3. Pre-Operative Assessment of Cardiac Function Flashcards
Clinical predictors of perioperative cardiac risk
Defined as myocardial infarction, heart failure or death,
and its incidence in adults undergoing non-cardiac surgery is quoted as being in the
order of 0.5–1%
Clinical predictors
Minor predictors
advanced age, any abnormalities in the ECG, any rhythm other than sinus,
reduced FRC, past history of cerebrovascular accident
and uncontrolled systemic hypertension
Intermediate predictors i
prior myocardial infarction, mild angina pectoris,
diabetes mellitus, compensated cardiac failure
and renal impairment
Major predictors of risk include
unstable coronary syndrome, decompensated heart failure,
any potentially malignant cardiac arrhythmia
severe valvular disease.
Risk classifications
the Goldman index, which was first described in 1977, identified
nine independent variables amongst which were recent myocardial infarction and
heart failure.
modified by Detsky but still remained cumbersome to apply
has since been validated in several studies is that described by Lee
et al. in 1999. This is a further simplification of Goldman which identifies six independent
predictors of adverse cardiac outcome.
Lee’s
In outline summary, these are
(1) high risk surgery,
(2) ischaemic heart disease,
(3) heart failure,
(4) cerebrovascular disease,
(5) type 1 diabetes mellitus
(6) chronic renal impairment.
(In patients with none of these factors the cardiac risk is 0.5%. In patients with three or more the risk is 9%.)
POSSuM
The Physiological and Operative Severity Score for the enumeration
of Mortality and Morbidity (POSSuM) is a more complex scoring system that
uses variable weighting for factors known to be associated with worse outcomes (see
under ‘Scoring Systems’ in Chapter 5.)
Surgery-specific risk: high-risk surgery
(>5% cardiac risk):
includes all emergency major operations
(especially in the elderly),
prolonged procedures involving large fluid shifts or blood loss,
major vascular and peripheral vascular surgery
Of intermediate-risk (1–5%) are intraperitoneal and intrathoracic surgery,
orthopaedic and prostatic surgery,
carotid endarterectomy
other head and neck surgery
Low-risk procedures (<1%) include breast surgery, cataract surgery and endoscopic
procedures
Evaluation and Investigation of Patients Identified as Being at Risk
metabolic equivalent of task level (MET). One MET
represents the oxygen consumption of a resting adult (3.5 ml kg/m
4 METs representing normal daily activities such as climbing a flight of stairs
Cardiac risks are increased in patients unable to meet a four-MET
demand.
Symptoms can be classified according to the New York Heart Association functional classification for patients with cardiac disease
(NYHA)
Class I – ordinary physical activity causes no symptoms.
— Class II – slight symptomatic limitation of physical activity.
— Class III – marked limitation of physical activity.
— Class IV – symptoms on minimal exertion; may have symptoms at rest.
Electrocardiography:
may reveal ischaemic,
hypertrophic and conduction abnormalities. A normal ECG, however, does not
exclude cardiac pathology; hence the value of exercise ECG stress testing which may
unmask ischaemic heart disease and establish thresholds at which symptoms appear
Echocardiography
: this identifies impaired left ventricular function, determines the
ejection fraction (EF), gives information about ventricular wall and septal motion
abnormalities, and detects valvular heart disease. The EF as determined by echocardiography
is not a good predictor of adverse perioperative cardiac events, and in fact
the retrospective analysis of a large cohort of patients (40,000) who underwent
resting echocardiography as part of pre-operative assessment prior to non-cardiac
surgery demonstrated that there were no outcome differences between this group
and controls
Dobutamine stress echocardiography
Dobutamine stress echocardiography: this is useful in patients in whom treadmill
exercise testing is not possible and gives more information than the investigation
performed at rest. Dobutamine increases cardiac output and myocardial oxygen
demand, and a stress echocardiogram can identify regional wall motion abnormalities
which may develop as the myocardium develops areas of focal ischaemia.
Dipyridamole–thallium scintigraphy scanning:
Dipyridamole–thallium scintigraphy scanning: dipyridamole prevents the cellular
uptake of adenosine and so potentiates its powerful vasodilatory effects on the small
resistance vessels of the coronary circulation. In patients without coronary artery
disease, blood flow can increase fivefold, but if there is a significant coronary stenosis
the distal vessels are already maximally dilate
Coronary angiography
Coronary angiography: although invasive, this investigation gives definitive information
about the myocardial arterial supply in patients who are at such high
potential risk that coronary revascularization should be considered.
Cardiopulmonary exercise testing (CPET):
- in CPET patients are exposed to
incremental increases in workload on a cycle ergometer (some centres have arm
ergometers for patients with peripheral vascular disease in whom lower limb claudication pain may end testing prematurely). - Inspired and expired gas analysis allows
estimation of maximal oxygen consumption, or VO2 max, which is a guide to the
patient’s functional capacity. - To achieve 4 METs, which is a very modest level of
activity, a subject needs a VO2 max of 15 ml O2 kg min - Postoperative physiological
stress imposes a lower demand of around 5.0 ml O2 kg min–1, but this is sustained
over a much longer period, and so patients who cannot achieve 15 ml O2 kg min–1
are at risk of cardiac insufficiency after surgery. - This is because most subjects are
unable to sustain oxygen consumption at any more than 40% of VO2 max for any
prolonged period. - identifies the anaerobic threshold (AT),
which is the point at which the oxygen consumption of exercising muscle
outstrips aerobic supply and metabolism switches to anaerobic glycolysis with the
production of lactic acid.
An AT of less than 11 ml kg1 min1 is associated with higher mortality rates, particularly if signs of myocardial ischaemia accompany the ergonomic test. - A low AT indicates poor ventricular function and an inability to
increase oxygen supply in response to the physiological stress of major surgery.
Biological markers:
Biological markers: in response to myocardial ischaemia or to abnormal stretch of
the ventricular wall, cardiac myocytes release natriuretic peptides (NP).
Elevated NP concentrations are powerful and consistent predictors of postoperative cardiac events.
Troponins are a marker of myocardial injury and do not predict preoperative
risk, although peak troponin levels following surgery do correlate with
postoperative mortality at 30 days.
