Alternating contractility in pulsus alternans studied in the isolated canine heart

Left bundle branch block increases left ventricular diastolic pressure during tachycardia due to incomplete relaxation

We investigated whether tachycardia in left bundle branch block (LBBB) decreases left ventricular (LV) diastolic distensibility and increases diastolic pressures due to incomplete relaxation, and if cardiac resynchronization therapy (CRT) modifies this response. Thirteen canines were studied at baseline heart rate (120 beats/min) and atrial paced tachycardia (180 beats/min) before and after induction of LBBB and during CRT. LV and left atrial pressures (LAP) were measured by micromanometers and dimensions by sonomicrometry. The time constant τ of exponential pressure decay and degree of incomplete relaxation at mitral valve opening (MVO) and end diastole (ED) based on extrapolation of the exponential decay were assessed. Changes in LV diastolic distensibility were investigated using the LV transmural pressure-volume (PV) relation. LBBB caused prolongation of τ (P < 0.03) and increased the degree of incomplete relaxation during tachycardia at MVO (P < 0.001) and ED (P = 0.08) compared with normal electrical activation. This was associated with decreased diastolic distensibility seen as upward shift of the PV relation at MVO by 18.4 ± 7.0 versus 12.0 ± 5.0 mmHg, at ED by 9.8 ± 2.3 versus 4.7 ± 2.3 mmHg, and increased mean LAP to 11.4 ± 2.7 versus 8.5 ± 2.6 mmHg, all P < 0.006. CRT shifted the LV diastolic PV relation downwards during tachycardia, reducing LAP and LV diastolic pressures (P < 0.03). Tachycardia in LBBB reduced LV diastolic distensibility and increased LV diastolic pressures due to incomplete relaxation, whereas CRT normalized these effects. Clinical studies are needed to determine whether a similar mechanism contributes to dyspnea and exercise intolerance in LBBB and if effects of CRT are heart rate dependent.NEW & NOTEWORTHY Compared with normal electrical conduction, tachycardia in left bundle branch block resulted in incomplete relaxation during filling, particularly of the late activated left ventricular lateral wall. This further resulted in reduced left ventricular diastolic distensibility and elevated diastolic pressures and thus amplified the benefits of cardiac resynchronization therapy in this setting.

Invasive Hemodynamics of Myocardial Disease: Systolic and Diastolic Dysfunction (and Hypertrophic Obstructive Cardiomyopathy)

Heart failure is a clinical diagnosis that is supported by various laboratory, imaging, and invasive hemodynamic measures. There is no single diagnostic test. A variety of structural and/or functional myocardial abnormalities can lead to the inability of the heart to fill or eject blood. Despite ejection fraction being the most commonly assessed measure of systolic function in clinical practice, it is a poor measure of contractility because it is susceptible to loading conditions and chamber size. Invasive hemodynamic assessment remains of great importance in the evaluation of patients with myocardial disease or hypertrophic cardiomyopathy.

Mechanical alternans in human idiopathic dilated cardiomyopathy is caused with impaired force-frequency relationship and enhanced poststimulation potentiation

Mechanical alternans (MA) is frequently observed in patients with heart failure, and is a predictor of cardiac events. However, there have been controversies regarding the conditions and mechanisms of MA. To clarify heart rate-dependent contractile properties related to MA, we performed incremental right atrial pacing in 17 idiopathic dilated cardiomyopathy (DCM) patients and in six control patients. The maximal increase in left ventricular dP/dt during pacing-induced tachycardia was assessed as the force gain in the force-frequency relationship (FG-FFR), and the maximal increase in left ventricular dP/dt of the first post-pacing beats was examined as the force gain in poststimulation potentiation (FG-PSP). As a result, MA was induced in 9 DCM patients (DCM MA(+)) but not in the other 8 DCM patients (DCM MA(-)), and not in any of the control patients. DCM MA(+) had significantly lower FG-FFR (34.7 ± 40.9 vs 159.4 ± 103.9 mmHg/s, P = 0.0091) and higher FG-PSP (500.0 ± 96.8 vs 321.9 ± 94.9 mmHg/s, P = 0.0017), and accordingly a wider gap between FG-PSP and FG-FFR (465.3 ± 119.4 vs 162.5 ± 123.6 mmHg/s, P = 0.0001) than DCM MA(-) patients. These characteristics of DCM MA(+) showed clear contrasts to those of the control patients. In conclusion, MA is caused with an impaired force-frequency relationship despite significant poststimulation potentiation, suggesting that MA reflects ineffective utilization of the potentiated intrinsic force during tachycardia.

