The hemodynamic effects of ventricular pacing with and without atrioventricular synchrony in patients with normal and diminished left ventricular function

Ventriculoatrial synchrony induced heart failure

OBJECTIVE AND IMPORTANCE

Endless loop tachycardia or pacemaker-mediated tachycardia, and atrioventricular desynchronization arrhythmia or repetitive non-reentrant ventriculoatrial synchrony (RNRVAS) are two forms of reverse impulse conduction - ventriculoatrial (VA) synchrony. Although VA synchrony can theoretically cause aggravation of heart failure, clinical cases describing severe consequential heart failure are lacking.

CLINICAL PRESENTATION AND INTERVENTION

We describe a case of a 60-year-old patient who underwent primary percutaneous coronary intervention and mitral valve surgery. Implantation of a two-chamber pacemaker was also performed during the same hospitalization due to development of third-degree atrioventricular block. Ten months later, he presented with a severe form of heart failure with a significant reduction of left ventricular ejection fraction (LVEF). The atrial lead was displaced and VA synchrony was registered (RNRVAS-like condition). The pacemaker was reprogrammed and VA synchrony induced heart failure was successfully resolved. Echocardiographic follow-up showed improvement in LVEF.

CONCLUSION

Ventriculoatrial conduction can be present even when the patient has a complete atrioventricular block. Atrial lead displacement and consequently loss of atrial capture with preserved sensing can be a predisposing factor for initiation of ventriculoatrial synchrony. Permanent ventriculoatrial synchrony may provoke aggravation of heart failure.

Electrophysiological interventions for treatment of congestive heart failure in pediatrics and congenital heart disease

Heart failure therapy, while well tested in the adult population, therapeutic interventions are less well defined in the pediatric population. Several treatment strategies are available for the adult patient with heart failure, thought few of these therapies have been proven in children. Morbidity and mortality in the pediatric population with a failing heart is significant, and rhythm management as well as strategies to improve hemodynamics are important in the care of these children. This review will address issues of rhythm management and resynchronization therapy in pediatric and congenital heart disease patients with heart failure.

The influence of fluid and diuretic administration on the index of atrial contribution in sequentially paced patients

AIMS

To examine whether acute changes in patient hydration can change atrial contribution (AC) to circulatory function.

METHODS AND RESULTS

Atrial contribution was quantified by beat-to-beat changes in the amplitude of pulse oximetry signal in 24 paced outpatients. Changes in body weight were used for assessment of changes in total body water. The first measurement was performed at steady state. The second measurement was made after infusion of saline (5 mL/kg) and the third measurement was obtained 2 h after a bolus of furosemide (1 mg/kg). Changes found after furosemide administration (compared with steady state): a substantial decrease in body weight from median 78.6 (interquartile range 65.7-86.5) to 77.1 (64.4-85.6) kg (P < 0.001), accompanied by an increase in AC from 30.4 (20.2-47.1) up to 43.3 (30.6-80.9)% (P < 0.001). An increase in heart rate and shortening of the atrioventricular conduction time occurred during acute hypohydration in some of the subjects.

CONCLUSION

Administration of furosemide was followed by a decrease in body weight and an increase in AC to stroke volume. This suggests that in conditions where pre-load is reduced cardiac output is preserved by an increase in AC enforced by sympathetic activation.

A Fast and Simple Echocardiographic Method of Determination of the Optimal Atrioventricular Delay in Patients After Biventricular Stimulation

The optimization of atrioventricular (AV) delay is known to significantly contribute to maximum cardiac performance. The aim of this study was to validate a new, fast, and simple echocardiographic method of identifying the AV delay that provides the maximum cardiac output (CO). Right heart catheterization and Doppler echocardiography of transmitral filling were performed simultaneously in 18 patients with heart failure and at least minimum functional mitral regurgitation treated with atrial synchronized biventricular pacing. CO derived from catheterization and Doppler filling parameters were measured at the predicted optimal AV delay (oAVD), the short AV delay (oAVD - 50 ms), and the long AV delay (oAVD + 28 ms on average/range, +10 ms to +50 ms) during a constant heart rate. The AV delay was regarded as optimal if the end of atrial contraction (represented by the end of A wave of transmitral filling) coincided with the beginning of ventricular contraction (heralded by the onset of the systolic component of mitral regurgitation). Prediction of the optimal AV delay included the following steps: (1) The maximum AV delay at which full ventricular capture is still preserved was found under electrocardiographic control. (2) This value, decreased by 5 to 10 ms, was designated as "the testing long AV delay," and the time interval from the end of the A wave to the onset of the systolic component of mitral regurgitation (time t1) was measured at this setting. (3) oAVD was simply calculated as "the testing long AV delay"- time t1. The CO measured at the oAVD (4.5 +/- 0.7 1. min-1) significantly exceeded those at the short AV delay (4.3 +/- 0.7 1. min-1, P < 0.01) and the long AV delay (4.4 +/- 0.8 1. min-1, P < 0.01), respectively. The method correctly determined the maximum CO in 78% of the patients. In conclusion, Doppler echocardiography enables very rapid and accurate optimization of AV synchrony in patients after the implantation of a biventricular pacemaker.

