesis of embryonic development. The therapeutic potential of these cells has not been tested, but they can be recruited from bone marrow and may be a means to accelerate endogenous revascularization in patients with ischemia.

MECHANISMS OF ANGIOGENESIS

MECHANISMS OF ANGIOGENESIS

MECHANISMS OF ANGIOGENESIS

Angiogenesis occurs by the budding of new blood vessels from existing vessels (Fig. 14.1). Inflammation and hypoxia are the two major stimuli for new vessel growth. Hypoxia regulates angiogenesis predominantly by activating transcription factors, hypoxia-inducible factors (HIF) 1 and 2, which, in turn, activate the angiogenesis gene expression cascades, including vascular endothelial growth factor (VEGF), platelet growth factor, angiopoietin 1 and 2, as well as stromal cell-derived factor 1α. Based on this concept, HIF-1 promotes sprouting of blood vessels and neovascularization by homing of stem cells and enhancing vascular endothelial cell proliferation. HIF-2 mediates vascular maintenance. Inflammation stimulates angiogenesis mainly by the secretion of inflammatory cytokines derived primarily from macrophages. In either of these events, the result is production of VEGF and other potent angiogenic peptides. VEGF interacts with specific receptors on endothelial cells that, in turn, activate pathways to break down the extracellular matrix and stimulate proliferation and migration toward an angiogenic stimulus and recruitment of stem cells, pericytes, and smooth muscle cells to establish the three-dimensional structure of a blood vessel. After making appropriate connections with the vascular system, the newly formed vessel is capable of maintaining blood flow and providing oxygen to the tissue in need.

LEFT HEART CATHETERIZATION

LEFT HEART CATHETERIZATION

LEFT HEART CATHETERIZATION

Left heart catheterization is distinct from coronary angiography, which involves the cannulation and interrogation of the coronary arteries. Patients who undergo coronary angiography or right heart catheterization typically also undergo left heart catheterization as part of a comprehensive hemodynamic evaluation. The common indications for left heart catheterization include the evaluation of LV hemodynamics, LV systolic function, cardiomyopathy, valvular disease (e.g., aortic stenosis or mitral regurgitation), and intracardiac shunts (e.g., ventricular septal defects). The absolute contraindications for left heart catheterization include patient refusal, known or suspected LV thrombus, and mechanical prosthetic aortic valves. The relative contraindications for left heart catheterization include active bleeding, severe thrombocytopenia, severe coagulopathy, active infection, severe peripheral vascular disease, pregnancy, and patient inability to cooperate.

RIGHT HEART CATHETERIZATION

RIGHT HEART CATHETERIZATION

RIGHT HEART CATHETERIZATION

Right heart catheterization generally involves the introduction of a balloon-tipped catheter into the right atrium (RA), right ventricle (RV), and pulmonary artery (PA). The use of an inflatable balloon on the tip enables rapid and safe passage of the catheter through the venous system and right heart chambers; this technique was developed in the 1970s by Dr. Harold Swan, Dr. William Ganz, and colleagues. A PA catheter has a port at the distal tip, a port that is approximately 30 cm proximal from the distal tip, an inflatable balloon at the distal tip, and a thermistor near the distal tip. The distal and proximal ports can be used to transduce pressure, or serve as access for fluids and medications. The balloon can be inflated to temporarily occlude the PA, which allows the distal port to transduce a “wedge” pressure. The thermistor can be used to measure the temperature change of fluid injected into the proximal port; this measurement is used in the calculation of cardiac output. A comprehensive preprocedural evaluation that includes history, physical examination, routine laboratory data, a 12-lead ECG, and a transthoracic echocardiogram can help guide appropriate patient selection, procedural planning, and data interpretation.

DIAGNOSTIC CORONARY ANGIOGRAPHY

DIAGNOSTIC CORONARY ANGIOGRAPHY

DIAGNOSTIC CORONARY ANGIOGRAPHY

CORONARY ANATOMY

The right coronary artery (RCA) arises from the right coronary sinus and runs in the right atrioventricular (AV) groove (Fig. 12.1). The conus artery is typically the first branch that arises from the RCA and supplies the right ventricular outflow tract. The sinoatrial nodal and AV nodal branches also arise from the RCA and supply the sinus node and the AV node, respectively. Marginal branches usually arise from the mid-RCA and supply the right ventricular wall. The distal RCA gives rise to right posterolateral branches and the posterior descending artery (PDA) in 85% of cases (defined as right dominance). The PDA arises from the left circumflex (LCX) in 8% of cases (defined as left dominance), and from both the RCA and LCX in 7% of cases (defined as co-dominance). The PDA runs in the posterior interventricular groove and supplies the posterior aspect of the interventricular septum.