Murmur and Doppler alternans in critical pulmonary stenosis

Pulsus alternans is a well-recognized clinical entity in which alternating strong and weak pulses are detected. It usually is secondary to underlying myocardial failure. Murmur alternans (alternation in murmur intensity) has been described in aortic stenosis and a few right-sided lesions such as pulmonary hypertension and embolism. This report describes a case of murmur alternans in critical pulmonary stenosis that also showed Doppler alternans on echocardiography. The underlying cause was right ventricular systolic dysfunction.

Systolic and diastolic pulsus alternans in severe heart failure

Pulsus alternans is usually a systolic phenomenon. We present a case of a patient with severe heart failure, and systolic and diastolic pulsus alternans. This case may help clarify the mechanism of pulsus alternans.

Arterial and Left Ventricular Pressures Illude Transient Alternans of Contractility during Postextrasystolic Potentiation

We have previously found that the postextrasystolic (PES) potentiation (PESP) of the left ventricular (LV) contractility (Emax) decays typically in transient alternans even in the normally ejecting canine heart. This contradicted the general expectation that arterial pressure (AP) and LV pressure (LVP) usually decay exponentially during PESP. We hypothesized this contradiction to be due to the different cardiodynamic behaviors of AP and LVP from LV Emax during PESP. We tested this hypothesis by measuring AP, LVP, LV volume, Emax, effective arterial elastance (Ea) as an index of afterload, and pulse pressure (PP) during PESP in eight anesthetized open-chest dogs by using the conductance catheter system. We changed Ea by changing the total peripheral resistance (TPR) with methoxamine hydrochloride (iv) and repeated the measurements. Although the Emax alternans patterns during PESP were comparable between the normal and high afterloads, LVP and PP were slightly potentiated and alternated under the normal afterload, whereas LVP and PP were obviously potentiated and alternated under the high afterload. We also simulated the effects of Ea/Emax on the transient alternans of AP and LVP on a computer. Despite the same alternans pattern of Emax, a higher Ea/Emax, which is typical in heart failure, caused a larger PP alternans, whereas a lower Ea/Emax, which is typical in normal hearts, almost eliminated it. These results suggest that a transient alternans of LV contractility during PESP could be overlooked when AP and LVP are monitored in in situ normal hearts.

Both diastolic and systolic function alternate in pulsus alternans: a case report and review

Pulsus alternans is occasionally seen in the setting of heart failure. This case describes a patient with both these findings, and alternating diastolic and systolic left ventricular function on color Doppler and Doppler tissue imaging.

Mechanical alternans in patients with chronic heart failure

BACKGROUND

Clinical implications of mechanical alternans in patients with chronic heart failure have remained uncertain. In this study, prevalence, characteristics, and prognostic implications of mechanical alternans were investigated.

METHODS AND RESULTS

Consecutive 51 patients with dilated cardiomyopathy underwent diagnostic cardiac catheterization using a micromanometer-tipped catheter. Under basal conditions, 7 of 35 patients with sinus rhythm showed mechanical alternans. Physiologic tachycardia (110 bpm) induced mechanical alternans in another 15 patients with sinus rhythm and in another 10 of 16 patients with atrial fibrillation. Low doses of dobutamine also induced mechanical alternans in another 8 patients, but a high dose of dobutamine eliminated mechanical alternans. Consequently, 40 patients (78%) showed mechanical alternans. Mechanical alternans was always accompanied by alternating changes of positive dP/dt, a parameter of contractility during isovolumetric contraction time, but negative dP/dt was occasionally constant. Concordant mechanical alternans between both ventricles was more prevalent than discordant alternans. The left ventricular end-diastolic volume indices and end-systolic volume indices of patients with mechanical alternans were larger than those of patients without. The left ventricular ejection fraction of patients with alternans was significantly lower than that of patients without.

CONCLUSIONS

Mechanical alternans was highly prevalent in patients with chronic heart failure. The origin of mechanical alternans seems to exist before or at the isovolumetric contraction time.