Left ventricular function in atrial fibrillation during overdrive pacing

OBJECTIVE

Our purpose was to measure the effect of ventricular pacing in patients with atrial fibrillation (AF) on stroke volume and cardiac output.

BACKGROUND

Unceasing variation in cycle length in AF decreases stroke volume and cardiac output. Because ventricular-inhibited pacing after atrioventricular node ablation has been reported to improve left ventricular performance, we tested the hypothesis that overdrive pacing would produce a similar benefit by regularizing cycle length.

METHODS AND RESULTS

We studied 18 patients with chronic AF and permanent pacemakers. The aortic time velocity integral (TVI) was measured with continuous-wave Doppler and was used as a surrogate measure of stroke volume (stroke volume = TVI x aortic valve area, and aortic valve area is constant whether in AF or during pacing). For each patient, the linear relation between preceding cycle length and TVI in AF was used to estimate relative stroke volume (TVI compared within each patient) at a preceding cycle length of 666 ms in AF, and a similar comparison between AF and pacing was made at the minimum allowable pacing rate. Relative stroke volume in AF was then compared with relative stroke volume at both the fixed cycle (666 ms) and the minimum allowable rate. During pacing at 666 ms, relative stroke volume increased significantly by 18% (t = 2.8, P =.048), but there was no difference in cardiac output during pacing at the minimum possible rate and the corresponding preceding cycle length in AF.

CONCLUSION

Our data suggest that regularization of ventricular rhythm by overdrive pacing in patients with AF only improves stroke volume (and by extension, cardiac output) at pacing rates at the outer limit of and above the normal physiologic range.

Pacing redistributes glycogen within the developing myocardium

Electrical pacing at physiological rate induces myocardial remodeling associated with regional changes in workload, blood flow and oxygen consumption. However, to what extent energy-producing pathways are also modified within the paced heart remains to be investigated. Pacing could particularly affect glycogen metabolism since hypertrophy stimulates glycolysis and increased workload favors glucose over fat oxidation. In order to test this hypothesis, we used the embryonic chick heart model in which ventricular pacing rapidly resulted in thinning of the ventricle wall and thickening of the atrial wall. Hearts of stage 22HH chick embryos were submitted in ovo to asynchronous and intermittent ventricular pacing delivered at physiological rate during 24 h. The resulting alterations of glycogen content were determined in atrium, ventricle and conotruncus of paced and sham-operated hearts. Hemodynamic parameters of the paced and spontaneously beating hearts were derived from computerized image analysis of video recordings. With respect to sham, paced hearts showed a significant decrease in glycogen content (nmoles glucose units/microg protein; mean+/-S.D.) only in atrium (1.48+/-0.40 v 0.84+/-0.34, n=8) and conotruncus (0.75+/-0.28 v 0.42+/-0.23, n=8). Pacing decreased the end diastolic and stroke volumes by 34 and 44%, respectively. Thus, the rapid glycogen depletion in regions remote from the stimulation site appears to be associated with regional changes in workload and remodeling. These findings underscore the importance of the coupling mechanisms between metabolic pathways and myocardial remodeling in the ectopically paced heart.

Cardiac performance early after cardioversion from atrial fibrillation

BACKGROUND

The mechanism for early improvement in cardiac function after cardioversion from atrial fibrillation is unknown.

METHODS

We measured ventricular volumes and load-independent contractility during atrial fibrillation and within 24 hours after cardioversion to sinus rhythm in 15 adult patients (10 men, 5 women; mean age 63+/-4 years, range 31 to 81 years). Duration of atrial fibrillation ranged from <1 day to 6 months.

