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CARDIAC SURGERY

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david dever

on 24 December 2013

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Transcript of CARDIAC SURGERY

C A R D I A C S U R G E R Y
E-learning
presentation
G62
V E S S E L S
V A L V E S
C O N D U C T I O N
R I S K
F A C T O R S

M E D I C A L
M A N A G E M E N T

A R R H Y T H M I A S
E P I C A R D I A L
P A C I N G

1 2 L E A D
E C G

The chambers of the heart consist of two
ventricles
, with thick muscular walls, and two
atria
, with thinner, less muscled walls.

A
septum
divides the ventricles and extends between the atria dividing the heart into left and right sides.

The right atria receives de-oxygenated blood from the
vena cava
and the right ventricle pumps it to the lungs through the
pulmonary arteries
. The lungs oxygenate the blood and return it to the left atria via the
pulmonary veins
where the left ventricle pumps it throughout the body via the
aorta

Blood supply to the heart is via two main coronary arteries, left and right, commonly referred to as
LCA and RCA.

The LCA quickly divides into the
Circumflex
branch and the
anterior descending branch (LAD)
.

Should these vessels become blocked or partially occluded in anyway, then an
imbalance
between
oxygen supply and demand
occurs within the myocardium and
ischemia
may develop
S U R G I C A L
M A N A G E M E N T

The narrowing of major vessels, resulting in diminished blood flow, means that the artery cannot respond efficiently to any increase in oxygen demand, hence myocardial ischemia is more likely to occur.
Symptoms include dyspnoea, chest pain, and decreased exercise tolerance.

Coronary artery disease
can be treated medically or through revascularization, by angioplasty, stenting or coronary artery bypass grafting (CABG).

A
CABG
is a major surgical intervention and consists of suturing either a segment of the saphenous (major leg vein) vein or radial artery to a small opening in the aorta at one end and to a coronary artery at the other, or using the distal end of the internal mammary artery sutured into the coronary artery, thus bypassing the obstructed or diseased segment.


Prior to surgery patients undergo an Echo and Angiogram to accurately assess cardiac function. Copies of these reports must accompany them to theatre.

The patient requires a full pre-operative shave of the inner thigh, calves and groin as well as forearm and chest area - see right.
Pre-op Tips
Valvular heart disease is a condition characterised by impaired function of one or more of the
four
main heart valves2.

One, or both, of two basic functional abnormalities may be present:
STENOSIS:
impeded forward flow through on open valve

REGURGITATION:
backward leaking of blood through a closed valve

The left sided valves (mitral and aortic) are often the most commonly affected with mitral valve disease the most prevalent.

Valvular dysfunction increases cardiac workload
, i.e., regurgitation forces the heart to pump increased volumes and stenosis necessitates the generation of increased pressure to overcome increased resistance to flow.

Myocardial response to these pressures is the development of chamber
dilation
and
hypertrophy
, in an effort to enhance the heart’s pumping capability.

Causes of valve disease
include :
Rheumatic Fever
congenital abnormalities
Endocarditis
Malformation secondary to coronary artery disease.

Symptoms include fatigue, dyspnoea, palpitations and murmur. Surgical treatment of the flawed valve entails either replacement or repair.

Often only the chordae or leaflets may fail and therefore only part of the valve requires replacement or repair.

Replacement of the annulus ring may be all that is required to improve performance
In most cases, replacement of the heart valve requires the patient to be on some form of anti-coagulation therapy to prevent clots developing on or around the device.
Warfarin
education is a vital part of the nurses role to ensure compliance and understanding.

Valves used fall in the catergories:
mechanical
porcine
bovine
tissue.

They are coated to prevent rejection and have a lifetime of approx 10 - 15 years.


Pre-op Tip
All patients must have a dental check up prior to surgery to ensure maximal oral health. The tooth canal is a common portal of entry for bacteria in valve disease.
Post-Op Tip
A full septic screen and blood cultures should be sent for any valve patient who reaches 37.5 or above.
CARDIAC

SURGERY
The electrical conduction system for the heart is made up of a number of specific pathways that enable the myocardium to contract in an orderly efficient manner in response to demand.

