Dosdall Derek J, Ideker Raymond E
Department of Biomedical Engineering, University of Alabama at Birmingham, Birmingham, Alabama 35294-0019, USA.
Heart Rhythm. 2007 Mar;4(3 Suppl):S51-6. doi: 10.1016/j.hrthm.2006.12.030. Epub 2006 Dec 28.
Intravascular ventricular defibrillation and intravascular atrial defibrillation have many similarities. An important factor influencing the outcome of the shock is the potential gradient field created throughout the ventricles or the atria by the shock. A minimum potential gradient is required throughout the ventricles and probably the atria in order to defibrillate. The value of this minimum potential gradient is affected by several factors, including the duration, tilt, and number of phases of the waveform. For shock strengths near the defibrillation threshold, earliest activation following failed shocks arises in a region in which the potential gradient is low. The defibrillation threshold energy can be decreased by adding a third and even a fourth defibrillation electrode in regions where the shock potential gradient is low for the shock field created by the first two defibrillation electrodes and giving two sequential shocks, each through a different set of electrodes. However, the addition of more electrodes and sequential shocks complicates both the device and its implantation. Because patients are conscious when the atrial defibrillation shock is given, they experience pain during the shock, which is one of the main drawbacks of intravascular atrial defibrillation. Unfortunately, the pain threshold for defibrillation shocks is so low that a shock less than 1 J is uncomfortable and is not much less painful than shocks several times stronger. Therefore, even though electrode configurations exist that have lower atrial defibrillation threshold energy requirements than the atrial defibrillation threshold with standard defibrillation electrode configurations used in implantable cardioverter-defibrillators (ICDs) for ventricular defibrillation, they are not clinically practical because their shocks are almost as painful as with the standard ICD electrode configurations. Such electrode configurations would make the ICD more complicated, leading to greater difficulty and longer time required for implantation.
血管内心室除颤和血管内心房除颤有许多相似之处。影响电击结果的一个重要因素是电击在整个心室或心房中产生的电位梯度场。为了实现除颤，整个心室以及可能整个心房都需要有一个最小电位梯度。这个最小电位梯度的值受几个因素影响，包括波形的持续时间、倾斜度和相位数量。对于接近除颤阈值的电击强度，电击失败后最早的激活出现在电位梯度较低的区域。通过在前两个除颤电极产生的电击场中电位梯度较低的区域添加第三个甚至第四个除颤电极，并依次进行两次电击，每次通过不同的电极组，可以降低除颤阈值能量。然而，增加更多电极和依次电击会使设备及其植入变得复杂。因为在进行心房除颤电击时患者是清醒的，他们在电击过程中会感到疼痛，这是血管内心房除颤的主要缺点之一。不幸的是，除颤电击的疼痛阈值非常低，以至于小于1焦耳的电击就会让人不舒服，而且并不比几倍强度的电击疼痛程度低多少。因此，尽管存在一些电极配置，其心房除颤阈值能量要求低于用于心室除颤的植入式心脏复律除颤器（ICD）中使用的标准除颤电极配置的心房除颤阈值，但它们在临床上并不实用，因为它们的电击几乎与标准ICD电极配置的电击一样疼痛。这样的电极配置会使ICD更加复杂，导致植入难度更大、所需时间更长。