RESULTS

After cardioversion, left ventricular ejection fraction increased from 51%+/-4% to 61%+/-4% (P=.001, 95% confidence intervals for the difference, 7% to 15%), stroke volume increased from 57+/-4 mL to 76+/-6 mL (P < .001, 95% confidence intervals 8 to 32 mL), and mean cycle length increased from 0.77+/-.04 seconds in atrial fibrillation to 1.02+/-.04 seconds in sinus rhythm (P=.002, 95% confidence intervals, 0.1 to 0.4 seconds). Cardiac contractility, as expressed by the slope and the intercept of the relation between rate-corrected circumferential velocity of fiber shortening and end-systolic wall stress (Vcfc/ESWS) remained unaltered in 13 of 15 patients, suggesting that intrinsic inotropic state was unchanged immediately after return of normal sinus rhythm. Finally, a significant correlation was observed between improvement in stroke volume and peak A-wave velocity (r=0.79, P=.035).

CONCLUSION

Both left ventricular stroke volume and ejection fraction increase immediately after cardioversion, whereas intrinsic cardiac contractility is largely unchanged. These data suggest that the mechanism of this increase is enhanced left ventricular diastolic filling due mostly to increased cycle length and return of left atrial mechanical function.

Acute effects of intraoperative multisite ventricular pacing on left ventricular function and activation/contraction sequence in patients with depressed ventricular function

INTRODUCTION

We hypothesized that simultaneous right and left ventricular apical pacing would result in improvement in left ventricular function due to improved coordination of segmental ventricular contraction. Structural changes in ventricular muscle present in dilated cardiomyopathy compromise ventricular excitation and mechanical contraction.

METHODS AND RESULTS

Eleven patients with depressed left ventricular function having cardiac surgery underwent epicardial multisite pacing with continuous transesophageal echocardiographic imaging. Quantitative measurement of percent fractional area change was performed, and segmental changes in contraction sequence resulting from simultaneous right and left ventricular pacing were assessed by application of phase analysis to recorded transesophageal images. There was no statistically significant difference between the paced QRS duration achieved with simultaneous right and left ventricular apical pacing and the native QRS duration (139+/-39 msec vs 106+/-18 msec, P = NS), but all other paced modes resulted in longer QRS durations. Percent fractional area change improved with simultaneous right and left ventricular apical pacing but not with other paced modes (41.5+/-11.9 vs 34.3+/-9.7, P < 0.01). Phase analysis demonstrated a resequencing of segmental left ventricular activation/contraction when compared to baseline ventricular activation.

CONCLUSION

Simultaneous right and left ventricular apical pacing results in acute improvements in global ventricular performance in patients with depressed ventricular function. Improvements may result from pacing-induced global coordination through recruitment of left and right ventricular apical and septal segments critical to effective ventricular contraction.

Effect of ventricular pacing on coronary blood flow in patients with normal coronary arteries

Although ventricular pacing is thought to produce impairment of left ventricular function by altering the sequence of ventricular activation and AV dyssynchrony, little is known about the effect of ventricular pacing on coronary blood flow. We measured coronary blood flow and coronary flow reserve in the left anterior descending coronary artery during sinus rhythm, and during both atrial and ventricular pacing at a rate of 100 ppm in 14 patients with normal coronary arteries. The double product increased significantly during both types of pacing. Coronary arterial diameter during ventricular pacing significantly increased compared to that during both sinus rhythm and atrial pacing. Coronary flow velocity during ventricular pacing was significantly lower compared to that during both sinus rhythm and atrial pacing. Coronary blood flow increased significantly during atrial pacing (30.7% +/- 12.1%; P < 0.001), but not significantly during ventricular pacing (23.6% +/- 47.0%; P = ns). While coronary flow reserve during both atrial (3.9 +/- 1.3) and ventricular pacing (3.8 +/- 0.9) was lower compared to its value during sinus rhythm (4.5 +/- 1.5), the difference was not significant. There was a significant positive correlation between the coronary flow reserve during sinus rhythm and the increase of coronary blood flow during ventricular pacing (R2 = 0.78; P < 0.001). We concluded that an increase in coronary blood flow during ventricular pacing is not a common finding regardless of the increase in metabolic demand. The increase of coronary blood flow during ventricular pacing was less in patients with a reduced coronary flow reserve. These findings suggest that preservation of AV synchrony and the presence of a normal sequence of ventricular activation may play an important role in preserving coronary blood flow in this subset of patients.