From the SA node the impulse spreads throughout the
L) & R) atria
and down to the AV node.
The
Sino atrial
node is the hearts
dominant pacemaker.
It is located at the base of the pulmonary vein in the right atria and its depolarization is depicted as the
P wave
on ECG
A
t the AV node the impulse is delayed to allow atrial contraction to eject blood into the ventricle (the atrial “kick”) and complete ventricular filling.

The time it takes the impulse to get from the SA node to the AV node is represented by the
PR interval
on ECG
The impulse then continues through the
Bundle of His
to the left and right bundle branches, where the impulse is disseminated into the
Purkinje fibres
for ventricular depolarisation to occur. This event is represented as the
QRS complex
on ECG










Depolarisation of the ventricular muscle mass causes ventricular contraction and ejection of the blood from the ventricles. Following this the heart enters a resting phase known as
repolarisation
(shown as the
T wave
on ECG)
Coronary artery disease
, is one of the most common diseases affecting the adult population.

It is caused by a process known as
Atherosclerosis
which causes irregularity and thickening inside arterial walls.

It is recognised by the deposition of artheroma, or plaque.

The causes of arthrosclerosis, referred to as risk factors, are multi-faceted and can often be related to a combination of factors such as
age
diet
genetics
gender
lifestyle
weight
smoking etc.
Drug therapy plays an important part in patient care post cardiac surgery.
Statin therapy
in the form of cholesterol lowering agents help in slowing the coronary artery disease process.

Blood thinning agents such as
Aspirin
help maximise blood through diseased arteries thus lowering the workload of the heart

If the patient has suffered a myocardial infarction;
diuretics
, anti-hypertensives in the form of
ACE inhibitors
and rate control agents such as
beta-blockers
all help to reduce the work demands placed on the heart.

These drugs form the cornerstone of medical management for all patients post cardiac surgery. As a nurse it is you role to ensure they are prescribed.
Pre-op Tips
Aspirin must be witheld 7 days prior to surgery to lessen the risk of bleeding intra-operatively
Post-op Tips
It is important to attempt to re-start a patients pre-op beta-blocker as early as possible after surgery to decrease the risk of
rebound tacchycardia
which can be caused by their abrupt cessation.
Pre-op Tips
Post-op Tips
Maintence of strict blood pressure control is imperative post cardiac surgery to lessen the strain placed on newly sutured vessels.

.
Two primary issues confronted the original pioneers of open heart surgery;

1: how to maintain blood supply to other vital organs while the heart is stopped
2: how to avoid ischemia in a heart devoid of blood supply


In the late 1940s research by Dr John Gibbon resulted in the development of a machine called Cardiopulmonary Bypass (CPB) .

CPB works in place of the patient’s heart and lungs
by providing blood flow and gaseous exchange.

Venous cannulae are used to drain blood from the right side of the heart via the vena cava into the CPB circuit. As the blood is pumped through the circuit it is oxygenated, filtered, cooled or warmed, and then returned to the body through arterial cannulae inserted in the aorta, or in some cases, the femoral artery. Cannulating the aorta carries risk and may lead to aortic dissection and embolisation of plaque into the cerebral vessels.

CPB is managed by a senior anaesthetist called a “perfusionist”.

Early studies suggested that by inducing a state of hypothermia, thereby reducing metabolic activity and oxygen demand, the operative period could be endured longer while decreasing potential for tissue damage to other vital organs.
The act of inducing hypothermia in cardiac surgery is referred to as myocardial protection.

Once CPB has been commenced and hypothermia achieved ( 280 C – 320C ), the aorta is then cross clamped providing the surgeon with a bloodless field within which to work. Collateral vessels in the pericardial attachments and pulmonary vein walls continue to provide some blood flow during the period of cross-clamping .

Cardiac arrest is induced and maintained using a cardioplegic solution and the surgeon is now ready to begin the specific procedure on a non-beating heart.

