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Title: Interpreting blood tests and the ECG: practical risk assessment


1
Interpreting blood tests and the ECG practical
risk assessment
Cardiovascular courses 29th October 2008
  • Dr T S Dhanjal PhD MRCP

2
Aims of the talk
  • Understand why we do blood tests.
  • What to the blood tests mean?
  • The importance of risk stratification.
  • The Electrocardiograph (ECG).

3
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.

4
Detection of secondary hypertension
Serum Potassium
Low
Lowish
Normal
High
3.7 5.2 mEq/l
3.7 4.0
Hyperaldosteronism
Renal Failure
Primary (Conns)
Secondary (RAS)
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Biochemical Conns
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Hyperkalaemia
  • May develop in Renal Failure.
  • Drugs
  • ACE I
  • ARBs
  • Potassium sparing diuretics

10
Serum Sodium
  • High / highish
  • Primary hyperaldosteronism
  • Low / lowish
  • Secondary hyperaldosteronism (Malignant
    Hypertension or renal disease)
  • Diuretic overuse

11
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).

12
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.

13
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.

14
Poggio et al 2005
15
Reciprocal creatinine chart
16
Blood Glucose
  • Type 2 DM increases risk of cardiovascular,
    renal, retinal and neuropathic complications.
  • Screen in hypertensive patients
  • Random glucose gt 11.1 mmol/l.
  • OGTT.
  • Is it more important to aggressively control
    hypertension ?
  • UKPDS trials

17
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.

18
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 ?

19
Pheochromocytoma
20
Haematology
  • Detection of polycythaemia
  • Raised RBC, Hb RBC volume.
  • Primary (PCV) or secondary (hypoxia).
  • Gaisboks syndrome.
  • Mean Cell Volume
  • Increased by alcohol and hypothyroidism.
  • Connective tissue disease
  • Platelets, ESR, autoimmune antibodies etc.

21
Lipid profile
  • For assessment of cardiovascular risk.

22
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
23
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 200591v1-v52
24
Assessment of end-organ damage
  • Kidneys
  • Urinalysis.
  • Microvasculature
  • Retinopathy.
  • Heart
  • ECG.
  • Echocardiography.

25
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

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28
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 gt/ 3.5 mV (35
mm) and/or R wave in aVL gt/ 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 gt132 g/m2 in men and gt109
g/m2 in women. For men S in V3 plus R in aVL
gt2.8 mV (28 mm) For women S in V3 R in aVL
gt2.0 mV (20 mm)
Cornell voltage-duration measurement QRS
durationCornell Voltage gt 2440 ms mV
29
Electrocardiographic assessment of LVH (2)
Sensitivity and specificity for selected ECG
criteria of LVH  
Criterion Sensitivity () Specificity ()
Sokolow Lyon Voltage 22 100
Cornell Voltage Criteria 42 96
Cornell Voltage Duration Criteria 51 95
RaVL gt 11 mm 11 100
Romhilt-Estes gt 4 points 54 85
Romhilt-Estes gt 5 points 33 94
30
Summary
Potassium Diuretics, renal disease, Conns.
Sodium Primary hyperaldosteronism.
Creatinine Monitor renal function.
Glucose Screen for diabetes mellitus.
Urate Diuretics, alcohol.
LFTs Alcohol.
Calcium Primary hyperparathyroidism
Total Cholesterol / HDL Calculate cardiovascular risk.
Haemoglobin Polycythaemia, CRF.
Mean cell volume Alcohol.
Platelets Connective tissue disease.
Urinalysis Proteinuria, Haematuria, Glycosuria.
ECG Left ventricular hypertrophy.
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