Risk stratification for cardiac patients coming for non-cardiac surgeries

K. Mahalakshmi

Consultant Anesthesiologist, Kauvery Hospital, Chennai

Background

In pre anesthetic assessment patients are evaluated based on their comorbidities and the type of surgery that they will be undergoing. The American Society of Anesthesiologists’ (ASA) Physical Status Classification System helps to categorize patient’s physiological status so that the operative risk can be predicted.

Cardiac patients are under ASA class III, and include patients with stable congenital cardiac abnormality, valvular heart disease, coronary heart disease, heart failure, arrhythmias, diastolic dysfunction, low ejection fraction, ischemic heart disease, cardiac stents in situ, pulmonary artery hypertension, pericardial diseases, or with cardiac devices like pacemakers and ventricular assisted devices for heart failure.

The surgical procedure has the potential to aggravate the morbidity and mortality risk in patients with cardiac disease. Preoperative risk stratification helps in reducing the risk of complications.

Table 1. Surgical risk estimate according to type of surgery or intervention

When a cardiac patient is scheduled for elective no cardiac surgery (NCS) their day-to-day functional capacity, dyspnea, history of chest pain, pedal edema etc are inquired into. If symptomatic, patient is referred to the cardiologist for medical management and further evaluation to get symptoms under control.

Investigations such as 12 lead electrocardiogram and echocardiogram are done to semi quantitatively assess cardiac risk. Atrial fibrillation, AV block, Q wave indicative of previous MI etc are looked for.

Evaluation and optimization of anemia are recommended before scheduling intermediate or high risk NCS.

Electrolyte abnormalities such as hypokalemia and hypomagnesmia are commonly seen in patients receiving diuretics, and need to be corrected.

Biomarkers such as Troponin I that quantifies myocardial injury, and BNP and NTproBNP that quantifies haemodynamic cardiac wall stress, are estimated where necessary.

Laboratory testing of coagulation profile is mandatory to check. Aassessment of anticoagulant drug concentrations may be required.

TEE is strongly recommended in patients with poor functional capacity and/or highNT-proBNP/BNP, and in patients with cardiac murmurs, before accepting for intermediate and high risk NCS. Relevant investigations are also required in suspected new CVD or unexplained signs or symptoms suggestive of decompensation, before high risk NCS.

Trans Thoracic Echo examination can be accepted as an alternative for TEE to avoid delaying surgery for preoperative triage.

Coronary CT Angiography is recommended as an alternative to invasive coronary angiography for excluding non-ST segment elevation acute coronary syndrome and when patients are unsuitable for noninvasive functional testing before undergoing non urgent, intermediate and high risk ncs.

Invasive coronary angiography is considered only in stable chronic coronary syndrome patients undergoing elective surgical carotid endarterectomy.

Exercise Stress test is considered to diagnose obstructive CAD only if noninvasive imaging not available.

Risk score calculators

The revised cardiac risk index

General risk reduction strategies

Control of CV risk factors including blood pressure, dyslipidemia, Diabetes.
Smoking cessation > 4 weeks before NCS is recommended to reduce post-operative complications and mortality.

Recommendations for pharmacological treatment:

Preoperative initiation of beta blockers is recommended in advance of NCS. This is to be considered in patients who have known CAD or myocardial ischemia.
In patients who are on chronic beta blocker therapy before surgery, it is recommended to maintain the same in the perioperative period.
Statins should be continued when patients are already in routine treatment, and considered preoperatively in high-risk surgery.
Renin angiotensin aldosterone system inhibitors and calcium channel blockers are recommended to be withheld on the day of surgery in order to avoid intra op and post-operative hypotension.
Diuretics dose should be adjusted well in advance to achieve an optimal fluid balance before surgery, and to avoid fluid retention and dehydration.
Thromboprophylaxis is deemed necessary according to type of NCS, duration of immobilization and patient related factors.
Prophylaxis of infective endocarditis in NCS should be consistent with standard protocols
Anti-arrhythmic drugs should be continued; ablation is performed when patient is symptomatic or has recurrent SVT.
For AF patients undergoing emergency NCS with hemodynamic instability emergency electrical cardioversion is recommended. Amiodarone is used to control heart rate and in hemodynamically unstable pre-operative situations.

Bradyarrhythmia

Temporary cardiac pacing should be limited to urgent NCS if bradycardia is hemodynamically compromising and provokes ventricular tachyarrhythmia. Patients with fascicular block are at high risk for developing complete heart block.

Peri operative handling of antithrombotic agents

Management of patients on treatment with antithrombotic agents and needing surgery should take into consideration patient and procedure related risk of bleeding and thrombosis.

