Cardiomyopathy
Figure 2: Protocols of Positive (A) and Negative (B) Clinical T-wave Alternans (TWA) Test
investigated. And it seems less likely to help in patients with the more complex arrhythmic substrates which are more prone to cause SCD.
Risk Stratification for Implantation of a Cardioverter-defibrillator in Primary Prevention of Sudden Cardiac Death Does the Current Risk Stratification Need to Be Improved?
Although backed by sound scientific evidence, the current identification of candidates for an ICD for the primary prevention of SCD is far from optimal. A meta-analysis of the above-mentioned large RCT showed that, with the current risk stratification, only approximately one in four patients (22.9 %, range 17.8–31.4 %) received appropriate and possibly life-saving intervention in the form of an ICD.26
Combined with the
important upfront financial cost, the need for frequent follow-up and the inevitable complications of a device featuring intracardiac leads, this makes the cost-effectiveness of ICD therapy a polemical issue among today’s health economics. Gaining one quality-adjusted life year has been estimated to cost around €30,000 and the cost estimates have been repeatedly challenged, making decisions regarding reimbursement difficult in this era of economic uncertainty.27
Moreover,
although the risk stratification that is being used does identify a subpopulation in which the incidence of SCD is higher than in the general population, the absolute number is only a minority compared with the number of SCD cases in a broader population without depressed LVEF or even without ischaemic cardiomyopathy.28
Implantable Cardioverter-defibrillators
and has led to guidelines regarding ICD implantation for secondary prevention that are relatively straightforward and effective (see Table 1). The extremely high mortality of SCD at its very first presentation implied that ICD therapy should not be restricted to survivors of previous VA.11 The first and second Multicenter Automatic Defibrillator Implantation Trial (MADIT I & II), the Multicenter Unsustained Tachycardia Trial (MUSTT) and the Sudden Cardiac Death in Heart Failure Trial (SCD HeFT) were landmark RCTs all showing significantly improved survival in patients who had suffered an MI and were considered to be at high risk of SCD based on a limited number of parameters – of which depressed left ventricular ejection fraction (LVEF) was the most important (see Table 2).19,22–24
The implantable cardioverter-defibrillator (ICD), a subcutaneous implanted device that detects VA through a lead placed in the right ventricle (see Figure 1) and automatically treats these arrhythmias by delivering anti-tachy pacing or ultimately a high power DC shock, emerged in clinical practice in the early 1980s. This therapy does not prevent VA, but it does prevent SCD following VA. The benefit on mortality was convincingly shown in survivors of a previous sustained VA20,21
The forthcoming guidelines regarding the primary prevention of SCD were somewhat more complex than those for secondary prevention ICD implantation (see Table 1) but still allowed implementation in daily clinical routine.
Radiofrequency Ablation
Radiofrequency ablation for VA is another recently studied approach. The rationale is straightforward: through the creation of lesions on critical points in the scar tissue, the circuit allowing re-entry is interrupted and the risk of VA lowered. The technique has been shown to significantly reduce VT recurrence in patients with previous MI.25 Unfortunately, it has only proven effective in the limited subset of patients with stable VT. Its impact on SCD-related mortality or the possibility to avoid ICD implantation have currently not been
136
The quasi-monopoly of reduced LVEF in the risk stratification for a primary prevention ICD implantation (see Table 2) has the advantage of simplicity, but also has major drawbacks. The rationale behind its use as a predictor of SCD is that reduced LVEF reflects advanced cardiac remodelling leading to an arrhythmic substrate. Nevertheless, LVEF has relatively low sensitivity and specificity for arrhythmia leading to SCD: the majority of SCD patients do not have low ejection fraction and the majority of patients with low LVEF will never experience SCD.29
Another
important issue is the strong predictive value of low LVEF for total mortality, as patients with low LVEF are also at high risk of non-sudden cardiac death. SCD and non-sudden cardiac death risks are to be seen as competing:30
an ICD implantation from being useful.31,32
a very high risk of dying from heart failure will prevent Thus, very low LVEF might
rather be a marker of particular ICD-resistant mortality.
The Quest for the Telltale of Specific Arrhythmic Risk The efficacy of ICD implantation can only be improved if it is possible and easy to identify patients at high risk of arrhythmia but at low risk of non-arrhythmic death. This ‘electrophysiologist’s holy grail’ has urged many to look for new, preferentially non-invasive approaches to detect factors that act as a trigger for, or create a substrate for re-entry leading to, VA and subsequent SCD. The most important pathophysiological factors that have been identified are ventricular ectopy, myocardial scar, slowed ventricular conduction, imbalance in autonomic tone and heterogeneity in ventricular repolarisation. Here we briefly present the rationale and – where already known – the value of these factors (in a systematic structure similar to that used in a consensus document issued by the American Heart Association, American College of Cardiology and Heart Rhythm Society33
). Ventricular Ectopy
Ambulatory ECG (Holter) monitoring can easily detect ventricular premature beats (VPBs) and non-sustained VT (NSVT). The presence of
EUROPEAN CARDIOLOGY
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76