Refractory Heart Failure: A Therapeutic Approach

Optimal “triple therapy” for patients with chronic congestive heart failure (CHF) includes diuretics, digoxin, and either angiotensin-converting enzyme inhibitors or hydralazine plus nitrates. Refractory CHF is defined as symptoms of CHF at rest or repeated exacerbations of CHF despite “optimal” triple-drug therapy. Most patients with refractory CHF require hemodynamic monitoring and treatment in the intensive care unit. If easily reversible causes of refractory CHF cannot be identified, then more aggressive medical and surgical interventions are necessary. The primary goal of intervention is to improve hemodynamics to palliate CHF symptoms and signs (i.e., dyspnea, fatigue, edema). Secondary goals include improved vital organ and tissue perfusion, discharge from the intensive care unit, and, in appropriate patients, bridge to cardiac transplantation. Medical interventions include inotropic resuscitation (e.g., adrenergic agents, phosphodiesterase inhibitors, allied nonglycoside inodilators), load resuscitation (e.g., afterload and preload reduction with nitroprusside or nitroglycerin; preload reduction with diuretics and diuretic facilitators, such as dopaminergic agents or ultrafiltration), and electrical resuscitation (e.g., prevention of sudden death, correction of new or rapid atrial fibrillation, or dual chamber pacing in the setting of relative prolongation of the PR interval and diastolic mitral/tricuspid regurgitation). Surgical interventions are temporizing (e.g., intra-aortic balloon pump and other mechanical assist devices) or definitive (e.g., coronary artery revascularization, valvular surgery, and cardiac transplantation). Although these interventions may improve immediate survival in the short term, only coronary artery revascularization and cardiac transplantation have been shown to improve long-term survival.

Dual-chamber pacing with a short atrioventricular delay in congestive heart failure: a randomized study

OBJECTIVES

This prospective study assessed the initial hemodynamic effects and long-term clinical benefits of dual-chamber pacing with a short atrioventricular (AV) delay in patients with chronic heart failure who had no traditional indication for pacemaker implantation.

BACKGROUND

Dual-chamber pacing with a short AV delay has been proposed as a nonpharmacologic treatment for drug-refractory heart failure. Both initial and long-term hemodynamic as well as functional benefits have been reported. All previous studies have used an AV delay of 100 ms. Despite encouraging results, these previous studies have been anecdotal and uncontrolled.

METHODS

This double-blind, randomized, crossover trial included 12 subjects with chronic congestive heart failure despite optimal medical therapy. Patients were required to be in sinus rhythm with no evidence of significant bradyarrhythmias. On the day after implantation of a dual-chamber pacemaker, invasive hemodynamic measurements were made at varying AV delays between 100 and 200 ms. Patients were then randomized to either dual-chamber pacing with a 100-ms AV delay or backup mode (VVI at 40 beats/min). After 4 to 6 weeks, crossover to the other pacing mode was programmed.

RESULTS

Hemodynamic measurements on the day after pacemaker implantation demonstrated no benefit of pacing with any AV delay compared with intrinsic conduction. At the optimal AV interval for each patient, neither cardiac output (4.5 +/- 1.5 vs 4.7 +/- 1.6 liters/min [mean +/- SD]) nor wedge pressure (16 +/- 10 vs 17 +/- 8 mm Hg) improved significantly from baseline measurements during intrinsic conduction. The long-term pacing protocol was completed in nine patients. Ejection fraction was 16 +/- 6% with dual-chamber (VDD mode) pacing and 18 +/- 4% in backup mode (p = NS). No patient had an increase in ejection fraction by > or = 5% with VDD pacing, nor did any patient improve in New York Heart Association functional class with short AV delay dual-chamber pacing. Also, there were no significant reductions in body weight or diuretic requirements during this pacing period.

CONCLUSIONS

Dual-chamber pacing with a short AV delay does not improve hemodynamic and clinical status or ejection fraction measured on the day after pacemaker implantation in patients with chronic congestive heart failure. Routine use of pacemaker therapy with a short AV delay aas a primary treatment of heart failure in patients without standard arrhythmic indications is unwarranted.

Hemodynamic recovery, atrial natriuretic peptide, and catecholamines during simulated ventricular tachycardia: effects of ventriculoatrial conduction

Ventriculoatrial (VA) sequence and neurohumoral responses may be important modulators of hemodynamic recovery during VT. We studied the effects of VA conduction on blood pressure recovery, and levels of atrial natriuretic peptide (ANP), epinephrine, and norepinephrine during simulated VT. After diagnostic coronary angiography, VT was simulated by rapid right ventricular pacing (150 beats/min, 3 mins) in a consecutive series of patients. Whenever the patients demonstrated VA dissociation during ventricular pacing, they were included in the study. After 10 minutes of recovery, a group of nine patients then underwent an additional VA pacing (150 beats/min, 3 mins, VA delay of 150 msec). Intra-arterial blood pressure was continuously monitored, and plasma ANP and catecholamine levels were measured before, during, and after both pacing protocols. The mean arterial pressures declined rapidly by 26% and 30% after initiation of ventricular and VA pacing, respectively. The blood pressure then gradually recovered, the hemodynamic recovery being better during VA pacing. Plasma ANP and catecholamine levels increased toward the end of both pacing periods. The observed increase in ANP concentration was more prominent during VA pacing than ventricular pacing (P < 0.001), whereas catecholamine levels increased similarly. The results show that during simulated VT hemodynamic recovery is partially dependent on VA sequence. The increases in circulating ANP and catecholamines occur too slowly to account for the rapid changes in blood pressures observed after initiation of simulated VT. Therefore, other mechanisms, such as reflex stimulation of the sympathoadrenergic nervous system, must be involved, too. ANP release increases when atrial contraction frequency increases, but the exact determinants for this release remain unknown.

