Metabolic and hemodynamic responses to exercise during atrial fibrillation and sinus rhythm

The effect of atrial fibrillation and the ventricular rate control on exercise capacity

BACKGROUND

Atrial fibrillation (AF) is a common cardiac arrhythmia, affecting approximately 1.5 million patients in the United States.

HYPOTHESIS

This study was designed to determine the effect of AF and the ventricular rate control during AF on cardiovascular performance as measured by exercise endurance on a standard Bruce protocol.

METHODS

Sixty-three patients with AF who underwent exercise stress testing during both sinus rhythm and AF were analyzed. Heart rate, blood pressure, heart rate acceleration, exercise duration, and left ventricular (LV) systolic function were measured.

RESULTS

Atrial fibrillation resulted in a small but statistically significant decrease in exercise endurance (426 +/- 180 vs. 402 +/- 168 s, p < 0.05). The drop in exercise tolerance was consistent regardless of the underlying heart condition or adequate ventricular rate control during AF. Heart rate in AF was consistently faster than in sinus rhythm, at rest, and at peak exercise (63 vs. 79 beats/min and 125 vs. 149 beats/min, respectively, p < 0.001).

CONCLUSION

Our analyses indicated that (1) the loss of atrioventricular synchrony had minimal effect on cardiovascular performance in patients with preserved LV function, (2) the decrease in cardiovascular performance was related to loss of atrioventricular synchrony but not to underlying heart disease or ventricular rate control, and (3) compensation for the loss of the atrial contribution was provided by consistently faster heart rate during AF.

Atrial and ventricular pressures in atrial flutter

The hemodynamic effects of atrial flutter (AF) are unknown. The purpose of the present study was to investigate the changes in atrial and ventricular pressures after induction of AF. In 23 patients with paroxysmal AF (age 59 +/- 9 years), a hemodynamic study was performed both during sinus rhythm and after induction of the tachyarrhythmia. During AF, 13 patients showed a fixed 2:1 AV conduction and 10 patients showed variable conduction. Mean right and left atrial pressures increased (P < 0.001) and right and left ventricular end-diastolic pressures decreased (P < 0.001) after induction of AF. Both the increase in mean atrial pressures and the decrease in ventricular end-diastolic pressures were present either in the patients with fixed 2:1 AV (heart rate: 133 +/- 15 beats/min) or in those with variable conduction (heart rate 96 +/- 15 beats/min), but were more marked in the former. AF produces an impairment of atrial function, as evidenced by the increase in mean atrial pressures and reduction in ventricular end-diastolic pressures in the absence of an elevated heart rate. The mechanisms responsible for the increase in mean atrial pressures are unknown; however, atrial contractions against closed AV valves seem to play an important role.

Acute treatment of atrial fibrillation: why and when to maintain sinus rhythm

Although not usually immediately life threatening, atrial fibrillation (AFib) poses a significant long-term risk to health. The best-documented and probably largest long-term risk in this condition is from thromboembolic complications, but this has been shown to be largely overcome by moderate intensity anticoagulation. In addition, however, AFib has significant detrimental effects on exercise capacity and overall quality of life, can cause or exacerbate heart failure, and imposes significant health-care burdens. Cardioversion, usually by transthoracic direct current shock, restores sinus rhythm in > 80% of patients, but recurrence of AFib over the weeks and months that follow decreases the value of this strategy. Antiarrhythmic drugs lessen the recurrence rate and add to the overall efficacy of achieving the treatment goal of restoring and maintaining sinus rhythm, rather than accepting permanent AFib with ventricular rate control and long-term thromboembolic prophylaxis. Whereas clear evidence exists that abolishing AFib makes patients feel better in the short-to-medium term, data on the economic viability or long-term efficacy of such a strategy are sparse. Management trials in AFib currently ongoing will provide some answers, but the decision as to whether restoring sinus rhythm is feasible and realistic in individual patients will remain a decision to be made on a case-by-case basis.

Hemodynamics of idiopathic paroxysmal atrial fibrillation

The hemodynamics of induced atrial fibrillation (AF) was investigated in 15 patients (ages 58 +/- 11 years) with paroxysmal AF presenting without organic heart disease or hypertension. A hemodynamic study was performed both during sinus rhythm and after the induction of AF. The mean heart rate increased from 73 +/- 11 to 128 +/- 18 beats/min (P < 0.001) after AF. Systolic and mean aortic pressures did not significantly change, and diastolic aortic pressure increased (78 +/- 11 vs 89 +/- 12 mmHg, P < 0.01). Left ventricular end-diastolic pressure decreased during AF (9 +/- 3 vs 6 +/- 2.6 mmHg, P < 0.005), whereas mean pulmonary wedge pressure increased (8 +/- 2 vs 12 +/- 4 mmHg, P < 0.001). Systolic pulmonary arterial pressure did not show significant variations, and there was a slight but statistically significant increase in the diastolic and mean pulmonary arterial pressures (P < 0.01). The right ventricular end-diastolic pressure decreased during AF (5.6 +/- 2 vs 3.8 +/- 2 mmHg, P < 0.01), whereas mean right atrial pressure showed a trend toward an increase. Stroke volume markedly decreased (P < 0.001) while the cardiac index did not significantly change. Systemic vascular resistance, pulmonary arteriolar resistance, and the arteriovenous O2 difference showed no significant variations after the induction of AF. These results suggest that in subjects without organic heart disease, paroxysmal AF is well tolerated hemodynamically, and the rise in the atrial pressures during AF is not related to an increase in the ventricular end-diastolic pressure.