Relation of heart rate and blood pressure turbulence following premature ventricular complexes to baroreflex sensitivity in chronic congestive heart failure

Reduced heart rate variability (HRV) and attenuated baroreflex sensitivity (BS) after myocardial infarction and in patients with chronic congestive heart failure (CHF) are associated with poor prognosis. Recent studies have shown that a large proportion of the prognostic power from HRV measurements is localized in heart rate turbulence immediately after ventricular premature complexes. The mechanism of heart rate turbulence remains unknown. In the present study, we explore its relation to BS. In 45 patients with CHF and > or =3 ectopic beats in a 30-minute period, measurements of RR interval and continuous, noninvasive blood pressure (BP) were studied at rest. In response to an ectopic beat, average heart rate turbulence was 9.4 ms/beat (SD 6.1). Mean BP turbulence was 0.72 mm Hg/beat (SD 0.56). Using the ratio of heart rate and BP turbulence slopes to estimate BS showed good agreement (r = 0.67, p < 0.0001) with the alpha-index method (BSalpha). This relation was attributable to a marked correlation between heart rate turbulence and BSalpha (r = 0.70, p <0.0001); there was no correlation between BP turbulence and the BSalpha (r = 0.1, p = NS). Twenty-nine percent of patients had postectopic pulsus alternans, with a mean decay time of 1.4 beats (SD 0.5). The presence of pulsus alternans was associated with a significantly lower heart rate turbulence slope (6.3 [SEM 1.0] vs 10.7 [SEM 1.2] ms/beat, p = 0.03). Thus, heart rate turbulence is an effective measure of the baroreflex, correlating strongly with a standard measure. This is because it is the heart rate, rather than the BP, response to an ectopic beat that conveys the information relevant to BS measurement.

Coupling interval from slow to tachycardiac pacing decides sustained alternans pattern

We discovered that the coupling beat interval from a slow to a tachycardiac pacing period considerably affected the pattern of the beat-to-beat alternation of the tachycardia-induced sustained contractile alternans. We analyzed the relationship between the coupling interval and the pattern and amplitude of the alternans in the isovolumic left ventricle of canine blood-perfused hearts. The alternans pattern and amplitude varied transiently over the first 30-50 beats and became gradually stable over the first minute in all 12 hearts. We discovered that stable alternans, even under the same tachycardiac pacing, had three different strong-weak beat patterns depending on the coupling interval. A relatively short coupling interval produced a representative sustained alternans of the strong and weak beats. A relatively long coupling interval produced a similar sustained alternans but in a reversed order of even- and odd-numbered beats counted from the coupling interval. However, sustained alternans disappeared after 1-3 specific coupling intervals. We conclude that ventricular pacing rate does not solely determine the pattern and amplitude of sustained contractile alternans induced by tachycardia.

Intracoronary measurement of pulsus alternans

Pulsus alternans is typically found in patients with left ventricular systolic dysfunction. We describe a woman with biventricular systolic dysfunction and pulsus alternans in the right ventricle, pulmonary artery, and aorta. Coronary angiography revealed an intermediate stenosis in the proximal left anterior descending (LAD) coronary artery. Pulsus alternans was demonstrated in the mid LAD using a 0.014" guidewire-mounted pressure sensor. An abnormal fractional flow reserve was measured in the LAD. Cathet. Cardiovasc. Intervent. 51:335-338, 2000.

Myocardial mechanical restitution and potentiation partly underlie alternans decay of postextrasystolic potentiation: simulation

We have reported that the postextrasystolic potentiation (PESP) decays in alternans or monotonically, respectively, depending on whether the first postextrasystolic beat interval has a compensatory pause or not, in the canine left ventricle. To get better mechanistic insight into the alternans PESP decay, we hypothesized that the myocardial mechanical restitution and potentiation could partly account for both types of PESP decay. To test this hypothesis, we simulated PESP decay on a computer using a documented equation combining myocardial mechanical restitution and potentiation. We changed the first postextrasystolic beat interval after a fixed extrasystolic beat interval without changing regular and other postextrasystolic beat intervals. The simulated PESP decayed in alternans or monotonically as a function only of the first postextrasystolic beat interval. Thus, the myocardial mechanical restitution and potentiation could partly account for both alternans and monotonic decay of PESP. We conclude that myocardial mechanical restitution and potentiation may partly underlie the initial two alternating beats, the first beat being the most potentiated and the second beat being the most depressed, of alternans PESP decay in the canine heart.