Recent improvements in the form of"the Octopus" have made it possible to hold the beating heart steady while operating thereby eliminating the need for cardiopulmonary bypass.

The patients who undergo "Off-pump" surgery seem to progress better as they do not suffer any of the adverse effects attributed to cardiopulmonary bypass, ie, visual disturbances, hallucinations, risk of air emboli etc

Even if a patient is booked for Off-pump surgery the Bypass machine is still assembled in the event thatcomplications arise that force the surgeon to switch to more conventional means
Once surgery has been completed and the heart has warmed sufficiently enough to resume a spontaneous rhythm, weaning from CPB is commenced and in some instances defibrillation (5-10 joules) may be required to establish a stable, perfusing rhythm.

Once off the CPB, inotropic support and/or temporary pacing are frequently required initially, to ensure adequate arterial pressure, renal function and cardiac output are maintained.

Subcostal drains are placed in position and the chest
cavity is then closed in layers. The patient is transported
directly to the Intensive Care Unit with the anaesthetist
for overnight monitoring and pressure support.

As with any type of surgery there are a number of potential complications that also arise in the acute post-open heart surgery phase.
COMPLICATIONS OF CARDIAC SURGER
Y
Haemorrhage
Low cardiac output
Hypertension
Arrhythmias
Stroke
Renal Failure
Respiratory
Nerve injury

Haemorrhage
is always a risk factor in any type of surgery and frequently can be corrected. Initially post CPB, bleeding may not be apparent until the body warms and blood pressure increases. The volume of drainage into the sub costal drains (tubes that drain from the
pericardium, mediasteinum
and
pleural cavity
that are inserted at the time of theatre) alert nursing staff to continued excessive bleeding. If the bleeding is excessive or if the drains become clotted, cardiac tamponade may occur. As blood accumulates in the pericardial space or mediastinum, pressure increases against the heart, reducing ventricular movement2 . In these situations, relief of the pressure is called a sternotomy. Signs and symptoms of
cardiac tamponade
are :
increased heart rate
decreased blood pressure and urine output
increased CVP
excessive or abrupt cessation of SCC drainage.
Low cardiac output is another common problem post operatively that may result in stroke or acute renal failure. It can be caused by bleeding, hypovolaemia, arrhythmia, or myocardial dysfunction. The first line of treatment is to ensure adequate (cardiac) preload filling pressures by means of increased volume. Sustained low filling pressures despite volume replacement suggests haemorrhage2
Low output despite adequate preload may indicate a problem with cardiac function, i.e. infarction or pre-existing impaired ventricular function. Treatment in this instance usually relies on inotropic support such as Dopamine, Dobutamine, etc.
Temporary pacing may also be used to optimise cardiac rate and rhythm.

Low cardiac output
is another common problem post operatively that may result in stroke or acute renal failure. It can be caused by bleeding, hypovolaemia, arrhythmia, or myocardial dysfunction. The first line of treatment is to ensure adequate (cardiac) preload filling pressures by means of increased volume.

Low output despite adequate preload may indicate a problem with cardiac function, i.e. infarction or pre-existing impaired ventricular function. Treatment in this instance usually relies on inotropic support such as Dopamine, Dobutamine, etc.

Temporary pacing may also be used to optimise cardiac rate and rhythm.

Hypertension
may develop from a variety of means, either mechanical, or rebound from cessation of beta-blockers or as the patient wakes from anaesthesia and becomes intolerant to mechanical ventilation and endotracheal suctioning. They may also become increasingly aware of pain.

As hypertension exacerbates bleeding and stresses newly sutured vessels, it is important to gain control quickly through the use of ACE inhibitors, beta-blockers, trinitrates, further sedation or analgesia.
Arrhythmias
are common and usually treated effectively with defibrillation, temporary pacing, electrolyte replacement or anti-arrhythmic medication. Approximately 30% of patients undergoing open heart surgery will experience post operative AF.


