TỔNG QUAN Pacing Therapy for Bradyarrhythmias

• Flows through the tip electrode cathode • Stimulates the heart • Returns through body fluid and tissue to the IPG anode A Unipolar Pacing System Contains a Lead with Only One Electrode

Pacing Therapy for Bradyarrhythmias

those of past years.

• Compared to the very first

pacemakers paced only in the lower chamber, we’ve had pacemakers that function in both the upper and lower chambers of the heart (DDD/R

pacemaker).

• One of the most notable development was a type of pacemaker that can change its pacing rate because of sensor(s) inside the pacemaker The DDDR pacemaker.

• A pacemaker is really a system that has two

parts: a small metal

titanium can containing

the electronic circuitry

and a long-lasting battery, called a pulse generator and an insulated wire,

called a lead

What is a pacemaker?

• Contains a battery that

provides the energy for

sending electrical

impulses to the heart

• Houses the circuitry that

• Pulse generator: power

• Endocardial or transvenous leads

• Myocardial/Epicardial leads

Types of Leads

Transvenous Leads Have Different “Fixation” Mechanisms

Transvenous Leads

• Active Fixation

– The helix (or screw)

extends into the

endocardial tissue

– Allows for lead positioning

anywhere in the heart’s chamber

Myocardial and Epicardial Leads

• Leads applied directly to the

Conduction Pathways

• Body tissues and fluids

are part of the conduction

pathway between the

anode and cathode

Tissue

Cathode Anode

• Begins in the pulse

generator

• Flows through the lead and

the cathode (–)

• Stimulates the heart

• Returns to the anode (+)

During Pacing, the Impulse:

Impulse onset

*

• Flows through the tip

electrode (cathode)

• Stimulates the heart

• Returns through body

fluid and tissue to the IPG (anode)

A Unipolar Pacing System Contains a Lead with Only One Electrode Within the Heart; In This System, the Impulse:

Cathode

Anode

+

-Unipolar leads

• Unipolar leads may have

a smaller diameter lead body than bipolar leads

• Unipolar leads usually

exhibit larger pacing

artifacts on the surface ECG

• Flows through the tip

electrode located at the end of the lead wire

• Stimulates the heart

• Returns to the ring

electrode above the lead tip

A Bipolar Pacing System Contains a Lead with Two Electrodes Within the Heart In This System, the Impulse:

Cathode

Today Pacemakers

• One lead implanted in

Benefits of Dual Chamber Pacing

• Provide AV Synchrony

• Provide ventricular backup if A-to-V conduction is lost where a single chamber pacing system

cannot.

Proven Benefits of Atrial Based Pacing

Study Results

Higano et al 1990

Gallik et al 1994 Santini et al 1991 Rosenqvist et al 1991

Sulke et al 1992

Improved cardiac index during low level exercise (where most patient activity occurs) Increase in LV filling

30% increase in resting cardiac output Decrease in pulmonary wedge pressure Increase in resting cardiac output

Increase in resting cardiac output, especially

in patients with poor LV function Decreased incidence of mitral and tricuspid valve regurgitation

Proven Benefits of Atrial Based Pacing

Suppression of atrial dysrhythmias Improved morbidity (less AF, CHF, embolic events) after

3 plus uears, compared to VVI

• Stimulate cardiac depolarization

• Sense intrinsic cardiac function

• Respond to increased metabolic demand by providing rate responsive pacing

• Provide diagnostic information stored by the pacemaker

Most Pacemakers Perform Four Functions:

Rate Responsive Pacing

Rate Response

• Rate responsive (also called rate modulated)

pacemakers provide patients with the ability to vary heart rate when the sinus node cannot provide the appropriate rate

• Rate responsive pacing is indicated for:

– Patients who are chronotropically incompetent (heart rate

cannot reach appropriate levels during exercise or to

meet other metabolic demands)

– Patients in chronic atrial fibrillation with slow ventricular

response

Rate Responsive Pacing

• Cardiac output (CO) is determined by the combination

of stroke volume (SV) and heart rate (HR)

• SV X HR = CO

• Changes in cardiac output depend on the ability of the

HR and SV to respond to metabolic requirements

Rate Responsive Pacing

• SV reserves can account for increases in cardiac output of up to 50%

• HR reserves can nearly triple total cardiac output in response to metabolic demands

Rate Responsive Pacing

• When the need for oxygenated blood increases, the pacemaker ensures that the heart rate increases to provide additional cardiac output

Adjusting Heart Rate to Activity

Normal Heart Rate Rate Responsive Pacing Fixed-Rate Pacing

Daily Activities

A Variety of Rate Response Sensors Exist

• Those most accepted in the market place are:

– Activity sensors that detect physical movement and increase

the rate according to the level of activity

– Minute ventilation sensors that measure the change in

respiration rate and tidal volume via transthoracic impedance readings

Rate Responsive Pacing

• Activity sensors employ a

piezoelectric crystal that

detects mechanical

signals produced by

movement

• The crystal translates the

mechanical signals into

electrical signals that in

turn increase the rate of

the pacemaker

Piezoelectric crystal

Rate Responsive Pacing

• Minute Ventilation (MV) is the volume of air introduced into the lungs per unit of time

• MV has two components:

– Tidal volume–the volume of air introduced into the lungs in a

single respiration cycle

– Respiration rate–the number of respiration cycles per minute

Rate Responsive Pacing

• Minute ventilation can be measured by measuring the changes in electrical impedance across the chest cavity

to calculate changes in lung volume over time