Cardiac Ischaemia

Tests to assess cardiac ischaemia should be individualised according to patients’ clinical scenario. Generally, a 12‐lead electrocardiogram (ECG) is required for all patients during anaesthetic assessment (see Chapter 12) and for all patients who described symptoms of angina, asymptomatic patients with diabetes mellitus, patients with prior coronary revascularisation, asymptomatic patients with two or more atherosclerotic risk factors, those patients who have had prior hospital admissions for cardiac causes and any elderly patients (age >65 years). Exercise stress test is recommended in patients with high clinical likelihood of having cardiac ischaemia. However, since many patients undergoing bariatric surgery are not able to exercise to maximal heart rate, pharmacological stress testing (e.g. dobutamine stress echocardiogram tests) is widely used for this population group and is a good predictor of peri‐operative cardiac events. Thallium‐201 nuclear cardiac imaging is another modality for non‐invasive cardiac ischaemia studies, but its accuracy is reduced in patients who have a BMI of more than 30 kg m⁻². There are also increasing evidence for the role of cardiac computed tomography angiogram to evaluate the coronary vasculature in patients who are unable to tolerate exercise. However, a person who is very large may not fit into the opening of a conventional CT scanner or may be over the weight limit.

Coronary angiography is the diagnostic procedure for patients with coronary luminal diseases and can also be used therapeutically (e.g. balloon angioplasty with or without stent placement) in patients with known coronary artery disease. Percutaneous coronary intervention (PCI) does not decrease the risk of peri‐operative cardiac events except in those patients in whom PCI is indicated for acute coronary syndrome, but will likely delay surgery due to the direct mechanical effects of angioplasty or the requirement of prolonged anti‐platelet therapy. Evidence suggests that patients who undergo PCI with balloon therapy alone (without stent) should ideally undergo surgery between four and eight weeks after catheterisation. Before four weeks, the dilated blood vessels have not fully healed and after eight weeks the risk of restenosis is high.

The use of dual anti‐platelet therapies with clopidogrel and aspirin which is required after coronary artery stenting to prevent stent thrombosis increases the risk of bleeding during the peri‐operative period. The American College of Cardiology and The American Heart Association recommend that dual anti‐platelet treatment is required for at least one month in patients receiving bare metal stents and for one year with drug eluting stents. Accordingly, patients should not undergo surgery within the first year of stent placement. If however patients requires dual therapy for more than one year after stent placement, clopidogrel and other thienopyridines should be stopped five to ten days pre‐operatively and restarted ten days post‐operatively while aspirin can be continued through the peri‐operative period. Concurrent use of a proton pump inhibitor is recommended to start one week pre‐operatively to minimise the risk of gastrointestinal bleeding.

Atrial Fibrillation

Obesity has been reported in numerous studies to be a major risk factor for atrial fibrillation (AF) independent of age, diabetes, hypertension and gender, while weight loss is associated with reversal of AF. Framingham Heart Study and a meta‐analysis have indicated that a rise in BMI parallels a marked increase in AF risk. The Women’s Health Study found that for every 1 kg m⁻² increase in BMI, there was a 4.7% increase in risk of developing AF. The pathogenic mechanism is multi‐factorial and includes haemodynamic changes associated with obesity, the impact of epicardial adipose tissue biology, obesity‐related inflammatory cytokines, fibrosis and lipotoxicity on the myocardium, direct electrophysiological effects on left atrial cardiomyocyte and autonomic dysfunction in obesity. The two pillars of AF managements are anticoagulation and rate/rhythm control.

Anticoagulation is required to minimise thromboembolic complications associated with AF. This is undertaken either by warfarin therapy (where patients with BMI > 40 kg m⁻² have a significantly higher warfarin requirements) or the use of direct oral anticoagulants (DOACs), such as abigatran, apixaban, rivaroxaban and edoxaban. However, there is less large‐scale clinical trial data or pharmacokinetic analyses with DOAC in patients of high BMI. Therefore, continued caution is recommended when considering DOAC use in the morbidly obese, particularly for those requiring anticoagulation for VTE treatment. This is in line with current guidance from the International Society on Thrombosis and Haemostasis days. A second pillar of AF management is rate/rhythm control. Cardioversion is one of the most commonly performed procedures for patients in AF. However, patients with a higher body weight have been found to have a lower success rate with cardioversion. This is likely to be due to a lower energy being delivered to the heart in patients with a higher body weight. If rate control is chosen, beta‐blocker is the treatment of choice, while digoxin or verapamil can be used for patients who has contraindication to beta‐blocker (Figure 9.3).

Heart Failure

The Framingham Heart Study identified obesity as an independent risk factor for the development of heart failure, with the risk increasing by 5% in men and 7% in women for every 1 kg m⁻² in BMI. Heart failure is a significant factor for peri‐operative cardiac events. Pre‐operative assessment must therefore screen for signs and symptoms of heart failure. Symptoms of heart failure includes lethargy, exertional shortness of breath, leg oedema, orthopnoea (shortness of breath when lying flat) and paroxysmal nocturnal dyspnoea (attack of severe shortness of breath and coughing that generally occur at night). Signs of heart failure are the presence of an S3 gallop, jugular venous distention, peripheral oedema, bilateral crackles on lung auscultation and evidence of pulmonary vascular redistribution on chest X‐ray. We normally have a low threshold to request a brain natriuretic peptide (BNP) test for patients with clinical suspicion of heart failure. Cross‐sectional echocardiography may be needed to assess severity of heart failure, but its clinical utility is reduced in obese patients due to poor view of the cardiac function. Treatment includes the use of diuretic, renin–angiotensin‐system blockers (such as ACE inhibitor or angiotensin 2 receptor blockers), beta‐blockers as well as additional agents like aldosterone blockers, or combination agents, such as entresto (sacubitril/valsartan) or hydralazine/nitrate and ivabradine. In selected patients, the use of cardiac re‐synchronisation therapy maybe indicated. Close collaboration with a cardiologist during the pre‐operative workup will facilitate the smooth progression through pre‐operative cardiac investigation and optimisation of treatment.

Hypertension

Obesity increases the risk of the development of hypertension, which in turn is associated with an increased risk of left ventricular hypertrophy, a powerful risk factor for cardiovascular death. Considerable evidence also suggests that obesity hypertension is associated with an increased risk of renal insufficiency. The presence of hypertension is an independent risk factor for mortality after open or laparoscopic gastric bypass with an odds ratio of 2.8. Although therapy for obesity‐related hypertension for the most part follows the standard line of high blood pressure treatment (Figure 9.4) but with a greater emphasis on diet, treatment with beta‐blockers has been shown to decrease the risk of myocardial infarction and cardiovascular death in high‐risk patients. When indicated, beta‐blockers should be initiated several weeks prior to surgery and titrated to achieve a resting heart rate of 50–60 beats per minute. Since bariatric surgery is an elective procedure, we recommend delaying surgery until adequate blood pressure control is achieved (e.g. <160/100). Thereafter, elective surgery should proceed for patients who attend the pre‐operative assessment clinic if their blood pressure is less than 180 mmHg systolic and 110 mmHg diastolic when measured in clinic. Ambulatory blood pressure recording is required for patients with persistent hypertension despite anti‐hypertensive therapy. If there is any clinical suspicion, investigation for secondary causes of hypertension (such as primary hyperaldosteronism, phaeochromocytoma, bilateral renal artery stenosis and obstructive sleep apnoea) needs to be undertaken.

Valvular Heart Disease

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