What is complete heart block?
Complete heart block occurs when the electrical signal can’t pass normally from the atria, the heart’s upper chambers, to the ventricles, or lower chambers. If the atrioventricular (AV) node is damaged during surgery, complete heart block may result. Sometimes complete heart block occurs spontaneously without surgery.
What are the structural abnormalities of complete heart block?
- Fibrosis (replacement of some of the normal cells with fibrous tissue due to cell death due to age) of AV node
- Necrosis / infarction of AV node (death of all or most of cells as a result of coronary artery disease)
What are the physiological abnormalities of complete heart block?
-Complete failure of the AV node to transmit electrical impulse from atria to ventricles
-Atria have electrical activity and contract independently of the ventricles which
develop their own pacemaker activity – usually at a much slower rate (NB all heart cells can initiate a heart beat – though under normal circumstances follow the sinus node in the atria and atrioventricular node in the ventricles)
Normally:
- Transmission of electrical depolarization wave from atria (referred to as “top” of the heart) to ventricles (“bottom” of the heart)
- AV node induces a short delay in transmission – to allow atria to contract before ventricles contract (prevents both contracting together which would not allow tricuspid and mitral valves to open)
What are the prior events to complete heart block?
Elderly patient who may have had a prior myocardial infarction; be taking beta- blocker or other rate lowering drugs (digoxin, verapamil) that act to block AV node.
What are the experienced symptoms of complete heart block?
- Complete heart block can either present gradually and in isolation (chronic complete heart block; tiredness and breathlessness with exercise)
- Or suddenly with other symptoms (acute complete heart block : light-headedness or collapse with loss of consciousness)
- If caused by coronary artery disease (angina or myocardial infarction) these symptom will also be present (usually chest pain)
What are the clinical signs of complete heart block?
-Pulse / heart rate – is slow (often much lower than 60 beats per minute)
-Blood pressure often low
-Patient may be seen to suddenly lose consciousness for some seconds (called cardiac
syncope)
What are the medical/ surgical intervention for complete heart block?
- Ambulance / paramedic staff may administer atropine (blocks vagus nerve and acetyl choline allowing the heart rate to rise)
- A temporary pacemaker may be introduced immediately on arrival in hospital (a wire is introduced into a vein and from there into the right ventricle – allowing a small electrical impulse to be sent to stimulate the heart)
What are the primary and secondary preventions for complete heart block?
If complete heart block persists despite patient recovering from any associate myocardial infarction – and after stopping heart rate lowering drugs – then a permanen pacemaker is needed – and is effective
What is DVT?
Deep vein thrombosis (DVT) is a blood clot that develops within a deep vein in the body, usually in the leg. Blood clots that develop in a vein are also known as venous thrombosis. DVT usually occurs in a deep leg vein, a larger vein that runs through the muscles of the calf and the thigh.
What are the structural abnormalities of DVT?
Blockage of the vein by blood clot (thrombosis) which usually first appears in the calf (lower leg) but may then extend above the knee (femoral vein) and possibly into the pelvis (iliac veins) and abdomen (inferior vena cava)
What are the deep veins in the body?
Deep veins of the leg (femoral and popliteal veins) and pelvis (iliac veins)
What are the physiological abnormalities of DVT?
- Thrombophilia (tendency to develop thrombosis) often expresses itself with recurrent thromboses
- DVT patients may have hereditary thrombophilia, including deficiencies in the anticoagulation factors protein C, protein S, antithrombin, or mutations in the factor V and prothrombin genes
What are prior events to DVT?
-The most common risk factors are recent surgery or hospitalisation
-Low molecular weight heparin prevention treatment helps reduce the risk of this
-Advanced age, obesity, infection, immobilisation, use of combined
(oestrogen-containing) forms of hormonal contraception, tobacco usage and air travel (“economy class syndrome”, a combination of immobility and relative dehydration)
-A family history can reveal a hereditary factor in the development of DVT
What are experienced symptoms of DVT?
-Swelling of right or left calf
-Pain in calf
-There may be no symptoms related to the leg – but sudden pulmonary
embolus may occur
What are the clinical signs of DVT?
-Swelling and redness of the leg and dilation of the surface veins
-Tenderness over veins when applying gentle pressure
-Physical examination is unreliable for excluding the diagnosis of deep vein
thrombosis
What are the abnormal test results for DVT?
- Ultrasound of the leg demonstrates absence or reduction of venous flow and presence of thrombus within vein(s)
- In a low-probability situation, current practice is to commence investigations by testing for D-dimer levels (This is a cross-linked fibrin degradation product - an indication that thrombosis is occurring, and that the blood clot is being dissolved by plasmin)
What are the medical/ surgical intervention for DVT?
- Immediate anticoagulation with low molecular weight heparin
- 3 to 6 month anticoagulation with Direct Oral Anticoagulant or Warfarin
Primary and secondary prevention of DVT?
- Early and regular walking
- Hospitalized patients – Low molecular weight heparin (e.g. Enoxaparin)
- Compression stockings may prevent clots in some patients
- Long-term anticoagulation therapy may be required
What is Fallots Tetralogy?
Tetralogy of Fallot is a combination of four congenital abnormalities. The four defects include a ventricular septal defect (VSD), pulmonary valve stenosis, a misplaced aorta and a thickened right ventricular wall (right ventricular hypertrophy)
What are structural abnormalities of Fallots Tetralogy?
- Ventricular Septal Defect (VSD) – a hole in the heart
- Pulmonary stenosis – a narrowing of the pulmonary valve
- Overriding aorta – position is over the right as well as left ventricle
- Right ventricular hypertrophy – more muscular due to high pressure
What are the physiological abnormalities of Fallots Tetralogy?
- Low oxygenation of blood due to the mixing of oxygenated and deoxygenated blood in the left ventricle via the VSD
- Preferential flow of the mixed blood from both ventricles through the aorta because of the obstruction to flow through the pulmonary valve
- This is known as a right-to-left shunt
What are the prior events of Fallots Tetralogy?
Patients are born with this set of abnormalities with no recognisable prior events / causes (genetic and environmental factors are believed to be causative)
What are the experienced symptoms of Fallots Tetralogy?
- Primary symptom is low blood oxygen saturation with or without cyanosis (blue appearance due to low level of oxygen in arterial blood)
- From birth (congenital) or developing in the first year of life
- Difficulty in feeding
- Failure to gain weight
- Retarded growth and physical development
- Dyspnoea on exertion
What are the clinical signs of Fallots Tetralogy?
-Heart murmur which may range from almost imperceptible to very loud
-Clubbing of the fingers and toes
-Polycythaemia (excess of red blood cells)
-“Tet spells” characterized by a sudden, marked increase in cyanosis followed
by syncope, and may result in hypoxic brain injury and death
-Older children will often squat during a “tet spell” which increases systemic
vascular resistance and allows for a temporary reversal of the shunt
