There were 778 patients who underwent surgery within 4 days of their SAH. The clinical characteristics and outcomes are shown in and these did not differ significantly among patients who did (n=588, 76%) and did not (n=190, 24%) have a preoperative ECGs. The 222 IHAST subjects who had surgery ≥ 5 days after SAH had lower preoperative WFNS, Fisher, and NIHSS scores in comparison to those subjects having surgery within 4 days. No patients were excluded from the study on the basis on a prior history of arrhythmia or a pacemaker.
Population Characteristics and Primary Outcomes
In the ECG subpopulation, 378 (64%) had a good three-month outcome (GOS 1) and 31 (5%) died. In 23 patients (74%), neurological injury (cerebral infarction, cerebral edema, intracranial hypertension, hydrocephalus, etc.) was the primary cause of death. Of these 23 patients, 2 had fatal anoxic brain injury following resuscitation from cardiac arrest. Of the remaining 8 patients, 2 deaths were due to sepsis and its sequelae, and 6 deaths were primarily on a respiratory basis (including two patients with fatal pulmonary emboli). Of the 6 patients dying primarily on a respiratory basis, 3 had co-existing neurologic injuries. Therefore, neurological injuries were the primary or contributing cause of death in 26 (84%) of the patients. Bradycardia and hypotension were coded as minor contributors to death in 1 patient each.
summarizes the study's ECG findings. At least one morphological ECG abnormality was present in 468 patients (80%) and a total of 907 different abnormalities were present. The most common abnormality was non-specific ST-T wave changes (NSSTTWA), followed by ST elevation, T wave inversion, and ST depression. ECG abnormalities were most commonly observed in the anterior leads. There were no significant associations between the number or type of observed ECG abnormalities and either the preoperative WFNS or Fisher class. Compared to a published study of pre-operative ECGs in patients undergoing any type of non-cardiac surgery (with a mean age of 60), the SAH study patients were more likely to have an abnormal ECG (80% vs 25%) and ST depression (7% vs 3%) but less likely to have Q waves (6% vs 10%).14
Preoperative ECG Characteristics
For the primary analysis, the step one models showed that for GOS (1−5) ST depression had a significant univariate association with outcome (FE P = 0.026), and both NSSTTWA (FE P = 0.085) and QTc (AOV P = 0.051) had non-significant associations. Four ECG variables had significant univariate associations with mortality (GOS5): NSSTTWA (FE P = 0.020), ST depression (FE P = 0.047), heart rate (FE P = 0.019), and QTc (TT P = 0.038).
The step two models, designed to test the independence of the ECG variables from each other (but without inclusion of clinical covariates), showed that, for GOS (1−5), ST Depression (OR 2.0, CI 1.2−3.5, P = 0.011) and QTc (OR 1.004 per 1 msec increase, CI 1.000−1.009, P = 0.043) were significantly associated outcome, and Q/QS waves had a non-significant association (OR 1.7, CI 0.9−3.0, P = 0.076). Both NSSTTWA (OR 3.0, CI 1.1−8.1, P=0.026) and QTc (OR 1.009 per 1 msec increase, CI 1.002−1.016, P=0.018) were significantly associated with mortality.
The results for the step three GOS (1−5) model, that included clinical covariates, are shown in . Age, preoperative WFNS, posterior aneurysm location, and aneurysm size were significant and independent predictors of GOS score. In this model, there was only a non-significant association between QTc and GOS score.
Multivariate Predictors of GOS Score (1−5)
The results for the step three mortality model, that included clinical covariates, are shown in . Age and preoperative WFNS grade were the only clinical variables that remained in this model. Heart rate had a non-linear relationship with mortality such that 2nd quartile rates (61−70 bpm) were associated with lowest risk, and both the lowest and highest heart rate quartiles were associated with increased mortality (). There was also a significant association between NSSTTWA and mortality; QTc had a non-significant association.
Multivariate Predictors of Mortality (GOS5)
Figure 1 The Y axis indicates the unadjusted 3 month mortality rate. The first three bars from the left on the X axis indicate the lower three quartiles quartiles of heart rate on the pre-operative ECG. The top quartile is divided in the figure into 81−100 (more ...)
Secondary analyses explored associations between the ECG predictors (heart rate, QTc, and NSSTTWA) and cardiovascular and neurological hospital outcomes. There was a significant association between QTc and postoperative hypotension (OR 1.011 per 1 msec increase, CI 1.00−1.02, P=0.048), which occurred in 16 (3%) of the ECG study subjects. There was also an association between top quartile heart rates and treatment with vasopressors or inotropes for cardiovascular indications (HR >80 vs. 61−70, OR 2.5, CI 1.3−5.0, P=0.008). Finally, the presence of NSSTTWA was associated with the use of vasopressors for cardiovascular indications (OR 2.2, CI 1.2−4.1, P=0.010 and with pulmonary edema (OR 1.9, CI 1.0−3.5, P=0.043).