cardiovascular system and heart ischemia (infarction) incl. detection of heart ischemia using...
TRANSCRIPT
Cardiovascular system and
Heart ischemia (infarction) incl. Detection of heart ischemia using
bioimpedance measurement
Andres Kink
2012
CONTENTS
CARDIOVASCULAR SYSTEM
MYOCARDIAL ISCHEMIA
ANATOMY OF THE HEART
CARDIOVASCULAR SUSTEM AND CORONARY CIRCULATION
CARDIAC RHYTM AND ARTIFICIAL PACING
PRINCIPLES OF RATE CONTROL
Energy as product of low temperature burning of food products inside the body
To maintain life, every living animal organism must have additional energy inflow as food and oxygen.
To save excess of food for future is possible due to intracellular systems. But the same is not possible for oxygen. Oxygen is gaseous, and to accumulate it inside the body in reasonable quantity will take too much energy.
In this text we will focus on energy as energy units (joule) or as units of used oxygen to get energy.
CARDIOVASCULAR SYSTEM
Oxygen and food substrate delivery system for cells
Most of animals (not included fishes) have specialized oxygen carrying system to maintain body tissues oxygenation:
Blood as solute to carry oxygen
Lungs as barrier between atmosphere and blood.
Circulation system as tubing system to carry oxygen rich blood to every cell in body, and to collect waste from it.
Cellular system to produce ATP from energetic substances and oxygen.
CARDIOVASCULAR SYSTEM
Definition:
Myocardial ischemia is an imbalance between oxygen supply of the myocard and oxygen demand of the myocard.
In general ischemia is a decrease in the blood supply to a bodily organ, tissue, or part caused by constriction or obstructionof the blood vessels.
In the case of the heart the ischemia means a narrowing of the coronary artery(s) sufficient to prevent adequate blood supply to the myocardium.
This narrowing may progress to a point where the heart muscle is damaged (infarction)._____________________________________
MYΣ+KAPΔΊA = myocard (muscle + heart, in the contemp. Greek: ο μυς της καρδιάς) (in Latin: MUS(CULUS) = mouse, muscle)IΣX…+AΊMIA = isch(a)emia (Greek: stop+blood)IN+FARCTUS = infarct (Latin: in+filled)
MYOCARDIAL ISCHEMIA
TRANSIEN TREVERSIBLE
DYSFUNCTIO N O F SUBCELLULAR M ECHANISM SNO PERM ANENT STRUCTURAL DAM AG E
PERM ANENT STRU CTURAL DAM AG E
G LO BAL M YO CARDIAL ISCHEM IA
MYOCARDIAL ISCHEMIA
Possible types of ishemia
Ishemia as energy imbalance
Energy imbalance is result of non-equal oxygen supply related to oxygen consumption.
Ischemia with myocardial cell damage is often described in heart as myocardial infarction. Myocardial infarction is not reversible process, cell necrosis is healed by scar formation.
Short time myocardial ischemia is not dangerous, because myocardial has limited protection against lack of oxygen.
MYOCARDIAL ISCHEMIA
Epidemiology
Heart ischemic conditions are most leading reason for mortality in world.
