Clinical Assessment and ICD Trouble-shooting

Any of the problems associated with conventional pacing may also be an issue with ICDs. In addition, however, there are more specific potential problems. ICD patients are likely to attend the ED for one of the following reasons.

Delivered shock therapy whilst conscious

To a large extent this is why the device is implanted, but further evaluation is always needed. Even a single shock may be extremely disturbing for the patient, and at the far end of the scale is 'ICD storm', where repeated defibrillation occurs again and again. The first step is to determine whether the therapy was appropriate (for VF/untreated VT), or inappropriate (usually due to misidentification of the rhythm, or “noise” artefact secondary to lead fracture).

Clinical assessment within the ED will include the following:

• Identification and management of pro-arrhythmic electrolyte abnormalities: esp. K+ and Mg++
• Identification and management of acute myocardial ischaemia (ie an acute coronary syndrome – ACS): approximately 5% of sustained monomorphic VT occurs as a result of acute ischaemia. This can be evaluated through the clinical history, the ECG and biomarkers of myocardial necrosis. A small troponin leak is well recognised in association with cardioversion, either external or internal, and is not necessarily indicative of high risk ACS. The resting ECG may be helpful but may be obscured by pre-existing abnormalities such as LBBB. If an ACS is suspected, the patient should be managed in conventional fashion with anti-thrombotic and anti-ischaemic therapy
• Identification of lead fracture: a plain chest x-ray is helpful, but by no means definitive
• Identification of decompensated left ventricular failure: this can result in ventricular arrhythmias due to LV wall stretch, and should be treated conventionally. Once again, the history, physical examination and CXR are the major diagnostic tools

A patient who is well, with a stable rhythm, and who has had a very limited number of shocks, does not necessarily require admission. These patients can be discharged if the investigations listed above are normal, and follow-up arranged for the next working day by the pacing clinic where device interrogation can occur. If abnormalities are detected on investigation in the ED, then further evaluation as an in-patient is indicated.

Syncope

It should be remembered that syncope may not necessarily be secondary to a cardiac cause, even in patients with ICDs.

In the context of a patient with an ICD it is important to consider the following issues:

• Sustained bradycardia is unlikely if the ICD has pacing functions, but is possible if there is any evidence suggestive of pacemaker failure (as covered above)
• VF will rapidly lead to loss of consciousness. A shock would obviously pass unnoticed by the patient
• Patients who have had sustained VT  may or may not be aware of palpitations immediately beforehand, and there is often a degree of retrograde amnesia following a shock / collapse; a normal ECG at presentation does not exclude this as a cause

Once again, device interrogation will reveal the nature of any delivered therapy; proper assessment and evaluation of the syncopal patient will take more time than is available in the ED, and admission is usually appropriate.

Associated cardiac symptoms

Chest pain, palpitations and dyspnoea may all be seen in ICD patients attending the ED, whether related to the underlying cardiac condition, or as a manifestation of issues around therapy from the device. In general, these should be approached as they would for any other patient. The possibility of pneumothorax following recent implantation should not be forgotten, nor the possibility of device infection/endocarditis if a non-specific infective picture is apparent.

Unrelated issues

Clearly ICD patients may present with other intercurrent problems. This does not usually present difficulties, but a few specific points should be borne in mind:

• MRI scanning should not be undertaken without appropriate cardiology consultation since damage can be caused to the device and the patient
• Emergency surgery: it is rare for the ICD itself to present problems at surgery. There is a theoretical risk that electrical noise from the diathermy current may be interpreted as ventricular fibrillation and lead to a shock. This is rare with modern equipment, particularly if the surgical field and diathermy pads are distant to the heart. Even if a shock is delivered, it poses no risk to the surgeon or staff. Ideally though, the defibrillation therapy can be programmed off for the duration of the surgery
• Patients who are dead or dying: If ICD patients have reached the stage where, for whatever reason, it is accepted that they are for palliation rather than active treatment, the ICD should be electively reprogrammed with the tachyarrhythmia therapy disabled. This may not be possible if the deterioration is very sudden. In these situations, an external magnet should be taped in place above the device