IBHRE CCDS cheat sheet

Pacemaker code (NBG): position 1 chamber paced (A, V, D), position 2 chamber sensed, position 3 response (I inhibited, T triggered, D dual), position 4 rate modulation (R), position 5 multisite (e.g., biventricular). VVI 60 means ventricular pacing, ventricular sensing, inhibition at 60 bpm base rate.

Pacing threshold is the minimum output (voltage or pulse width) capturing myocardium; acute thresholds are typically <1.0 V at 0.4 ms, and a rise above roughly 2.0 V at 0.4 ms or a >1 V increase from implant suggests lead maturation problem, microdislocation, or exit block.

Strength-duration relationship: chronaxie (~0.5 ms for myocardium) is the pulse width at twice rheobase voltage; programming pulse width near chronaxie minimizes energy while preserving capture, and lowering pulse width raises voltage threshold.

Sensing: P/R wave amplitude must exceed the programmed sensitivity; typical acute requirements are P wave >1.5-2.0 mV and R wave >5 mV, with slew rate and pacing/sensing lead separation (P wave <1.0 mV or R wave <3-4 mV) indicating poor sensing and risk of undersensing or far-field oversensing.

Impedance reflects lead integrity: pacing impedance typically 300-1200 ohms; a sudden rise (>2000 ohms or doubling) suggests conductor fracture or loose set screw, while a fall (<200-300 ohms) suggests insulation breach or fluid ingress.

ICD defibrillation threshold (DFT) is the lowest energy terminating VF; a safety margin of at least 10 J below maximum device output is commonly targeted, and high DFT prompts system revision (lead repositioning, additional coil, or subcutaneous array).

Tachycardia detection: VF zone typically >200-220 bpm; VT zones set below VF with detection intervals (number of intervals to detect, NID) balancing sensitivity against false therapy; SVT discriminators include sudden onset, stability, and morphology criteria.

ICD shocks are biphasic; first-shock success depends on shock polarity, coil configuration, and shock impedance (typically 40-80 ohms for transvenous systems). Reversed polarity or high impedance reduces delivered energy and success.

Upper limit of vulnerability (ULV) is the highest shock energy that still fails to convert VF; ICD testing confirms adequate margin by demonstrating conversion at ULV and at maximum output.

Pacemaker code (NBG): position 1 chamber paced (A, V, D), position 2 chamber sensed, position 3 response (I inhibited, T triggered, D dual), position 4 rate modulation (R), position 5 multisite (e.g., biventricular). VVI 60 means ventricular pacing, ventricular sensing, inhibition at 60 bpm base rate.

Pacing threshold is the minimum output (voltage or pulse width) capturing myocardium; acute thresholds are typically <1.0 V at 0.4 ms, and a rise above roughly 2.0 V at 0.4 ms or a >1 V increase from implant suggests lead maturation problem, microdislocation, or exit block.

Strength-duration relationship: chronaxie (~0.5 ms for myocardium) is the pulse width at twice rheobase voltage; programming pulse width near chronaxie minimizes energy while preserving capture, and lowering pulse width raises voltage threshold.

Sensing: P/R wave amplitude must exceed the programmed sensitivity; typical acute requirements are P wave >1.5-2.0 mV and R wave >5 mV, with slew rate and pacing/sensing lead separation (P wave <1.0 mV or R wave <3-4 mV) indicating poor sensing and risk of undersensing or far-field oversensing.

Impedance reflects lead integrity: pacing impedance typically 300-1200 ohms; a sudden rise (>2000 ohms or doubling) suggests conductor fracture or loose set screw, while a fall (<200-300 ohms) suggests insulation breach or fluid ingress.

ICD defibrillation threshold (DFT) is the lowest energy terminating VF; a safety margin of at least 10 J below maximum device output is commonly targeted, and high DFT prompts system revision (lead repositioning, additional coil, or subcutaneous array).

Tachycardia detection: VF zone typically >200-220 bpm; VT zones set below VF with detection intervals (number of intervals to detect, NID) balancing sensitivity against false therapy; SVT discriminators include sudden onset, stability, and morphology criteria.

ICD shocks are biphasic; first-shock success depends on shock polarity, coil configuration, and shock impedance (typically 40-80 ohms for transvenous systems). Reversed polarity or high impedance reduces delivered energy and success.

Upper limit of vulnerability (ULV) is the highest shock energy that still fails to convert VF; ICD testing confirms adequate margin by demonstrating conversion at ULV and at maximum output.

Pacemaker code (NBG): position 1 chamber paced (A, V, D), position 2 chamber sensed, position 3 response (I inhibited, T triggered, D dual), position 4 rate modulation (R), position 5 multisite (e.g., biventricular). VVI 60 means ventricular pacing, ventricular sensing, inhibition at 60 bpm base rate.

Pacing threshold is the minimum output (voltage or pulse width) capturing myocardium; acute thresholds are typically <1.0 V at 0.4 ms, and a rise above roughly 2.0 V at 0.4 ms or a >1 V increase from implant suggests lead maturation problem, microdislocation, or exit block.

Strength-duration relationship: chronaxie (~0.5 ms for myocardium) is the pulse width at twice rheobase voltage; programming pulse width near chronaxie minimizes energy while preserving capture, and lowering pulse width raises voltage threshold.

Sensing: P/R wave amplitude must exceed the programmed sensitivity; typical acute requirements are P wave >1.5-2.0 mV and R wave >5 mV, with slew rate and pacing/sensing lead separation (P wave <1.0 mV or R wave <3-4 mV) indicating poor sensing and risk of undersensing or far-field oversensing.

Impedance reflects lead integrity: pacing impedance typically 300-1200 ohms; a sudden rise (>2000 ohms or doubling) suggests conductor fracture or loose set screw, while a fall (<200-300 ohms) suggests insulation breach or fluid ingress.

ICD defibrillation threshold (DFT) is the lowest energy terminating VF; a safety margin of at least 10 J below maximum device output is commonly targeted, and high DFT prompts system revision (lead repositioning, additional coil, or subcutaneous array).

Tachycardia detection: VF zone typically >200-220 bpm; VT zones set below VF with detection intervals (number of intervals to detect, NID) balancing sensitivity against false therapy; SVT discriminators include sudden onset, stability, and morphology criteria.

ICD shocks are biphasic; first-shock success depends on shock polarity, coil configuration, and shock impedance (typically 40-80 ohms for transvenous systems). Reversed polarity or high impedance reduces delivered energy and success.

Upper limit of vulnerability (ULV) is the highest shock energy that still fails to convert VF; ICD testing confirms adequate margin by demonstrating conversion at ULV and at maximum output.