Ineffective diastolic filling in tachycardia-induced cardiomyopathy with total pulsus alternans

We report a case of total pulse alternans in a patient with paroxysmal ectopic atrial tachycardia and echocardiographic findings obtained before and after radiofrequency catheter ablation (RFCA) that terminated the arrhythmia. The patient was a 27-year-old man with history of paroxysmal palpitations with worsening episodic dizziness, chest tightness, and dyspnea. Electrocardiography (ECG) showed atrial tachycardia at 160 to 170 beats/min while the simultaneous pulse was in the 80s beats/min. Echocardiogram showed that aortic and mitral valves opened with alternating excursions and outflow velocities. Furthermore, despite similar ventricular wall thickening during systole of consecutive cardiac cycles, there was alternating mitral valve opening during diastole of the same cycles, providing direct evidence that ineffective diastolic filling and mitral valve opening may play a role in the pathogenesis of pulse alternans. Repeat ECG and echocardiography after the successful RFCA showed normal sinus rhythm and normal opening excursion and the velocity across the aortic and mitral valves.

Pseudo-alternans of left ventricular end diastolic pressure. A case report

The authors report a case of left ventricular end diastolic pressure alternans without systolic alternans in a patient with bradycardia and tachypnea. This is an artifact due to the heart rate falling in a 2:1 ratio to the respiratory cycle. Alternation of left ventricular end diastolic pressure should be interpreted carefully in patients with bradycardia.

Left ventricular diastolic pulsus alternans in hypertrophic cardiomyopathy

We examined left ventricular (LV) diastolic pulsus alternans associated with systolic pulsus alternans in a patient with hypertrophic cardiomyopathy. Alternation in abnormal LV diastolic pressure waveforms persistently declining into mid-diastole (incomplete relaxation) and normal diastolic pressure were noted. Diastolic pulsus alternans was not corrected by isoproterenol and may possibly be independent of systolic pulsus alternans.

Postextrasystolic transient contractile alternans in canine hearts

We found that postextrasystolic potentiated contractility after a spontaneous extrasystole most frequently decayed as a transient alternans over several beats in excised, cross-circulated, atrially paced canine hearts. This type of heart preparation; which we have been using consistently in mechanoenergetic studies, had normal coronary blood perfusion pressure as well as flow and mechanoenergetic performance. Spontaneous atrial and ventricular extrasystoles occurred occasionally in every heart. Arrhythmic changes in left ventricular (LV) pressure at a fixed volume reflected corresponding changes in contractility. We analyzed nearly 3,600 cases of postextrasystolic potentiation in 68 hearts; 84% decayed as transient alternans, 6% decayed exponentially, and 10% belonged to neither type. We found that a postextrasystolic compensatory pause always preceded the transient alternans after either an atrial or ventricular extrasystole at any constant atrial pacing rate (85-188 beats/min). The decay was either exponential or nonalternating when the pause did not exist after an atrial extrasystole during occasional pacing failure. Therefore, the compensatory pause after either an atrial or ventricular extrasystole seems essential for the postextrasystolic transient alternans of LV contractility in the type of canine heart preparation we have been using.

Right ventricular dynamics during left ventricular assistance in closed-chest dogs

To determine the effects of left ventricular assist device (LVAD) support on global right ventricular (RV) systolic mechanics, 8 closed-chest, conscious, sedated dogs were studied after placement of an LVAD (left ventricle to femoral artery bypass) and implantation of 27 tantalum markers into the left ventricular and RV walls for computation of biventricular volumes and geometry. Biplane cinefluoroscopic marker images and hemodynamic parameters were recorded during transient vena caval occlusion at various levels of LVAD support. Right ventricular contractility was assessed using end-systolic elastance and preload recruitable stroke work, and the myocardial (pump) efficiency of converting mechanical energy to external work (stroke work/total pressure-volume area) was calculated. With full LVAD support, RV end-diastolic volume increased from 60 +/- 15 to 62 +/- 17 mL (p < 0.002), pulmonary artery input impedance decreased from 940 +/- 636 to 587 +/- 347 dyne.s/cm5 (p < 0.007), and measurement of RV and left ventricular septal-free wall dimensions demonstrated a significant leftward septal shift (p < 0.0005). Global RV end-systolic elastance and preload recruitable stroke work decreased from 2.4 +/- 1.0 to 1.7 +/- 0.7 mm Hg/mL (p < 0.004) and 14.1 +/- 3.3 to 12.1 +/- 3.9 mm Hg (p < 0.02), respectively; however, RV power output and myocardial efficiency did not change significantly (p > 0.74 and p > 0.33, respectively). Therefore, during LVAD support, global RV contractility is impaired with leftward septal shifting, but RV myocardial efficiency and power output are maintained through a decrease in RV afterload and an increase in RV preload.