Stroke
is a very real complication of any major surgery, and a small risk exists in the peri operative phase of cardiac surgery also. Should any plaque be dislodged from the aorta during cross-clamping there is always a risk of stroke. Air left in the heart post CPB weaning may result in cerebral ischemia and small emboli may form in the heart chambers secondary to atrial fibrillation or myocardial infarction. 70% of strokes occur on the table and the other 30% in the early post-op period.2

Renal Failure
can occur either as a result of hypovolemia and/or low cardiac output. Characterized by an increasing serum
creatinine
and
potassium
the patient may require diuretics or inotropes in varying dosages.
Severe failure may require the need for haemodialysis. In such patients all nephrotoxic drugs (e.g. ACE inhibitors, non-steroidals etc.) are withheld until blood results show a downward trend.


Respiratory complications
range from the development of
pleural effusions
that may require drainage, through to
atelectasis
and
chest infection
needing subsequent antibiotic therapy. Patients will often develop some degree of lobe collapse, usually lower, and usually left greater than right. This is expected, hence the importance of deep breathing, coughing and mobilisation.

sternal wires
ECG leads
crappy lungs
Nerve injury
is usually a relatively minor side effect, however may be quite debilitating for the patient initially.
Phrenic nerve palsy may occur as a result of the cardioplegic solution contacting the phrenic nerve intra-operatively. The result is impaired pulmonary function due to diaphragmatic instability.

Brachial plexis injury may occur as a result of sternal retraction and positioning of the patient during the procedure. The results may vary from parasthesia in the fingers to severe pain down the arm. Both these palsy’s resolve over time.
Post-op Tips
Pre-op Tip
Pre-operative ECG is an essential tool in ascertaining baseline conduction attributes or deficits, making diagnosis of any post-operative abnormalities easier.
Post - op Tip
Patients undergoing valve surgery are more likely to develop conduction issues post-operatively due to trauma caused around the AV node by the surgeon cutting the myocardium to access the mitral or aortic valve.
Electrocardiography is a powerful diagnostic tool used widely in the pre-operative and post -operative setting in relation to coronary artery disease and cardiac surgery.

It helps clinicians pinpoint trouble spots throughout cardiac anatomy and is used in conjunction with patient history, blood results and physical examination to refine diagnoses.
Nursing staff in the care of patients post cardiac surgery should strive to become proficient in the ability to read and diagnose 12 lead ECG
The 12 lead ECG is a map of the electrical activity of the heart. When a 12-
Lead ECG is recorded it provides 12 different views of the heart.
This allows decisions to be made about ECG changes that cannot be made
reliably using one view alone.
The ECG consists of the:
·
Rhythm Strip
- This runs along the bottom of the ECG and is usually
derived from lead II. We use the rhythm strip to analyse the
rhythm.

·
Right half
- Comprises the unipolar chest leads (precordial V1 – V6)

·
Left Half
- Comprises the bipolar limb leads (I, II, III) and the augmented
unipolar limb leads (aVR, aVL, aVF).
RIGHT
LEFT
Rhythm Strip
Imagine the ECG electrodes are
cameras
that look from the chest wall into the heart.

An impulse from the SA node usually runs in a downward diagonal direction from the centre of the chest to the L) foot.

If an impulse heads
TOWARDS
a lead you will get a
positive
deflection on the ECG in that lead i.e the complex will move above the isometric line

Likewise if an impulse moves AWAY from a lead you will get a negative inflection
The
chest leads (precordial V1 – V6)
provide a transverse view through the heart.

The position of the heart in the thoracic cavity is such that the left ventricle lies anterior to the chest wall.

Therefore, there is no direct view of the right ventricle or posterior aspect of the left ventricle from the precordial leads.
The
limb leads
provide us with a
vector view of the heart drawn
as such
This helps clinicians to map conduction pathways and deviations
Different groups of leads tell us about conduction throughout specific sections of the heart.

