Kyuhyun Wang

Hemodynamic Predictors of Myocardial Oxygen Consumption During Static and Dynamic Exercise

Hemodynamic predictors of myocardial oxygen consumption (MVO2) during static and dynamic exercise were examined in ten normal subjects. Studies were done under the following circumstances: 1) during upright bicycle exercise at an average heart rate of 147 beats/min, 2) during static exercise with an isometric load in the left hand equal to 17% of the maximal voluntary contraction (MVC), and 3) during combined dynamic exercise (average heart rate 147 beats/min) and static exercise using 17% MVC of the left hand. Mean myocardial blood flow (MBF) was 181 ml/100 gm LV/min during dynamic exercise, 98 ml/100 gm LV/min during static exercise, and 201 ml/100 gm LV/min during combined static and dynamic exercise. Addition of a static load to the dynamic load resulted in a higher blood pressure (average 12 mm Hg), MVO2 and MBF than during dynamic exercise alone. MVO2 correlated best with products of heart rate and blood pressure regardless of whether the blood pressure was obtained by a central aortic catheter (r = 0.88) or by a blood pressure cuff (r = 0.85).When the current data were combined with previous data, 82 determinations of MVO2 and MBF in 29 normal subjects during several levels of upright exercise were available for analysis. Forty-four determinations were done during dynamic upright exercise, 18 during exercise after propranolol, ten during combined static and dynamic work, and ten during static work alone. MVO2 correlated best with the product of heart rate and blood pressure (r = 0.86). Heart rate alone correlated better with MVO2 (r = 0.82) than did the tension time index (r = 0.65) or the product of systolic blood pressure, heart rate, and ejection time (r = 0.68). The readily measured variables of heart rate and of heart rate × blood pressure correlated well with MVO2 in normal young men during exercise under a wide variety of circumstances.

Effect of Propranolol on Myocardial Oxygen Consumption and Its Hemodynamic Correlates during Upright Exercise

Measurements were made of heart rate, aortic blood pressure, systolic ejection period/beat, myocardial blood flow, and myocardial oxygen consumption in nine normal young men during three bouts of upright bicycle exercise: 1) at the workload which produced a heart rate of 120 beats/minute, 2) at the higher workload necessary to produce a heart rate of 120 beats/minute after administration of intravenous propranolol 0.25 mg/kg, and 3) with infusion of propranolol, at the same workload as the first exercise bout. Comparing exercises 1 and 2, we found a much higher workload was required to produce the same heart rate after propranolol. The blood pressure, heart rate-blood pressure product, and myocardial oxygen consumption were the same despite the much greater level of exertion. Comparing exercises 1 and 3, the heart rate, blood pressure, heart rate-blood pressure product, and myocardial oxygen consumption were all significantly lower during exercise 3 after propranolol despite the fact that the same degree of exercise was being done. As in previous studies, the heart rate-blood pressure product was an excellent correlate of myocardial oxygen consumption despite the change in contractility induced by propranolol. The systolic ejection period was prolonged significantly altering the tension-time index (TTI), which became an inadequate index of myocardial oxygen consumption. It is concluded that the heart rate-blood pressure product is a good index of myocardial metabolic needs during exercise and the relationship is undistorted by marked changes in contractility, but the tension-time index is a poor correlate. This data emphasizes the fact that the relative metabolic loads for the whole body and for the heart are determined separately and may not change in parallel with a given intervention.

Complete Heart Block Complicating Bacterial Endocarditis

Among 142 cases of bacterial endocarditis (BE), complete heart block (CHB) was found in six cases (4%) and first-degree (1°) or second-degree (2°) A-V block in 14 cases (10%).The aortic valve was involved in 18 of 20 cases with atrioventricular (A-V) conduction disturbance, including all six cases of CHB.Anatomic observations (four autopsy, one operative) were made in five of the six cases of CHB. In these cases, a common finding, in addition to involvement of the aortic valve, was extension of the infection to adjacent structures resulting in cardioaortic fistulae. CHB likely resulted from extension of infection to the major conduction tissues.Five of the six patients with CHB died suddenly while in the hospital. One patient was treated with electric pacing while the infection was being controlled and, 38 days later, underwent successful replacement of the aortic valve. Conduction abnormalities are important possible complications of aortic valvular BE. Prompt pacing may be a lifesaving procedure, allowing eradication of infection as a prelude to surgical therapy.

Prosthetic aortic valvular endocarditis.