Cardiac alternans: diverse mechanisms and clinical manifestations

OBJECTIVES

The purpose of this review is to assemble the widely dispersed information about cardiac alternans and to categorize the types and mechanisms of alternans, their clinical manifestations and possible therapeutic implications.

BACKGROUND

The phenomena of mechanical and electrical alternans have been of continuing interest to both physiologists and clinicians. Recent studies have enhanced this interest because of the reported association of alternans with experimental myocardial ischemia and cardiac arrhythmias.

METHODS

The review formulates concepts based on extensive review of published studies and personal observations.

RESULTS

Cardiac alternans has been subdivided into the following four categories: 1) mechanical, 2) electrical, 3) in association with myocardial ischemia, and 4) in association with cardiac motion. Mechanical alternans can be explained by hemodynamic or inotropic alterations, or both. Mechanical alternans in the ventricular muscle is accompanied by alternans of action potential shape. In the Purkinje fibers, action potential duration alternates without change in shape and is determined by the duration of the preceding diastolic interval. However, in ventricular muscle fiber, alternans can occur in the presence of constant diastolic intervals. T wave alternans reflects changes in action potential duration and is frequently associated with a long QT interval. Electrocardiographic manifestations of conduction alternans occur at many different sites within the conducting system and myocardium. During myocardial ischemia, additional mechanisms of repolarization alternans have been proposed. Alternans occurring in the presence of a large pericardial effusion is attributed to swinging motion of the heart maintaining two-beat periodicity.

CONCLUSIONS

Since its origin as "pulsus alternans" described by Traube in 1872, the definition of alternans has evolved into a term encompassing multiple physiologic and pathologic phenomena that, although united by the term cardiac alternans, diverge widely with respect to etiology, mechanism and clinical significance.

Dynamic properties of cardiovascular systems

A recently derived mathematical model of an isolated heart is extended here to a closed-loop cardiovascular system. Taking the end-diastolic volume as state variable, the authors show that the closed-loop cardiovascular system can be described by a one-dimensional nonlinear discrete dynamical system that depends on parameters describing the systolic and diastolic properties of the heart, heart rate, total peripheral resistance, and arterial capacitance. Studies of this model show that the system possesses a rich spectrum of dynamical behavior, from stable points through stable cycles to a "chaotic" behavior. It is shown that such an analysis of dynamic behavior yields those domains in the parameter space that correspond to a normal and abnormal beating heart, when the heart ejects time-invariant and time-variant (periodic or aperiodic) stable stroke volumes, respectively. Determination of such domains may lead to better understanding of the specific pathologic mechanism involved in the evolution of an abnormal beating heart.

Electromechanical concordance in alternans during sustained tachycardias

Electrical alternans and mechanical alternans are intriguing phenomena that have been reported to occur during tachycardias. Their precise pathophysiologic mechanism and in particular their interrelation have not been well defined. This report documents an unusual electromechanical concordance in alternans during sustained supraventricular tachycardia and ventricular tachycardia in two patients, raising interesting possibilities on the underlying mechanism of the concordant phenomena. The findings highlight the principle of excitation--contraction coupling of the heart.

Mechanisms of pulsus alternans: its relation to alternation of regional contraction and elevated ST segment

The aim of this study is to investigate the correlation between pulsus alternans and changes in regional myocardial contraction on the ST segment of the epicardial electrocardiogram (ECG) in open-chest dogs with coronary flow reduction and pacing. With flow reduction and pacing, alternation of regional contraction appeared primarily in shortening of the end-systolic length, and secondly in elongation of the end-diastolic length. Regional mechanical alternans was observed along with alternation of the ST segment of the epicardial ECG and was followed by pulsus alternans in some dogs. When adenosine triphosphate (ATP) content was measured at the end of the experiment, its level was preserved in dogs with pulsus alternans following regional mechanical alternans more than in those with regional mechanical alternans alone. We concluded that regional mechanical alternans is caused by the alternate changes in intrinsic contractility, probably due to alternations of Ca++ transients, since it was accompanied by ST electrical alternans. In addition, pulsus alternans might be beneficial to ischemic myocardium by causing a decrease in the consumption of high energy phosphates.

