Heart rate, control

Transfer to alternative agents-After achieving adequate heart rate control and stable clinical status, transition to alternative antiarrhythmic agents may be accomplished. 

Kojda, G., Laursen, J.B., Ramasamy, S., Kent, J.D., Kurz, S., Burchfield, J., Shesely, E.G., Harrison, D.G. Protein expression, vascular reactivity and soluble guanylate cyclase activity in mice lacking the endothelial cell nitric oxide synthase contributions of NOS isoforms to blood pressure and heart rate control, Cardiovasc. Res. 1999, 42, 206-213. 

Gehrmann J, Meister M, et al. 2002. Impaired parasympathetic heart rate control in mice with a reduction of functional G protein beta-gamma-subunits. Am J Physiol Heart Circ Physiol 282 H445-H456. 

Rohrer DK, Schauble EH, Desai KH, Kobilka BK, Bernstein D. Alterations in dynamic heart rate control in the P,-adrenergic receptor knockout mouse. Am J Physiol 1998 274 H1184-H1193. 

Ellenbogen KA, Dias VC, Plumb VJ, et al. A placebo-controlled trial of continuous intravenous diltiazem infusion for 24-hour heart rate control during atrial fibrillation and atrial flutter A multicenter study. J Am Coll Cardiol 1991 18 891-897. 

Snake venoms include toxins showing high selectivity for subtypes of muscarinic acetylcholine receptors, which control a variety of processes including the modulation of the heart rate, control of motor systems, and the modulation of learning and memory, as well as toxins that block particular subtypes of voltage-dependent sodium or potassium channels in neurons. 

These results indicate that the dependency of image quahty on the average heart rate decreases with the increasing temporal resolution of the CT scanners. Another conclusion from these studies is that until the use of 64-shce CT for noninvasive coronary imaging, the administration of (3-receptor antagonists is advisable when the heart rate exceeds a certain threshold (60 or 65 bpm). With dual-source CT, heart rate control through the use of beta-blockers is no longer required (Fig. 15.2). 

Scheffel H, Alkadhi H, Plass A, et al. (2006) Accuracy of dualsource CT coronary angiography first experience in a high pretest probability population without heart rate control. Eur Radiol 16 2739-2747... 

Raby KE, Brull SJ, Timimi F, Akhtar S, Rosenbaum S, Naimi C, Whittemore AD. The effect of heart rate control on myocardial ischemia among high-risk patients after vascular surgery. Anesth Analg 1999 88(3) 477-82. 

Although blood pressure control follows Ohm s law and seems to be simple, it underlies a complex circuit of interrelated systems. Hence, numerous physiologic systems that have pleiotropic effects and interact in complex fashion have been found to modulate blood pressure. Because of their number and complexity it is beyond the scope of the current account to cover all mechanisms and feedback circuits involved in blood pressure control. Rather, an overview of the clinically most relevant ones is presented. These systems include the heart, the blood vessels, the extracellular volume, the kidneys, the nervous system, a variety of humoral factors, and molecular events at the cellular level. They are intertwined to maintain adequate tissue perfusion and nutrition. Normal blood pressure control can be related to cardiac output and the total peripheral resistance. The stroke volume and the heart rate determine cardiac output. Each cycle of cardiac contraction propels a bolus of about 70 ml blood into the systemic arterial system. As one example of the interaction of these multiple systems, the stroke volume is dependent in part on intravascular volume regulated by the kidneys as well as on myocardial contractility. The latter is, in turn, a complex function involving sympathetic and parasympathetic control of heart rate intrinsic activity of the cardiac conduction system complex membrane transport and cellular events requiring influx of calcium, which lead to myocardial fibre shortening and relaxation and affects the humoral substances (e.g., catecholamines) in stimulation heart rate and myocardial fibre tension. 