Silent myocardial ischemia is dangerous condition witch leads very offen to myocardial infarction (muscle tissue necrosis)
MYOCARDIAL ISCHEMIA
Ischaemic heart disease world map DALY - WHO2004
MYOCARDIAL ISCHEMIA
ANATOMY OF THE HEART
CARDIOVASCULAR SYSTEM, and
CORONARY CIRCULATION
Xxx
Physiology of the coronary arteries
CARDIOVASCULAR SYSTEM, and CORONARY CIRCULATION
CARDIOVASCULAR SYSTEM, and CORONARY CIRCULATION
Coronary artery disease
Coronary reserve
CARDIOVASCULAR SYSTEM, and CORONARY CIRCULATION
Special Features of Coronary Circulation
At rest, coronary blood flow BF = 5%
of cardiac output CO = 250ml/min = 60-80ml/100gm/min
During exercise rises by 2 … 5 times (coronary vasculature has a high vasodilator reserve capacity)
Coronary Blood Flow is phasic
Total Coronary Flow is greater during diastole
CARDIOVASCULAR SYSTEM, and CORONARY CIRCULATION
Therefore, the most crucial factors for perfusing coronary arteries are - aortic pressure - duration of diastole
Myocardial O2 demand
The cardiac muscle always depends on aerobic oxidation of substrates, even during heavy exercising
The cardiac muscle has the highest O2 uptake (VO2) compared to other tissues of the body (12…15 volume%; 7…9 ml O2/100gm/min)
This is achieved by a dense network of capillaries, all is perfused at rest (no capillary reserve)
Maximal extraction of O2 from RBCs (almost no reserve of O2 extraction)
CARDIOVASCULAR SYSTEM, and CORONARY CIRCULATION
Pressure volume area inside of ventricles (left ventricle)
CARDIOVASCULAR SYSTEM, and CORONARY CIRCULATION
Cardiac cycle and
pressure-volume area
Cardiac Output (CO) determined thru
Heart Rate (HR) and Stroke Volume (SV)
CARDIOVASCULAR SYSTEM, and CORONARY CIRCULATION
Frank Starling Curves
Ability of the heart to change force of contraction in response to changes in venous return.
If EDV increases, there is a corresponding increase in stroke volume, suggesting heart failure and inotropy.
Reduced stroke volume suggests increased preload and decreased ejection fraction.
CARDIOVASCULAR SYSTEM, and CORONARY CIRCULATION
Cardiac OutputCardiac Output is the volume of blood (in liters)
ejected by the heart in one minuteStroke Volume is the volume of blood (in liters)
ejected by the heart in one beatWhen the body is under stress (physical, emotional),
the heart tries to increase cardiac output … by increasing the rate according to this formula
Cardiac Output = Heart Rate x Stroke Volume
CO = HR x SV
CARDIOVASCULAR SYSTEM, and CORONARY CIRCULATION
Bradycardia or “low heart rate”
CARDIOVASCULAR SYSTEM, and CORONARY CIRCULATION
Artifical heart assisting devices
The first artificial pacemaker to maintain heart rhythm was induced by Steiner in Germany to avoid cardiac arrest as a side effect of chloroform anaesthesia.
Steiner's study (1871) was performed in chloroform arrested hearts of horses, donkey, dogs, cats and rabbits.
In the next year the same method was used in humans by Green in the United Kingdom.
The first pacemakers had interrupted galvanic (direct-current) stimuli and were connected by 13 cm long needles directly to the myocardium.
Modern era of implantable pacemakersThe first implantable pacemaker was made by Swedish inventor
Dr. Rune Elmqvist, and implanted in 1958 by Dr. Ake Senning.
The first demand pacemaker was introduced by Berkovits in June 1964. Demand pacemaker have additional sensing unit to avoid competition with heart own pacemaker (sinus node), and to save battery energy.
