PubMed · 1364182
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J M Cruickshank, P Lund-Johansen. 1992. Do we need more beta-blockers?. https://pubmed.ncbi.nlm.nih.gov/1364182/
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BACKGROUND: Baroreflex-mediated parasympathetic stimulation has variable effects on heart rate variability (HRV). We postulated that a quadratic function would describe the relationship between HRV and parasympathetic effect better than a linear function. METHODS AND RESULTS: Twenty-nine normal volunteers (15 women; mean age 39+/-12 years) were studied after beta-adrenergic blockade with intravenous propranolol. Five-minute ECG recordings were made during graded infusions of phenylephrine and nitroprusside to achieve baroreflex-mediated increases and decreases in parasympathetic effect, respectively. Time- and frequency-domain measures of HRV were calculated from the R-R interval tachograms. The R-R interval and the vagal-sympathetic effect (VSE=R-R interval/intrinsic R-R interval) were used as indices of parasympathetic effect. The data were fit to both quadratic and linear models. In each case, the quadratic model (with a negative coefficient for the squared term) was superior to the linear model. There was some evidence that age influenced the responsiveness of the HRV parameters with changing parasympathetic effect, although the regression analysis was significant only in the models for MSSD (P<0.03) and pNN50 (P<0.001). CONCLUSIONS: The relationship between HRV and parasympathetic effect is best described by a function in which there is an ascending limb where HRV increases as parasympathetic effect increases until it reaches a plateau level; HRV then decreases as parasympathetic effect increases. Because there is marked interindividual variation in this relationship, differences in HRV between individuals may reflect differences in this relationship and/or differences in autonomic effects.
BACKGROUND: A paced rhythm can mask the electrocardiographic features of an acute myocardial infarction, complicating timely recognition and treatment. OBJECTIVE: To evaluate characteristics, treatment, and outcomes among patients presenting with paced rhythms during myocardial infarction. DESIGN: Retrospective cohort study. SETTING: U.S. acute care hospitals. PATIENTS: 102 249 Medicare beneficiaries at least 65 years of age who were treated for acute myocardial infarction between 1994 and 1996. MEASUREMENTS: Provision of three treatments for acute myocardial infarction (emergent reperfusion, aspirin, and beta-blockers), death at 30 days, and long-term follow-up. RESULTS: 1954 patients (1.9%) presented with paced rhythms during myocardial infarction. These patients were older; were predominantly male; and had higher rates of congestive heart failure, diabetes, and previous infarction. They were significantly less likely to receive emergent reperfusion (relative risk [RR], 0.27 [95% CI, 0.22 to 0.33]), aspirin (RR at admission, 0.91 [CI, 0.88 to 0.94]; RR at discharge, 0.87 [CI, 0.83 to 0.92]), and beta-blockers at admission (RR, 0.89 [CI, 0.82 to 0.96]). In addition, there was a trend toward decreased use of beta-blockers at discharge (RR, 0.91 [CI, 0.76 to 1.06]). Crude mortality rates were higher among patients with paced rhythms than among those without at 30 days (25.8% vs. 21.3%; P = 0.001) and at 1 year (47.1% vs. 36.1%; P = 0.001). Among patients with paced rhythms, risk for death at 30 days decreased after adjustment for illness severity and decreased use of therapy (RR, 1.03 [CI, 0.93 to 1.14]). Patients with paced rhythms remained at additional risk for long-term mortality (hazard ratio, 1.12 [CI, 1.06 to 1.18]). CONCLUSIONS: Patients with paced rhythms were less likely than those without to receive treatment for acute myocardial infarction and had poorer short- and long-term outcomes. However, this mortality risk diminished after adjustment for treatment. This suggests that improved recognition and treatment of myocardial infarction may improve outcomes, particularly in the short term.
CONTEXT: Patients who undergo major vascular surgery are at increased risk of perioperative cardiac complications. High-risk patients can be identified by clinical factors and noninvasive cardiac testing, such as dobutamine stress echocardiography (DSE); however, such noninvasive imaging techniques carry significant disadvantages. A recent study found that perioperative beta-blocker therapy reduces complication rates in high-risk individuals. OBJECTIVE: To examine the relationship of clinical characteristics, DSE results, beta-blocker therapy, and cardiac events in patients undergoing major vascular surgery. DESIGN AND SETTING: Cohort study conducted in 1996-1999 in the following 8 centers: Erasmus Medical Centre and Sint Clara Ziekenhuis, Rotterdam, Twee Steden Ziekenhuis, Tilburg, Academisch Ziekenhuis Utrecht, Utrecht, and Medisch Centrum Alkmaar, Alkmaar, the Netherlands; Ziekenhuis Middelheim, Antwerp, Belgium; and San Gerardo Hospital, Monza, Istituto di Ricovero e Cura a Carattere Scientifico, San Giovanni Rotondo, Italy. PATIENTS: A total of 1351 consecutive patients scheduled for major vascular surgery; DSE was performed in 1097 patients (81%), and 360 (27%) received beta-blocker therapy. MAIN OUTCOME MEASURE: Cardiac death or nonfatal myocardial infarction within 30 days after surgery, compared by clinical characteristics, DSE results, and beta-blocker use. RESULTS: Forty-five patients (3.3%) had perioperative cardiac death or nonfatal myocardial infarction. In multivariable analysis, important clinical determinants of adverse outcome were age 70 years or older; current or prior angina pectoris; and prior myocardial infarction, heart failure, or cerebrovascular accident. Eighty-three percent of patients had less than 3 clinical risk factors. Among this subgroup, patients receiving beta-blockers had a lower risk of cardiac complications (0.8% [2/263]) than those not receiving beta-blockers (2.3% [20/855]), and DSE had minimal additional prognostic value. In patients with 3 or more risk factors (17%), DSE provided additional prognostic information, for patients without stress-induced ischemia had much lower risk of events than those with stress-induced ischemia (among those receiving beta-blockers, 2.0% [1/50] vs 10.6% [5/47]). Moreover, patients with limited stress-induced ischemia (1-4 segments) experienced fewer cardiac events (2.8% [1/36]) than those with more extensive ischemia (>/=5 segments, 36% [4/11]). CONCLUSION: The additional predictive value of DSE is limited in clinically low-risk patients receiving beta-blockers. In clinical practice, DSE may be avoided in a large number of patients who can proceed safely for surgery without delay. In clinically intermediate- and high-risk patients receiving beta-blockers, DSE may help identify those in whom surgery can still be performed and those in whom cardiac revascularization should be considered.