These are known as :
Anterior
Inferior
Septal
Lateral
For example aVF and Lead II are usually always
+ve
because the impulse travels
towards
that lead
SA
Similarly aVR is usually always
-ve
as the impulse moves
away
from that lead
One small square on the ECG paper equals 0.04 sec

One large square equals 0.2 sec

A rhythm strip is 6 seconds long
Normal PR interval is less than 1 second (1 large square)

Normal QRS width is less than 0.8 sec (2 small squares)

ST elevation is considered if the ST segment rises 2 small squares above the isometric line

QT interval should be less than half the RR interval
When reading an ECG consider:

Rate
- fast vs slow ,ie, tachycardia vs bradycardia

Rhythm
- regular vs irregular ie, sinus or not

Landmarks
- P wave for every QRS
- PR interval less than 1 large square
-QRS width less than 2 small squares
- presence of ST elevation

Presence
of any ectopic or premature beats

Compare
with previous ECGs
Impulses that occur occur outside of the normal pathway are called
ECTOPIC
.

In the acute setting they are usually a sign of cardiac
irritability
Ventricular ectopic (VEB)
Some impulses are generated before the inherent rate.These are called
PREMATURE
beats

They can be either atrial or ventricular

These are also a clue to irritability in the acute setting
Electrophysiology
The origins of the cardiac cycle begin at the cellular level where there is a shift of charged particles, or ions, across the cellular membrane. This movement of ions results in depolarisation and repolarisation and is known as the action potential of the cell.

Action potential is a momentary change in electrical potential on the surface of a cell, especially of a nerve or muscle cell, that occurs when it is stimulated, resulting in the transmission of an electrical impulse

This impulse is transmitted along the cardiac conduction pathway to produce PQRST complexes.

There are 5 stages to the action potential of the cell, numbered 0-4 .
The resting membrane potential (4), depolarisation (0),
early rapid repolarisation (1),
plateau phase (2),
repolarisation (3)
and finally back to the
resting membrane potential. (4).
How Action Potential relates to the QRS
All cardiac cells have
4
inherent properties

Automaticity
- the ability to generate an impulse. This is an in-built safety mechanism should the dominant pacemaker (the SA node) fail to fire.

Excitability
- the ability to receive and respond to an impulse. This can be heightened by cardiac surgery, trauma or electrolyte imbalance and increases the risk of developing an arrhythmia through irritability

Conductivity
- the ability to pass on an impulse to neighboring cells

Contractility
- the ability of the cell to contract in response to depolarisation
If the inherent electrical system of the heart does not generate impulses or fails to conduct impulses, it is possible to stimulate and induce depolarisation and subsequent contraction by means of current from an external source.


Cardiac Pacing is the delivery of an artificial electrical stimulus in order to initiate and maintain an adequate cardiac rate, rhythm and output.

Cardiac pacing may be initiated either as a prophylactic or emergency measure.

Conduction disturbances resulting from myocardial infarction, surgery or trauma may be transient in nature and may resolve during the healing process.

Cardiac rate and output in the early post-operative phases of cardiac surgery may not meet metabolic demand.

External pacing allows us to maximise cardiac output in order to meet this demand.

Medtronic pacing box
Temporary epicardial pacing may achieve one or both of the following:
(1) Control of rate
(1) Support of rate

Pacing is indicated when there is failure of the inherent pacemakers to initiate a rate to maintain a reasonable blood pressure or where the normal conducting pathways are unable to conduct an impulse effectively, eg, bradycardias, AV blocks.

The atrial contribution to cardiac output may be up to 30%. It is therefore desirable to enable the atria and ventricles to function in sequence when possible. If there is evidence of normal AV conduction it would therefore be preferable to choose a mode of pacing that has the ability to deliver the current to the atria.

In an Emergency situation, pace the ventricles.


The components of temporary pacing systems include pacing wires, a connecting lead and a battery-powered pulse generator.

The pacing wires and lead are insulated and provide a loop between the external pulse generator and the epicardium.

Epicardial Pacing Wires (EPW) are lightly secured to the epicardium during surgery and pulled through the skin where they are secured externally. In this unit, the ventricular wire will be on the left and the atrial on the right. There is no negative or positive wire.