Pacemakers
Sensory systems
ECG based interval measurements Movement analysis (acceleration, ..) Temperature measurement Impedance based
Lung impedance Intraventricular impedance, mostly right
ventricle Myocardial impedance
Rate adaptive pacing
Heart rate is regulated to maintain body energetic needs
First generation target was night time heart rate reduction
New generation is multisensor (accelometer, ECG, temperature, bioimpedance based, …) based optimal heart rate calculation
Why Rate Response?Rate response is the pacemaker’s ability to increase
the pacing rate in response to physical activity or metabolic demand
Rate response mimics the healthy heartSpecial sensor(s) required
Accelerometer Piezoelectric crystal Minute ventilation (transthoracic impedance) Blood temperature Single or combination
Intracardiac bioimpedance measurement
Normal Chronotropic Response
Chronotropic Incompetence If the patient’s heart cannot increase its rate appropriately
in response to increased activity, the patient is chronotropically incompetent
Chronotropic incompetence (definitions): Maximum heart rate < 90% x (220 - Age) Maximum heart rate < 120 bpm
Causes aging drugs heart disease
SensorsRate-responsive pacemakers rely on sensor(s) to detect
patient activityThe ideal sensor should be
Physiologic Quick to respond Able to increase the rate proportionally to the patient’s
need Able to work compatibly with the rest of the
pacemaker Able to work well with minimum energy demands or
current drain Easy to program and adjust
Types of Sensors
Activity sensors Vibration sensors (piezoelectric sensors) Accelerometers
Physiologic sensors Minute ventilation Temperature Evoked response QT interval Closed loop system (CLS)
Virtual sensors
Activity Sensor/Vibration
Responds rapidly No special pacing leads required Easy to manufacture and program Can be “fooled” by pressure on the can or footfalls (like walking
downstairs)
Activity/ Accelerometer
Responds rapidly No special pacing leads required Easy to manufacture and program Cannot be “fooled” by pressure on the can
Minute Ventilation
Minute VentilationUses low-level electrical signals to
measure resistance across the chest (“transthoracic impedance”)
Requires no special sensorRequires bipolar pacing leadsMetabolic
Temperature
A thermistor is mounted in the lead (not the can) Requires a special pacing lead Metabolic Response time can be slow
Evoked ResponseMeasures the QRS
depolarization areaTheory: the QRS
depolarization decreases in area with exercise
Requires no special leadsMay be affected by
changes in postureOnly works when the
device is pacing
QT IntervalMeasures the interval
between the pacing spike and the evoked T-wave
Theory: This interval shortens with exercise
Requires no special pacing lead
Works only when the device is pacing
Rate-Responsive Parameters to Program
Base rateMaximum tracking rate (in DDDR devices)Maximum sensor rateThresholdSlopeReaction timeRecovery time
Rate-Responsive Pacing
Threshold
Threshold is the amount of activity needed to cause sensor activity
Can also be set to AUTO Measures variations in the last 18 hours of
activity Adjusts threshold automatically Displays Measured Average Sensor value
when pacemaker is interrogated Offset values can be programmed for more
fine-tuning
Threshold in Action
Threshold Programming Considerations
AUTO allows the pacemaker to automatically adjust to the patient’s changing activity levels Updates every 18 hours
AUTO with Offset can further fine-tune the settings A negative value makes it more sensitive (less activity is
needed to start rate response) A positive value makes it less sensitive (more activity is
needed to start rate response)Considerations
Patient age, lifestyle, everyday activities Patient’s fitness level (how likely is he to go jogging?) How well patient tolerates higher-rate pacing
Slope
Slope describes the sensor-drive pacing rate for a given level of activity
AutoSlope Based on recent activity levels
Slope in Action
Slope Programming ConsiderationsSlope determines “how much” rate response is
given for a specific activitySlope factors:
The patient’s age, activities, lifestyle How well he can tolerate rapidly paced
activity How much rate response he needs
Reaction Time
When the sensor determines the patient needs rate response, the Reaction Time parameter regulates how quickly rate response is delivered
Programmable to: Fast, Medium, SlowConsider the patient’s age, lifestyle, activities,
and how quickly he would need rate response Athletic patients probably need a faster
reaction time than couch potatoes Younger, fitter patients probably need a faster
reaction time than older, sedentary patients
Reaction Time in Action
Recovery TimeRecovery time determines the minimum
time it will take the sensor-driven rate at the maximum sensor rate to go back down to the programmed based rate
Similar to Reaction TimeProgrammable as Fast, Medium, Slow,
and Very SlowProgramming considerations are the
usual: Patient age, lifestyle, activity levels Tolerance of rate transitions (can he
tolerate a rapid change in rate?)