Mechanism of sustained mechanical alternans. Effect of variations in ventricular billing volume

This study investigations the phenomenon of sustained mechanical alternans (SMA) through the use of quantitative criteria. Discrete analysis is used to demonstrate that the hemodynamic variables during SMA are governed by a simple mathematical relation. The analysis shows that the value of the slope created by the two alternating beats on the stroke volume (SV)-end-diastolic volume (EDV) plane is gamma = (mu - 1) (1 + beta)/(mu - beta), where mu = SVs/SVw, and SVs and SVw denote the strong and weak beats, respectively, in the presence of one contractile state, and the beats associated with the higher and lower contractile states, respectively, in the presence of two alternating contractile states; beta = FVs/FVw, where FVs and FVw are the filling volumes after SVs and SVw, respectively. This equation is valid, whether SMA is exhibited in the presence of one or two contractile states and irrespective of the SV-EDV functional relation. Assuming constant afterload, a criterion based on this slope (gamma) is described to determine if SMA is caused by variations in EDV and FV. The slope of the SV-EDV curve in the presence of one contractile state (denoted as gamma) was determined directly (34 runs in eight dogs) by preventing FV in a beat, after a steady state, using a remote-controlled mitral valve. The slope gamma = 0.892 +/- 0.078 was found to agree with data in the literature. In 10 other dogs, mitral flow and aortic flow were measured in 55 series of SMA. In 51 series, gamma was greater than 1. Because the experimental slope in the presence of one contractile state, gamma, is smaller than or equal to 1, the possibility that one contractile state is involved in this series is rejected. On the other hand, when two contractile states are involved, the slope that the two successive beats create on the SV-EDV plane, gamma, is determined by connecting the two SV-EDV relations. This slope tends to be greater than 1. Thus, in these 51 series, SMA cannot be explained as a result of the Frank-Starling mechanism and variations in FV but as a result of two alternating contractile states. In the other four series, the value of gamma can be compatible either with the presence of one contractile state or with two alternating contractile states. This quantitative analysis enables the classification of the various types of SMA into subcategories with well-defined features. The quantitative analysis presented here shows that the common genesis of SMA is an alternating contractile state.

Stability analysis of one-dimensional dynamical systems applied to an isolated beating heart

In this paper we propose a new model of an isolated beating heart. The model is described by a one-dimensional non-linear discrete dynamical system which depends on several parameters. Applying stability analysis we investigate the dynamic properties of the non-linear system. We find those domains in the parameter space in which the equilibrium point of the system (the fixed point) and the periodic orbits are attractors and in which they are unstable. These domains correspond to a normal and abnormal beating heart, i.e. when the end diastolic volumes are stable time invariant and time variant, respectively. On transition between these domains there is a bifurcation which gives rise to a pair of attracting points of period 2. This case corresponds to the simplest type of period doubling behavior of an abnormal beating heart, called mechanical alternans. Our results provide qualitative and quantitative predictions which can be used for comprehensive experimental design.

Evidence for a link between mechanical and electrical alternans in acutely ischaemic myocardium of anaesthetized dogs

In order to examine the relation between mechanical alternans and associated electrical alternans during acute myocardial ischaemia, we determined the effect of a ventricular premature beat and calcium antagonists on mechanical and electrical alternans during acute coronary occlusion in anaesthetized dogs. Isometric contractions and unipolar electrocardiograms were recorded from ischaemic myocardium. During coronary occlusion, mechanical alternans was accompanied by electrical alternans, which was an alternate change in the ST segment elevation, i.e. the higher ST and the lower ST. Electrical alternans was frequently discordant and in some cases accompanied by discordant mechanical alternans. Both discordant electrical and mechanical alternans became concordant and were potentiated after the ventricular premature beat. In all cases, concordant mechanical alternans was accompanied by concordant electrical alternans and vice versa. In this situation, the higher and the lower ST corresponded to the larger and the smaller contractions respectively. Thus, a fixed correspondence was observed between mechanical and electrical alternans. A fixed correspondence was also observed between mechanical alternans and the variation in the time taken for repolarization of the monophasic action potential. Verapamil and diltiazem inhibited both electrical and mechanical alternans. The present results support the idea that a common mechanism, such as a beat-to-beat cycle of the transmembrane and intracellular movement of calcium ions, may play a role in the mechanisms of electrical and mechanical alternans.