Improved ventilatory response to exercise after cardioversion of chronic atrial fibrillation to sinus rhythm

The purpose of this study was to assess hemodynamic and respiratory measures of submaximal and maximal exercise performance in patients with chronic atrial fibrillation, before and one month after cardioversion to sinus rhythm. Restoration of sinus rhythm (n = 16) produced significant reductions in resting and exercise heart rates, 14 percent to 20 percent (p < 0.01). Due to a proportionately larger increase in stroke volume, cardiac output increased by 9 percent during low-level exercise (p < 0.01) and by 7 percent during exercise above the anaerobic threshold (p < 0.05). Minute ventilation was reduced by 7 percent during low-level exercise (p < 0.01) and by 9 percent above the anaerobic threshold (p < 0.05). The ratio between minute ventilation and carbon dioxide elimination was significantly reduced (p < 0.01). Maximum oxygen uptake (+8 percent; p < 0.01) and maximal tolerated work load (+6 percent; p < 0.05) increased. Hemodynamic changes during exercise were similar in patients with (n = 7) or without (n = 9) disopyramide prophylaxis. Restoration of sinus rhythm induced improvement in hemodynamics and in efficiency of ventilation, thereby reducing the ventilatory demand during submaximal exercise.

Left atrial function in acute transient left ventricular ischemia produced during percutaneous transluminal coronary angioplasty of the left anterior descending coronary artery

Left atrial (LA) function was studied in 32 patients during percutaneous transluminal coronary angioplasty of the proximal left anterior descending artery with a dual micromanometer positioned transseptally in the left atrium and in the left ventricle. In 10 patients LA and left ventricular (LV) cineangiography was performed 30 minutes before percutaneous transluminal coronary angioplasty and 30 seconds after the occlusion of the left anterior descending coronary artery. Thirty seconds after left anterior descending occlusion, LV peak systolic pressure decreased from 135 +/- 12 to 106 +/- 9 mm Hg (p less than 0.05) and LV maximum dP/dt decreased from 1,634 +/- 136 to 1,137 +/- 127 mm Hg/s (p less than 0.01). Simultaneously, LA mean pressure increased from 11 +/- 2 to 29 +/- 1 mm Hg (p 177 +/- 13 to 381 +/- 21 mm Hg (p less than 0.001). There was a difference between LV end-diastolic pressure and LA mean pressure of 1.5 mm Hg at rest and 7.8 mm Hg during ischemia and LA pulse pressure increased from 16 +/- 3 to 26 +/- 3 mm Hg (p less than 0.05) together with increase of LA A and V waves peak pressure. LV stroke volume index decreased from 46 +/- 5 to 43 +/- 3 ml/m2 (difference not significant). The LA maximal volume increased from 18 +/- 2 to 29 +/- 3 ml/m2 (p less than 0.001). LA volume before LA contraction increased from 29 +/- 2 to 54 +/- 3 ml/m2 (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of cardioversion on maximal exercise capacity in patients with chronic atrial fibrillation

To evaluate the effect of cardioversion on exercise capacity, 11 male patients (59 +/- 8 years) with chronic atrial fibrillation underwent maximal exercise testing using gas exchange techniques before and after successful cardioversion to normal sinus rhythm. Testing was conducted 1 day prior to and a mean of 39 (range 10 to 95) days following cardioversion. Heart rate, blood pressure, and respiratory gas exchange responses were evaluated at rest, at a standard submaximal workload (3.0 mph/0% grade), at the gas exchange anaerobic threshold, and at maximal exertion. Cardioversion resulted in a mean decrease in resting heart rate of 37 beats/min (113 +/- 16 versus 76 +/- 10 beats/min, p less than 0.001). While mean heart rate was approximately 50 beats/min lower following cardioversion at both submaximal stages of exercise p less than 0.001), oxygen uptake was not different. At maximal exercise, heart rate was markedly reduced (192 +/- 24 to 144 +/- 21 beats/min, p less than 0.001) and maximal oxygen uptake was higher (1.86 +/- 0.5 to 2.06 +/- 0.5 L/min, p less than 0.05) after cardioversion. In addition, an improved efficiency of ventilation was observed at exercise levels exceeding 60% of maximal oxygen uptake.

