Effects of cardiac denervation on atrioventricular nodal accommodation and hysteresis.

Conduction through the atrioventricular (AV) node is significantly altered by changes in autonomic tone. AV nodal accommodation (time-dependent changes in AV nodal conduction after a sudden change in atrial cycle length) and AV nodal hysteresis (asymmetry of AV nodal accommodation after directionally opposite atrial pacing cycle length changes) have been characterized in humans. Studies in dogs after cardiac transplantation suggest that the rapid phase of AV nodal accommodation is altered following ablation of neural input to the AV node.

A placebo-controlled trial of continuous intravenous diltiazem infusion for 24-hour heart rate control during atrial fibrillation and atrial flutter: a multicenter study.

The safety and efficacy of a 10- to 15-mg/h continuous infusion of intravenous diltiazem were evaluated in 47 patients with atrial fibrillation or flutter who first responded to 20 mg or 20 mg followed by one or more 25-mg bolus doses of open label intravenous diltiazem. Of the 47 patients, 44 responded to the bolus injection and were randomized under double-blind conditions to receive either a continuous infusion of intravenous diltiazem (10 to 15 mg/h) (23 patients) or placebo (21 patients) for up to 24 h. Seventeen (74%) of the 23 patients receiving diltiazem infusion and none of the 21 with placebo infusion maintained a therapeutic response for 24 h (p less than 0.

Sympathetic neural responses to induced ventricular tachycardia.

Although sympathetic mechanisms play a major role in buffering abrupt arterial pressure reductions, including those that occur during tachyarrhythmias, human sympathetic nervous system responses to ventricular tachycardia have not been measured. Muscle sympathetic nerve activity was recorded directly from the peroneal nerve in 16 patients during diagnostic induction of 19 episodes of sustained monomorphic ventricular tachycardia (average rate 189 beats/min, range 130 to 250). Average systolic and diastolic pressures decreased from 149/78 to 61/49 mm Hg by 10 s and increased toward baseline levels to 88/64 mm Hg by 1 min of ventricular tachycardia.

A prospective study of changes in right ventricular dP/dt during ventricular tachycardia.

The automatic implantable cardioverter defibrillator (AICD) has significantly decreased mortality in high risk ventricular tachycardia (VT) patients. The AICD provides treatment based on ventricular rate, sometimes leading to high energy shocks in conscious patients with stable VT, or patients with sinus or supraventricular tachycardia. Other physiological parameters, such as maximal positive and negative systolic right ventricular (RV) dP/dt (RV + dP/dtmax, RV - dP/dtmax, respectively), may be included in detection algorithms for future implantable defibrillators.

Utility of adenosine administration during intraoperative mapping in a patient with the Wolff-Parkinson-White syndrome.

Adenosine is an endogenous nucleoside that is administered intravenously and has potent chronotropic and dromotropic effects. This drug is distinguished from verapamil by its very short half-life. This makes it an ideal agent for use in the operating room where long lasting electrophysiological effects may not be desirable.

Subnormal parasympathetic activity after cardiac transplantation.

Heart period variability (standard deviation of 120 consecutive RR or PP intervals) was used to assess baseline parasympathetic activity in 18 patients with congestive heart failure before and after orthotopic cardiac transplantation, and was compared to that of 16 age-matched control subjects. Mean heart period variability (+/- standard error of the mean) was significantly greater (p less than 0.05) in control subjects (58 +/- 5 ms) than in the patients at any time before or after transplantation.

Arrhythmias in patients with CHF. Should they be treated?

Ventricular arrhythmias are a major cause of death in patients with congestive heart failure. Dr Ellenbogen and his associates discuss the current thinking, based on recent studies, concerning use of antiarrhythmic agents to prevent sudden cardiac death in these patients. As they point out, the proper antiarrhythmic therapy may be crucial to long-term survival.

The plasma catecholamine responses to ventricular pacing: implications for rate responsive pacing.

Many patients with VVI and VVIR pacemakers will alternate between periods of sinus rhythm and ventricular pacing. These rhythm shifts may be poorly tolerated by some patients. Changes in plasma catecholamine levels during these rhythm shifts may contribute to these patients' symptoms.