Changes in myocardial metabolism and transcardiac electrolytes during simulated ventricular tachycardia: effects of beta-adrenergic blockade

Myocardial ischemia, electrolyte changes, and fluctuations in autonomic tone may play an important role in the presentation of malignant ventricular arrhythmias. beta-Adrenoceptor blocking agents have been shown to decrease the incidence of ventricular fibrillation and sudden cardiac death in patients with coronary artery disease. Therefore we investigated the changes in myocardial metabolism and transcardiac electrolytes during simulated ventricular tachycardia before and after beta-adrenergic blockade. Six patients with normal coronary arteries (group 1) and 12 patients with documented coronary artery disease (group 2) were included in the study. The right ventricle was paced with electrode catheters to a constant cycle length of 400 msec for 3 minutes. Blood samples were withdrawn simultaneously from the coronary sinus and femoral artery to determine the transcardiac differences in metabolic variables and electrolytes before the pacing, at the end of the pacing, and 2 minutes thereafter. After pacing, the patients were given intravenous propranolol (0.15 mg/kg), and the protocol was repeated. Intraarterial blood pressure and electrocardiogram were monitored continuously. There was a rapid decline of the mean arterial blood pressures after initiation of the pacing in both study groups, whereafter the pressures began to rise. Propranolol somewhat blunted the blood pressure recovery, especially in group 2. Norepinephrine levels increased during the pacing in both patient groups, and the increase was accentuated by beta-adrenergic blockade. The femoroarterial coronary sinus difference in lactate turned negative, and pH, PCO2 and potassium differences increased in group 2 during pacing. However, the myocardial energy state remained relatively good as estimated from the nonsignificant change in the transcardiac differences of the plasma adenosine catabolites. There were no changes in the metabolic variables or transcardiac electrolytes in group 1 patients during pacing. Propranolol did not prevent the metabolic ischemia, but it did prevent the pacing-induced decrease in coronary sinus potassium and increase in transcardiac potassium difference. Propranolol also decreased arterial levels of free fatty acids and their extraction in group 2 patients during pacing. In conclusion, blood pressure decay during simulated ventricular tachycardia is followed by instantaneous sympathoadrenergic activation. In patients with coronary artery disease, this process is accompanied by metabolic ischemia and net transfer of extracellular potassium into the intracellular space. The metabolic and electrolyte changes may result in alterations of electrophysiologic millieau, thereby also modifying the clinical characteristics of ventricular tachycardia. Propranolol decreases arterial levels of free fatty acids and prevents changes in transcardiac electrolytes observed in coronary artery disease patients during simulated ventricular tachycardia. These effects of propranolol may be of clinical significance.

Increased risk of progressive hemodynamic deterioration in advanced heart failure patients requiring permanent pacemakers

To determine the influence of long-term permanent pacing systems on survival in patients with severe left ventricular dysfunction, data from 557 consecutive patients hospitalized with advanced heart failure for cardiac transplant evaluation and discharged on medical therapy were reviewed. Permanent pacemakers were identified in 42 (8%) patients. One-year actuarial risk of death from heart failure or urgent transplantation in paced patients was higher (49%) than that of a control group, matched for the severity of heart failure (15%, p = 0.003). Sudden death did not differ between paced patients and controls.

