Relation between upper limit of vulnerability and defibrillation threshold in humans

Area of Science:

• Cardiology
• Electrophysiology
• Medical Device Technology

Background:

• An upper limit of vulnerability (ULV) exists in canines, correlating with defibrillation threshold (DFT).
• The existence and correlation of ULV with DFT in humans remained undetermined.
• Understanding ULV is crucial for implantable cardioverter-defibrillator (ICD) safety and efficacy.

Purpose of the Study:

• To determine if an upper limit of vulnerability exists in humans.
• To investigate the correlation between the upper limit of vulnerability and the defibrillation threshold in patients.
• To assess the safety of determining ULV during ICD implantation.

Main Methods:

• The up-down algorithm was used to determine the shock strengths for 50% probability of reaching the upper limit of vulnerability (ULV50) and defibrillation threshold (DFT50) in 13 patients.
• ULV50 was assessed during specific phases of the cardiac cycle (T waves).
• No major complications were reported during the procedures.

Main Results:

• An upper limit of vulnerability was demonstrated in all tested patients.
• The ULV50 (300 ± 138 V or 6.8 ± 5.8 J) was significantly lower than the DFT50 (347 ± 167 V or 9.1 ± 7.3 J).
• A strong significant correlation was found between ULV50 and DFT50 (r = 0.90 for voltage, r = 0.93 for energy).

Conclusions:

• An upper limit of vulnerability is present in human subjects.
• The ULV50 is significantly lower than the DFT50 in humans.
• A significant correlation exists between ULV50 and DFT50, supporting its relevance in defibrillation.