His bundle pacing: troubleshooting during follow-up.

Follow-up of pacemaker systems for His bundle pacing (HBP) requires electrocardiogram (ECG) knowledge and creative thinking. This relates to ventricular threshold measurement in which it can be difficult to distinguish between selective HBP and loss of capture with pseudofusion since, by definition, intrinsic QRS complexes and those selectively paced via the His bundle look identical. Threshold testing in HBP is best performed in unipolar pacing mode, recording of a 12-lead ECG and pacing in VVI mode significantly above the intrinsic rate. Peculiarities of HBP relate to oversensing by the His bundle lead of atrial activity or the His bundle potential itself, leading to ventricular asystole or incorrect measurements during sensing testing. Ventricular undersensing and the use of His bundle plus additional right ventricular leads may lead to complex ECGs. However, other daily pacemaker problems (such as tachycardia above the upper rate limit or premature beats) and specific phenomena (such as paradoxical cardiac memory) may also be demanding in ECG troubleshooting of HBP.