Right ventricular pacing alters left ventricular synchrony and loading conditions, each of which may independently influence left ventricular relaxation. Addition of a properly timed atrial ...contraction by using sequential atrioventricular (AV) pacing minimizes changes in left ventricular loading conditions, but ventricular asynchrony persists. To separate the effects of altered loading from those of asynchrony, the effects of right ventricular pacing and sequential AV pacing on the rate of isovolumic pressure decline (relaxation time constant), myocardial (segment) lengthening rate and chamber (minor axis dimension) filling rate were examined. In 12 open chest anesthetized dogs, left ventricular pressure (micromanometer) and either left ventricular free wall segment length transients (n = 6) or minor axis dimension transients (n = 6) were measured during right atrial, right ventricular and sequential AV pacing; length and dimension were measured using ultrasonic crystals.
Compared with right atrial pacing, right ventricular pacing produced a decrease in systolic pressure, a reduction in fractional shortening, a prolongation of the relaxation time constant (23.5 ± 0.7 to 29.8 ± 0.8 ms, p < 0.05), slower peak segment lengthening rate (6.2 ± 0.6 to 4.6 ± 0.8 s−1, p < 0.05) and a slower rate of increase in chamber dimension (3.5 ± 0.1 to 2.7 ± 0.1 s p < 0.05). In contrast, systolic pressure and fractional shortening did not change during sequential AV pacing; however, the relaxation time constant remained prolonged (23.5 ± 0.7 to 30.0 ± 0.8 ms, p < 0.05) and peak lengthening and filling rates (5.9 ± 0.6 versus 5.3 ± 0.8, p < 0.05 and 3.5 ± 0.1 versus 3.0 ± 0.1 s−1, p < 0.05, respectively) showed small but statistically significant declines.
Thus, pacing-induced left ventricular asynchrony caused a decrease in the global and regional indexes of left ventricular relaxation rate that is not closely related to left ventricular loading conditions or shortening.
Cardiac diseases, particularly coronary artery disease and its risk factors, are associated with the majority of perioperative complications in patients undergoing major noncardiac surgery. Risks are ...remarkably low overall, yet for selected patients undergoing high-risk procedures, the chances of complications remain reasonably high. The literature has focused largely on identifying patients in whom complications are most likely to occur, using clinical assessment, including RFI, specialized cardiac testing, and perioperative monitoring. Characteristics of the patient and the surgery both influence outcomes. Current practices may have swung toward excessive testing, especially in patients whose surgical risks are low or moderate. Surprisingly little attention has been devoted to the evaluation of preoperative interventions for reducing perioperative risk. Some observations support the feasibility of performing noncardiac surgery in some high-risk groups using support devices or temporizing techniques. The general application of percutaneous or surgical revascularization as a means of reducing perioperative risk has not been assessed and to date represents an expensive and perhaps risky strategy. In patients who satisfy the usual symptomatic or prognostic criteria for coronary revascularization, its timing should depend on the urgency and risk of the noncardiac procedure. Finally, patients with cardiac devices--pacemakers, prosthetic valves, implantable debrillators, and antitachycardia devices--and survivors of congenital and transplant surgery have specific needs that require careful attention, going beyond the usual vigilance required in the perioperative period.
To separate the effects of hemodialysis on loading conditions from those on contractile state, six patients with concentric left ventricular hypertrophy and normal left ventricular function were ...studied before, during, and after hemodialysis. Two-dimensional-directed M-mode ultrasound was used to measure left ventricular dimensions and wall thickness; a sphygmomanometer and carotid pulse recording were used to determine peak and end-systolic blood pressure. From these data, meridional stress at end systole was calculated and stress-dimension and stress-shortening relations were derived; measurements of metabolic parameters were made simultaneously. Heart rate and systolic blood pressure were stable throughout dialysis. Reductions in left ventricular dimensions and increased shortening were evident by 30 minutes of dialysis and were largely complete by mid-dialysis. These changes coincided with a decrease in potassium and an increase in ionized calcium but not in pH, which changed only in the latter half of dialysis. When stress-dimension and stress-shortening relations were examined, both individual and group data for all coordinates before, during, and after dialysis demonstrated an excellent linear fit consistent with a single contractile state. We conclude that in stable patients with left ventricular hypertrophy, the reduction in heart size and improvement in shortening are due primarily to reductions in preload and afterload.
The effects of an acute increase in left ventricular systolic pressure and the effects of an intravenous isoproterenol infusion on myocardial (segment) lengthening rate and chamber (minor axis ...dimension) filling rate were examined in 12 anesthetized dogs. Measurements of left ventricular systolic pressure (by micromanometer) and of segment length and chamber dimension transients (by ultrasonic crystals) were made in variably afterloaded beats (three-beat descending aortic cross-clamp) before and during an isoproterenol infusion that raised (+)dP/dt by 40%. During the baseline state, we found an inverse relation between the peak rate of increase in minor axis dimension (+)dD/dt and systolic pressure over a wide range of systolic pressures (110-160 mm Hg) and end-systolic dimensions (25-40 mm); peak (+)dD/dt and end-systolic dimension were also inversely related. During isoproterenol infusion, end-systolic dimension fell from 29.7 +/- 3.1 to 28.0 +/- 3.1 mm and (+)dD/dt increased from 79.6 +/- 8.0 to 90.1 +/- 8.7 mm/sec; however, the slope and y intercept of the relation between (+)dD/dt and end-systolic dimension were unchanged. Peak (+)dD/dt at a common end-systolic dimension of 31 mm was nearly equal during baseline and isoproterenol states (64.2 +/- 6.3 vs. 65.1 +/- 6.6 mm/sec). Similar results were found using segment length transients. We interpret these data to indicate that (+)dD/dt is strongly influenced by changes in systolic pressure and dimension and that isoproterenol-induced changes in (+)dD/dt are mediated, at least in part, through changes in systolic pressure and dimension.