Infective endocarditis (IE) continues to be one of the most serious complications following cardiovascular surgery, particularly that for replacement of valves. In order to define more clearly the clinical course and the role of surgical therapy, clinical and necropsy data were reviewed in 16 adult patients with prosthetic aortic valvular endocarditis (PAVE) and compared with the experience cited in the literature. Positive blood cultures were obtained in each of the patients with bacterial endocarditis. Gram positive bacteria predominate and the onset of infection is usually later than 25 days postoperatively. In 11 of 16 patients, aortic insufficiency was recognized. Autopsy material demonstrated large perivalvular abscesses which loosened the attachment of the prosthetic valve in each case and which made successful operation unlikely. Aortic insufficiency appears to be of prognostic importance, since patients who developed aortic insufficiency early in the course of PAVE died. Survivors included patients who made an excellent response to medical therapy and who either did not develop aortic insufficiency or developed aortic insufficiency either late in the course or even after cure of PAVE, Poor response to medical therapy and progressive aortic insufficiency even in the absence of left ventricular failure appear to be indications for prompt surgical replacement of the prosthetic aortic valve.

Bicuspid Aortic Valve Comparison of Congenital and Acquired Types

Two dominant types of congenital bicuspid valves are described. The classical type is characterized by the presence of a low ridge or raphe along the aortic aspect of the conjoined cusp. The other is characterized by a tall raphe, the upper edge of which corresponds with the upper level of the aortic cusps. Some such ridges may result from acquired fusion of the adjacent halves of two cusps (yielding an acquired bicuspid valve). In other cases, the ridge is a protrusion of the aorta and not derived from fused cuspid tissue. Such valves are considered to portray a condition which may be termed pseudoacquired congenital bicuspid aortic valve. The acquired bicuspid valve in some cases is compounded of this congenital process and acquired fusion of cuspid tissue. The ratio of classical congenital bicuspid to pseudoacquired congenital bicuspid aortic valve is 4 to 1. Exceptional forms of pseudoacquired congenital bicuspid aortic valves are also described.

The Premature Ventricular Complex as a Diagnostic Aid

Premature ventricular complexes (PVCs) can provide clues to the physical or electrocardiographic diagnosis through the associated compensatory pause, the break in the regularity of the rhythm, or the morphology of the PVC itself. A PVC may allow visualization of the P wave or of atrial flutter waves that would otherwise be obscured in the electrocardiogram. It can also be useful in distinguishing an S3 gallop from an S4 gallop. The compensatory pause that follows a PVC may allow normal conduction of the next QRS complex in a patient with a rate-dependent intraventricular conduction defect, and this normalized QRS complex may contain important diagnostic findings. A PVC can also reveal a myocardial infarct pattern when the sinus complex fails to do so. Although the need to treat PVCs is currently being de-emphasized, their diagnostic utility should not be overlooked.

Electrocardiograms of Wolff-Parkinson-White syndrome simulating other conditions

The ECGs of WPW syndrome may mimic myocardial infarct patterns (Fig. 1). If the h wave is oriented superiorly, it may register as an abnormal Q wave in the inferior leads, and the tracing can be mistaken for an inferior myocardial infarct (Fig. 1, A). If the h wave is oriented superiorly and anteriorly, an inferoposterior infarct is simulated (Fig. 1, B), whereas if it is oriented posteriorly, an anteroseptal myocardial infarct is simulated (Fig. 1, C). A h wave oriented to the right may mimic a high lateral myocardial infarct (Fig. 1, D). When the h wave is oriented to the right and anteriorly, the ECG will simulate posterolateral myocardial infarct (Fig. 1, E). Ruskin et al. 2 reported that among 44 patients with WPW syndrome referred to their institution, 31 (70%) had negative h waves in one or more leads simulating myocardial infarct pattern. Fifteen (34%) of these 44 patients were actually referred to them with an erroneous diagnosis of myocardial infarction. The clues to the correct diagnosis are the short PR interval and more typical A waves in other leads. Another clue is that when the A wave is negative,

AV dissociation, an inevitable response.

Background: The independent activation of the atria and ventricles, AV dissociation, is a common phenomenon that occurs during a wide variety of electrophysiologic circumstances. The clinical significance of AV dissociation is often misunderstood.

Pseudo AV block secondary to concealed premature His bundle depolarizations

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Response to letter to the editor by Dr. Jastrzebski

Ann Noninvasive Electrocardiol 2011;16(4):416–417