Attenuation of pulsus alternans during coronary angiography

Following coronary angiography in a patient with cardiomyopathy and pulsus alternans, we observed a transient but marked attenuation of the alternation in pulse pressure associated with an elevation in pulmonary artery pressure. Attenuation of pulsus alternans has been rarely reported and may represent further deterioration of ventricular function.

Changes in intracellular calcium during mechanical alternans in isolated ferret ventricular muscle

Alternans in heart is important as pulsus alternans in cardiac failure and electrophysiological alternans in myocardial ischemia. The explanation of this phenomenon is still unclear. We attempted to investigate the cellular mechanisms of alternans by measuring intracellular free calcium concentration [( Ca2+]i) with the photoprotein aequorin in isolated ferret papillary muscles. Tension and length were also recorded simultaneously. Transient mechanical alternans lasting five to 20 contractions could be reliably induced in this preparation by following a 30-second rest period with stimulation at a fast rate (2-4 Hz). Production of sustained mechanical alternans, which lasted longer than 20 contractions and could persist for several hundred contractions, required additional interventions, consisting of a lower temperature (25 degrees C), a lower external calcium concentration (1 mM), and a lower pH (6.91) than control conditions (0.33-0.5 Hz, 30 degrees C, 2 mM Ca2+, pH 7.36). Transient mechanical alternans was associated with transient in-phase alternation of aequorin light and, hence, [Ca2+]i. Sustained mechanical alternans was associated with sustained in-phase alternation of aequorin light as well as incomplete relaxation of tension. However, when muscles were switched from isometric to unloaded isotonic contraction, relaxation between stimuli was complete but contraction and the aequorin light signal continued to alternate. The addition of 10 mM caffeine or 10 microns ryanodine abolished transient and sustained mechanical alternans and also abolished the associated alternation of aequorin light. Commensurate with the action of ryanodine, which allows the sarcoplasmic reticulum to reaccumulate calcium to a limited extent after a period of rapid stimulation, sustained mechanical alternans sometimes reappeared in an attenuated form 30 to 50 contractions after the addition of ryanodine. These results demonstrate that incomplete muscle relaxation between beats need not be present for alternans to occur, and support the hypothesis that alternans is caused by intracellular calcium cycling involving the sarcoplasmic reticulum.

Stretch activated ion channels in ventricular myocytes

Patch-clamp recordings from ventricular myocytes of neonatal rats identified ionic channels that open in response to membrane stretch caused by negative pressures (1 to 6 cm Hg) in the electrode. The stretch response, consisting of markedly increased channel opening frequency, was maintained, with some variability, during long (greater than 40 seconds) stretch applications. The channels have a conductance averaging 120pS in isotonic KCl, have a mean reversal potential 31 mV depolarized from resting membrane potential, and do not require external Ca++ for activation. The channels appear to be relatively non-selective for cations. Since they are gated by physiological levels of tension, stretch-activated channels may represent a cellular control system wherein beat-to-beat tension and/or osmotic balance modulate a portion of membrane conductance.

Clinical and hemodynamic characteristics of patients with inducible pulsus alternans

Pulsus alternans can be found in some patients with abnormal left ventricular function and also can develop after spontaneous premature beats. The purposes of this study were to: (1) determine the inducibility of pulsus alternans in a series of patients referred for routine cardiac catheterization and (2) define the clinical and hemodynamic characteristics of those who develop pulsus alternans. In 104 patients referred for right and left heart catheterization, atrial premature beats and rapid atrial pacing were used to try to provoke pulsus alternans. The 29 patients who developed pulsus alternans in response to these maneuvers were older (63 +/- 6 vs 59 +/- 10 years, p less than 0.01) and had a greater incidence of valvular heart disease (45% vs 23%, p less than 0.01) and congestive heart failure (38% vs 17%, p less than 0.05). Aortic stenosis was the most prevalent valve lesion found. Those who developed pulsus alternans in response to pacing were further characterized by higher left ventricular systolic (143 +/- 42 vs 121 +/- 23 mm Hg, p less than 0.02) and end-diastolic pressures (17 +/- 9 vs 13 +/- 6 mm Hg, p less than 0.05), higher pulmonary artery systolic pressure (35 +/- 14 vs 29 +/- 11 mm Hg, p less than 0.04), and lower left ventricular ejection fractions (0.42 +/- 0.13 vs 0.53 +/- 0.14, p less than 0.001). Eight patients (28%) with inducible pulsus alternans had a normal left ventricular ejection fraction (greater than 0.50) and left ventricular end-diastolic pressure (less than 13 mm Hg).(ABSTRACT TRUNCATED AT 250 WORDS)

