Failing hearts are more vulnerable to dobutamine and caffeine–induced ventricular arrhythmias: Ameliorated with dantrolene treatment

Figure 1. Echocardiographic images (left) from a sham control rat (top) and a myocardial infarction (MI)–heart failure (HF) rat (bottom) showing that the anterior wall thickness (indicated by a pair of white triangles) in MI-HF rats is much less than the posterior wall, due to MI and subsequent scaring of the anterior wall. For comparison, the anterior wall thickness and posterior wall thickness are similar in the sham control rat. Photographs (right) show a heart from a sham control rat (top) and a heart from a MI-HF rat (bottom). Note the MI scar in the anterior wall of the heart.

Figure 2. Echocardiographic parameters in the 3 studied groups (the sham control [sham] group, the myocardial infarction–heart failure [MI] group, and the myocardial infarction–heart failure plus dantrolene [MI+Dan] group). n = 10 in all groups. ∗P < .01 vs the sham control group. HR = heart rate; LVAWTd = left ventricular anterior wall thickness in diastole; LVAWTs = left ventricular anterior wall thickness in systole; LVDd = left ventricular diameter in diastole; LVDs = left ventricular diameter in systole; LVFS = left ventricular fractional shortening; LVPWTd = left ventricular posterior wall thickness in diastole; LVPWTs = left ventricular posterior wall thickness in systole.

Figure 3. Left ventricular (LV) hemodynamics in the 3 studied groups (sham group, myocardial infarction–heart failure [MI] group, and myocardial infarction–heart failure plus dantrolene [MI+Dan] group). n = 10 in all groups. ∗P < .01 vs the sham control group. +dP/dt = positive change in pressure over time; –dP/dt = negative change in pressure over time; LVEDP = left ventricular end-diastolic pressure; LVSP = left ventricular systolic pressure.

Figure 4. Electrocardiography recording from a myocardial infarction–heart failure rat showing sinus rate and various ventricular tachyarrhythmias induced by dobutamine and caffeine challenge. A: Sinus rate. B: Bigeminy premature ventricular contraction (PVC). C: A type of ventricular tachycardia (VT). D: Another type of VT and PVC.

Figure 5. Electrocardiography recording from different myocardial infarction–heart failure rats showing various forms of ventricular tachycardia. A: An example of bidirectional ventricular tachycardia (VT). B. Another example of bidirectional VT. C. An example of monomorphic VT. D. An example of polymorphic VT.

Figure 6. Ventricular tachyarrhythmia (VTA) inducibility and duration in the 3 studied groups (sham group, myocardial infarction–heart failure [MI] group, and myocardial infarction–heart failure plus dantrolene [MI+Dan] group). n = 10 in all groups. ∗P < .01 vs the sham control group. #P < .05 vs MI group.

Figure 7. Recording of calcium sparks in isolated ventricular myocytes. Examples of confocal line scanning images of the calcium sparks from a myocyte isolated from a sham control rat (sham), and from a myocardial infarction–heart failure rat without dantrolene treatment (MI), and from a myocardial infarction–heart failure rat with dantrolene treatment (MI+Dan) are shown. The bar graph shows the qualitative calcium spark data. n = 5 in sham and n = 6 in both MI and MI+Dan groups. ∗P < .01 vs the sham control and MI-HF dantrolene groups.