Delayed improvement in exercise capacity after cardioversion of atrial fibrillation to sinus rhythm

In some patients symptoms improve after the restoration of sinus rhythm from atrial fibrillation. To assess the size and mechanism of such change, exercise capacity and pulsed Doppler left ventricular inflow velocities were assessed in 20 patients with established atrial fibrillation. Treadmill exercise capacity was assessed by measuring maximal oxygen consumption and anaerobic threshold before and on day 1 and 28 days after elective DC cardioversion. The relative contribution of atrial contraction to left ventricular filling was determined by relating the maximum height of the A wave to the maximum height of the E wave (A/E) of the Doppler velocity time curve. Cardioversion was successful in 14 patients. Maximal oxygen consumption and anaerobic threshold were unchanged on day 1 and increased by day 28 in all 14 patients. The percentage improvement was inversely related to the baseline values; however, the absolute improvement was small in all patients. The mean A/E ratio increased significantly from day 1 to day 28 in all 14 patients. Thus the restoration of sinus rhythm was associated with a delayed improvement in exercise capacity that may in part be due to a slow improvement in atrial contractility and peak cardiac output after cardioversion.

Reevaluation of the role of atrial systole to cardiac hemodynamics: evidence for pulmonary venous regurgitation during abnormal atrioventricular sequencing

Twenty open-chest dogs with experimental AV heart block were evaluated hemodynamically, angiographically, and by M-mode echocardiography to further elucidate mechanisms whereby abnormal AV sequencing results in decreased cardiac hemodynamics. During fixed-rate AV pacing, there was a consistent decrease in cardiac output, left ventricular and aortic pressures, and left ventricular dimensions with an increase in left atrial pressure as the AV interval was decreased from 100 to 0 msec, and there were further changes when the AV interval was set at -50 and -100 msec. The hemodynamic consequences of atrial fibrillation with regular ventricular rhythms were similar to the effects of an AV interval of 0 msec. It is important to note that retrograde blood flow into the pulmonary venous system (pulmonary venous regurgitation) was demonstrated by left atrial angiography at AV intervals of both -50 and -100 msec. However, left ventricular angiography failed to reveal mitral regurgitation during fixed-rate pacing at any AV interval or during atrial fibrillation with regular ventricular rates. Thus, during tachyarrhythmias characterized by abnormal AV sequencing, not only is there the loss of active atrial contribution to ventricular filling but there is also evidence for a retrograde or "negative atrial kick" further compromising cardiac hemodynamics.

Hemodynamics and echocardiograms before and after cardioversion of atrial fibrillation to normal sinus rhythm

Hemodynamic and echocardiographic measurements were obtained in 15 patients prior to cardioversion and immediately, one, three, and five hours after cardioversion of atrial fibrillation to normal sinus rhythm. At five hours after cardioversion, there was improvement in cardiac index (P less than 0.005), in stroke index (P less than 0.005), and in stroke work index (P less than 0.025), but no significant change in heart rate, mean pulmonary capillary wedge pressure, left atrial dimemsions (LAD), left ventricular end-diastolic dimensions (LVEDD), or left ventricular end-systolic dimension (LVESD). At follow-up one week to nine months after cardioversion, 10 of the 15 patients (67 percent) remained in normal sinus rhythm. Neither the size of the left atrium, changes in hemodynamics, LAD, LVEDD, or LVESD, nor the presence or amplitude of the A-wave on the mitral valve echogram correlated with the persistence or normal sinus rhythm.

Echographic assessment of atrial transport, mitral movement, and ventricular performance following electroversion of supraventricular arrhythmias

Controversy attends the extent and temporal sequence of improvements in hemodynamic function resulting from the return of atrial contraction following cardioversion of supraventricular arrhythmias. Thus, mitral, left atrial (LA) and left ventricular (LV) echograms were obtained before and one hour after conversion of supraventricular arrhythmias to normal sinus rhythm by direct current countershock in patients with chronic coronary disease or cardiomyopathies without valvular dysfunction. The duration of the rhythm disturbance varied from one day to five years in 22 patients and was indeterminate in 13. Atrial systole immediately produced prominent mitral "A" waves with anterior valve excursion of 7.5 mm (range 3 to 12) in 33 of the 35 patients (94%). The two patients with atrial electromechanical dissociation reverted to atrial fibrillation within one week. Cardioversion caused a decline in LA diameter (3.5 to 3.2 cm, P less than .001) and a rise in LV end-diastolic dimension (5.2 to 5.5 cm, P less than .001) while LV end-systolic dimension was unchanged (4.2 cm). Thereby stroke volume rose. Heart rate fell an average of 16 beats/min. Depressed cardiac output was improved + 0.84 L/min/m-2. Thus, in the majority of patients with acute or chronic supraventricular arrhythmias without mitral valve disease, cardioversion promptly restores effective atrial contraction, decreases LA size, and results in substantial hemodynamic benefit.