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abstract & commentary
Synopsis: Early and late occurrences of sustained venticular tachycardia or ventricular fibrillation denote a high-risk group for both short- and long-term mortality.
Source: Newby KH, et al., for the GUSTO Investigators. Circulation 1998;98:2567-2573.
Newby and colleagues review the gusto-i database to determine the incidence, acute outcome, and prognostic significance of sustained ventricular tachycardia (VT) and ventricular fibrillation (VF) in patients with acute myocardial infarction (MI). GUSTO-I enrolled 41,020 patients admitted within six hours of the onset of chest pain. Patients were randomized to receive one of four regimens: streptokinase plus subcutaneous heparin, front-loaded tissue plasminogen activator plus intravenous heparin, streptokinase plus intravenous heparin, or tissue plasminogen activator and streptokinase plus intravenous heparin. Nurse coordinators in each center later reviewed the charts of the patients enrolled in the study for documentation of any sustained ventricular arrhythmias. VF was defined as irregular undulations of variable contour and amplitude on ECG that produced prompt hemodynamic compromise requiring DC shock for termination. Sustained VT was defined as a wide complex tachycardia of probable ventricular origin lasting more than 30 seconds or requiring early electrical cardioversion. No systematic review of the rhythm strips was performed. In particular, we are not provided data about the cycle length or morphology of the episodes of VT. Arrhythmias were classified as either early if they occurred within two days of admission or late if they were observed more than two days after admission.
Sustained VT, VF, or both were reported in 4188 patients (10.2%). VT and/or VF was associated with older age, previous infarct, hypotension, higher Killip class, and lower ejection fraction. Higher early and late mortality rates were seen in patients with sustained ventricular arrhythmias compared with those without arrhythmias. In-hospital mortality was 18.6% in those with VT only, 24% in those with VF only, and 44% in those with both VT and VF. These values contrasted with a mortality rate of 4.2% among patients who did not have any sustained ventricular arrhythmias. Long-term mortality was also elevated in those with ventricular arrhythmias. Total one-year mortality rates for those with VT only, VF only, and both VT and VF were 24.2%, 26.0%, and 48.4%, respectively. Patients with none of these arrhythmias had a one-year mortality of 7.2%. Both early and late ventricular arrhythmias were associated with higher mortality. For VT, the one-year mortality was 38.9% for those with early VT and 49.0% for those for late VT. For VF, the one-year mortality rates were 22.0% and 39.3% for early and late VF, respectively. For patients with both VT and VF, the one-year mortality rates were 47.0% and 59.6% for patients with early and late presentations, respectively. Catheterization findings that correlated with ventricular arrhythmias included a higher incidence of TIMI grade 0 flow and lower ejection fractions. Newby et al conclude that, despite the use of thrombolytic therapy, early and late occurrences of sustained VT or VF denote a high-risk group for both short- and long-term mortality.
Comment by John P. DiMarco, MD, PhD
The clinical significance of early ventricular arrhythmias in patients with acute MI remains controversial. This is primarily due to the fact that VT and VF may be produced by a number of electrophysiologic phenomena in the setting of acute ischemia. VF that occurs in the setting of acute ischemia may have little significance if the patient suffers little myocardial damage from the infarction and has no complications from the resuscitation. However, when VF occurs in the setting of acute infarction and the infarction either results in ventricular dysfunction or ventricular dysfunction was present previously, VF may be a marker of continued electrical instability. VT may also be due to different mechanisms. In the first hours to days after acute MI, benign sustained ventricular arrhythmias due to enhanced automaticity in damaged Purkinje fibers may be seen. These accelerated idioventricular rhythms may meet the ECG definition for VT but have limited long-term significance. Sustained monomorphic VT with a stable cycle length of longer than 230 msec is usually not seen in the first hours after MI unless prior infarction had occurred or if antiarrhythmic drugs were used. When this type of sustained VT develops after the first 24-48 hours, it tends to be malignant and is associated with a high mortality. VT that has a short cycle length (< 230 msec) probably does not represent a stable substrate and behaves more like VF. In this paper, we are not provided any information about the cycle length or morphology of the VT. It is, therefore, likely that what is reported as VT really includes accelerated idioventricular rhythms, VTs arising from prior infarctions, VT seen after antiarrhythmic drugs were administered for VF, VT with short cycle lengths, and more stable arrhythmias.
The data from this large study do point out the fact that patients who have ventricular arrhythmias as a group continue to be at risk. However, careful examination of the other clinical factors in the patient’s course and the ECG and clinical features of the arrhythmia should be used to judge whether the patient requires aggressive antiarrhythmic intervention after recovery.