Comparison of right ventricular impedance, pulse pressure and maximal dP/dt for determination of hemodynamic stability of ventricular arrhythmias associated with coronary artery disease.

By monitoring hemodynamic parameters, a future generation of automatic implantable defibrillators will provide tiered therapy of ventricular arrhythmias according to the associated hemodynamic compromise. Changes in intracardiac impedance permit beat-to-beat assessment of ventricular volumes and make this parameter attractive as a rapid discriminator of hemodynamic compromise during arrhythmias. Beat-to-beat changes in right ventricular (RV) impedance were measured before, during and after 27 episodes of ventricular tachyarrhythmias induced in 17 men (64 +/- 7 years, mean +/- standard deviation; left ventricular ejection fraction 41 +/- 11%).

A prospective study of right ventricular pulse pressure and dP/dt to discriminant-induced ventricular tachycardia from supraventricular and sinus tachycardia in man.

In the future, automatic implantable cardioverter defibrillators (AICD) may incorporate sensors to differentiate hemodynamically stable from unstable ventricular tachycardias (VT). These sensors should also discriminate between ventricular and supraventricular tachycardias to avoid inappropriate responses from the device. Right ventricular pulse pressure (RVPP) and maximal systolic right ventricular dP/dt (dP/dt) were measured before, during and after 91 episodes of hemodynamically stable VT (VTs), hemodynamically unstable VT (VTus), supraventricular tachycardia (SVT) and sinus tachycardia (ST) induced in 49 male patients.

Increased vagal cardiac nerve traffic prolongs ventricular refractoriness in patients undergoing electrophysiology testing.

Stimulation of the vagus nerve in animals causes prolongation of sinus cycle length, atrioventricular nodal conduction and ventricular refractoriness. Vagal stimulation appears to have a protective effect in animal models of sudden death. The electrophysiologic effects of enhanced vagal activity on right ventricular (RV) refractoriness in man have not been studied previously.

Changes in regional adrenergic tone during sustained ventricular tachycardia associated with coronary artery disease or idiopathic dilated cardiomyopathy.

The hemodynamic tolerance of an episode of ventricular tachycardia (VT) can vary widely from no decrease in systolic blood pressure to severe hypotension. Little is known about the factors responsible for these different responses in man. Previous animal studies have suggested an important role for vasoconstriction mediated by the alpha-adrenergic nervous system.

Usefulness of right ventricular pulse pressure as a potential sensor for hemodynamically unstable ventricular tachycardia.

The automatic implantable cardioverter defibrillator has had a major impact on the management of patients with ventricular tachyarrhythmias. Future devices will offer tiered therapy for ventricular arrhythmias, based on a sensor capable of discriminating hemodynamically stable from unstable ventricular tachycardia (VT). We studied 27 patients with sustained VT/ventricular fibrillation during 70 episodes of sustained ventricular arrhythmias (greater than 30 seconds or requiring cardioversion).

Electrophysiological effects of adenosine in the transplanted human heart. Evidence of supersensitivity.

After cardiac transplantation, the denervated donor atria and ventricles demonstrate increased sensitivity to infusions of sympathomimetic amines. Recently, supersensitivity of the canine sinus and atrioventricular (AV) nodes to acetylcholine has also been demonstrated after parasympathetic denervation. Acetylcholine and the endogenous nucleoside adenosine exert similar electrophysiological effects in both the sinus and AV nodes, and share a common transduction process.

Correlation of an invasive measure of right ventricular pressure and mean arterial pressure.

Recently, cardiac pacemakers have been introduced which increase heart rate during exercise. Current rate responsive pacemakers achieve this objective by monitoring minute ventilation via a transvenous impedance measurement and provides a proportional heart rate increase with increases in minute ventilation. These devices are independent of hemodynamic parameters.

New insights into pacemaker syndrome gained from hemodynamic, humoral and vascular responses during ventriculo-atrial pacing.

Ventricular pacing is performed during programmed electrical stimulation and during normal functioning of single chamber (VVI or VVIR) pacemakers. In many patients, retrograde ventriculoatrial (V-A) conduction may occur and evoke hemodynamic and reflex neurohumoral responses, which are unique to this pacing mode. Accordingly, forearm blood flow, forearm vascular resistance, mean and phasic arterial pressure, cardiac output and plasma norepinephrine, epinephrine and dopamine were measured during atrial, ventricular and V-A pacing at a cycle length of 600 ms (100 beats/min) before and after regional alpha blockade with intraarterial phentolamine in 16 patients with a left ventricular ejection fraction greater than 35% and little or no symptoms of congestive heart failure.