CARDIAC MAGNETIC RESONANCE IMAGING

CARDIAC MAGNETIC RESONANCE IMAGING

CARDIAC MAGNETIC RESONANCE IMAGING

CMR imaging has continued to advance as a robust cardiac noninvasive imaging technique. Through electromagnetic manipulation of biological hydrogen protons, CMR provides assessment of cardiac structure, function, perfusion, tissue characterization, blood flow velocity, cardiac masses, valvular heart disease, pericardial disease, and vascular disease. Continued improvements in hardware and pulse sequence design have allowed for improved image quality, speed of data acquisition, and reliability, further increasing the usefulness of CMR for clinical applications. CMR is similar to echocardiography in that neither uses ionizing radiation to acquire high-resolution images, which avoids the exposures inherent in invasive coronary angiography and SPECT imaging. CMR offers viewing cardiac motion in any view. In addition, the versatility of CMR permits imaging of a large field of view in nearly any plane, which allows for the assessment of both cardiac and noncardiac pathologies.

CARDIAC COMPUTED TOMOGRAPHY

CARDIAC COMPUTED TOMOGRAPHY

CARDIAC COMPUTED TOMOGRAPHY

For decades, investigators sought to develop new technologies that would allow rapid noninvasive imaging of the heart. One such technology that has evolved rapidly in the past several decades has been CCT. CCT now permits visualization of the coronary arteries and lumen, as well as providing assessment of cardiac function, valvular structures, prosthetic materials, the pericardium, left atrial anatomy, congenital heart disease, pulmonary arterial and venous anatomies, and diseases of the aorta.

Sunday, October 18, 2020

OTHER USES OF CARDIAC NUCLEAR MEDICINE

OTHER USES OF CARDIAC NUCLEAR MEDICINE

OTHER USES OF CARDIAC NUCLEAR MEDICINE

Equilibrium Radionuclide Ventriculography (Multiple-Gated Acquisition Scan)

Multiple-gated acquisition (MUGA) scanning is an approach used to quantify both left and right ventricular function, based on images generated after the injection of 99mTc-labeled erythrocytes. The labeling procedure can be performed in vitro using a commercially available kit (UltraTag; Mallinckrodt, St. Paul, Minnesota), in vivo, or semi–in vitro. The in vitro method provides the highest labeling efficiency and best images, but it is the most laborious, time-consuming, and expensive technique. Once the circulating blood pool has been appropriately labeled, determination of wall motion abnormalities, left ventricular volumes, and EFs can be made. These measures are accurate, repeatable, and reproducible, and are often used for serial follow-up of EFs in patients who receive cardiotoxic drugs, particularly chemotherapeutic agents. In some cases, MUGA is used for the serial follow-up of HF patients.

CARDIAC STRESS IMAGING

CARDIAC STRESS IMAGING

CARDIAC STRESS IMAGING

Stress imaging studies combine either EST or an infusion of either dobutamine or a coronary vasodilator with imaging of the heart. Imaging can be accomplished by a variety of modalities; those most commonly used are echocardiography or nuclear imaging. MRI has also been used, and CT is being studied as a modality for stress imaging. Stress imaging is preferred over EST without imaging in several settings: (1) when the ECG is uninterpretable for myocardial ischemia; (2) when a patient is unable to adequately exercise (but can undergo a pharmacological stress imaging study); or (3) when a treadmill stress test is positive for ischemia in a low-risk patient, and correlation by imaging is preferred to cardiac catheterization. Individuals with an abnormal baseline ECG, particularly with ST-segment abnormalities, should be referred for a stress imaging study, because ECG changes in the setting of an abnormal baseline are far less specific for CAD. Patients with significant left ventricular hypertrophy on their baseline ECG or those taking digoxin have similar limitations for interpretation of ischemia with exercise. Stress imaging could be used as a primary modality, rather than ECG-only stress testing, in patients with an intermediate to high pretest likelihood of disease because of its higher sensitivity and specificity. Even with rapid advances in other modalities, stress imaging remains a highly effective and available modality to evaluate ischemia and function at present, and it is likely that this will be the case in coming years.

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