Effects of dual-chamber pacing with short atrioventricular delay in dilated cardiomyopathy

Mitral or tricuspid regurgitation of long duration may so shorten the ventricular filling time in dilated cardiomyopathy that stroke volume is limited. We assessed the effects of changing the atrioventricular interval during temporary or permanent dual-chamber DDD pacing in twelve dilated cardiomyopathy patients with short ventricular filling times due to regurgitation. We measured ventricular filling time and cardiac output with doppler echocardiography and exercise capacity on a treadmill, at baseline and with the best atrioventricular delay during pacing. The durations of both mitral and tricuspid regurgitation were significantly shorter at the shorter atrioventricular interval (mean reductions 85 [95% CI 60-110] ms and 110 [75-150] ms, respectively; p < 0.001 for both). There were consequent increases in left-ventricular and right-ventricular filling times (65 [35-95] ms and 90 [60-120] ms, p < 0.001). For each 50 ms reduction in atrioventricular delay, left-ventricular filling time increased by 35 ms in six subjects with presystolic mitral regurgitation and right-ventricular filling time by 30 ms in nine subjects with presystolic tricuspid regurgitation. At the short atrioventricular interval, cardiac output was greater than baseline (by 1.1 [0.8-1.4] l/min, p < 0.01) and there were rises in exercise duration (104 [45-165] s, p < 0.05) and maximum oxygen consumption (2.1 [1.5-2.7] ml kg-1 min-1, p < 0.05). There was a decrease in the Likert visual analogue score of breathlessness at peak exercise (8.6 [SD 2.1] vs 4.9 [3.1], p < 0.01). Although from a small sample, these findings suggest that DDD pacing with a short atrioventricular delay may have therapeutic potential in patients with dilated cardiomyopathy, even in the absence of conventional indications for pacemaker implantation.

Identifying patients for rate responsive atrial pacing: a new method for patient selection and pacemaker programming

In patients with sinus node disease (SND) and chronotropic incompetence, atrial rate adaptive stimulation (AAI,R pacing) is regarded as the most appropriate pacing mode. Since coronary artery disease is the most common etiology in these patients, we evaluated a new technique combining two-dimensional transesophageal echocardiography and atrial transesophageal pacing to detect pacing induced wall motion abnormalities and assess safe upper rate limits. Thirty-five patients were studied: 26 with and 9 without angiographic coronary artery disease. Stable atrial capture was achieved in all patients using 12 +/- 3 msec pulse width and 12 +/- 4 mA current strength. Sensitivity and specificity for the detection of coronary artery disease was highest for transesophageal echocardiography during pacing (sensitivity 81%, specificity 100%). Simultaneous 12-lead ECG during pacing had lower values (sensitivity 57%, specificity 75%). Pacing induced wall motion abnormalities preceded ST segment changes in all patients. Exercise stress testing showed similar values (sensitivity 62%, specificity 89%). It is concluded that simultaneous transesophageal echocardiography and transesophageal pacing is a safe and useful technique in selecting patients for AAI,R pacing and for the detection of safe upper rate limits, particularly when coronary artery disease is suspected.

The hemodynamic importance of atrial systole: a function of the kinetic energy of blood flow?

The relative importance of atrial systole on left ventricular filling was investigated at rest and during exercise in 25 patients with dual chamber pacemakers. The mean blood flow velocity over the mitral valve, the velocities of the rapid filling phase (E), the active filling phase (A), and the E/A ratio were determined by pulsed Doppler-echocardiography. The patients were first examined at rest during AV sequential pacing (DVI) at 70 and 104 beats/min. The investigation was subsequently repeated during atrial synchronous pacing (VDD) at rest and during supine submaximal exercise at workloads adjusted to achieve heart rates corresponding to those during DVI pacing. The mean blood flow velocity at rest did not differ between DVI and VDD pacing at 70 beats/min (0.46 vs 0.49 m/sec). When the resting heart rate was increased to 104 beats/min (DVI) the mean blood flow velocity increased to 0.56 msec (P < 0.001). At a corresponding heart rate during exercise (VDD) the velocity increased to 0.70 msec (P < 0.001). At a resting heart rate of 70 beats/min the E/A ratio (n = 14) did not differ significantly between DVI and VDD pacing. With an increased resting heart rate (DVI) the E/A ratio decreased from 0.94 +/- 0.45 to 0.78 +/- 0.18; NS. When the heart rate increased during exercise (VDD) the E/A ratio increased from 0.75 +/- 0.14 to 0.97 +/- 0.16; P < 0.001. There was a positive correlation between the increase of the mean blood flow velocity and the increase of the E/A ratio during exercise (r = 0.69, P < 0.01). No such correlation was found when the heart rate was changed at rest. Thus, the importance of atrial systole on ventricular filling diminishes during exercise in accordance with increasing blood flow velocity, which by physical principles is related to the kinetic energy. The relative importance of atrial systole is hence inversely correlated to the kinetic energy of the blood flow.