Oral anti-platelets and anti-coagulants

These drugs are withheld or continued, and resumption decided, according to the patient’s history of CAD symptoms, age, creatinine clearance and risk benefit ratio of bleeding from spinal or epidural and from the type of surgery.

Bridging therapy is mandatory if there is recent history of CV events within 6 months, patient with poor mobility and age more than 70years.

In patients with recent PCI who are coming for NCS, the management is discussed between the anesthesiologist, cardiologist and surgeon, keeping the bleeding and ischemia risk in mind.

Patients with ACS or CCS for NCS should undergo diagnostic and therapeutic interventions as recommended. In case of emergency NCS the priority for surgery on a case-to-case basis should be considered.

Heart failure is an established risk factor, it depends on whether the LV systolic function is preserved or reduced. Acute exacerbation of HF before NCS has higher perioperative mortality. It is important to assess volume status and signs of organ perfusion.

In patients with Hypertrophic obstructive cardiomyopathy with LV outflow obstruction avoidance of prolonged pre-operative fasting and dehydration is important to reduce risk of increased obstruction. Medications are to be continued to treat LV outflow obstruction.

In patients with VADs, NCS should be performed in surgical centers that have access to VAD teams.

Valvular heart disease increases the perioperative risk and complications depending upon the severity of VHD and type of NCS, when the pathology is obstructive, for e.g., symptomatic Aortic Stenosis or Mitral Stenosis.

Patients with Aortic valve stenosis and normal LVEF can safely undergo low to intermediate risk NCS.

Patients with Mitral valve stenosis are prone for pulmonary edema. Tachycardia and fluid overload are to be avoided.

Risk of CV events is increased in moderate to severe MS, with high pulmonary artery pressure on echo, and in symptomatic patients.

With Aortic valve regurgitation, when the disease is mild to moderate, NCS can be performed without additional risk.

Etiology of Mitral valve regurgitation should be assessed; if of ischemic etiology, patients are at increased CV complications. Hence severe primary MR with severe LV dysfunction needs trans catheter or surgical intervention before NCS is offered.

Adult congenital heart disease with coexistence of HF, pulmonary hypertension, arrhythmia, hypoxemia and damage to other organs (kidneys, liver, lung and endocrine) may increase the risk and worsen the prognosis. Multimodal diagnostic evaluation is important preoperatively.

In patients with Pulmonary artery hypertension, perioperative risk factors are the following: reduced six-minute walk performance, functional class >II, CAD, previous pulmonary embolism, chronic renal insufficiency and severe right ventricular dysfunction. Surgery related risk factors are emergency surgery, duration of anesthesia >3 hours and intra operative requirement for vasopressors. Echocardiography plays a key role in the preoperative work up. All drugs are continued such as endothelin receptor antagonists, phosphodiesterase inhibitors and prostacyclin analogues.

Conclusion

The risk of CV complications in patients undergoing NCS is determined by patient age, comorbidities, type of surgery or procedure. Clinical examination, patient functional capacity and noninvasive tests represent the cornerstone of preoperative cardiac assessment. It is important to communicate with patients clearly and concisely, with simple verbal and written instruction about changes in medication in the pre and post operative phases. Management in the perioperative phase of NCS aims to avoid hemodynamic imbalance while ensuring sufficient cardioprotective action.

Abbreviations

ACEI: angiotensin-converting-enzyme inhibitor

AF: atrial fibrillation

ACS: acute coronary syndrome

CHD: congenital heart disease

CAD: coronary artery disease

CV: cardiovascular

BNP: B-type natriuretic peptide

ECG: electrocardiogram

NCS: non cardiac surgery

LMWH: low molecular weight heparin

MI: myocardial infarction

MS: mitral stenosis

NT-pro BNP: N-terminal pro-B-type natriuretic peptide

PCI: percutaneous coronary intervention

RAAS: renin angiotensin aldosterone system

SVT: supraventricular tachycardia

TEE: transoesophageal echocardiography

VHD: valvular heart disease

References

Glance LG, et al. The Surgical Mortality Probability Model: derivation and validation of a simple risk prediction rule for noncardiac surgery. Ann Surg. 2012:255:696-702.
Duceppe E, et al. Canadian Cardiovascular Society guidelines on perioperative cardiac risk assessment and management for patients who undergo noncardiac surgery. Can Cardiol. 2017;33:17-32.

Dr. K. Mahalakshmi

Anaesthesiologist

Risk stratification for cardiac patients coming for non-cardiac surgeries