Animal studies show effects of methyl parathion similar to those seen in people. In addition, short-term high exposure of animals to methyl parathion caused decreased heart rate. This may be the result of methyl parathion s effects on the nerves that control the heart. Methyl parathion decreased the ability of animals to fight infections in some studies, but not in others. It is not known whether any of these effects occur in people. It is not known whether methyl parathion affects the ability of animals to reproduce. Studies in animals have not shown that methyl parathion causes cancer. 

Expert opinion is a source, frequently elicited by survey, that is used to obtain information where no or few data are available. For example, in our experience with a multicountry evaluation of health care resource utilization in atrial fibrillation, very few country-specific published data were available on this subject. Thus the decision-analytic model was supplemented with data from a physician expert panel survey to determine initial management approach (rate control vs. cardioversion) first-, second-, and third-line agents doses and durations of therapy type and frequency of studies that would be performed to initiate and monitor therapy type and frequency of adverse events, by body system and the resources used to manage them place of treatment and adverse consequences of lack of atrial fibrillation control and cost of these consequences, for example, stroke, congestive heart failure. This method may also be used in testing the robustness of the analysis [30]. 

Lohmoller G, Matuschke A et al (1989) [False-positive test of autonomic neuropathy in HIV infection and AIDS Case control study of heart rate variability in 62 HIV positive patients]. Med Klin (Munich) 84(5) 242-245... 

In randomized, controlled, clinical trials, calcium channel blockers were as effective as p-blockers at preventing ischemic symptoms. Calcium channel blockers are recommended as initial treatment in IHD when /3-blockers are contraindicated or not tolerated. In addition, CCBs may be used in combination with /3-blockers when initial treatment is unsuccessful. However, the combination of a (1-blocker with either verapamil or diltiazem should be used with extreme caution since all of these drugs decrease AV nodal conduction, increasing the risk for severe bradycardia or AV block when used together. If combination therapy is warranted, a long-acting dihydropyridine CCB is preferred. (3-Blockers will prevent reflex increases in sympathetic tone and heart rate with the use of calcium channel blockers with potent vasodilatory effects. 

FIGURE 6-6. Decision algorithm for long-term ventricular rate control with oral drug therapy for patients with paroxysmal or permanent atrial fibrillation, bpm, beats per minute CCB, calcium channel blocker (diltiazem or verapamil) HF, heart failure LV, left ventricular function LVEF, left ventricular ejection fraction. (Algorithm adapted with permission from Tisdale JE, Moser LR. Tachyarrhythmias. In Mueller BA, Bertch KE, Dunsworth TS, et al. (eds.) Pharmacotherapy Self-Assessment Program, 4th ed. Kansas City American College of Clinical Pharmacy 2001 ... 

Monitor the patient to determine whether the goal of ventricular rate control is met heart rate less than 100 bpm or decrease in heart rate of 20% from the pretreatment value. 

Monitor vital signs (i.e., temperature and heart rate) and laboratory assessments (i.e., WBC count) daily to assess resolution of infection and efficacy of pain medications. When possible, interview the patient to obtain additional information about pain control. 

Pyruvate kinase (PK) is one of the three postulated rate-controlling enzymes of glycolysis. The high-energy phosphate of phosphoenolpyruvate is transferred to ADP by this enzyme, which requires for its activity both monovalent and divalent cations. Enolpyruvate formed in this reaction is converted spontaneously to the keto form of pyruvate with the synthesis of one ATP molecule. PK has four isozymes in mammals M, M2, L, and R. The M2 type, which is considered to be the prototype, is the only form detected in early fetal tissues and is expressed in many adult tissues. This form is progressively replaced by the M( type in the skeletal muscle, heart, and brain by the L type in the liver and by the R type in red blood cells during development or differentiation (M26). The M, and M2 isozymes display Michaelis-Menten kinetics with respect to phosphoenolpyruvate. The Mj isozyme is not affected by fructose-1,6-diphosphate (F-1,6-DP) and the M2 is al-losterically activated by this compound. Type L and R exhibit cooperatively in... 

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