Defibrillation threshold testing in patients with hypertrophic cardiomyopathy.

INTRODUCTION: Implantable cardioverter-defibrillators (ICDs) decrease sudden cardiac death in patients with hypertrophic cardiomyopathy (HCM). One of the vital aspects of ICD implantation is the demonstration that the myocardium can be reliably defibrillated, which is defined by the defibrillation threshold (DFT). We hypothesized that patients with HCM have higher DFTs than patients implanted for other standard indications. METHODS: We retrospectively reviewed the medical records of patients implanted with an ICD at the University of Maryland from 1996 to 2008. All patients with HCM who had DFTs determined were included. Data were compared to selected patients implanted for other standard indications over the same time period. All patients had a dual-coil lead with an active pectoral can system and had full DFT testing using either a step-down or binary search protocol. RESULTS: The study group consisted of 23 HCM patients. The comparison group consisted of 294 patients. As expected, the HCM patients were younger (49 ± 18 years vs 63 ± 12 years; P < 0.00001) and had higher left ventricular ejection fractions (66% vs 32%; P < 0.000001). The average DFT in the HCM group was 13.9 ± 7.0 Joules (J) versus 9.8 ± 5.1 J in the comparison group (P = 0.0004). In the HCM group, five of the 23 patients (22%) had a DFT ≥ 20 J compared to 19 of 294 comparison patients (6%). There was a significant correlation between DFT and left ventricle wall thickness in the HCM group as measured by echocardiography (r = 0.44; P = 0.03); however, there was no correlation between DFT and QRS width in the HCM group (r = 0.1; P = NS). CONCLUSIONS: Our results suggest that patients with HCM have higher DFTs than patients implanted with ICDs for other indications. More importantly, a higher percentage of HCM patients have DFTs ≥ 20 J and the DFT increases with increasing left ventricle wall thickness. These data suggest that DFT testing should always be considered after implanting ICDs in HCM patients.

Mortality based on the presenting electrocardiogram in patients with myocardial infarction in the troponin era.

BACKGROUND: Studies reporting short-term mortality in patients with myocardial infarction (MI) based on the initial electrocardiogram (ECG) are often limited by requiring an ischemic ECG for inclusion. Because few patients with normal or nonspecific findings were included, outcomes in these patients are less clear, especially in the troponin era. METHODS: Consecutive patients diagnosed as having MI using troponin I (TnI) over a 6-year period were included and classified into 8 mutually exclusive groups based on the initial ECG using standard criteria. Patients were included in only 1 group. The MI size was estimated using multiples of peak creatine kinase-MB (CK-MB), and 30-day mortality rate was assessed. RESULTS: Among 1641 patients with MI, patients with ST elevation represented only 22% of all MIs. Patients with ST elevation had the largest MI size, with 2 of 3 having a peak CK-MB greater than 10 times normal. In contrast, most of the patients representing all the other ECG groups had a peak CK-MB less than 5 times normal, with approximately 1 of 3 having no CK-MB elevation and were diagnosed by TnI elevation alone. Patients could be separated into a high-risk group (ST elevation, ischemia, other, or left bundle-branch block), in which mortality rate exceeded 9% (mean, 14%), and a lower-risk group (prior MI, left ventricular hypertrophy, nonspecific changes, and normal), in which the 30-day mortality rate averaged 6% (P < .001; range, 5.23%-7.1%). CONCLUSIONS: Specific ECG findings other than ischemia portend poor outcomes in patients with MI. Once MI is diagnosed, patients are no longer low risk.