Infective endocarditis, especially when it involves prosthetic valves, is a serious, often fatal illness. Although antibiotics are essential in management, surgery is required in many patients who ...develop even incipient heart failure and structural complications. Early identification and referral results in improved mortality and morbidity rates, and there is evidence that surgery should play a larger role in managing infective endocarditis. Patients with intracardiac pacemakers and cardioverting devices represent a growing reservoir of patients with the potential to develop endocarditis.
Segmental early relaxation, a form of left ventricular asynchrony, refers to lengthening of a myocardial segment before mitral valve opening. This phenomenon may occur in normal and diseased hearts; ...when it is seen in a diseased ventricle it may occur in either the abnormally contracting segment or the normal segment. Experimental data indicate that altered loading conditions, especially nonuniform distribution of load or functional inhomogeneities (as may occur with regional ischemia), or both, may result in asynchronous relaxation of the left ventricle.
Objectives. The Veterans Affairs Non-Q-Wave Infarction Strategies In-Hospital (VANQWISH) trial was designed to compare outcomes of patients with a non–Q wave myocardial infarction (NQMI) who were ...randomized prospectively to an early “invasive” strategy versus an early “conservative” strategy. The primary objective was to compare early and late outcomes between the two strategies using a combined trial end point (all-cause mortality or nonfatal infarction) during at least 1 year of follow-up.
Background. Because of the widely held view that survivors of NQMI are at high risk for subsequent cardiac events, management of these patients has become more aggressive during the last decade. There is a paucity of data from controlled trials to support such an approach, however.
Methods. Appropriate patients with a new NQMI were randomized to an early “invasive” strategy (routine coronary angiography followed by myocardial revascularization, if feasible) versus an early “conservative” strategy (noninvasive, predischarge stress testing with planar thallium scintigraphy and radionuclide ventriculography), where the use of coronary angiography and myocardial revascularization was guided by the development of ischemia (clinical course or results of noninvasive tests, or both).
Results. A total of 920 patients were randomized (mean follow-up 23 months, range 12 to 44). The mean patient age was 61 ± 10 years; 97% were male; 38% had ST segment depression at study entry; 30% had an anterior NQMI; 54% were hypertensive; 26% had diabetes requiring insulin; 43% were current smokers; 43% had a previous acute myocardial infarction; and 45% had antecedent angina within 3 weeks of the index NQMI.
Conclusions. Baseline characteristics were compatible with a moderate to high risk group of patients with an NQMI.
To test the hypothesis that patients with normal serum levels of creatine kinase (CK) but elevated percentages of MB isoenzyme fractions in suspected myocardial infarction may have sustained ...clinically significant events, we studied the hospital course of 347 consecutive patients admitted with suspected myocardial infarction. Two hundred twenty-three patients had normal CK levels (182 +/- 44 IU) and normal MB percentages (normal group), 68 had elevated levels of both CK (1395 +/- 178 IU) and MB percentage (10.5 +/- 0.6) (macroinfarction group), and 40 had normal CK levels (96 +/- 7 IU) but elevated MB percentages (9.6 +/- 0.5) with typical enzyme curves (microinfarction group). Compared to the normal group, microinfarction patients were older, had more congestive heart failure, required more intensive monitoring and therapy during longer stays, and sustained a higher in-hospital mortality rate. Thus, these microinfarction patients are at increased risk and therefore warrant aggressive treatment and further evaluation.
Ten normal subjects performed the Valsalva maneuver before and after the administration of propranolol (1 mg/kg). Changes in left ventricular (LV) size and function were assessed with noninvasive ...techniques (echocardiography and sphygmomanometer). Data were obtained at baseline, at 20 seconds of the strain phase (phase II) and 10 seconds after the release of strain (phase IV). In the control state (before propranolol), blood pressure decreased during phase II and exceeded baseline after the release of strain ("overshoot") in phase IV; after the administration of propranolol, the pressure overshoot characteristic of phase IV was no longer present. End-diastolic dimension decreased during the strain phase, but returned to baseline values during recovery in both control and propranolol states. LV stress-dimension and stress-shortening relations before and after propranolol indicate that an increase in LV contractility beginning during phase II and extending into phase IV was attenuated after propranolol. Although the absence of phase IV blood pressure overshoot may be clinically useful in identifying patients with impaired left ventricular function, beta-adrenergic receptor blocking agents can also produce this hemodynamic response in the presence of normal ventricular function.
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