IMPLICATIONS OF 2 D ECHO IN PRE ANAESTHETIC EVALUATION

DR SAURABH BARDE

Practicing Consultant Anaestheologist,
Nagpur

Two dimensional echocardiography (2 D Echo) is a widely available sophisticated and specialised non-invasive ultrasound imaging technique of the heart. Echocardiography (echo) enables direct visualization of the various chambers of the heart, valves, adjacent structures and major connecting vessels. Echocardiography can be performed by either transthoracic approach (TTE) or by trans-esophageal approach (TEE). Trans thoracic echocardiography is commonly performed approach for evaluation of the heart.

Echocardiography may help in stratifying perioperative cardiac risk by evaluation of severity and nature of cardiac disease before subjecting the patient to anaesthesia. Cardiac disease is a potential source of perioperative complications in any non-cardiac surgery. Major cardiac complications rate between 2%-3.5% and perioperative mortality between 0.5%-1.5% has been described after major non cardiac surgery with prolonged hemodynamic and cardiac stress.

Routinely echocardiographic evaluation is done at rest. Such evaluation done at rest does not have strong evidence in predicting post-operative outcomes even in patients with active cardiac conditions and poor functional status. Stress echocardiography may be better predictor in this regard.

Echocardiography provides information about following things:

1. Left Ventricular (LV) Systolic Function
2. Left Ventricular Diastolic Function
3. Right Ventricular (RV) Function & Pulmonary Artery Pressure
4. Valvular Lesions
5. Septal defects
6. Inferior Vena Cava status

LV systolic function:

Systole is characterised by uniform synchronous contractility of all the walls of left ventricle and the septum. Myocardial ischaemia or infarction can alter the synchrony and echo may show hypokinesia, akinesia or dyskinesia of the affected part and this is described as Regional Wall Motion Abnormality (RWMA) of LV.

The fraction amount of the total blood ejected out of LV during systole is considered as Ejection Fraction (EF). Normal value of LVEF is 50-70%. LV dysfunction is classified depending on the EF as Mild (40-49%), Moderate (30-39%) and Severe (less than 30%).

There is a positive correlation between LV dysfunction and perioperative morbidity and mortality. Any degree of LV dysfunction has been found to be associated with perioperative myocardial infarction and cardiogenic pulmonary edema.

LV Diastolic Function:

Diastole characterises left ventricular relaxation and LV filling dynamics. Normally relaxed LV will have compliant walls and it will accommodate most of the blood coming from left atrium (LA) during diastole. Such LV will also eject blood normally abiding Starling’s law if there is no LV systolic dysfunction.

Any condition that hampers compliance of the LV wall will cause stiffening of LV altering its relaxation leading to Diastolic Dysfunction. Diastolic dysfunction (DD) is defined as “inability of the LV to fill during rest or exercise, to a normal end-diastolic volume without an abnormal increase in LV end diastolic pressure (LVEDP).

Predisposing conditions which can cause diastolic dysfunction are hypertension, LV hypertrophy (LVH), older age, female gender, obesity, diabetes, chronic kidney disease and coronary artery disease (CAD).

Left ventricular diastolic dysfunction (LVDD) is graded as 1, 2 and 3 depending on the severity. Severe the diastolic dysfunction, stiffer are the LV walls. Because of stiffening of LV walls, left ventricular end diastolic pressure increases compared to normal ventricles with same amount of blood during diastole.

To fill the LV with adequate blood volume during diastole, LA has to actively pump the blood leading to increase in LA pressures with resultant back pressure changes in pulmonary venous circulation. This causes rise in pulmonary venous pressure and ultimately rise in pulmonary capillary wedge pressure (PCWP).

High LVEDP and pulmonary venous pressures predispose the patient to exertional dyspnoea and pulmonary edema (also termed as Diastolic Heart Failure) even with small amount of change in end diastolic volume. So sudden volume overload should be avoided in diastolic dysfunction of higher grades.

Diastolic Heart Failure (DHF) has prevalence of around 50% in all heart failures and carries poor prognosis with survival similar to poor ejection fraction patients. DHF is sometimes also called as Heart Failure with Normal Ejection Fraction (HFNEF). These patients have poor exercise tolerance and lower metabolic equivalents (METs). The exercise intolerance may be due to failure to increase cardiac output during exercise, secondary to impaired LV filling and a failure of the Frank-Starling mechanism. Tachycardia during perioperative period can have similar effects and therefore heart rate control is of utmost importance in patients with advanced diastolic dysfunction.

Right Ventricular Function:

Right ventricle receives less attention than left ventricle. Right ventricular dysfunction significantly increases the resulting morbidity and mortality in perioperative period. Echocardiography is the only practical investigation available for confirmation of the diagnosis of right ventricular failure and is accurate for the evaluation of pulmonary hypertension.

