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Differential DiagnosisDr Laura bland
Most errors in clinical reasoning are not due to incompetence or inadequate knowledge but to frailty of human thinking under conditions of complexity, uncertainty, and pressure of time.
Ian Scott ; BMJ 339:22-25
Differential Diagnosis
Static Process Patient
encounter
Differential Diagnosis
Diagnostic testing
Final diagnosis
History Physical
PHYSICAL
DIFFERENTIAL
HISTORY
Differential DiagnosisDynamic Process
Where do you begin?
Use available information
• Age• Gender• Chief complaint• Vital signs
Thought process…..
Epidemiology, chief complaint, vital signs
Differential diagnosis
Focused history and physical assessment
Problem list
Refine differential diagnosis
Further history
? Final diagnosis
Example case: 25 year old male with“cough, fever, headache, tired”
Cough Fever Headache
Fatigue
infection autoimmune vascular nutrition
trauma infection exposure metabolic
congenital inflammation
neoplasm infection
exposure endocrine neurologic endocrine
meds/drugs neoplasm psychogenic meds/drugs
neoplasm meds/drugs infection exposure
neurologic metabolic meds/drugs neoplasm
psychogenic exposure trauma autoimmune
Warning: Don’t fall into these traps
• Availability (Past similar/ a lot of it about/ common conditions)
• Anchoring (first diagnosis, ignore new evidence)• Representativeness (Best fit: not making differential
diagnosis)• Confirmation bias / Attribution bias (selective
listening – make it fit)• Premature closure (before all evidence)• Framing effect (favouring a diagnosis because of
context/ Friday afternoon)• Momentum (drawing others into your belief)
Differential Diagnosis of Chest Pain
• There are literally dozens of illnesses, injuries and conditions that can cause chest pain
• Such as– Ischaemia– Pericarditis– PE– Hyperventilation– Dyspesia– Trauma
History• Age• Previous episodes• Fever• URTI• Trauma• Stress• Emotional upset• Cardiac disease
– HTN– CAD– Angina
• Phlebitis
Associated Signs/Symptoms• Dyspnoea• Diaphoresis• Nausea/vomiting• Lightheaded• Syncope• Neuro changes• Hypo or hypertension• Decreased/absent breath sounds• Cyanosis• Haemoptysis• Pulsating abdo mass• Rash or lesions• Pain on palpation
Aggravating and Alleviating Factors
Aggravating Alleviating• Rest or decreased movement• Position• Sitting up• Leaning forward• Decreased or shallow breathing• Diet• Antacids• Medications
• Breathing• Movement• Stress• Exertion• After eating• After ETOH• Laying down• Situational/Anxiety
Case Example: 24 year old male with chest pain
An introduction to ECGs
Structure and function of the heart
Superior vena cava
Lung
Tricuspid valve
Right ventricle
Inferior vena cava
Tissue cells
Aorticvalve
Aorta
Left ventricle
Mitral valve
Pulmonary vein
Pulmonary artery
Left atrium
Right atrium
O2
CO2
O2
CO2
O2
O2
CO2
CO2
Initiation and spread of electrical activation
Sino-atrial node
Purkinje fibresRight & leftbundle branches
Atrioventricular bundle (bundle of His)
Atrioventricularnode
The Einthoven triangle
Right arm Left arm
Left leg
Einthovens Triangle - Lead positions
ECG paper
5 Large squares = 1 second
Time
1 Large square = 0.2 second1 Small square = 0.04 second
2 Large squares = 1 cm
6.1
Spread of electrical activity through the atria
P
Atrioventricular node and the bundle of His
Repolarisation of Ventricle
Spread of electrical activity throughout the ventricle
R
QS
T
Depolarisation of Ventricles
PRinterval
Basic ECG waveform
Mill
ivol
ts
Milliseconds
0 200 400 600
-0.5
0
0.5
1.0
P
R
QS
T
The heart in action
P
R
QS
T
The heart in action
P
R
QS
T
Rule 1
PRinterval
Mill
ivol
ts
Milliseconds
0 200 400 600
-0.5
0
0.5
1.0
P
R
T
Q
S
PR interval should be 120 to 200 milliseconds or 3 to 5 little squares
Rule 2M
illiv
olts
Milliseconds
0 200 400 600
-0.5
0
0.5
1.0
QRS
P
R
T
Q
S
The width of the QRS complex should not exceed 110 ms, less than 3 little squares
Components of the ECG
When analysing ECG’sAsk the following questions:
Is it regular?What is the rate?Are there P waves?
Is there a P wave before every QRS complex ?
Is there a QRS complex after every p wave ?
Is the PR interval normal?Is the QRS width normal?IS the ST segment iso- electric?Iso- electric line is where the P wave starts and there is no electrical activity.
The Electrical System (continued)
Normal Sinus RhythmThis is the rhythm that most healthy hearts produce.
The Electrical System (continued)
Ventricular Fibrillation (VF)If a heart rhythm is abnormal it is said to be an Arrhythmia. Ventricular Fibrillation is a life threatening rhythm that will not provide ATP. The only treatment for VF is defibrillation. VF is basically a seizure of the heart. It provides no pumping action. The vast majority of all cardiac arrest patients are in VF initially. VF must be defibrillate quickly or it will convert to aysytole.
The Electrical System (continued)
Ventricular Tachycardia (VT)This arrhythmia, Ventricular Tachycardia is a life threatening rhythm that will not provide ATP. The only treatment for VT is defibrillation. VT occurs when the ventricles fire too fast to pump the blood adequately.
Dorset Ambulance NHS Trust Education Department
The Electrical System (continued)
AsystoleThis arrhythmia, Asystole is a life threatening rhythm that will not provide ATP. The only treatment for asystole is medication. Asystole occurs when the heart’s electrical system has totally failed. A victim with asystole rarely survives. Defibrillation has no effect on asystole.
Dorset Ambulance NHS Trust Education Department
Sequence of changes in evolving AMI
1 minute after onset 1 hour or so after onset A few hours after onset
A day or so after onset Later changes A few months after AMI
Q
R
P
QT
STR
P
Q
ST
P
QT
ST
R
P
S
T
P
QT
ST
R
P
Q
T
7.18