Relationship between beat-to-beat changes in hemodynamic state and action potential duration of the left ventricle during rapid ventricular pacing in man

A relationship between beat-to-beat changes in hemodynamic state and action potential duration (APD) of the left ventricle was studied by pacing the right ventricle with a constant cycle length (400 msec) for 3 minutes and recording simultaneously the intraarterial pressure and left ventricular monophasic action potential in 16 patients (mean age 51 +/- 8 years) undergoing routine cardiac catheterization. The APD measured at the point of 90% repolarization (APD-90) shortened gradually from a baseline value of 305 +/- 25 msec to a minimum of 246 +/- 25 msec (P less than 0.001) by 160 +/- 10 seconds after the onset of pacing. After reaching the minimum duration, the APD and blood pressure were measured from 30 consecutive beats. The magnitude of beat-to-beat variation in the APD was directly correlated to variation in the mean arterial blood pressure (r = 0.65, P less than 0.01). Beat-to-beat changes in hemodynamic and electrical state were related in that an increase of at least 10 mmHg in the blood pressure of one beat was associated with an increase in the APD of the concomitant beat by at least 5 msec. In six patients with ventriculoatrial dissociation during the rapid ventricular pacing, the sequential ventriculoatrial pacing decreased the beat-to-beat variation of APD from 2.8% +/- 1.4% to 0.8% +/- 0.7% (P less than 0.01) and variation of blood pressure from 6.4% +/- 3.2% to 1.4% +/- 0.9% (P less than 0.01). The observed association between beat-to-beat changes in hemodynamic state and APD of the left ventricle demonstrates that an immediate force-interval relationship exists in the human left ventricle.

Blood pressure, plasma atrial natriuretic peptide and catecholamines during rapid ventricular pacing and effects of beta-adrenergic blockade in coronary artery disease

To study neurohumoral control mechanisms of the hemodynamic response to ventricular tachycardia, arterial blood pressure, plasma atrial natriuretic peptide (ANP) and catecholamine levels were monitored during simulated ventricular tachycardia before and after administration of beta blockade. Tachycardia was simulated by ventricular pacing at 150 beats/min for 150 seconds in 9 patients without and 14 with angiographically demonstrable coronary artery disease (CAD). The effects of intravenous propranolol (0.15 mg/kg) were evaluated in 7 control subjects and in 13 patients with CAD. Arterial blood pressure decreased to its minimum within 5 seconds after onset of pacing in all patients, the decrease being 27 and 30% (p = not significant) in the groups without and with CAD, respectively. Propranolol did not affect the initial decline, but blunted subsequent recovery. The ANP baseline levels were similar in both groups, increasing by 60% (p less than 0.05) and 71% (p less than 0.02) in the groups without and with CAD, respectively, during ventricular pacing. After administration of propranolol the increase in ANP was 180% in both groups. Rapid ventricular pacing did not affect catecholamine levels before propranolol, but after propranolol norepinephrine increased by 71 (p less than 0.02) and 97% (p less than 0.01) in patients without and with CAD, respectively. There was a significant correlation (r = 0.53, p = 0.001) between pacing-induced ANP and norepinephrine changes, but changes in arterial blood pressure did not correlate with those in either of these hormones. Thus, beta-adrenergic blockade blunts blood pressure recovery during simulated ventricular tachycardia. However, this is partly counterbalanced by increased circulating norepinephrine levels.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of posture on the response to atrioventricular synchronous pacing in patients with underlying cardiovascular disease

In order to determine whether the hemodynamic benefit of atrioventricular synchronous pacing is maintained in the upright position, 14 patients with dual chamber pacemakers were paced in VVI mode and DDD mode in both the supine and standing position. The hemodynamic response was assessed by measuring the velocity time integral derived from the pulsed-wave Doppler signal in the left ventricular outflow tract during VVI pacing and dual chamber pacing at three different AV delays (125, 200, 250 ms). In the supine position, the velocity time integral during VVI pacing was 14.6 +/- 3.0 cm and this increased during DDD pacing at all three AV delays (17.7 +/- 3.3, 17.9 +/- 3.0, 17.5 +/- 3.5 cm). In the upright position, the velocity time integral during VVI pacing was 12.9 +/- 3.5 cm and this increased with DDD pacing (15.5 +/- 3.3, 15.1 +/- 4.0, 15.1 +/- 3.9 cm). It was concluded that although stroke volume decreases when assuming the upright position, the beneficial response to dual chamber pacing is maintained and equals that observed in the supine position.

