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Effect of electrode pad size on defib - Coggle Diagram
Effect of electrode pad size on defib
Studies
Canine studies
Dahl, 1973
8, 12.8, 4.3 cm
Connell, 1973
• 3 paddle sizes tested: 4.5, 8.0, 12.8 cm ○ Standard-standard: 8-8 ○ Large-large: 12.8-12.8 ○ Standard-large: 8-12.8 Small-small: 4.5-4.5
Pad size inversely correlated with impedance
Hoyt, 1981
various sizes (8.5, 10, 12, 14, 16 cm in diameter)
Increased transthoracic current
Pagan-Carlo, 1997
4, 5.8, 8, 10 cm diameter
50, 100, 150 J
Did electrical mapping with electrical array placed on ventricles near LAD
Unequal size pairs also studied
Cathode on left chest
Strongest correlation: voltage gradient and [heart weight to chest radius ratio]
In silico
Canine
Karlon, 1993
12cm may be slightly better than 8cm
8 cm and 12 cm electrodes
Human
Camacho, 1995
8cm and 12 cm electrodes
29% decrease in paddle impedance for 12 cm compared to 8 cm
Recommend that 12 cm paddles are better than 8 cm
Impedance
Transthoracic current flow during shock is determined by energy and transthoracic impedance
Greater surface area
increase in current, decrease in resistance
Lower transthoracic impedance
Atkins D.L., Sirna S., Kieso R. Pediatric defibrillation: Importance of paddle size in determining transthoracic impedance. J. Crit. Care. 1989;4:319. doi: 10.1016/0883-9441(89)90071-3.
Lower impedance + greater contact surface area maximizes transthoracic current but not necessary intracardiac voltage gradient
Pagan-Carlo, 1997
Impedance is directly proportional to electrode surface area
Electrode pads do not have to be the same size
"Irrespective of the interface, impedance was progressively lower with increasing surface area of paddle electrodes from 4.5 to 12.8 cm in diameter."
Connell, 1973
Impedance with larger 12 cm paddles is 1/3 smaller than for small 8 cm paddles
Karlon, 1993
29% decrease in paddle impedance for 12 cm compared to 8 cm
Camacho, 1995
Electrode pads do not have to be the same size
Connell, 1973
Proportion of thorax occupied by lung is an important determinant of impedance
Pagan-Caro, 1997
Electrode skin interface
Connell, 1973
Tested dry, cream, paste, saline pads
Relationship between impedance and electrode size still holds irrespective of electrode interface materail
Defib success rates
Greater electrode surface area means greater defib success rates
Kugelberg
Ewy
BUT beyond a certain point, rate of successful defib declined
Ewy
Current
intracardiac
current is maximum at a certain optimal paddle size.
greater defibrillation success in dogs could be obtained with 12.8-cm-diameter paddles than with either 8-cm-diameter or 13 X 20-cm paddles.
GA Ewy - Proceedings of the cardiac defibrillation conference, 1975 Defibrillator paddle electrodes. GA Ewy Proceedings of the cardiac defibrillation conference, 39-44, Purdue University Indiana, 10/1975
13-cm-diameter paddles increased total transthoracic current during human defibrillation compared with 8-cm paddles
Kerber, 1979
Reasonable because current is preferentially distributed at the edge of an electrode; increasing ratio of edge length to the geometric surface area more efficiently transfers current from electrode to tissue
Newman, Resistance for flow of current to a disk
Larger (>13 cm diameter) defib paddles will result in increased current
Increased cardiac current will probably improve defib success rate
Hoyt, 1981
Small electrodes deliver higher current densities than larger ones
Pagan-Carlo, 1997
No significant differences in distribution of current density between 12cm and 8 cm paddles
Karlon, 1993
Highest current density falls beneath central region of the paddles for both 8cm and 12cm
Karlon, 1993
More uniform current distribution in myocardium for 12 cm paddles compared to 8 cm paddles
Karlon, 1993
Camacho, 1995
Ramirez, 1989
Fraction of delivered current reaching the heart was lower with 12 cm paddles than 8 cm paddles
Karlon, 1993
Biological effects
Necrosis
When the time
interval between discharges was constant, more necrosis was produced with smaller-sized paddle electrodes (because small electrodes have greater impedance)
Dahl, 1973
Shorter time interval between discharges, greater myocardial necrosis
Ideally, wait >3 minutes between discharges
Dahl, 1973
Less likely to occur when when electrode pad has a large cross-sectional area, so high points of current density do not develop
Hoyt, 1981
(based on Dahl's results)
Camacho, 1995
(human FEM studies)
Damage occurs when paddle currents are 5x defib threshold
Babbs et al.
Karlon, 1993
Less damage to the heart when paddles are larger for a given energy dosage
Karlon, 1993
Intracardiac voltage gradients
Significantly greater with large paddles
(reasonable because large area can generate wider electric field)
Each anatomy had a specific electrode pad size that optimized the max intracardiac voltage gradient
Strongest correlation: voltage gradient and [heart weight to chest radius ratio]
Pagan-Carlo, 1997
Larger electrode pads maximized voltage gradient with increased heart weight to chest radius ratio
Pagan-Carlo, 1997
the largest electrodes did not necessarily result in the max intracardiac gradient
Pagan-Carlo, 1997
Surrogate for intracardiac current (direct relationship)
Pagan-Carlo, 1997
Intracardiac potential gradients had an optimal value in mid-range of paddle sizes (parabolic relaitonship)
Hoyt, 1981
Greater electrostatic field generated with larger pads
Dalzell, 1989
Polarity
polarity has little effect on transthoracic current, impedance, and intrathoracic voltage
Pagan-Carlo, 1997
Paddle positioning
Larger paddles tend to deemphasize paddle position differences in distribution of myocardial current
Karlon, 1993
Different paddle positionings do have different efficacies
Karlon, 1993