Pharmacological characterization of conduction over a Mahaim fiber: evidence for adenosine sensitive conduction.

The presence of a nodoventricular pathway (Mahaim fiber) has been invoked to explain certain distinctive electrocardiographic and electrophysiological observations. The presence of an atrioventricular or atriofascicular fiber with decremental conduction properties has been documented in many of these patients. We report the case of a patient with a Mahaim fiber and the response to conduction over this pathway after adenosine, procainamide, encainide, verapamil, edrophonium, phenylephrine and isoproterenol.

Bradyarrhythmias, emergency pacing, and implantable defibrillation devices.

This article reviews new developments in the field of cardiac pacing. Special emphasis is placed on dual chamber temporary pacing, external transthoracic cardiac pacing, and antitachycardia pacing. The role of the automatic implantable cardioverter defibrillator (AICD) in patients with sudden cardiac death is also explored with emphasis on the presentation of such patients to intensive care units.

Neurohumoral and hemodynamic effects of lower body negative pressure in patients with congestive heart failure.

Baroreflex modulation of forearm vascular resistance (FVR) has been reported to be abnormal in patients with congestive heart failure (CHF). However, the neurohumoral mechanisms for this impairment are not defined. We assessed the responses of arterial pressure, FVR, plasma norepinephrine, and plasma renin activity to lower body negative pressure in 29 patients with compensated CHF (New York Heart Association class III and IV) and in 11 normal age-matched control subjects.

Subnormal heart period variability in heart failure: effect of cardiac transplantation.

Heart period variability and arterial baroreceptor-cardiac reflex function were studied in cardiac transplant patients to determine if correction of heart failure restores parasympathetic control mechanisms toward normal. Heart period variability (standard deviation [SD] of 120 consecutive RR or PP intervals) was measured at supine rest in 34 patients with congestive heart failure (23 patients receiving diuretics, digoxin or vasodilators and 11 patients weaned from all medications), 30 cardiac transplant patients (both innervated recipient and denervated donor atrial rates) and 16 age-matched healthy control subjects. Arterial baroreflex gain was evaluated with intravenous bolus injections of phenylephrine in 22 transplant patients.

Pericardial repair of endocardial defect following regional endocardial resection for ventricular tachycardia.

Regional endocardial resection is the accepted surgical treatment for sustained monomorphic ventricular tachycardia. In patients requiring extensive endocardial resection, or with large aneurysms involving the interventricular septum, the resulting defect may result in weakened myocardium and, ultimately, ventricular septal defect or ventricular rupture. A new approach for repair of the resulting defect is proposed using an autogenous pericardial patch sutured to normal endocardium and included in the aneurysm repair.

Arterial baroreflex abnormalities in heart failure. Reversal after orthotopic cardiac transplantation.

Arterial baroreflex control of the heart and peripheral circulation is markedly impaired in humans and animals with congestive heart failure. After reversal of heart failure in animal models, arterial baroreflex control of heart rate remains impaired for up to 8 months. Cardiac transplantation restores normal ventricular function and completely reverses heart failure, but does it normalize arterial baroreflex control of heart rate in humans? We studied baroreflex sensitivity in 11 patients with severe heart failure, six normal control patients, and 23 patients at 2 weeks to 4 years after orthotopic cardiac transplantation.

Utility of introducing ventricular premature complexes during reciprocating tachycardia in specifying the location of left free wall accessory pathways.

The usefulness of the response to single and double ventricular premature complexes (VPCs) introduced during reciprocating tachycardia (RT) in predicting the location of a left free wall accessory pathway was studied in 55 patients with the Wolff-Parkinson-White syndrome. One VPC introduced from the right ventricle into narrow QRS RT when the His bundle was refractory resulted in retrograde atrial preexcitation in 25 of 55 (45%) patients, while 30 (55%) showed no preexcitation. Double VPCs produced retrograde atrial preexcitation in 9 of 26 patients not responding to a single VPC.