Lack of influence of atrioventricular delay on stroke volume at rest in patients with complete atrioventricular block and dual chamber pacing

Dual chamber pacing (DDD) maintains atrioventricular (AV) sequence; AV delay programmability modifies the relationship between atrial and ventricular contraction. To evaluate the hemodynamic effects of such a modification, ten patients with a DDD unit for complete AV block were studied by time-motion (M-mode) and Doppler echocardiography during inhibited ventricular pacing (VVI), atrial-triggered ventricular pacing (VDD) and atrioventricular sequential pacing (DVI) at different AV delay (90, 140, 190, 240 msec). A significant improvement in stroke volume (SV) (15%-20%, P less than 0.05) was seen during DDD versus VVI pacing; no changes, however, were observed in the same patient with different AV delay or during DVI versus VDD pacing. These data suggest that programming of AV delay does not affect systolic performance at rest; longer diastolic filling times recorded during DDD pacing with "short" AV delay (90-140 msec) do not seem to be a hemodynamically relevant epi-phenomenon of PM programming.

Developmental sequelae of fixed-rate ventricular pacing in the immature canine heart: an electrophysiologic, hemodynamic, and histopathologic evaluation

Permanent, fixed-rate ventricular pacing (VVI) is associated with hemodynamic deterioration in the adult with compromised myocardial function. The effects of this pacing mode on the intact, immature heart, however, are largely unknown. Twelve beagle puppies (age 3 to 4 months) were equally divided into paced and age-matched control groups. All underwent identical hemodynamic and electrophysiologic evaluations. Transepicardial atrioventricular block and pacemaker insertion were additionally carried out in the paced group. After 4 months of observation, repeat hemodynamic and electrophysiologic measurements followed by histopathologic examinations were done in all puppies. The paced group exhibited significant (p less than 0.05) elevations of right atrial and pulmonary artery pressures, alterations in sinus node function, and prolongation of ventricular refractory periods compared with the control group. Initiation of dysrhythmias by programmed electrical stimulation was observed only among the paced group of puppies. Histologic examination demonstrated myofibrillar cellular disarray, dystrophic calcifications, prominent subendocardial Purkinje cells, and an increase in variable-sized, disorganized mitochondria only in the paced specimens. These findings indicate that permanent, apically-initiated VVI pacing ultimately predisposes to adverse cellular changes associated with hemodynamic and electrophysiologic deterioration in the intact, developing immature canine heart.

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. During V-A pacing, cardiac output decreased by 10%, whereas forearm vascular resistance increased from 52 +/- 7 to 70 +/- 9 U (p less than 0.001) and plasma norepinephrine increased from 183 +/- 27 to 232 +/- 27 pg/ml (p less than 0.01). Phentolamine nearly abolished the increase in forearm vascular resistance in response to V-A pacing (18 +/- 4.1 U before vs 5.8 +/- 1.5 U after, p less than 0.05). The change in forearm vascular resistance with V-A pacing correlated with systolic arterial pressure, but not with changes in mean arterial pressure, pulse pressure, cardiac output, mean or peak right atrial pressure, pulmonary artery or pulmonary capillary wedge pressure. These results suggest that forearm vascular resistance responses to V-A pacing are mediated mainly by alpha-adrenergic receptors, through the arterial baroreflexes.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamic benefit of atrioventricular synchrony: prediction from baseline Doppler-echocardiographic variables

The purpose of this study was to determine if baseline Doppler-echocardiographic variables of systolic or diastolic function could predict the hemodynamic benefit of atrioventricular (AV) synchronous pacing. Twenty-four patients with a dual chamber pacemaker were studied. Baseline M-mode and two-dimensional echocardiograms were obtained and Doppler-echocardiographic measurements of mitral inflow and left ventricular outflow were made in VVI mode (single rate demand) and in VDD (atrial synchronous, ventricular inhibited) and DVI (AV sequentially paced) modes at AV intervals ranging from 50 to 300 ms. Forward stroke volume and cardiac output were determined in each mode at each AV interval from the left ventricular outflow tract flow velocities, and the percent increase in cardiac output over VVI mode was determined. M-mode measurements, including left ventricular end-diastolic dimension, shortening fraction and left atrial size and Doppler measurement of diastolic filling, including peak early velocity and percent atrial contribution, did not correlate with the percent increase in cardiac output during physiologic pacing. The stroke volume in VVI mode correlated significantly with the percent increase in cardiac output during physiologic pacing (r = -0.61, p less than 0.005 for VDD mode and r = -0.55, p less than 0.05 for DVI mode). Five of the 15 patients with VVI stroke volume less than 50 ml but none of the 9 patients with stroke volume greater than 50 ml had ventriculoatrial (VA) conduction.(ABSTRACT TRUNCATED AT 250 WORDS)