Pulsus alternans induced by inferior vena caval occlusion in man

To assess the effect of rapid preload reduction on left ventricular performance in nonischemic cardiomyopathy, 11 patients were studied during inferior vena caval (IVC) balloon occlusion. Five developed sustained pulsus alternans. During pulsus alternans, the strong beats demonstrated systolic performance characteristics similar to baseline values, despite a drop in both left ventricular (LV) end-diastolic diameter (66 +/- 13 to 61 +/- 13 mm; p less than 0.05) and LV end-diastolic pressure (21 +/- 8 to 9 +/- 6 mmHg; p less than 0.05). In contrast, the weak beats demonstrated a reduction in peak systolic pressure (130 +/- 36 to 109 +/- 33 mmHg; p less than 0.02), fractional shortening (20% +/- 4% to 17% +/- 9%; p less than 0.05) and peak positive dP/dt (1,006 +/- 224 to 921 +/- 287 mmHg; p less than 0.05). Measures of diastolic performance (peak negative dP/dt, the time constant of LV relaxation, the length of diastasis, and LV end-diastolic stress) were not different between baseline beats and the strong beats; and only LV end-diastolic stress differed when baseline beats were compared to the weak beats. When the strong beats were compared to the weak beats during induced pulsus alternans, significant differences were observed in peak systolic pressure, peak positive dP/dt, and fractional shortening, but no differences in any measured diastolic parameter was observed. A slight difference was noted in the left ventricular end-diastolic diameters, with the weak beat consistently beginning at a slightly smaller diameter (61 +/- 13; mm vs 59 +/- 13; p less than 0.05). In summary, these data are consistent with an augmentation and deletion of intrinsic contractile forces in association with an alternation in preload on a beat-to-beat basis as best describing left ventricular performance during pulsus alternans.

Left ventricular pulsus alternans in patients with hypertrophic cardiomyopathy and severe obstruction to left ventricular outflow

Left ventricular pulsus alternans (LVPA), a rhythmic beat to beat variation in left ventricular systolic pressure and outflow gradient, was noted in 35 of 200 ventricular systolic pressure and outflow gradient, was noted in 35 of 200 patients with hypertrophic cardiomyopathy undergoing hemodynamic study. LVPA was not associated with significant systemic pulsus alternans nor right ventricular pulsus alternans. All patients with LVPA had severe outflow gradients at rest or during provocation. Of 61 patients with severe basal outflow gradients (greater than 80 mm Hg), 12 demonstrated LVPA at rest. Eight of these patients underwent ventricular septal myotomy-myectomy; all had successful abolition of basal outflow gradient. Of the seven of these eight patients who underwent postoperative hemodynamic study and who were in sinus rhythm, none demonstrated LVPA. Eleven of 60 patients with basal outflow gradients ranging from 10 to 70 mm Hg demonstrated LVPA during maneuvers provocative for outflow gradients (mean gradient 90 +/- 37 mm Hg). Two of these patients underwent ventricular septal myotomy-myectomy; neither had a gradient nor LVPA during provocation postoperatively. Twelve additional patients with basal outflow gradients ranging from 0 to 115 mm Hg had LVPA after ectopic beats, generally occurring during maneuvers provocative for outflow gradients, associated with severe outflow gradients (mean gradient 130 +/- 39 mm Hg) during the postextrasystolic beat. None of the 41 patients without an outflow gradient, basal or during provocation, was found to have LVPA. Thus LVPA is commonly seen in during provocation, was found to have LVPA. Thus LVPA is commonly seen in patients with hypertrophic cardiomyopathy and severe left ventricular outflow gradients and may represent inadequate left ventricular contractile function in the presence of high left ventricular systolic pressures.

Recurrence of pulsus alternans after fentanyl injection in a patient with aortic stenosis and congestive heart failure

Following aortic valve replacement in a patient with aortic stenosis and cardiac failure, marked pulsus alternans recurred immediately after intravenous injection of 0.5 mg fentanyl, without concomitant changes in heart rate, mean left atrial pressure, or the electrocardiogram. Pulsus alternans is known to occur in association with heart failure and aortic stenosis, but has not been reported previously in response to anaesthetic drugs. Mechanisms of pulsus alternans are discussed, and the possible contributory role of fentanyl is considered.