Severe pulmonary hypertension is associated with a 7% mortality rate in non-cardiac surgery in which right ventricular failure is a contributing cause of death.

Valvular Lesions:

Valvular heart disease is an independent risk factor for peri-operative mortality and morbidity. Lack of symptoms in patients of Valvular heart disease patients may be falsely reassuring. Classifying clinically detected murmur as normal or abnormal may be difficult and should always be assessed by echocardiography to know its severity and consequences.

Stenotic lesions are fixed cardiac output lesions and patient may get decompensated by tachycardia and sudden volume overload. Stenotic lesions cause pressure overload on proximal chamber of the heart and may also result in back pressure changes. Atrial outflow stenotic lesions will cause enlargement of the atrium and back pressure changes like pulmonary hypertension or hepatic congestion with IVC fullness. Ventricular outflow stenosis will cause ventricular hypertrophy.

The documented prevalence of aortic stenosis of moderate to severe degree in elderly hip fracture patients is around 8%. These patients may have reduced activity in day to day life and therefore they may not exhibit the symptoms. Delay in fracture hip surgery is associated with higher morbidity and mortality. But urgency of surgery should not preclude the echography evaluation of the patient.

Regurgitant lesions will cause volume overload in the receiving chamber. These lesions are better tolerated by the patients unless there is decompensation. Ultimately both the types of Valvular lesions will cause back pressure changes with involvement of pulmonary circulation in most of the patients.

Septal Defects:

Echocardiography is sensitive enough to detect atrial septal defect (ASD) and ventricular septal defect (VSD). The incidence of asymptomatic probe-patent foramen ovale may be as high as 27% of the population as a whole. Preoperative diagnosis of this condition is important especially in case of surgeries performed in sitting position or steep reverse Trendelenberg position for fear of paradoxical air embolism. Some hospitals consider patent foramen ovale as absolute contraindication to surgery in sitting position.

VSD usually presents with symptoms in early age. If untreated, such patients have higher right sided pressures and their consequences.

Inferior Vena Cava Status:

 Changes in volume status of inferior vena cave during phases of respiration can give clue about intravascular fluid status of the patient. This helps in the decision making whether to administer fluids or vasopressors in patients of poor LV function, higher grade diastolic dysfunction with normal LV function and patients in intensive care units with shock and variable LV function likely to be scheduled for surgery.

Role of echocardiography in obstetrics patients:

With delayed pregnancies in advanced age for various reasons, the incidence of cardiac diseases is increasing in obstetric patients. Congenital Heart disease, coronary artery disease and peri partum cardiomyopathy are leading causes of maternal mortality. Breathlessness at rest or on exertion as a symptom is common in pregnancy and can cause diagnostic dilemmas in this group of population. Perioperative management of such complex patients can be very challenging for an attending anaesthesiologist. Echocardiography is recommended as a first-line investigation in the diagnosis and management in severe chest pain and shortness of breath.

There are studies which demonstrated that echocardiography is redefining the status of hypertension in preeclampsia. Some pregnant women would appear to have a high cardiac output with mild elevations in systemic vascular resistance, while others have a low cardiac output and a high systemic vascular resistance. There is a strong agreement that diastolic dysfunction and pericardial effusion are more common in women with untreated pre-eclampsia.

Recommendations of 2 D Echo in Pre Anaesthesia Check-up:

Various societies over the world have strongly recommended pre-operative echocardiography in following situations:

• To assess left ventricular function and Valvular pathology
• If there are new clinical signs of cardiac failure
• New finding of systolic murmur in those aged over 60 and in any patient if in addition the ECG is abnormal or there are cardiac symptoms
• Assessment of known moderate or severe aortic stenosis if the valve has not been imaged within the last 1-2 years
• Diagnosis and assessment of pulmonary hypertension

Impact of 2 D Echo:

• Echocardiography in non-cardiac surgery and obstetric practice is an emerging technological application
• It helps in stratifying perioperative cardiac risk by evaluation of severity and nature of cardiac disease before subjecting the patient to anaesthesia
• It helps in deciding the requirement of vasopressor and/or invasive monitoring in perioperative period
• It helps in increasing hospital efficiency and streamlining post-operative resource allocations like reservation of high dependency unit beds or ICU beds.

Greater accuracy of preoperative assessment can reduce post-operative referrals to HDU areas and also reduce surgical cancellation rates for want of bed in critical care areas.

References:

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   Anaesthesia 2014, 69, 764–776
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   Sherif F. Nagueh, Otto A. Smiseth et al
   J Am Soc Echocardiogr 2016;29:277-314.
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   Queenie Lo and Liza Thomas
   AJUM February 2010; 13 (1): 14–26
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   Journal of Anaesthesiology Clinical Pharmacology | July-September 2014 | Vol 30 | Issue 3
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   Patricia A. Pellikka, Adelaide Arruda-Olson et al
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