Recovery Time in Action
Maximum Sensor Rate
Maximum Sensor Rate is the fastest possible rate the pacemaker will pace in response to sensor input
It does not have to be the same setting as Maximum Tracking Rate (fastest rate the pacemaker will pace the ventricle in response to sensed atrial activity)
The Maximum Sensor Rate must be a rate that the patient can tolerate Maximum heart rate formula (220-age) x .90 is highest
possible setting But if patient cannot tolerate the maximum heart rate,
set the Maximum Sensor Rate to a rate he can tolerate
ThresholdThreshold defines how much activity must occur
before the sensor “sees” activityMost patients do well with AUTOIf AUTO needs some further adjustment, use the
offset feature If sensor seems to react too often or too quickly,
program a positive offset If sensor does not seem to react soon enough or
at all, program a negative offset
Reaction and Recovery TimesReaction time determines how fast rate
response goes to work If the patient does not tolerate abrupt changes
in rate, program this to SLOWRecovery time determines how quickly a sensor-
driven rate goes back to the base rate MEDIUM is a good setting for most patients SLOW can expose the patient to prolonged
periods of pacing at a higher-than-necessary rate
SlopeSlope is “how much” rate response a
patient receives once the sensor determines rate response is needed
AUTO is a good middle-of-the-road choice
Problem
How to control the pacing rate avoiding imbalance between energy consumption and energy supply of the myocardium, estimating:
minute volume (MV) of ventilation
relative stroke volume (SV)
diastolic time (tdiast)
AVOID ISCEMIA, NOT TO MEASURE IT !
Cardiovascular System with a Rate Adaptive Pacemaker
Measurement of Cardiac (ŻC) and Respiratory (ŻR) Impedances
Possible gates for heart rate control
No gates, fixed heart rate Heart rate (slope control) Ventricular volume, minimal stroke volume to
maintain body needs Energy based control : ratio of PVA to
myocardial perfusion index during cardiac cycle
Control system
Optimal v. min-max rate control
Optimal heart rate Mostly
technical, not from real heart physiology
Underestimates heart rate variability importance
Min-max rate gates
Allows to act as supervisory system for other cont. algorithms
Possibility to increase patient cardiovascular system adaptation
Energy Balance
kAVDVE mc
diastmc tR
PV
SVPWE
myocardial myocardial blood volumeblood volume
oxygen uptake oxygen uptake (art(artererio-venous io-venous
differdiffereence)nce)
energetical energetical coefficientcoefficient
(balance)(balance)
hydraulic coronary resistance hydraulic coronary resistance (energy balance(energy balance))
SV
tkAVDR diast
Simplified Calculations
Simplified Calculations (cont.)
kSV
kSV
AVDt
AVDt
R
RCRR
restdiast
restrestdiastrest
,
CRSV
SV
t
t
restdiast
restdiast ,
6to2max CRRR
RCR
min
rest
coronary resistance ratiocoronary resistance ratio
coronary reservecoronary reserve healthy hearthealthy heartarteriosclerosisarteriosclerosis
the condition for the condition for mymyoocardium’s energy cardium’s energy balancebalance
Volume Measurement - Theory
Gmeas = Gblood + Gp
Gp is parallel conductance of muscle and must be removed to estimate volume
Hypertonic saline bolus injection
Conductance signal increases
Gb-ED & Gb-ES both increase
Conductivity of blood changes but not the conductivity of the muscle
Experimental setup with an isolated pig’s heart
“ISHEMIA” data processing
Ischemic damage of myocardial cells
ECGEasy to measure,
Lots of data
SV, coronary perfusionDifficult to measureSmall pieces of data
INFORMATION:LIVE/DEAD
Rhythm type
Diff. to get prognosis
INFORMATION:Pump function
Ischemic status of cells
Easy to get prognosis
Conclusion
Rate response is almost a “standard feature” today
Pacemaker patients often suffer from at least a degree of chronotropic incompetence Many who are not chronotropically
incompetent now will become chronotropically incompetent with disease progression
There is no “perfect” sensorGate based control is important to avoid
“overpacing”
Conclusions
Our experimental studies and theoretical speculations confirm that:
Increased concern over maintenance of energy balance within the heart may be addressed by novel pacing control algorithms that require only relative stroke volume information, derivable from bioimpedance measurements.
New impedance measurement methods can permit more reliable results to make such feedback systems feasible for rate control.