Transcript Interpreting blood tests and the ECG: practical

Cardiovascular courses
29th October 2008
Interpreting blood tests and the
ECG: practical risk assessment
Dr T S Dhanjal PhD MRCP
Aims of the talk
• Understand why we do blood tests.
• What to the blood tests mean?
• The importance of risk stratification.
• The Electrocardiograph (ECG).
Why investigate ?
• To detect the secondary causes of hypertension.
• Assess for the consequences of hypertension.
• Risk stratification to determine overall
cardiovascular risk.
• Monitoring of treatment.
• Detection of disease association.
Detection of secondary hypertension
Serum Potassium
Low
Lowish
3.7 – 4.0
Normal
High
3.7 – 5.2 mEq/l
Hyperaldosteronism
Renal Failure
Primary (Conn’s)
Secondary (RAS)
Biochemical Conn’s
Serum measurements
Potassium
Conn’s syndrome
Secondary
hyperaldosteronism
(RAS, renin secreting
tumours)
Liquorice
(11b DHD inhibitor)
Liddle’s syndrome
Sodium
Renin
Aldosterone
Hyperkalaemia
• May develop in Renal
Failure.
• Drugs
– ACE I
– ARBs
– Potassium sparing
diuretics
Serum Sodium
• High / highish
– Primary hyperaldosteronism
• Low / lowish
– Secondary hyperaldosteronism (Malignant
Hypertension or renal disease)
– Diuretic overuse
Urea & Creatinine
• Creatinine
– breakdown product of creatine phosphate in muscle.
– usually produced at a fairly constant rate by the body.
– Filtered by the kidney and not re-absorbed.
– If the filtering of the kidney is impaired then blood levels
will rise.
– Used to determine Creatinine Clearance which
estimates the Glomerular Filtration Rate (GFR).
Monitoring Creatinine levels
• Isolated essential hypertension rarely results in renal
impairment.
• But concomitant disease (diabetes) or treatment (ACE I /
ARB) can exacerbate.
• Intrinsic renal disease can cause hypertension.
• Serum creatinine only rises with marked damage to
nephrons so not a good test to detect early stage kidney
disease.
• Problem with measuring creatinine clearance is a 24
hour urine collection is required.
Is eGFR the answer ?
• NSF for renal sevices requires laboratories to estimate
GFR using the MDRD formula.
• Fundamentally based on serum creatinine measurments so
why should it be any better?
• Just as sensitive as measuring serum creatinine over time.
• BUT variability of eGFR increases as actual GFR improves.
Poggio et al 2005
Reciprocal creatinine chart
Blood Glucose
• Type 2 DM increases risk of cardiovascular,
renal, retinal and neuropathic complications.
• Screen in hypertensive patients:
– Random glucose > 11.1 mmol/l.
– OGTT.
• Is it more important to aggressively control
hypertension ?
– UKPDS trials
Other serum biochemical tests
• Uric acid
– 40% of patients with hypertension.
– Increased with alcohol, thiazide diuretics.
• Liver function tests
– Excess alcohol intake.
– Steatohepatitis – diabetes, metabolic syndrome.
• Serum calcium
– Hypocalcaemia secondary to CRF.
– Hypertension associated with 1˚ Hyperparathyroidism.
– Hypercalcaemia also associated with thiazide
diuretics.
24 hour urine collection
• Young, thin patients with paroxysmal symptoms.
• Urinary metanephrines.
– Metabolite of epinephrine created by action of
catechol-O-methyl transferase on epinephrine.
• Creatinine Clearance using the Cockroft & Galt
formula.
• Sodium excretion to quantify salt intake.
• Degree of proteinuria - renal biopsy ?
Pheochromocytoma
Haematology
• Detection of polycythaemia
– Raised RBC, Hb & RBC volume.
– Primary (PCV) or secondary (hypoxia).
– Gaisbok’s syndrome.
• Mean Cell Volume
– Increased by alcohol and hypothyroidism.
• Connective tissue disease
– Platelets, ESR, autoimmune antibodies etc.
Lipid profile
• For assessment of cardiovascular risk.
Cardiovascular risk assessment
• JBS 2: Joint British Societies' guidelines on prevention of
cardiovascular disease in clinical practice, Heart, 2005.
• Prepared by: British Cardiac Society, British Hypertension Society,
Diabetes UK, HEART UK, Primary Care Cardiovascular Society, The
Stroke Association.
• The specific objective to reduce the risk of CVD and its complications
in high risk patients.
• 3 categories:
– Any form of established atherosclerotic CVD.
– Diabetes mellitus (type 1 or 2).
– Asymptomatic people without established CVD but who have a
combination of risk factors which puts them at high total risk
(estimated multifactorial CVD risk 20% over 10 years) of
developing atherosclerotic CVD for the first time.
Measure total cholesterol AND HDL
Joint British Societies' cardiovascular disease
(CVD) risk prediction chart: non-diabetic men.
Prepared by: British Cardiac Society, British Hypertension Society, Diabetes UK, HEART UK, Primary
Care Cardiovascular Society, The Stroke Association, Heart 2005;91:v1-v52
Assessment of end-organ damage
• Kidneys
– Urinalysis.
• Microvasculature
– Retinopathy.
• Heart
– ECG.
– Echocardiography.
Left Ventricular Hypertrophy
• LVH is one of the earliest manifestations of
hypertensive heart disease.
• Leads to diastolic dysfunction and heart failure
secondary to systolic dysfunction.
• Other cardiac complications:
– Myocardial Infarction.
– Atrial Fibrillation
Electrocardiographic assessment of LVH (1)
Sokolow-Lyon index:
There are two criteria with these widely used indices:
* Sum of S wave in V1 and R wave in V5 or V6 >/= 3.5 mV (35 mm)
and/or
* R wave in aVL >/= 1.1 mV (11 mm)
Cornell voltage criteria – These more recent criteria are based
upon echocardiographic correlative studies designed to detect a left
ventricular mass index >132 g/m2 in men and >109 g/m2 in
women.
For men: S in V3 plus R in aVL >2.8 mV (28 mm)
For women: S in V3 + R in aVL >2.0 mV (20 mm)
Cornell voltage-duration measurement
QRS duration×Cornell Voltage > 2440 ms × mV
Electrocardiographic assessment of LVH (2)
Sensitivity and specificity for selected ECG criteria of LVH
Sensitivity
(%)
Specificity
(%)
Sokolow Lyon Voltage
22
100
Cornell Voltage Criteria
42
96
Cornell Voltage Duration
Criteria
51
95
RaVL > 11 mm
11
100
Romhilt-Estes > 4 points
54
85
Romhilt-Estes > 5 points
33
94
Criterion
Summary
Potassium
Sodium
Creatinine
Glucose
Diuretics, renal disease, Conn’s.
Primary hyperaldosteronism.
Monitor renal function.
Screen for diabetes mellitus.
Urate
Diuretics, alcohol.
LFTs
Alcohol.
Calcium
Primary hyperparathyroidism
Total Cholesterol /
HDL
Calculate cardiovascular risk.
Haemoglobin
Mean cell volume
Polycythaemia, CRF.
Alcohol.
Platelets
Connective tissue disease.
Urinalysis
Proteinuria, Haematuria, Glycosuria.
ECG
Left ventricular hypertrophy.