Cardiac

Question 1

Cardiac Pacemakers

Answer 1

A pacemaker is an electric medical device to help manage irregular heartbeats called arrhythmias.

Pacemakers can also be used to treat some types of heart failure.

Question 2

heart conditions

Answer 2

• Tachycardia heartbeat that’s too fast
• Bradycardia heartbeat too slow
• Irregular heartbeat an arrhythmia
• Symptomatic bradycardias
• Mobitz Type 2 AV block
• Third degree heart block
• Severe heart failure (biventricular pacemakers)
• Hypertrophic obstructive cardiomyopathy (ICDs)

Question 3

What does a pacemaker do?

Answer 3

A pacemaker generates electrical impulses that help your heart beat at a normal rate, rhythm or both.

Question 4

Modern pacemakers have two parts:

Answer 4

1) the pulse generator, which contains the pacemaker’s battery & the circuit that generate electrical signals
2) one or more leads, which are thin wires that deliver electrical signals from the pulse generator to your heart

Question 5

Single-chamber pacemakers

Answer 5

• Have lead in the right ventricle ( if the AV conduction in the patient is abnormal) or right atrium (if issue is with the SA node).
• They stimulate depolarization in the right atrium and this electrical activity then passes to the left atrium and through the AV node to the ventricles normally.

Question 6

Dual-chamber pacemakers

Answer 6

Have leads in both the right atrium and right ventricle. This allows the pacemaker to synchronize the contractions of both atria and ventricles.

Question 7

Biventricular pacemakers have:

Answer 7

• Leads in right atrium, right ventricle and left ventricle.
• These are usually in patients with heart failure. The objective is to synchronize the contractions in these chambers to try to optimize the heart function. They are also called cardiac resynchronization therapy (CRT) pacemakers.

Question 8

Implantable Cardioverter Defibrillators (ICDs)

Answer 8

Implantable Cardioverter Defibrillators
continually monitor the heart and apply
a defibrillator shock to cardiovert the patient
back in to sinus rhythm if they identify a
shockable arrhythmia.

Question 9

Timing circuit:

Answer 9

The timing circuit determines the basic timing rate of

the pulse generator. It consists of an RC network, reference voltage source, a comparator etc.

Question 10

Pulse width circuit:

Answer 10

The stimulating pulse duration is determined by
the pulse width circuit. It is triggered by the output from the timing
circuit. The pulse width circuit is also an RC circuit as the timing
circuit. The output of the pulse width circuit is fed into the pace
limiting circuit.

Question 11

Pace limiting circuit:

Answer 11

The function of pace limiting circuit is to limit
the pacing rate. The maximum pacing rate is usually selected as 120
pulses per minute. The pace limit circuit limit the pacing rate by disabling the comparator for a preset interval of time.

Question 12

Heart stimulator circuit:

Answer 12

This is also called output circuit
since it provides the proper input pulse to stimulate the
heart and hence called heart stimulator circuit.

Question 13

Refractory circuit:

Answer 13

This circuit provides a period of time
following an output pulse or sensed R-wave. During this
time the amplifier will not respond to outside signals.

Question 14

R-wave sensing circuit:

Answer 14

The function of R-wave sensing
circuit is to detect or sense a spontaneous R-wave and
to reset the oscillator when the pulse is not needed.

Question 15

Reversion circuit (Return circuit):

Answer 15

It allows the amplifier to detect a
spontaneous R-wave. In the absence of R-wave, this circuit again allows the
oscillator to generate pulses at its preset rate. This circuit is called reversion
or return circuit since it allows to return the oscillator to its active state.

Question 16

Voltage monitor and controller:

Answer 16

This circuit continuously monitors the
battery voltage. As the pacing rate is depending on the efficiency of
battery, it has to be monitored regularly. If the battery voltage is decreased,
it triggers the energy compensation and pulse duration controller circuit.

Question 17

Energy compensation/ Pulse duration controller circuit:

Answer 17

If the battery
voltage is decreased the energy compensation circuit increases the pulse
duration so that the pulses delivered to the patient are not affected by the
battery charge loss.

Question 18

Rate slow down circuit:

Answer 18

It is a special circuit which slows down the
heart rate during certain conditions such as cell depletion. So the
cell depletion is monitored by the voltage controller circuit, and
whenever cell depletion occurs, the voltage monitor/controller
circuit activates the rate slow down circuit. This circuit slows down
the rate by limiting the current to the basic timing network

Question 19

defibrillator

Answer 19

defibrillator

• An external defibrillator is a device that delivers an electric shock to the
heart through the chest wall. This shock helps restore the heart to a
regular, healthy rhythm.

• Defibrillators are used to supply a strong electrical shock to the heart. Two
electrodes are placed on the chest and a shock is given. A typical
defibrillator device will deliver a shock for three to nine milliseconds

• external defibrillator includes a control box, a power source, delivery
electrodes, cables, and connectors

Question 20

AC Defibrillators

Answer 20

• A shock of 50 Hz is applied to the chest for a time of 0.25 to 1 second through electrodes.
• The procedure of applying electric shock to resynchronize heart is known as Countershock and continues until patient responds.
• Consists of a step-up transformer. A.C supply is given through switches and fuse to
primary winding of the transformer.
• The timing circuit is connected with switch, which is used to preset the time for the
defibrillator to deliver shock to the patient.
• A resistive and a simple capacitor network or monostable multivibrator forms the
timing circuit. They are connected to the electrodes that delivers electric shock to
the heart of the patient. Voltage value ranging between 250 V to 750 V is applied for
AC external defibrillation and 60 V to 250 V is applied for internal.
• To produce uniform and simultaneous contraction of heart muscles large currents
are used for external defibrillation. However, this results in skin burn under
electrodes and violent contraction of heart muscles. It also results in atrium
fibrillation and stops ventricular fibrillation.