The pacing box provides the stimulus to maintain a heart rate that can be controlled using a variety of programmed settings. Although the pacing boxes can be intimidating it is essential the cardiothoracic nurse has a thorough working knowledge of all pacing boxes available in this unit.


There are four main settings that can be programmed and adjusted when using external pacing boxes:

RATE
OUTPUT
SENSITIVITY
AV INTERVAL

RATE:
Rate indicates the specific speed you desire the heart to beat at.


OUTPUT:
Output is the amount of energy delivered by the pacing box. It is measured either as current in milliamps (mA), or as voltage measured in Volts. The main components essential to the determination of output are: -
1.
Pacing spike
- the pacing spike is a vertical line seen on ECG that is proof that the generator has discharged.
2.
Capture
– is a pacing spike followed by the desired waveform in line with the pacing mode being used. Evidence of a desired waveform (ie depolarisation) does not always mean it has been followed by a mechanical event (ie contraction). You must check for a pulse and blood pressure as evidence that this is occurring.




For example when pacing the atria you want to see a pacing spike before the P wave.
When pacing the ventricle you want to see a pacing spike followed by a widened (bizarre) QRS
Pacing spike
SENSITIVITY:
Sensitivity refers to whether or not the pacing box has been programmed to have the ability to sense underlying cardiac rhythm and respond to it. Pacing may either be:

Demand
- will sense inherent rate and will pace if rate of inherent activity detected is lower than rate setting on pacing box. OR
Fixed/asynchronous
- will not sense inherent rate and will pace regardless of inherent cardiac activity.

AV INTERVAL:
AV interval indicates the delay between delivery of atrial and ventricular pacing. (normal PR interval is 120 -200 milliseconds).

Modes
A coding system devised by the North American Society of Pacing and Electrophysiology and the British Pacing and Electrophysiology group provides us with a standard system for describing pacemaker functions or modes. The pacemaker code comprises of 5 categories that define pacing mode and uses letters arranged in a particular order depending on the desired pacemaker function.

With regard to Epicardial Pacing, this unit uses only the first 3 categories.

Position 1 chamber being paced (A= atria. V = ventricle. D = dual. )
Position 2 chamber being sensed (A= atria. V = ventricle. D = dual. )
Position 3 mode of response ( I = inhibit, O = override)

Examples:
AOO - has the ability to pace the atria
does not have ability to sense intrinsic activity
current delivery is not inhibited by intrinsic activity
This mode therefore has the ability to pace the atria at the rate set, regardless of the hearts intrinsic activity.

AAI – has the ability to pace the atria.
has the ability to sense atrial activity.
current delivery is inhibited when intrinsic P wave activity greater than the set rate is sensed

VVI – has the ability to pace the ventricle.
has the ability to sense ventricular activity.
current delivery is inhibited when a ventricular waveform is
sensed.

DVI – has the ability to pace the atria and the ventricle.
has the ability to sense ventricular activity.
current delivery is inhibited when intrinsic ventricular rhythm is
sensed.


Problems associated with pacing involve:

Failure to Pace:

The pacing box fails to discharge at the programmed interval. Check connections, battery, box.

Failure to Capture:

The pacing box discharges but fails to capture. Check connections, battery, box and output setting.


Failure to Sense:
The pacing box fails to detect intrinsic activity and delivers a paced beat. Increase sensitivity by lowering numerical value.

AV
SA
Rapid Atrial Fibrillation
No definite P waves
Irregular
Rate > 100 bpm
Atrial Flutter
Junctional Rhythm
Absent (or upside down) P waves
Bundle Branch block
Widened QRS ( > 2 small squares)
ST elevation usually evident
Notched appearence to QRS
Notching
SVT
Rapid rate ( > 150 bpm)
Narrow complex
Treament of all arrhythmia's involves:

Checking the patient - treat if symptomatic (SOB, low BP etc)
Perform ECG
Inform Medical Officer
Check electrolytes ( K+ & Mg+) replace as required

There are two types here
I) the PR interval gradually lenthens and then the QRS drops off
II) the occasional P wave has no corresponding QRS complex (as above)
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